JP2005026625A - Surface-emitting laser and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the uniformity and yield of processing by increasing the controllability of an oxidizing process. <P>SOLUTION: An area of an AlAs layer 15 to be oxidized is irradiated with laser light according to the pattern of a mask layer 18 and the difference in reactivity between the laser irradiated part and an unirradiated part is used to generate a difference in oxidation speed, thereby making the oxidation stop at a laser light irradiation boundary. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface emitting semiconductor laser having a high light output and a method for manufacturing the same.

  A surface-emitting semiconductor laser has a feature that a threshold current required for laser oscillation is smaller than that of an edge-emitting semiconductor laser. However, in order to reduce the threshold current, current and light are applied to a minute region. It is necessary to confine at the same time. Conventionally, by oxidizing an Al-containing layer such as an AlAs layer deposited on the light emitting layer from the lateral direction, an insulating layer is introduced into the vertical resonator, and a small non-oxidized region remaining without being oxidized ( Low threshold oscillation has been realized by narrowing the current path to the current confinement region. In particular, single mode oscillation can be realized by setting the size of the current confinement region to several μm or less (depending on the oscillation wavelength).

JP 2002-353562 A

  In order to oxidize the Al-containing layer deposited on the light emitting layer from the lateral direction and leave a current path having a diameter of several μm, it is necessary to perform uniform lateral oxidation within the wafer surface. When the lateral oxidation variation is large in the wafer surface, a device that has been oxidized excessively has a problem that current does not flow or output is extremely small due to the current path being blocked. Further, a device with little oxidation has a problem that the current path becomes large and becomes multimode, and the spread angle of the laser beam becomes large, so that the coupling efficiency with the optical fiber is lowered. These problems are caused by the controllability and uniformity of the oxidation process, and are caused by a small margin of processing conditions.

  In the conventional manufacturing method, the size of the oxide layer formed by oxidizing the Al-containing layer from the lateral end, in other words, the diameter of the current confinement region (current path diameter) is controlled by the oxidation rate and the oxidation time. It was. In order to ensure a sufficient allowance for the oxidation time, it is necessary to make the oxidation rate relatively slow, which causes a problem that the oxidation time becomes long and the productivity deteriorates.

  Furthermore, in the conventional Al-containing layer oxidation method, the shape of the oxidized region (in other words, the shape of the current confinement region that is a non-oxidized region) can be freely controlled, or a plurality of non-oxidized regions are arranged in the oxidized region. The shape of the oxidized region could not be patterned.

  In view of the above-described problems of the conventional technology, the present invention provides a method for manufacturing a surface emitting semiconductor laser with improved controllability of an oxidation process and improved processing uniformity and yield, and patterning the shape of an oxidized region. It is an object of the present invention to provide a method for manufacturing a surface emitting semiconductor laser capable of performing the same. Another object of the present invention is to provide a surface emitting semiconductor laser in which a plurality of current confinement regions are independently formed in an island shape.

  In order to achieve the above object, the present invention introduces an oxidation self-stop mechanism in which the lateral oxidation of the film stops at a certain place regardless of time. More specifically, by causing a large difference between the oxidation rate of the region to be oxidized and the oxidation rate of the non-oxidized region, the self-stop of oxidation is realized in a pseudo manner. Specifically, the oxidation rate is increased by irradiating the region to be oxidized with laser light. That is, according to the present invention, by irradiating the laser beam according to the pattern, the difference in the oxidation rate is utilized by utilizing the difference in reactivity generated between the irradiated part and the non-irradiated part, and the oxidation is self-stopped at the laser light irradiation boundary. Thus, the uniformity of the oxidation process and the yield are improved.

The wavelength of the laser beam to be irradiated is not absorbed by the material constituting the semiconductor multilayer film reflector, but is absorbed only by the light emitting layer. That is, if the band gap of the material having the smallest band gap among the materials constituting the semiconductor multilayer mirror is Eg _low and the band gap of the material constituting the light emitting layer is Eg _act , the wavelength of the laser beam to be irradiated A _irr needs to satisfy the following equation (1), where h is a Planck constant and c is the speed of light.
hc / Eg _low > A _irr > hc / Eg _act (1)

  The irradiated laser light is absorbed by the light emitting layer and generates heat, and accordingly, the semiconductor layer immediately above the light emitting layer is also heated to raise the temperature. As a result, there is a temperature difference between the region irradiated with laser light and the region not irradiated, and the oxidation rate is significantly different between the two regions. Therefore, oxidation is automatically performed at the boundary between the regions that should be oxidized layers during oxidation. It seems to have stopped. When the method of the present invention is used, the oxidation rate can be increased to shorten the oxidation time, thereby improving productivity and increasing the tolerance of the oxidation time, thereby improving in-plane uniformity and yield.

  A surface emitting semiconductor laser has a structure in which a lower multilayer reflector, a light emitting layer, an Al-containing layer having an oxidized region and a non-oxidized region surrounded by the oxidized region, and an upper multilayer reflector are sequentially formed on a substrate. However, the surface emitting semiconductor laser according to the present invention is characterized in that the Al-containing layer is provided with a plurality of independent non-oxidized regions each surrounded by an oxidized region.

  The plurality of independent non-oxidized regions have substantially the same shape, and are typically arranged in a two-dimensional array. The electrode is provided above the oxidized region sandwiched between two adjacent non-oxidized regions.

  A method of manufacturing a surface emitting semiconductor laser according to the present invention includes: a step of sequentially forming a lower multilayer reflector, a light emitting layer, an Al-containing layer for setting a current confinement region, and an upper multilayer reflector on a substrate; A step of exposing the end of the layer, a step of giving a temperature distribution to the Al-containing layer so that a region to be an oxidized region is at a higher temperature than a region to be a non-oxidized region, and a state in which the temperature distribution is given And a step of oxidizing the Al-containing layer from the exposed end portion.

  The temperature distribution can be given by selectively irradiating a region to be an oxidized region with laser light having a wavelength that is not absorbed by the upper multilayer mirror and absorbed by the light emitting layer. At this time, it is preferable to raise the temperature of the substrate to near the lower limit of the temperature at which the Al-containing layer can be oxidized. The selective irradiation of the laser beam can be performed through a mask having a shape of a current confinement region formed above the upper multilayer film reflecting mirror. The current confinement region can be composed of a plurality of independent regions arranged in a two-dimensional array.

  According to the present invention, in the method for manufacturing a surface emitting semiconductor laser, the controllability of the oxidation process can be improved, and the processing uniformity and yield can be improved. In addition, the shape of the oxidized region can be patterned.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram for explaining an example of a surface emitting semiconductor laser manufacturing method according to the present invention.
As shown in FIG. 1A, an n-type GaAs (100) substrate 11 having a thickness of 650 μm and a carrier concentration of 3 × 10 ¹⁸ cm ⁻³ is prepared, and a metal organic chemical vapor deposition method (MOCVD method) is formed thereon. The following layers were epitaxially grown in order. A GaAs buffer layer (carrier concentration 2 × 10 ¹⁸ cm ⁻³ , thickness 0.5 μm) 12 doped with Si, which is an n-type impurity, is deposited, and Si is also deposited thereon at a concentration of 2 × 10 ¹⁸ cm ⁻³ . The added n-type Al _0.12 Ga _0.88 As / Al _0.9 Ga _0.1 As semiconductor multilayer mirror 13 was formed. The film thickness of each layer in the multilayer reflector 13 was 51 nm and 61 nm, respectively, and a 20 nm composition gradient layer was inserted between each layer in order to reduce the resistance between the layers. Here, in order to increase the reflectance, 32 periods were prepared with these as one period. A quantum well in which 3.5 pairs of Al _0.3 Ga _0.7 As barrier layer 103 nm without addition of impurities, GaAs barrier layer 15 nm without addition of impurities and 7 nm of In _0.2 Ga _0.8 As quantum well layers are alternately deposited thereon. A light emitting layer 14 was formed by depositing an Al _0.3 Ga _0.7 As barrier layer 103 nm having no structure and impurities added in this order. Further, an AlAs layer 15 of 30 nm is deposited thereon for current confinement, and finally an Al _0.12 Ga _0.88 As / Al _0.9 Ga _0.1 As semiconductor multilayer mirror 16 to which C is added as a p-type impurity is provided. It was formed with the same film thickness configuration as the n-type semiconductor multilayer mirror 13.

  After producing the epitaxial wafer, a SiN surface protection film 17 was deposited to 150 nm by plasma CVD. An Au layer of 300 nm was deposited as the mask layer 18 only on the surface of the region (diameter 10 μm) where the AlAs layer 15 was not oxidized by photolithography and vapor deposition. The mask layer 18 is for creating a region where the light emitting layer 14 is irradiated with laser light and a region where the light is not irradiated. In order to oxidize the AlAs layer 15 in the lateral direction, it is necessary that the end of the AlAs layer 15 be in an environment and structure that can contact an oxidizing atmosphere (for example, water vapor). Therefore, as shown in FIG. 1B, photolithography, removal of the SiN surface protective film 17 and etching of the epitaxial layer are performed so as to form a mesa having a larger area (diameter 40 μm) than the area where the mask layer 18 is deposited. The end of the AlAs layer 15 was exposed to the mesa side wall.

Next, as shown in FIG.1 (c), the wafer was introduce | transduced into water vapor | steam atmosphere and the substrate temperature was heated up to 380 degreeC. The substrate temperature is raised in order to raise the substrate to the lower limit of the temperature at which the substrate can be oxidized and to create a state in which the oxidation rate is likely to change with respect to the temperature change. Thereafter, laser light is irradiated. In this embodiment, the materials constituting the semiconductor multilayer mirrors 13 and 16 are Al _0.12 Ga _0.88 As and Al _0.9 Ga _0.1 As, and these materials are shorter than 810 nm due to the size of the band gap. It absorbs light of a wavelength and can transmit only light having a longer wavelength. Since In _0.2 Ga _0.8 As that is the light emitting layer 14 can absorb light having a wavelength shorter than 980 nm, the wavelength of the irradiation laser light is appropriately 810 to 980 nm from the above formula (1). I understand. Therefore, in this example, the entire surface of the substrate was irradiated for 10 minutes using a semiconductor laser having an oscillation wavelength of 0.9 μm. The irradiated laser light is absorbed by the light emitting layer 14 in a region without a mask. Therefore, at the same time as the light emitting layer 14 is heated, the AlAs layer 15 immediately above the light emitting layer is also heated.

  FIG. 2 is a diagram showing the temperature dependence of the oxidation rate of the AlAs layer 15. By condensing and irradiating a laser beam with an output of 1 W to a diameter of 0.1 mm, a temperature increase of about 50 ° C. is expected, so that selective oxidation rate improvement by laser beam irradiation can be expected. In this example, since the region of the AlAs layer 15 where the irradiation laser beam is shielded by the mask layer 18 remains at 380 ° C., no oxidation occurs. On the other hand, since the region of the AlAs layer 15 irradiated with the laser light is heated to 430 ° C., the oxidation proceeds with the water vapor supplied from the exposed end of the AlAs layer 15. Thus, after the substrate temperature is lowered to 380 ° C. or less where oxidation does not occur, oxidation with high selectivity can be achieved by increasing the oxidation rate only at the irradiated portion by partial laser irradiation using a mask.

  FIG. 1 (d) shows a state after the end of oxidation. Since the AlAs layer 15 has a higher temperature in the unmasked region than in the masked region, the oxidation rate is increased. Therefore, since the difference in the oxidation rate is large at the boundary with the masked region, the oxidation is automatically stopped. Therefore, oxidation can be stopped according to the size of the mask. In this example, a non-oxidized region having substantially the same shape as the pattern shape of the mask layer 18 is formed inside the AlAs layer 15.

  As described above, according to the surface emitting semiconductor laser manufacturing method of the present invention, the shape of the oxidized region of the AlAs layer 15 can be freely controlled by the shape of the mask pattern. Further, since the tolerance of the oxidation time is increased, the uniformity within the wafer surface and the yield can be improved.

  Further, in the conventional current confinement region forming method, oxidation progresses uniformly laterally from the end face exposed by etching, and the oxidation rate cannot be controlled, so that the shape of the current confinement region (the shape of the light emitting region) is obtained. Inevitably becomes a shape similar to the mesa shape formed by etching. On the other hand, the current confinement region forming method of the present invention has a large degree of freedom regarding the shape of the light emitting region, and it becomes possible to form an oxidized region inside the non-oxidized region by adjusting the oxidation rate and the mask pattern.

  FIG. 3 is an explanatory view of an example of a surface emitting semiconductor laser manufactured by the manufacturing method of the present invention. FIG. 3 shows an example of a surface emitting semiconductor laser in which a plurality of independent light emitting regions are formed in one mesa. FIG. 3A is a schematic top view in one step of the manufacturing process. FIG. 3B is a schematic top view of the manufactured surface emitting semiconductor laser, and FIG. 3C is an AA cross-sectional view of FIG.

FIG. 3A is a schematic top view corresponding to FIG. 1B or FIG. In this embodiment, first, as in FIG. 1A, a GaAs buffer layer, an n-type Al _0.12 Ga _0.88 As / Al _0.9 Ga _0.1 As semiconductor multilayer mirror, an emission, on an n-type GaAs (100) substrate. A layer, an AlAs layer for current confinement, and a p-type Al _0.12 Ga _0.88 As / Al _0.9 Ga _0.1 As semiconductor multilayer reflector were sequentially epitaxially grown, and a SiN surface protective film was formed thereon. Next, in order to create a region that is not irradiated with laser light during laser light irradiation, an Au layer is deposited on the surface protective film by 300 nm, and is patterned to form four separated rectangular regions 21a to 21d. Layered. All four rectangular regions were 10 μm square.

  Thereafter, as described in FIG. 1B, photolithography, removal of the SiN surface protective film, and etching of the epitaxial layer are performed so as to form a mesa having a larger area (50 μm) than the area where the mask layers 21a to 21d are deposited. To expose the end of the AlAs layer on the side wall of the mesa. Next, the wafer was introduced into a water vapor atmosphere, the substrate temperature was raised to 380 ° C., and then the entire surface of the substrate was irradiated with a semiconductor laser having an oscillation wavelength of 0.9 μm for 10 minutes. The irradiated laser light is absorbed in the light emitting layer in the region without the mask, and the temperature of the light emitting layer is increased, and at the same time, the AlAs layer immediately above the light emitting layer is also heated. The region of the AlAs layer in which the irradiation laser light is shielded by the mask layers 21a to 21d has a low temperature and thus the oxidation rate is slow, and the region of the AlAs layer irradiated with the laser light has a high temperature and therefore from the exposed end of the AlAs layer. Oxidation proceeds with the supplied steam.

  Thus, the AlAs layer is oxidized leaving the same shape as the mask layers 21a to 21d, and four independent non-oxidized regions 24a to 24d, that is, current confinement regions are formed in the AlAs layer. FIG. 3B shows a state in which the upper electrode 22 is formed after the mask layers 21a to 21d are removed. The upper electrode 22 was formed above the oxidized region 23 of the AlAs layer so as to surround four independent current confinement regions.

  FIG. 3C schematically shows a state in which laser is emitted by supplying a current to the surface emitting semiconductor laser of this example. The current path flowing from the upper electrode 22 to the lower electrode 25 is limited in current path in the oxidized region 23 of the AlAs layer, enters the light emitting layer through the non-oxidized regions 24a to 24d, and emits light. Light emitted from the light emitting layer resonates in a laser resonator constituted by upper and lower semiconductor multilayer reflectors, and in the case of the illustrated example, is output as laser light 26 through the upper semiconductor multilayer reflector. In this case, as shown in the figure, laser beams 26 are generated from four independent light emitting regions corresponding to the four independent non-oxidized regions 24a to 24d, respectively. The surface-emitting semiconductor laser shown in the figure can be said to be a laser array composed of four minute surface-emitting semiconductor lasers.

  FIG. 4 is an explanatory view of a surface emitting semiconductor laser corresponding to FIG. 3 manufactured by a conventional method. 4 (a) and 4 (b) correspond to FIGS. 3 (b) and 3 (c), respectively.

  A structure having an oxidized region further inside the non-oxidized region as shown in FIGS. 3B and 3C cannot be manufactured by the conventional method using only the oxidation time control. As shown in b), a method is adopted in which the electrode shape is a lattice. That is, the electrode 22 is provided so as to cross over one large non-oxidized region 24e.

  With such a structure, there is a problem in that the amount of current that does not contribute to light emission increases, and the electro-optical conversion efficiency is low. On the other hand, according to the manufacturing method of the present invention, it is possible to eliminate a current that does not contribute to light emission by selective oxidation, so that the conversion efficiency can be improved. That is, as shown in the example of FIG. 3, in the manufacturing method of the present invention, if the oxidized region is connected, the oxidized region can be formed not only in the periphery but also in the inside. Together, it is possible to create an oxidized region. Compared with the conventional method, it is thereby possible to pass a current only through the light emitting part, so that high electro-optical conversion efficiency can be obtained. When the distance between the light emitting regions is reduced to about 1 μm, the interaction between the lasers becomes possible, so that a phase-locked laser array can be manufactured. If this method is used, it becomes possible to produce a phase-locked array having a higher conversion efficiency than the conventional one.

Process drawing explaining an example of the surface emitting semiconductor laser manufacturing method by this invention. The figure which shows the temperature dependence of the oxidation rate of an AlAs layer. Explanatory drawing of the other example of the surface emitting semiconductor laser manufactured with the manufacturing method of this invention. Explanatory drawing of the surface emitting semiconductor laser corresponding to FIG. 3 manufactured with the conventional method.

Explanation of symbols

11: Substrate, 12: Buffer layer, 13: Semiconductor multilayer mirror, 14: Light emitting layer, 15: AlAs layer, 16: Semiconductor multilayer reflector, 17: Surface protective film, 18: Mask layer, 21a to 21d: Mask layer, 22: upper electrode, 23: oxidized region, 24a to 24e: non-oxidized region, 25: lower electrode, 26: laser beam

Claims (11)

In a surface emitting semiconductor laser in which a lower multilayer reflector, a light emitting layer, an Al-containing layer having an oxidized region and a non-oxidized region surrounded by the oxidized region, and an upper multilayer reflector are sequentially formed on a substrate,
The surface-emitting semiconductor laser, wherein the Al-containing layer has a plurality of independent non-oxidized regions each surrounded by an oxidized region.   2. The surface emitting semiconductor laser according to claim 1, wherein the plurality of independent non-oxidized regions have substantially the same shape.   2. The surface emitting semiconductor laser according to claim 1, wherein the plurality of independent non-oxidized regions are arranged in a two-dimensional array.   4. The surface emitting semiconductor laser according to claim 3, wherein an electrode is provided above an oxidized region sandwiched between two adjacent non-oxidized regions. A step of sequentially forming a lower multilayer reflector, a light emitting layer, an Al-containing layer for setting a current confinement region, and an upper multilayer reflector on a substrate;
Exposing an end of the Al-containing layer;
Providing the Al-containing layer with a temperature distribution such that a region to be an oxidized region has a higher temperature than a region to be a non-oxidized region;
And a step of oxidizing the Al-containing layer from the exposed end portion in a state where the temperature distribution is given.   6. The method of manufacturing a surface emitting semiconductor laser according to claim 5, wherein in the step of giving a temperature distribution to the Al-containing layer, laser light having a wavelength that is not absorbed by the upper multilayer reflector but is absorbed by the light emitting layer is oxidized. A method of manufacturing a surface emitting semiconductor laser, wherein a region to be a region is selectively irradiated.   7. The method for manufacturing a surface emitting semiconductor laser according to claim 6, wherein the temperature of the substrate is raised to a temperature near a lower limit of the temperature at which the Al-containing layer can be oxidized.   8. The surface emitting semiconductor laser according to claim 6, wherein the selective irradiation of the laser beam is performed through a mask formed above the upper multilayer reflector. Manufacturing method.   9. The method for manufacturing a surface emitting semiconductor laser according to claim 8, wherein the mask has a shape of the current confinement region.   10. The method for manufacturing a surface emitting semiconductor laser according to claim 9, wherein the current confinement region includes a plurality of independent regions.   10. The method for manufacturing a surface emitting semiconductor laser according to claim 9, wherein the plurality of independent regions are aligned in a two-dimensional array.

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