CN215771900U

CN215771900U - Multi-junction distributed feedback semiconductor laser

Info

Publication number: CN215771900U
Application number: CN202121278399.1U
Authority: CN
Inventors: 罗毅; 王健
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2021-06-08
Filing date: 2021-06-08
Publication date: 2022-02-08
Anticipated expiration: 2031-06-08

Abstract

The utility model provides a multi-junction distributed feedback semiconductor laser, which comprises a substrate and a laser DFB-LD functional layer growing on the surface of the substrate; the DFB-LD functional layer comprises a plurality of semiconductor PN junctions and gratings; the multiple semiconductor PN junctions are distributed up and down and are electrically connected with each other, and a junction area of each PN junction is provided with a light emitting area; the grating is positioned on any one semiconductor PN junction or a connecting layer between the semiconductor PN junctions. The DFB-LD can increase the effective light-emitting area of the laser, improve the symmetry of the transverse light field distribution of the waveguide section, and reduce the parasitic capacitance parameter of the laser, thereby having the advantages of high power, high modulation rate and high optical fiber coupling efficiency.

Description

Multi-junction distributed feedback semiconductor laser

Technical Field

The utility model relates to the technical field of semiconductor lasers, in particular to a multi-junction distributed feedback semiconductor laser.

Background

High power, high modulation rate single mode semiconductor lasers have wide applications in the civilian and military fields. In the field of digital optical fiber communication, a high modulation rate single mode semiconductor laser has become an indispensable light source. In recent years, high-power and high-modulation-rate single-mode semiconductor lasers are widely applied to the dual-purpose fields of military and civilian, such as microwave photons, atomic clocks and the like. Compared with the traditional digital optical fiber communication, new application scenes such as microwave photon, atomic clock, coherent optical communication and the like put forward new requirements on the performance, such as power characteristics and the like, of the single-mode semiconductor laser. The high-power high-modulation-rate single-mode semiconductor laser with stable light output is researched and designed to meet the requirements of new application scenarios such as microwave photon, atomic clock, coherent optical communication and the like, and the single-mode semiconductor laser plays an important role in various fields of military, industry, aerospace, communication and the like in China, relating to national core competitiveness.

In view of the difficulty in research and manufacture of high-power and high-modulation-rate single-mode semiconductor lasers, only a few research units in developed countries can realize the laser. In the aspect of improving the single-mode characteristics of the semiconductor laser, people mainly introduce a frequency selection device to realize the single-longitudinal-mode operation of the laser at present, wherein the semiconductor laser comprises an external frequency selection device and a semiconductor laser with an internal frequency selection device. However, the semiconductor laser with an external frequency-selecting device has a complicated device structure, which is not favorable for outputting high-power laser. If a frequency selection device such as a grating is integrated in a semiconductor laser to form a Distributed Bragg Reflector (DBR) or a multi-junction Distributed Feedback (DFB) semiconductor laser, the structure of the laser can be simplified and the stability and reliability can be improved. Because the DBR laser can cause periodic nonlinearity in a current-optical power output curve due to mode hopping, the DFB laser can keep good linear output, and the high-power laser output can be realized under the condition of ensuring a single longitudinal mode. And the limitation of a transverse mode structure is added, so that the complete single-mode operation of a single longitudinal mode and a single transverse mode of the laser is realized. Due to the frequency-selective characteristic of the grating, the difference of the resonant cavity losses of the laser with different wavelengths is large, so that the laser can still keep a complete single-mode state, namely a dynamic single mode, under the condition of high-speed modulation.

However, the conventional DFB laser is difficult to achieve high output optical power of 100mW or more, and one of the important reasons is that the conventional DFB laser generally adopts a single PN junction to emit light, the transverse optical field distribution of the output cavity surface is limited, and the average optical power density is too large, which limits further increase of the laser power. In addition, because the light emitting size of the laser in the epitaxial growth direction is smaller than that in the horizontal direction, the far-field vertical divergence angle of the laser is far larger than that in the horizontal direction, and finally, an elliptical laser spot is output, so that the symmetry of the transverse optical field distribution of the waveguide section is poor, and the optical fiber coupling is influenced. The high-power laser output needs to increase the size in the epitaxial growth direction, and the thicker waveguide layer can introduce high-order transverse mode lasing, so that the far-field divergence angle of the laser is increased, and the improvement of the beam quality is not facilitated. In addition, in order to realize high-power output, the semiconductor laser usually adopts a cavity length more than mm magnitude, and the parasitic capacitance of the device is large, so that the high-speed modulation of the laser is not facilitated.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.

Therefore, the utility model aims to provide a multi-junction distributed feedback semiconductor laser, and the DFB-LD can increase the effective light-emitting area of the laser, improve the symmetry of the transverse optical field distribution of the waveguide section, and reduce the parasitic capacitance parameter of the laser, thereby having the advantages of high power, high modulation rate and high optical fiber coupling efficiency.

In order to achieve the above object, the present invention provides a multi-junction distributed feedback semiconductor laser, which comprises a substrate and a laser DFB-LD functional layer grown on the surface of the substrate;

the DFB-LD functional layer comprises a plurality of semiconductor PN junctions and gratings;

the multiple semiconductor PN junctions are distributed up and down and are electrically connected with each other, and a junction area of each PN junction is provided with a light emitting area;

the grating is positioned on the connecting layer between any one semiconductor PN junction or two adjacent semiconductor PN junctions.

Further, the plurality of semiconductor PN junctions are connected with each other through tunnel junctions.

Furthermore, the plurality of semiconductor PN junctions are two PN junctions, and the two PNs are connected in a mode of sharing one P region or one N region.

Furthermore, the tunnel junction is composed of heavily doped N-type and P-type materials, the grating is located at the tunnel junction and is composed of P-type semiconductors and N-type semiconductors which are periodically arranged along the light propagation direction, and the grating located at the tunnel junction periodically absorbs light energy or periodically passes through or blocks carrier energy.

Further, the light emitting region is composed of quantum wells, barriers, and confinement structures, respectively.

Further, the quantum well and the barrier are a compressively strained quantum well and a tensile strained barrier, respectively.

A method for preparing a multijunction distributed feedback semiconductor laser comprises the following steps:

sequentially epitaxially growing n (n is more than or equal to 1) PN junctions and a connecting layer between two adjacent PN junctions on the surface of the semiconductor substrate from bottom to top; each PN junction includes a P region, a light emitting region and an N region. The light emitting region is composed of a quantum well, a barrier and a separate confinement structure, preferably a compressively strained quantum well, a tensile strained barrier and a separate confinement structure. Tunnel junctions are preferentially adopted as connecting layers between two adjacent PN junctions, but when the substrate is made of non-doped semiconductor materials, the number of the PN junctions is 2, the connecting layers between the 2 PN junctions share an N region or a P region, the tunnel junctions are made of heavily doped P-type and N-type materials, and the arrangement directions of the P-type and N-type materials along the surface of the substrate from bottom to top are opposite to those of the PN junctions;

etching downwards to form a grating pattern when the n-i (i is not more than n-1) th PN junction or the connecting layer between two adjacent PN junctions grows to the position of the n-i (i is not more than n-1) th PN junction or the connecting layer between two adjacent PN junctions;

etching the nth PN junction and the n-1 and nth PN connecting layers to form a waveguide pattern;

manufacturing an insulating layer, opening an electrode window and manufacturing an electrode;

dissociating the resonant cavity and coating the end face.

Further, in the grating pattern etching process, the grating pattern extends downwards from the n-i PN junction or the connecting layer between two adjacent PN junctions to be etched to the n-j (i < j < n-1) PN junction, and the grating pattern is formed by adopting holographic interference lithography, electron beam lithography, nano imprinting or projection lithography and then etched; in the process of etching the waveguide pattern, the waveguide pattern extends from the nth PN junction and the connection layers of the (n-1) th PN junction and the nth PN to the connection layers of the (n-k) (k is more than or equal to 1 and less than or equal to n-1) th PN junction and the (n-k-1) th PN, and the waveguide pattern is formed by adopting contact type or projection type photoetching to form a photoresist pattern and then etching.

Furthermore, when the semiconductor substrate is doped and the bottom surface of the semiconductor substrate can form ohmic contact with the electrode, the ohmic contact layer forming ohmic contact with the electrode is continuously grown after the semiconductor substrate is epitaxially grown to n PN junctions.

Further, when the semiconductor substrate is an undoped semiconductor substrate, N is 2, and 2 PN junctions epitaxially grown in sequence from bottom to top share one P region or N region, and the grating pattern and the waveguide pattern are both located in the P region or N region of the uppermost layer of the 2 nd PN junction.

The utility model has the beneficial effects that:

(1) the traditional single PN junction DFB laser has smaller effective optical field sectional area of the waveguide, and is difficult to further improve the output optical power, but the utility model can improve the transverse size of an optical field along an x axis, namely from the bottom to the top (x axis) of the surface of a substrate to be nearly n times of that of the single PN junction laser by adjusting the distance between two adjacent PN junctions in an epitaxial structure and the number of the PN junctions, and the distribution of the optical field along the x direction is more uniform than that of the single PN junction laser, thereby effectively improving the output power of the DFB laser.

(2) In the field distribution of the traditional single PN junction DFB laser, the vertical substrate surface (x axis) and the parallel substrate surface (y axis) are seriously asymmetric, which shows that the near field distribution is narrow in the x axis direction and wide in the y axis direction, and the coupling efficiency of the DFB laser to an optical fiber is seriously influenced.

(3) The traditional high-power single PN junction DFB laser has a limited effective light-emitting sectional area, only can adopt a longer resonant cavity, thereby having larger parasitic capacitance parameters and influencing the modulation rate, and the multi-PN junction DFB laser greatly reduces the parasitic capacitance parameters, and the inherent junction capacitance of the multi-PN junction DFB laser is only 1/n of that of the single PN junction DFB laser in principle, thereby being beneficial to high-speed modulation.

(4) The multi-junction DFB laser provided by the utility model has the advantages of high power, high modulation rate, high optical fiber coupling efficiency and the like in principle, and is an ideal single-mode semiconductor laser.

Drawings

The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a schematic structural diagram of a multi-junction distributed feedback semiconductor laser according to an embodiment of the present invention, in which 3 PN junctions are connected through a tunnel junction;

fig. 2 is a schematic structural diagram of a multi-junction distributed feedback semiconductor laser according to another embodiment of the present invention, in which 3 PN junctions are connected through a tunnel junction;

fig. 3 is a schematic structural diagram of a multi-junction distributed feedback semiconductor laser according to another embodiment of the present invention, wherein 2 PNs are disposed in a common P region or N region.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. On the contrary, the embodiments of the utility model include all changes, modifications and equivalents coming within the spirit and terms of the claims appended hereto.

As shown in fig. 1, a multi-junction distributed feedback semiconductor laser (DFB-LD) according to an embodiment of the present invention defines a direction perpendicular to a surface of a substrate along a growth direction of a DFB-LD functional layer as an x-direction, a light propagation direction of the DFB-LD as a z-direction, a direction parallel to the surface of the substrate and perpendicular to the light propagation direction of the DFB-LD as a y-direction, the semiconductor laser DFB-LD comprises a substrate a and a functional layer b, wherein the functional layer b grows on the surface of the substrate a when viewed along the x direction, the functional layer b comprises a plurality of semiconductor PN junctions c and gratings d, 3 PN junctions are arranged in figure 1 for the convenience of clear view, there may be a plurality of PN junctions, each junction region of the plurality of semiconductor PN junctions c has its own light emitting region, the plurality of semiconductor PN junctions c are electrically connected to each other, and the grating d is located in the P region or N region of any one of the semiconductor PN junctions c or the connection layer between the semiconductor PN junctions.

The arrangement of the number of the PN junctions can improve the transverse size of the light field along the x axis, namely from the bottom to the top (x axis) of the surface of the substrate to be approximately n times that of a single PN junction laser, and the distribution of the light field along the x direction is more uniform than that of the single PN junction laser, thereby effectively improving the output power of the DFB laser.

In an embodiment of the present invention, a plurality of semiconductor PN junctions are connected by using a tunnel junction, that is, a PN-tunnel junction-PN manner or an NP-tunnel junction-NP manner (N and P refer to N region and P region of the PN junction, respectively) from bottom to top along the x direction.

In an embodiment of the present invention, when the plurality of semiconductor PN junctions are two PN junctions, the two PN junctions are connected to each other in a manner of sharing one P region or N region, that is, the two PN junctions are connected to each other in an NPN manner from bottom to top along the x direction, or the two PN junctions are connected to each other in a PNP manner from bottom to top along the x direction, where NPN and PNP denote an N region and a P region of a in the PN junction. However, the connecting layers between two adjacent PN junctions are preferentially connected by adopting the tunnel junctions, and the current between the PN junctions can only flow through the connecting layers, so that the DFB-LD can increase the effective light-emitting area of the laser, improve the symmetry of the transverse optical field distribution of the waveguide section, and reduce the parasitic capacitance parameters of the laser, thereby having the advantages of high power, high modulation rate and high optical fiber coupling efficiency.

In one embodiment of the utility model, the DFB-LD includes a plurality of gratings d along the x-direction, respectively located in P-regions or N-regions of a plurality of semiconductor PN junctions, or a connection layer between semiconductor PN junctions.

In one embodiment of the present invention, when a plurality of PN junctions are connected by tunnel junctions, that is, PN and NP in PN-tunnel junction-PN and NP-tunnel junction-NP operate in a forward conduction state, (where P in PN and NP denotes a P region of PN junction, and N denotes an N region of PN junction), the tunnel junctions include P-type and N-type semiconductors, but operate in a reverse tunneling state, and the grating is located at the tunnel junction and is composed of tunnel junction P-type semiconductors and tunnel junction N-type semiconductors periodically arranged along z direction; the grating positioned at the tunnel junction has periodic absorption to light or periodic passing or blocking to carriers; the tunnel junctions are localized tunnel junctions along the y-direction, and current between the PN can only flow through the tunnel junctions.

In one embodiment of the utility model, each light emitting region of the PN junction is comprised of a quantum well, a barrier and a separate confinement structure, wherein the quantum well and barrier are preferably compressively strained quantum well and tensile strained barrier. The quantum well material is indium gallium arsenic phosphorus multiple quantum well, or aluminum gallium indium arsenic multiple quantum well, or aluminum gallium arsenic multiple quantum well.

In one embodiment of the utility model, the tunnel junction is composed of heavily doped N-type and heavily doped P-type materials, the arrangement direction of the P-type and N-type materials along the surface of the substrate from bottom to top is opposite to that of the PN junction, and the N-type material can be one of heavily doped gallium arsenide, heavily doped indium phosphide, heavily doped aluminum gallium indium arsenide or heavily doped indium gallium arsenic phosphide; the P-type material is one of heavily doped gallium arsenide, heavily doped indium aluminum arsenic, heavily doped indium gallium arsenic, heavily doped aluminum gallium indium arsenic and heavily doped indium gallium arsenic phosphorus material.

To understand the specific structure of the multi-junction distributed feedback semiconductor laser (DFB-LD) in detail, in one embodiment of the present invention, the DFB-LD has a plurality of PN junctions, and for simplicity, only 3 PN junctions are shown in fig. 2, and in principle there may be any number of PN junctions. The DFB-LD comprises electrodes 0a, 4a, a substrate 10a, a functional layer disposed on the substrate 10a, the substrate 10a and the functional layer disposed between the electrodes 0a, 4 a; the functional layer comprises 3 PN junctions arranged on the substrate 10a, the connecting layers between two adjacent PN junctions are 21a and 32a, and the connecting layer 32a between two adjacent PN junctions is provided with a grating 204 a; the PN junction includes a P (or N)

region

101a, 201a, 301a, an N (or P)

region

103a, 203a, 303a, a

light emitting region

102a, 202a, 302a located between the PN junction N and P regions.

In addition, referring to fig. 3, in another embodiment of the present invention, a laser DFB-LD having two PN junctions sharing a P region (or an N region) includes

electrodes

0b, 4b, 5b, a substrate 10b having a functional layer disposed thereon; the functional layer comprises 2 PN junctions arranged on a substrate 10b, wherein the PN junctions comprise P (or N)

regions

101b and 201b, common N (or P)

regions

103b and 203b of the PN junctions, and

light emitting regions

102b and 202b positioned between the N region and the P region of the PN junctions;

electrodes

0b, 4b, 5b are disposed on top of the light emitting region 102b of the PN junction, on top of the

common N regions

103b, 203b of the 1 st and 2 nd PN junctions, and on top of the PN junction N region 201b, respectively.

More specifically, the multi-junction distributed feedback semiconductor laser (DFB-LD) in the application can be an InGaAsP/InP multi-junction distributed feedback semiconductor laser with the wavelength of 1.4-1.6 μm, an AlGaInAs/InP multi-junction distributed feedback semiconductor laser with the wavelength of 1.2-1.4 μm, and a GaAlAs/GaAs multi-junction distributed feedback semiconductor laser with the wavelength of 600-900 nm. Therefore, the four methods for fabricating the multi-junction distributed feedback semiconductor laser are described in detail by the following four specific fabrication examples, which are as follows:

the first concrete preparation example:

the specific embodiment introduces a method for preparing an InGaAsP/InP multi-junction distributed feedback semiconductor laser (DFB-LD) with a wavelength of 1550nm, which comprises the following steps:

referring to fig. 2, the following materials are epitaxially grown on a highly doped n-type InP substrate 10a from bottom to top in one pass: the 1 st PN junction N region 101a, i.e., N-type InP buffer layer (with thickness of 500nm and doping concentration of about 1 × 10)¹⁸cm^-3) (ii) a A light emitting region 102a of the 1 st PN junction, wherein the light emitting region 102a comprises, from bottom to top: an undoped lattice matching InGaAsP lower waveguide layer (thickness 50nm, optical fluorescence wavelength 1170nm), an InGaAsP active layer multiple quantum well (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1700nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1170nm), an undoped lattice matching InGaAsP upper waveguide layer (thickness 20nm, optical fluorescence wavelength 1170 nm); the 1 st PN junction P region 103a is P-type InP waveguide cladding (200 nm thick, doped with heavy dopant)Degree of 1 × 10¹⁸cm^-3) (ii) a 1 st, 2 PN junction tie layer 21a, PN junction tie layer 21a contains from the bottom up: heavily doped p-type InGaAs layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3) Heavily doped n-type InP layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3). The 2 nd PN junction N region 201a, i.e. N-type InP waveguide cladding (thickness 500nm, doping concentration about 1 × 10)¹⁸cm^-3) (ii) a A light emitting region 202a of the 2 nd PN junction, the light emitting region 202a comprising from bottom to top: an undoped lattice matching InGaAsP lower waveguide layer (thickness 50nm, optical fluorescence wavelength 1170nm), an InGaAsP active layer multiple quantum well (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1700nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1170nm), an undoped lattice matching InGaAsP upper waveguide layer (thickness 20nm, optical fluorescence wavelength 1170 nm); the 2 nd PN junction P region 203a is P-type InP waveguide cladding (thickness 200nm, doping concentration 1 × 10)¹⁸cm^-3) (ii) a The 2 nd and 3 rd PN junction connection layers 32a, the PN junction connection layer 32a includes from bottom to top: heavily doped p-type InGaAs layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3) Heavily doped n-type InP layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3)。

The manufacturing process of the grating pattern comprises the following steps: on the basis of a primary epitaxial growth structure, a photoresist pattern of a first-order grating with the period range of 230-250 nm is formed by adopting holographic interference lithography, electron beam lithography, nanoimprint lithography or projection lithography, and the grating pattern is transferred from the photoresist to a heavily doped n-type InP layer and a heavily doped p-type InGaAs layer by adopting a wet etching technology or a dry etching technology.

After the grating pattern is formed, a second epitaxial growth is performed to sequentially grow N-type InP waveguide cladding layers (with a thickness of 500nm and a doping concentration of about 1 × 10) including the 3 rd PN junction N region 301a¹⁸cm^-3) (ii) a A light emitting region 302a of the 3 rd PN junction, the light emitting region 302a of the PN junction comprising from bottom to top: undoped lattice-matched InGaAsP lower waveguide layer (thickness 50nm, optical fluorescence wavelength 1170nm), InGaAsP active layer multiple quantum well (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1700nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1170nm), undoped lattice-matched InGaAsP upper waveguide layer (thick InGaAsP upper waveguide layer)Degree 20nm, light fluorescence wavelength 1170 nm); the 3 rd PN junction P region 303a is a P-type InP waveguide cladding layer (thickness 1500nm, doping concentration 1 × 10)¹⁸cm^-3) P-type InGaAs ohmic contact layer (thickness 200nm, doping concentration about 1 × 10)¹⁹cm^-3)。

The manufacturing and forming process of the ridge waveguide structure comprises the following steps: using Inductively Coupled Plasma (ICP) with Cl₂、CH₄、H₂And Ar is reaction gas, the P-type InGaAs ohmic contact layer and the 3 rd PN junction P region 303 are etched to form a ridge waveguide structure, and the width range of the ridge waveguide is 2-3 mu m.

And depositing 100-200 nm of silicon oxide or silicon nitride as a passivation layer, wherein the color of the passivation layer is uniform. Depositing, photoetching and etching to form thick insulating layer close to the ridge waveguide, wherein the pattern of the insulating layer is parallel to one side of the ridge waveguide and is tightly attached to the ridge waveguide, and the distance is less than or equal to 1 micron; one side of the vertical ridge waveguide has a 50 μm gap as a cutting path for laser cleavage of the split. The thickness of the insulating layer is the same as the depth of the ridge waveguide, namely the upper surface of the insulating layer bonding pad is flush with the top of the ridge waveguide, and the height difference between the upper surface of the insulating layer bonding pad and the top of the ridge waveguide is less than or equal to 100 nm. The thick insulating layer preferably employs photosensitive BCB. Photoetching and etching the passivation layer on the top of the ridge waveguide, wherein the passivation layer on the top of the ridge waveguide is required to be completely etched, namely, the uniform white bright color of the InGaAs material exposed on the top of the ridge waveguide is observed by an optical microscope without any interference color of the passivation layer; while the passivation layer is not etched at all on the ridge waveguide sidewalls and in the regions outside the ridge waveguides.

Photoetching, depositing and stripping are carried out to prepare a P electrode pattern, the P electrode material is preferably Ti/Pt/Au, and the recommended thickness is 10/10/200 nm. The P electrode consists of a slender strip (the width is less than or equal to the width of the ridge waveguide and is 1 mu m), an electrode pad (a circle with the diameter of 100 mu m and the distance between the electrode pad and the ridge waveguide is less than or equal to 20 mu m) and a connecting part (the width is 20 mu m) of the electrode pad and the ridge waveguide. The InP substrate is thinned to around hundred microns and an N electrode is deposited, preferably of Ni/Ge/Au, with a suggested thickness of 10/10/200 nm. The length range of the laser cavity is 100-1000 mu m, and the dissociation cavity surface is observed as a uniform mirror surface without scratches on a microscope (the magnification is more than or equal to 1000 times). The two lasers are respectively plated with a high-reflectivity film and an anti-reflection film, the reflectivity of the high-reflectivity film is more than or equal to 99%, and the reflectivity of the anti-reflection film is less than or equal to 1%.

Specific preparation example two:

this example describes an AlGaInAs/InP multijunction distributed feedback semiconductor laser (DFB-LD) with a wavelength of 1550 nm.

As shown in fig. 3, the following materials are epitaxially grown once on a highly doped p-type InP substrate 10 b: the grating layer 104b of the 1 st PN junction, i.e. the p-type InGaAsP layer (thickness 10nm, doping concentration 1X 10)¹⁸cm^-3)。

The forming process of the grating pattern comprises the following steps: on the basis of the primary epitaxial structure, a photoresist pattern of a first-order grating with the period range of 230-250 nm is formed by adopting holographic interference lithography, electron beam lithography, nanoimprint lithography or projection lithography. The grating pattern is transferred from the photoresist to the grating layer 104b of the 1 st PN junction, i.e., the p-type InGaAsP layer, using a wet or dry etching technique.

After the grating pattern is manufactured, secondary epitaxial growth is carried out, and a 1 st PN junction P region 101b, namely a P-type InP buffer layer (with the thickness of 500nm and the doping concentration of about 1 multiplied by 10) is sequentially grown from bottom to top¹⁸cm^-3) (ii) a A light emitting region 102b of the 1 st PN junction, wherein the light emitting region 102b of the PN junction comprises from bottom to top: undoped lattice-matched AlGaInAs lower waveguide layers (thickness 50nm, optical fluorescence wavelength 1170nm), AlGaInAs active layer multiple quantum wells (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1700nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1170nm), undoped lattice-matched AlGaInAs upper waveguide layers (thickness 20nm, optical fluorescence wavelength 1170 nm); common N region 103b/203b of 1 st and 2 nd PN junctions, i.e. N-type InP waveguide cladding (thickness 200nm, doping concentration 1 × 1018 cm)^-3) (ii) a A light emitting region 202b of the 2 nd PN junction, wherein the light emitting region 202b of the PN junction comprises from bottom to top: undoped lattice-matched AlGaInAs lower waveguide layers (thickness 50nm, optical fluorescence wavelength 1170nm), AlGaInAs active layer multiple quantum wells (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1700nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1170nm), undoped lattice-matched AlGaInAs upper waveguide layers (thickness 20nm, optical fluorescence wavelength 1170 nm); p-type InP waveguide cladding layer (200 nm thick, 1 × 10 doping concentration) as P region 201b of 2 nd PN junction¹⁸cm^-3) (ii) a Grating of 2 nd PN junctionLayer 204b, i.e., a p-type InGaAsP layer (thickness 10nm, doping concentration 1X 10)¹⁸cm^-3)。

The forming process of the grating pattern comprises the following steps: on the basis of the primary epitaxial structure, a photoresist pattern of a first-order grating with the period range of 230-250 nm is formed by adopting holographic interference lithography, electron beam lithography, nanoimprint lithography or projection lithography. The grating pattern is transferred from the photoresist to the grating layer 204b of the 2 nd PN junction, i.e., the p-type InGaAsP layer, using a wet or dry etching technique.

And after the grating pattern is manufactured, secondary epitaxial growth is carried out. Sequentially growing a P region 201b including a 2 nd PN junction, i.e. a P-type InP waveguide cladding layer (with the thickness of 1500nm and the doping concentration of 1 × 10)¹⁸cm^-3) P-type InGaAs ohmic contact layer (thickness 200nm, doping concentration about 1 × 10)¹⁹cm^-3)。

The forming process of the ridge waveguide structure comprises the following steps: using Inductively Coupled Plasma (ICP) with Cl₂、CH₄、H₂And Ar is reaction gas, and a P-type InGaAs ohmic contact layer, a grating layer 204b of a 2 nd PN junction, a P region 201b of the 2 nd PN junction and a light emitting region 202b of the 2 nd PN junction are etched to form a first ridge waveguide structure, wherein the width range of the ridge waveguide is 1-2 mu m. Using Inductively Coupled Plasma (ICP) with Cl₂、CH₄、H₂Ar is reaction gas, a common N area 103b/203b of the 1 st PN junction and the common N area of the 2 nd PN junction and a light emitting area 102b of the 1 st PN junction are etched to form a second ridge waveguide structure, and the width range of the ridge waveguide is 4-5 mu m.

Photoetching, depositing and stripping are carried out to prepare a P electrode pattern, the P electrode material is preferably Ti/Pt/Au, and the recommended thickness is 10/10/200 nm. The P electrode 0b is located on top of the light emitting region 102b of the 1 st PN junction. The P electrode is composed of a long strip (width range 2-3 μm), an electrode pad (circle with diameter of 100 μm), and a connecting part (width of 20 μm) of the two. And (3) depositing, photoetching and etching to manufacture a thick insulating layer next to the common N region 103b/203b of the 1 st and 2 nd PN junctions, wherein the insulating layer pattern is parallel to one side of the common N region 103b/203b of the 1 st and 2 nd PN junctions, and the space is less than or equal to 1 mu m. The insulating layer covers the elongated portions of the top P-electrode of the light emitting region 102b of the 1 st PN junction, exposing the electrode pad portions. The thickness of the insulating layer is the same as the depth of the ridge waveguide, namely the upper surface of the insulating layer is flush with the tops of the common N regions 103b/203b of the 1 st and 2 nd PN junctions, and the height difference between the two regions is less than or equal to 100 nm. The insulating layer has a relative dielectric constant of not more than 4.0, and photosensitive BCB is recommended.

And photoetching, depositing and stripping are carried out to prepare an N electrode pattern, wherein the N electrode material is preferably Ni/Ge/Au, and the recommended thickness is 10/10/200 nm. The N electrode 5b is located on top of the common N region 103b/203b of the 1 st and 2 nd PN junctions. The N electrode is composed of a long and thin strip (width range 1-1.5 μm), an electrode pad (circle with diameter of 100 μm), and a connecting part (width of 20 μm) of the two. And (3) depositing, photoetching and etching to prepare a thick insulating layer close to the top p-type InGaAs ohmic contact layer, wherein the pattern of the insulating layer is parallel to one side of the p-type InGaAs ohmic contact layer, and the distance between the insulating layer and the p-type InGaAs ohmic contact layer is less than or equal to 1 mu m. The insulating layer covers the elongated portions of the top N electrodes of the common N regions 103b/203b of the 1 st and 2 nd PN junctions, exposing the electrode pad portions. The thickness of the insulating layer is the same as the depth of the ridge waveguide, namely the upper surface of the insulating layer is flush with the top of the p-type InGaAs ohmic contact layer, and the height difference between the upper surface of the insulating layer and the top of the p-type InGaAs ohmic contact layer is less than or equal to 100 nm. The insulating layer has a relative dielectric constant of not more than 4.0, and photosensitive BCB is recommended.

Photoetching, depositing and stripping are carried out to prepare a P electrode pattern, the P electrode material is preferably Ti/Pt/Au, and the recommended thickness is 10/10/200 nm. The P-electrode 4b is located on top of the P-type InGaAs ohmic contact layer. The P electrode is composed of a long strip (width range 1-2 μm), an electrode pad (circle with diameter of 100 μm), and a connecting part (width of 20 μm) of the two.

The InP substrate is thinned to around hundred microns. The length range of the laser cavity is 100-1000 mu m, and the dissociation cavity surface is observed as a uniform mirror surface without scratches on a microscope (the magnification is more than or equal to 1000 times). The two lasers are respectively plated with a high-reflectivity film and an anti-reflection film, the reflectivity of the high-reflectivity film is more than or equal to 99%, and the reflectivity of the anti-reflection film is less than or equal to 1%.

Specific preparation example three

This example describes a 1310nm wavelength AlGaInAs/InP multi-junction distributed feedback semiconductor laser (DFB-LD).

Referring to fig. 2, the following materials are epitaxially grown on a highly doped n-type InP substrate 10a from bottom to top in one pass: the 1 st PN junction N region 101a, i.e., N-type InP buffer layer (with thickness of 500nm and doping concentration of about 1 × 10)¹⁸cm^-3) (ii) a A light emitting region 102a of the 1 st PN junction, the light emitting region 102a comprising, from bottom to top: undoped lattice-matched AlGaInAs lower waveguide layers (thickness 50nm, optical fluorescence wavelength 1050nm), AlGaInAs active layer multiple quantum wells (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1460nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1050nm), undoped lattice-matched AlGaInAs upper waveguide layers (thickness 20nm, optical fluorescence wavelength 1050 nm); the 1 st PN junction P region 103a is P-type InP waveguide cladding (thickness 200nm, doping concentration 1 × 10)¹⁸cm^-3) (ii) a 1 st, 2 PN junction tie layer 21a, tie layer 21a contains from the bottom up: heavily doped p-type InGaAs layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3) Heavily doped n-type InP layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3). The 2 nd PN junction N region 201a, i.e. N-type InP waveguide cladding (thickness 500nm, doping concentration about 1 × 10)¹⁸cm^-3) (ii) a A light emitting region 202a of the 2 nd PN junction, the light emitting region 202a comprising from bottom to top: undoped lattice-matched AlGaInAs lower waveguide layers (thickness 50nm, optical fluorescence wavelength 1050nm), AlGaInAs active layer multiple quantum wells (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1460nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1050nm), undoped lattice-matched AlGaInAs upper waveguide layers (thickness 20nm, optical fluorescence wavelength 1050 nm); the 2 nd PN junction P region 203a is P-type InP waveguide cladding (thickness 200nm, doping concentration 1 × 10)¹⁸cm^-3) (ii) a The 2 nd and 3 rd PN junction connection layers 32a, the PN junction connection layer 32a includes from bottom to top: heavily doped p-type InGaAs layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3) Heavily doped n-type InP layer (thickness 10nm, doping concentration 1X 10)¹⁹cm^-3)。

The forming process of the grating pattern comprises the following steps: on the basis of the primary epitaxial structure, a photoresist pattern of a first-order grating with the period range of 200-210 nm is formed by adopting holographic interference lithography, electron beam lithography, nanoimprint lithography or projection lithography. The grating pattern is transferred from the photoresist to the heavily doped n-type InP layer and the heavily doped p-type InGaAs layer using wet or dry etching techniques.

And after the grating pattern is manufactured, secondary epitaxial growth is carried out. The sequential growth comprises3 PN junction N regions 301a, i.e. N-type InP waveguide cladding (thickness 500nm, doping concentration about 1X 10)¹⁸cm^-3) (ii) a A light emitting region 302a of the 3 rd PN junction, the light emitting region 302a comprising, from bottom to top: undoped lattice-matched AlGaInAs lower waveguide layers (thickness 50nm, optical fluorescence wavelength 1050nm), AlGaInAs active layer multiple quantum wells (2 pairs of quantum wells, well width 8nm, 1% compressive strain, optical fluorescence wavelength 1460nm, barrier width 10nm, 0.2% tensile strain, optical fluorescence wavelength 1050nm), undoped lattice-matched AlGaInAs upper waveguide layers (thickness 20nm, optical fluorescence wavelength 1050 nm); the 3 rd PN junction P region 303a is a P-type InP waveguide cladding layer (thickness 1500nm, doping concentration 1 × 10)¹⁸cm^-3) P-type InGaAs ohmic contact layer (thickness 200nm, doping concentration about 1 × 10)¹⁹cm^-3)。

The forming process of the ridge waveguide structure comprises the following steps: using Inductively Coupled Plasma (ICP) with Cl₂、CH₄、H₂And Ar is reaction gas, the P-type InGaAs ohmic contact layer and the 3 rd PN junction P region 303a are etched to form a ridge waveguide structure, and the width range of the ridge waveguide is 2-3 mu m.

And depositing 100-200 nm of silicon oxide or silicon nitride as a passivation layer, wherein the color of the passivation layer is uniform. Depositing, photoetching and etching to form thick insulating layer close to the ridge waveguide, wherein the pattern of the insulating layer is parallel to one side of the ridge waveguide and is tightly attached to the ridge waveguide, and the distance is less than or equal to 1 micron; one side of the vertical ridge waveguide has a 50 μm gap as a cutting path for laser cleavage of the split. The thickness of the insulating layer is the same as the depth of the ridge waveguide, namely the upper surface of the insulating layer bonding pad is flush with the top of the ridge waveguide, and the height difference between the upper surface of the insulating layer bonding pad and the top of the ridge waveguide is less than or equal to 100 nm. The relative dielectric constant of the insulating layer is not more than 4.0. Photosensitive BCB is suggested. Photoetching and etching the passivation layer on the top of the ridge waveguide, wherein the passivation layer on the top of the ridge waveguide is required to be completely etched, namely, the uniform white bright color of the InGaAs material exposed on the top of the ridge waveguide is observed by an optical microscope without any interference color of the passivation layer; while the passivation layer is not etched at all on the ridge waveguide sidewalls and in the regions outside the ridge waveguides.

The P electrode 4a is patterned by photoetching, deposition and stripping, and the material of the P electrode 4a is preferably Ti/Pt/Au, and the recommended thickness is 10/10/200 nm. The P electrode 4a is a slender strip (width is less than or equal to the width of the ridge waveguide and is 1 μm), an electrode pad (a circle with the diameter of 100 μm and the distance between the electrode pad and the ridge waveguide is less than or equal to 20 μm) and a connecting part (the width is 20 μm) of the electrode pad and the ridge waveguide. The InP substrate is thinned to around hundred microns and an N-electrode 0a is deposited, the N-electrode 0a material preferably being Ni/Ge/Au, with a suggested thickness of 10/10/200 nm. The length range of the laser cavity is 100-1000 mu m, and the dissociation cavity surface is observed as a uniform mirror surface without scratches on a microscope (the magnification is more than or equal to 1000 times). The two laser devices are respectively plated with a high-reflectivity film and an anti-reflection film, the reflectivity of the high-reflectivity film is more than or equal to 99%, and the reflectivity of the anti-reflection film is less than or equal to 1%.

Specific preparation example four

This example describes an AlGaAs/GaAs multijunction distributed feedback semiconductor laser (DFB-LD) with a wavelength of 850 nm.

As shown in fig. 3, the following materials are once epitaxially grown on a highly doped n-type GaAs substrate 10 b: grating layer 104b of the 1 st PN junction, i.e., n-type Ga_1-xAl_xAs layer (thickness 10nm, x is 0.2, doping concentration 1 × 10¹⁸cm^-3)。

The forming process of the grating pattern comprises the following steps: on the basis of the primary epitaxial structure, a photoresist pattern of the second-order grating is formed by holographic interference lithography, electron beam lithography, nanoimprint lithography or projection lithography. The grating pattern is transferred from the photoresist to the grating layer 104b of the 1 st PN junction, i.e., n-type Ga, by wet or dry etching technique_1-xAl_xOn the As layer.

After the grating pattern is manufactured, secondary epitaxial growth is carried out, and a 1 st PN junction N region 101b, namely an N-type GaAs buffer layer (with the thickness of 500nm and the doping concentration of about 1 multiplied by 10) is sequentially grown from bottom to top¹⁸cm^-3) (ii) a A light emitting region 102b of the 1 st PN junction, the light emitting region 102b comprising, from bottom to top: undoped lattice-matched Ga_1-xAl_xAs lower waveguide layer (thickness 50nm, x ═ 0.06), GaAs/Ga_1- _xAl_xAs active layer multiple quantum well (2 pairs of GaAs strained quantum well, well width 8 nm; barrier width 10nm, x ═ 0.06), undoped lattice matched Ga_1-xAl_xAn As upper waveguide layer (thickness 20nm, x ═ 0.06); common P region 103b/203b of 1 st and 2 nd PN junctions, namely Ga_1- _xAl_xAs waveguide cladding (thickness 200nm, x 0.45, doped withImpurity concentration 1X 10¹⁸cm^-3) (ii) a A light emitting region 202b of the 2 nd PN junction, the light emitting region 202b comprising, from bottom to top: undoped lattice-matched Ga_1-xAl_xAs lower waveguide layer (thickness 50nm, x ═ 0.06), GaAs/Ga_1-xAl_xAs active layer multiple quantum well (2 pairs of GaAs strained quantum well, well width 8 nm; barrier width 10nm, x ═ 0.06), undoped lattice matched Ga_1-xAl_xAn As upper waveguide layer (thickness 20nm, x ═ 0.06); n-type Ga as N-region 201b of 2 nd PN junction_1-xAl_xAs waveguide cladding (thickness 200nm, doping concentration 1X 10)¹⁸cm^-3) (ii) a Grating layer 204b of the 2 nd PN junction, i.e., n-type Ga_1-xAl_xAs layer (thickness 10nm, x is 0.2, doping concentration 1 × 10¹⁸cm^-3)。

The forming process of the grating pattern comprises the following steps: on the basis of the secondary epitaxial structure, a photoresist pattern of the second-order grating is formed by holographic interference lithography, electron beam lithography, nanoimprint lithography or projection lithography. Transferring the grating pattern from the photoresist to the grating layer 204b of the 2 nd PN junction, i.e., n-type Ga, by wet or dry etching_1-xAl_xOn the As layer.

After the grating pattern is manufactured, three times of epitaxial growth are carried out to grow the 2 nd PN junction N region 201b, namely N-type Ga_1- _xAl_xAs waveguide cladding (thickness 1500nm, doping concentration 1X 10)¹⁸cm^-3)。

The forming process of the ridge waveguide structure comprises the following steps: using Inductively Coupled Plasma (ICP) with Cl₂、BCl₃Ar is reaction gas, a 2 nd PN junction N area 201b, a 2 nd PN junction grating layer 204b and a 2 nd PN junction light emitting area 202b are etched to form a first ridge waveguide structure, and the width range of the ridge waveguide is 1-2 mu m. Using Inductively Coupled Plasma (ICP) with Cl₂、BCl₃Ar is reaction gas, a common P area 103b/203b of the 1 st PN junction and the common P area of the 2 nd PN junction and a light emitting area 102b of the 1 st PN junction are etched to form a second ridge waveguide structure, and the width range of the ridge waveguide is 4-5 mu m.

The N electrode 0b is patterned by photolithography, deposition and lift-off, and the material of the N electrode 0b is preferably Ni/Ge/Au, and the recommended thickness is 10/10/200 nm. The N electrode 0b is located on top of the light emitting region 102b of the 1 st PN junction. The N electrode 0b is composed of a long and thin bar (width range 2-3 μm), an electrode pad (circle with a diameter of 100 μm), and a connecting portion (width 20 μm) of the two. And (3) depositing, photoetching and etching to manufacture a thick insulating layer next to the common P region 103b/203b of the 1 st and 2 nd PN junctions, wherein the insulating layer pattern is parallel to one side of the common N region 103b/203b of the 1 st and 2 nd PN junctions, and the space is less than or equal to 1 mu m. The insulating layer covers the elongated portions of the top N electrode of the light emitting region 102 of the 1 st PN junction, exposing the electrode pad portions. The thickness of the insulating layer is the same as the depth of the ridge waveguide, namely the upper surface of the insulating layer is flush with the tops of the common P regions 103b/203b of the 1 st and 2 nd PN junctions, and the height difference between the two is less than or equal to 100 nm. The relative dielectric constant of the insulating layer is not more than 4.0. Photosensitive BCB is suggested.

The P electrode 5b is patterned by photoetching, deposition and stripping, and the material of the P electrode 5b is preferably Ti/Pt/Au, and the recommended thickness is 10/10/200 nm. The P electrode 5b is located on top of the common P region 103b/203b of the 1 st and 2 nd PN junctions. The P electrode 5b is composed of a long strip (width range 1-1.5 μm), an electrode pad (circle with diameter 100 μm), and a connecting portion (width 20 μm) between the two. And (3) depositing, photoetching and etching to manufacture a thick insulating layer close to the top 2 nd PN junction N region 201b, wherein the pattern of the insulating layer is parallel to one side of the 2 nd PN junction N region 201b, and the distance between the insulating layer and the side of the 2 nd PN junction N region 201b is less than or equal to 1 mu m. The insulating layer covers the elongated portions of the top P electrodes of the common P regions 103b/203b of the 1 st and 2 nd PN junctions, exposing the electrode pad portions. The thickness of the insulating layer is the same as the depth of the ridge waveguide, namely the upper surface of the insulating layer is flush with the top of the 2 nd PN junction N region 201b, and the height difference between the insulating layer and the top of the PN junction N region is less than or equal to 100 nm. The relative dielectric constant of the insulating layer is not more than 4.0. Photosensitive BCB is suggested.

The N electrode 4b is patterned by photoetching, deposition and stripping, and the material of the N electrode 4b is preferably Ni/Ge/Au, and the recommended thickness is 10/10/200 nm. The N electrode 4b is located on top of the 2 nd PN junction N region 201 b. The N electrode 4b is composed of a long strip (width range of 1 to 2 μm), an electrode pad (circle with a diameter of 100 μm), and a connecting portion (width of 20 μm) between the two.

The GaAs substrate is thinned to about hundred microns. The length range of the laser cavity is 100-1000 mu m, the length error is less than or equal to 1 mu m, and the dissociation cavity surface is observed as a uniform mirror surface without scratches on a microscope (the magnification is more than or equal to 1000 times). The two lasers are respectively plated with a high-reflectivity film and an anti-reflection film, the reflectivity of the high-reflectivity film is more than or equal to 99%, and the reflectivity of the anti-reflection film is less than or equal to 1%.

The concrete preparation example five:

this example describes an AlGaAs/GaAs multijunction distributed feedback semiconductor laser (DFB-LD) having a wavelength of 850nm, which was fabricated in the same manner as in the fourth specific fabrication example, except that the highly doped n-type GaAs substrate used in the fourth specific fabrication example was replaced with a non-doped GaAs substrate.

It should be noted that the terms "first," "second," and the like in the description of the present invention are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.

Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the utility model. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A multi-junction distributed feedback semiconductor laser is characterized by comprising a substrate and a laser DFB-LD functional layer growing on the surface of the substrate;

2. A multi-junction distributed feedback semiconductor laser as in claim 1 wherein said plurality of semiconductor PN junctions are interconnected by tunnel junctions.

3. A multi-junction distributed feedback semiconductor laser as in claim 2 wherein said plurality of semiconductor PN junctions are two PN junctions, the two PN junctions being connected in a manner to share a P-region or a N-region.

4. A multi-junction dfb semiconductor laser as claimed in claim 2 wherein the tunnel junction is comprised of heavily doped N-type and P-type materials, the grating is located at the tunnel junction and is comprised of P-type and N-type semiconductors arranged periodically along the direction of light propagation, and the grating located at the tunnel junction periodically absorbs light energy or periodically passes or blocks carrier energy.

5. The multi-junction distributed feedback semiconductor laser as in claim 4 wherein the heavily doped N-type is one of heavily doped gallium arsenide, heavily doped indium phosphide, heavily doped aluminum gallium indium arsenide, or heavily doped indium gallium arsenide phosphide; the heavily doped P-type material is one of heavily doped GaAs, heavily doped InAlAs, heavily doped InGaAs, heavily doped AlGaInAs or heavily doped InGaAsP material.

6. A multi-junction distributed feedback semiconductor laser as in claim 1 wherein said light emitting region comprises quantum wells, barriers and confinement structures, respectively.

7. The multi-junction distributed feedback semiconductor laser as in claim 6 wherein said quantum well is one of an indium gallium arsenide phosphide multi-quantum well, an aluminum gallium indium arsenide multi-quantum well or an aluminum gallium arsenide multi-quantum well.

8. A multi-junction distributed feedback semiconductor laser as in claim 1 wherein said substrate is a doped or undoped semiconductor.