JPS5810884A - Manufacture of semiconductor laser having embedded heterogeneous structure - Google Patents

Abstract

PURPOSE:To manufacture InGaAsPBHLD characterized by the small leaking current and therefore the excellent temperature characteristics by obtaining a current block layer for preventing a leaking current with excellent reproducibility. CONSTITUTION:A semiconductor layer including at least an active layer 303 is laminated on an N type InP substrate 1. On the surface of a wafer having the multilayered film structure described above, a stripe shaped diffused protecting mask 305 is formed. Then, P type impurities are selectively diffused to the part deeper than the active layer 303. A part of the entire part of said P type impurity region 306 is chemically etched selectively to the surface of the active layer, and a mesa stripe 307 is formed. The active layer 303 at the part other than said mesa stripe is melted back. Then only the upper surface of the mesa stripe 307 is removed, the N type current block layer 309 is laminated, a P type embedded layer 310 is laminated, an N-InGaAsP cap layer 311 is laminated, and the growing is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a buried heterostructure semiconductor laser, particularly an InP
The present invention relates to a method of manufacturing an InGaAsP [1-embedded heterostructure semiconductor laser using a t-substrate.

Buried heterostructure semiconductor lasers (hereinafter abbreviated as BH-LD) are attracting attention as light sources for optical fiber communications because they have excellent characteristics such as low oscillation threshold current, stabilized oscillation transverse mode, and high-temperature operation. Collected 0 For example, flat land, etc.P Electronic Materials Magazine Vol. 18 No. 12 published December 1979
As reported on pages 58 to 61 of the issue @
InGaAs P BH-LD with the shape shown in Figure 1
F production details.

By the way, compared to AjGa3 type laser, InGaAs
P-based lasers generally have a drawback in that the oscillation threshold current has a large temperature dependence, and the oscillation threshold current increases significantly even with a slight temperature rise. Especially InG
In a PBH-LD, the leakage current flowing through the InPO p-n junction around the active layer increases. It increases further as the temperature rises. Therefore, in order to prevent electrical leakage, the current confinement layer 107 and the n-type rad layer 102 are shown in FIG.
There is a p-type InP layer connected to the side surface of the active layer between
It is necessary to provide a mesa side surface and a pnpn structure.

By the way, in the manufacturing process of the BHLD shown in FIG.
In order to form the active layer 103 so as to be connected to the side surface of the active layer 103.

It is necessary to precisely control the etching depth when etching and etching into an inverted mesa shape and the growth thickness of the p-type InP current blocking layer 106, but it is necessary to precisely control the etching depth and the growth thickness of the p-type InP current blocking layer 106. It cannot be said that the mesa etching method using a mesa etching solution etc. has sufficient controllability, and the current blocking layer 106
It is difficult to form the InGaAsP BH at the desired position on the side surface of the active layer with good reproducibility.
-This results in a poor manufacturing yield of LD. Furthermore, in this example, during the second epitaxial growth, the mesa side surface 112 is exposed to a high temperature atmosphere for a long time, resulting in so-called thermal damage.

The drawback is that the oscillation threshold current density increases as the width of the active layer 103 becomes smaller, and the reliability is not sufficient.For example, in a constant output life test of 5mW at 50°C InGaAsP with active layer
Compared to LD, the deterioration rate is about 1 order of magnitude higher.

The object of the present invention is to eliminate the above-mentioned drawbacks by producing a highly reliable Indium alloy with low leakage current and excellent temperature characteristics.
The object of the present invention is to provide a method for producing GaAsP BHLD'gr with good reproducibility.

According to the present invention, the 1-position orientation is (100), To or (1
00) At least I n in the nearby n-type InP substrate
1-x G a x A s 1 ++ y P y
(0 < x < 1 e O < Y < 1) After forming a stripe-shaped diffusion protection mask along the <011> direction on the surface of a multilayer structure wafer in which semiconductor layers including active layer tubes are laminated, The p-type impurity is
a x A m 1 ++ y P y A step of selectively diffusing deeper than the active layer and a part 1+ of the selectively diffused p-type impurity region is entirely transferred to the above In 1-
a XA l 1-YP, selective chemical etching up to the surface of the active layer to form mesa stripes parallel to the <011>direction;
After melting back the n1-1G a xA s 1-A Py active layer, the n-type I n 1-x/Gax' A@1 , /P, / is formed except for only the upper surface of the mesa stripe.
(O <X'<
gAs 1-y#P,# A method for manufacturing a buried heterostructure semiconductor laser is obtained, which includes an epitaxial growth step of continuously laminating a buried layer over the entire surface.

Before explaining the examples, we will briefly explain the method of forming a buried active layer using the melt-back method. In order to remove this and grow a good epitaxial growth layer, a method is used in which the substrate surface is melted back using an In melt or an unsaturated InP solution just before the start of epitaxial growth. This removes the surface damage layer from the substrate surface by utilizing the fact that when the solution to be contacted is unsaturated, InP on the surface begins to dissolve into the solution.

This results in a clean surface with no heat damage. By the way, the effect of such meltback is In
InGaAsP also has a larger P value.

An InGaAsP layer having a composition with a longer wavelength has a property of being easily melted back. Therefore, as shown in FIG. 2(a), only a portion of the InP mesa stripe is left on the InGaAsP active layer 202.

By selecting meltback conditions using an InP unsaturated solution, the InGaAsP active layer 202t in the area other than the InP mesus drive 203 is removed as shown in FIG. 2(b).
- The so-called heat-damaged layer on the surface can be removed by melting back. This can be achieved by melting back at 620°C for 30 seconds using an unsaturated InP solution with a supersaturation degree △T = -10°C (unsaturated), as shown in Figure 2 (b). It becomes possible to leave the InGaAsP active layer 202i only in the InP mesa stripe 203 portion. In this case, InP mesa stripe 2
Since the InP mesa stripe 203 is slightly melted back, the corners of the InP mesa stripe 203 tend to be slightly rounded. Since the side surface of the active layer 102 is not exposed to a high-temperature atmosphere as in the case of the example shown in FIG. 1, the buried active layer is not subject to thermal damage. It becomes possible to manufacture a highly reliable buried heterostructure semiconductor laser with good reproducibility without significantly increasing the threshold current density.

FIG. 23 is a cross-sectional view showing the manufacturing method of the embodiment of the present invention. In FIG. 3(1), an n-InP buffer layer 302 (Te doped, 5 μm thick ), non-doped I n s, ye Ga
,,.

Aso, 5spe, as active layer 303 (wavelength 1.3 μm
Composition, thickness: 0.15 μm), p-InP cladding layer 304 (Zn doped, thickness: 0.6 μm) was sequentially stacked on an ordinary 1nGaAsP-InP DH wafer, and a p-type impurity selective diffusion protective mask of Sin, C
A VD film is deposited to a thickness of about 0.3 μm. A photoresist stripe with a width of 4 μm is completely formed along the <011> direction using the usual photolithography method, and this is used as a mask for etching using hydrofluoric acid. 1 Selective diffusion protection mask 3
A p-type impurity diffusion layer 306 is formed by diffusing Zn f as a primary p-type impurity except for Zn to a depth of about 1 2 μm. At this time, as shown in the figure, a selective diffusion protection mask 305
In FIG. 3 (2), a selective diffusion protection mask 3 is applied, leaving behind an undiffused layer with a width of 2 to 3 μm under the mask.
05t-This time it is used as an etching mask, and InP
Only the p-InP cladding layer 304 is etched using a selected etching solution, which is a 4:1 mixture of hydrochloric acid and pure water. Then select diffusion protection mask 305 with salt 9
A p-InP mesa 307 with a height of 1 μm? Form.

At this stage, as shown in the figure, n-InP is
A layer type 02 medium diffusion layer 306 #1 is formed in the buffer layer 302 . In Fig. 3 (3), the supersaturation degree of the solution was set to Δ'l' = -10°C for buried growth.
Areas other than mesa stripes ('
IJ, 7@”@J@A”@48 ps, ss active layer 3
03t meltback and BH-LD embedded: [
fl*, teoae, ioλm@j&PLH active layer 30
G? After forming the n-InP current blocking layer 309 (
'I'e dope.

(Thickness of flat part: 0.4 μm)' Grown on areas other than the upper surface of the t-mesa stripe. This is a patent application filed by the authors in 1232-1982.
As described in detail in 61, InPMit is layered except for the upper surface of the narrow mesa stripe, which is particularly convenient for preventing leakage current of BH-LD. N-In
GaAsP cap layer 311 (Te doped thickness 0.5
µm) to finish the growth. The p-n junction between the p-InP impurity diffusion layer 306 and the n-InP current blocking layer 309, which will become the current blocking layer during buried growth, is made of InP.
640G @, 80k” @, n P@, u active layer 30
It is formed right next to 8, and InGaAsP BH-
This is particularly effective in preventing LD leakage current. Finally, as shown in FIG. 3(4), a selective Zn diffusion layer 312 with a width of 8 μm and a depth reaching the p-InP buried layer 31G is formed on the obtained multilayer film wafer by the usual method, and then a selective Zn diffusion layer 312 is formed on the p-side. A
Au-Ge-Ni on the n side of the uZn ohmic electrode 313゜
Ohmic electrode 314 T-formed 110) The surface is opened to the Fabry-Perot resonator surface, and the In
GaAsP BH-LD is produced.

FIG. 4 is a perspective view of the embodiment of the present invention manufactured in this way. In FIG. 5, 402 is an I
n 6.7 (1()a 6 , @・AS・,ssP
・, ss active layer.

403 is a p-InP cladding layer, and n-Inpt<
A p-InP impurity diffusion layer 404 is provided in the buffer layer 409 in advance. Reference numeral 405 denotes an n-InP current blocking layer, which grows in the area excluding the upper part of the mesa, as shown in the figure. 406 and 407 are respectively p-In
PJl embedded layer, 1 with n-GaInAsP cap
Selective Zn diffusion layer 408t p-InP only on top of mesa
By forming the layer 7 to reach the buried layer 406, the current flows through In・, 7・Ga・, HAS・, ・SP・, a
It effectively flows only to the m active layer 402 portion. The p-type impurity diffusion layer 404 and n-In which become the current blocking layer
P=p-n junction of current blocking layer 405 is active layer 40
2, and this is InGaAsP B
This is particularly effective in preventing leakage current of H-LD. By using the melt-back method, there is less influence of thermal damage during the second epitaxial growth, and high reliability can be expected.
When applying a bias voltage that makes the positive side of K9 negative negative, the active layer 4020 part is forward biased as a pn junction, so radiative recombination occurs in this region, but most of the other regions become pnpn junctions. Therefore, it exhibits negative resistance characteristics, and almost no current flows below the turn-on voltage.

Therefore, since the current flows concentratedly in the active layer 402, 2
9 In the manufacturing method of the present invention, in which a low oscillation threshold current of about 0 mA was obtained, p-type impurity is selectively diffused to be formed deeper than the active layer 402, and a selective diffusion protection mask is used to diffuse the p-type impurity to the surface of the InGaAsP active layer. After selectively etching and melting back the active layer, a current layer is automatically and reliably formed in areas other than the top of the mesa, resulting in BH-LD.
The leakage current in the oscillation threshold current is reduced, and the thermally damaged layer introduced during the second epitaxial growth can be removed, resulting in excellent temperature characteristics of the oscillation threshold current. Moreover, a highly reliable BH-LD was obtained with good reproducibility.

In the embodiment of the present invention, the active layer is made of Iflo, tsGae, ssAle, ashs, ss with a thickness of 1.3 μm.
I am using k.

This is not limited to (lattice matching L I to InP substrate)
The emission wavelength range of the n1-x GaxAsl-y py mixed crystal (0<x<1° x 1) is from 1.1 μm to 1.
It does not matter if the crystal has any wavelength between 7 μm, and an n-InP layer (x'=0.
y'=1)t- was used, but this layer only needs to have the function of concentrating the current gold in the active layer, so n-type Inx-X'Ga X/A, which has a larger energy gap than the active layer, is used.
s 1 ++ y P yI layer, that is, active layer In1
−xGaxAs For P, O xj<x, y<,
y'kuit-man-77 n-type I n 1 ++X/ Ga x' A
I 1-y' P y1 layer or semi-insulating I
n 1-xl Gaz' As ly' P y'
The p-type InPjJl embedded layer can be a p-type 11 layer regardless of the energy gap of the active layer.
mm-xj GalaxyAsl-y* P, # (0>
x"<1°0<y" (1) A layer may be used.

The present invention is a manufacturing method that can obtain a current blocking layer for preventing leakage current of fnGaAsP BH-LD with good reproducibility, and the production yield of InGaAsP BH-LDO can be greatly improved. InGaAsPBH-LD is highly reliable because the effect of thermal damage on the active layer can be reduced.
can be obtained with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional InGaAsP BH-LD, FIG. 2 is a diagram showing the shape of buried active layer stripes formed by the melt-back method, and FIG. 3 is a diagram showing the manufacturing method according to the present invention. The sectional view, FIG. 4, is a perspective view of an embodiment of the invention. In the figure, 101 is an H-InP substrate, 102 is an n-InP substrate,
Far layer% 103 is InGaAsP active layer, 104 is p
-InP cladding layer, 105 is p-GaInAsP electrode layer, 106 is p-InP current blocking layer, 107 is n
-InP current blocking layer, 108 is n-InGaAsP
1°109 is 8i0. 110 is a p-type ohmic electrode. 111 is an n-type ohmic electrode, and 201 is an InP substrate. 202 is an InGaAsP layer, 203 is an InP mesa stripe, 204 is an fcInGaAsP layer left only at the bottom of the InP mesa stripe after meltback, and 303 is an In0
．． 7°Ga 00sOAs o, ss re, as active layer, 305 is a selective diffusion protection mask, and 306 is a p-type impurity diffusion layer. 307 is p-InP mesa stripe, 308 is In(
1,7゜Ga0jImuS@, 45 PO,li active layer, 31O is p-InP buried layer, 311 is n-
GaInAsP cap layer. 312 is a Zn diffusion layer, 313 is an Au Znn automatic electrode, 314 is an AuGe-Ni 9WAIL
402 is I"0jOG"0. IOA”0jiP1.IM
The active layer 4o4 is a p-type impurity diffusion layer 24o5 is n-In
P current pro, Figure 1/10 2σ in layer

Claims (1)

[Claims] At least In knee
x As1-yPy (0<x<1.0<y<1) After forming a stripe-shaped diffusion protection mask along the K<011> direction on the surface of the wafer, which has a multilayer film structure in which semiconductor layers including an active layer are laminated. , the second conductivity type impurity is I'
A step of selectively diffusing m-x GaxAs□-AP deeper than the active layer and selectively diffusing part or all of the p-type impurity region to the surface of the In 1-8GaxA, 1-APy active layer. etching to form mesa stripes parallel to the <011>direction;
After melting the active layer 1-F T , only the upper surface of the mesa stripe is removed by t.
−ytP y/(0<x'<xtY<Y'
<1) A current blocking layer is laminated, and the second
"-1-x'Gax#A"i -y" Py of conductivity type
1. A method for manufacturing a buried heterostructure semiconductor laser, comprising: an epitaxial growth step of continuously laminating a 111 embedded layer over the entire surface.