JP2005045107A - Surface emitting laser and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface emitting laser which can improve a characteristic and a reliability with a simple structure by reducing an invalid current, and to provide a method for manufacturing the laser. <P>SOLUTION: The mesa region 10 of an approximately cylindrical shape having an n-side multilayer reflective film 12, an active layer 13, a current narrowing layer 14, and a p-side multilayer reflective film 15 laminated in this order, is formed in a substrate 11. The mesa region 10 and an external region 30 surrounding the mesa region are interconnected by a girder 40 provided in a groove 20. An etching stop layer 16 and a contact layer 17 are laminated on a second multilayer reflective film 15 in this order. The contact layer 17 is formed in the mesa region 10 while avoiding the external region 30 and the girder 40. Since the contact layer 17 is not provided in the girder 40, a current can be reliably suppressed from leaking through the contact layer 17 and the girder 40 into the external region 30. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a surface emitting laser called a vertical cavity surface emitting laser (VCSEL).

  A surface emitting laser has a configuration in which an active layer is sandwiched between multilayer reflection films of AlGaAs called a DBR (Distributed Bragg Reflector) mirror. As a current confinement method for such a surface emitting laser, there is a method of forming a current confinement layer by oxidizing a part of a semiconductor layer having a high aluminum (Al) composition in a multilayer reflective film.

  The current confinement layer formed by oxidation contracts in volume and causes distortion in the upper and lower semiconductor layers. The bond between the current confinement layer and the upper and lower semiconductor layers is weak, and defects such as dislocations and cracks may occur due to thermal stress in the heating process after oxidation. There is a problem in that this defect propagates to the active layer during the laser operation to generate a non-light emitting region, which may deteriorate the reliability and characteristics of the laser.

In order to solve such a problem, FIG. 10 of Non-Patent Document 1 proposes a structure in which cracks due to thermal stress are prevented by partially coupling a mesa region and an external region. Yes. In this structure, current flows out from the coupling portion between the mesa region and the external region, resulting in a reactive current that does not contribute to light emission. Therefore, current is suppressed from flowing to the external region by performing ion implantation in the external region.
Bobby M. Hawkins, 4 others, Reliability of Various Size Oxide Aperture VCSELs, Figure 10, [online], Honeywell homepage, [Search May 27, 2003], <Publication HP; http://content.honeywell.com/vcsel/publications/tech.stm>, <Applicable literature; http://content.honeywell.com/vcsel/ pdf / ECTC311.pdf>

  However, such a conventional structure requires an expensive ion implantation apparatus, which increases the manufacturing cost. In addition, in order to form an ion concentration distribution in which no current flows to the external region, it is necessary to perform ion implantation several times by changing the implantation voltage, and there is a problem that it is difficult to establish conditions.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a surface emitting laser capable of reducing reactive current and improving characteristics and reliability with a simple configuration and a method for manufacturing the same. is there.

  A surface emitting laser according to the present invention includes a mesa region in which a first multilayer reflective film, an active layer, and a second multilayer reflective film are sequentially laminated on a substrate, an external region surrounding the mesa region with a groove interposed therebetween, and a mesa provided in the groove. A bridge girder that connects the region and the external region, and a contact layer that is formed in the mesa region while avoiding the external region and the bridge girder.

  The method of manufacturing a surface emitting laser according to the present invention includes a step of sequentially forming a first multilayer reflective film, an active layer, and a second multilayer reflective film on a substrate, and an etching stop layer and a contact layer on the second multilayer reflective film. A step of sequentially forming, a step of selectively removing the contact layer by etching using an etching stop layer, and a step of leaving the contact layer at a position where the mesa region is to be formed; a mesa region and an external region outside the contact layer; And a step of forming a bridge girder for connecting the mesa region and the external region to the groove.

  In the surface emitting laser according to the present invention, since the contact layer is formed in the mesa region while avoiding the external region and the bridge girder, current leakage is prevented from leaking to the external region via the contact layer and the bridge girder. .

  In the method of manufacturing the surface emitting laser according to the present invention, the first multilayer reflective film, the active layer, and the second multilayer reflective film are sequentially formed on the substrate, and then the etching stop layer and the contact layer are formed on the second multilayer reflective film. Are formed in order. Subsequently, the contact layer is selectively removed by etching using the etching stop layer, so that the contact layer remains at the planned formation position of the mesa region. After that, a groove that separates the mesa region and the external region is formed outside the contact layer, and a bridge girder that connects the mesa region and the external region is formed in the groove.

  According to the surface emitting laser of the present invention, since the contact layer is not formed in the bridge girder, it is possible to suppress the leakage current from diffusing from the contact layer to the external region via the bridge girder with a simple configuration. Therefore, it is possible to reduce the oscillation threshold of the laser and improve the light emission efficiency.

  According to the surface emitting laser manufacturing method of the present invention, the surface emitting laser of the present invention can be easily manufactured without using a complicated ion implantation process.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 shows a structure of a surface emitting laser according to an embodiment of the present invention, FIG. 2 shows a sectional structure taken along line II-II in FIG. 1, and FIG. 3 shows a sectional structure taken along line III-III in FIG. is there. This surface-emitting laser is, for example, a vertical cavity type (VCSEL), and has an n-side multilayer reflective film 12 made of an n-type semiconductor multilayer film, an active layer 13, a current confinement layer 14, and a p-type semiconductor multilayer film on a substrate 11. A p-side multi-layer reflective film 15 made of a substantially cylindrical mesa region 10 is laminated in this order. The mesa region 10 is surrounded by the outer region 30 with a substantially annular groove 20 therebetween. The mesa region 10 and the external region 30 are connected by a bridge girder portion 40 provided in the groove 20. An insulating film 50 (not shown in FIG. 1) made of, for example, silicon oxide (SiO _x ) is formed on the surfaces of the mesa region 10, the external region 30, and the bridge girder 40.

  The substrate 11 is made of, for example, n-type gallium arsenide (GaAs). The n-side multilayer reflective film 12 is a DBR mirror having a multilayer structure made of, for example, an n-type AlGaAs mixed crystal. The active layer 13 is made of, for example, gallium arsenide to which no impurity is added. The current confinement layer 14 has, for example, an annular high resistance region 14B obtained by oxidizing aluminum arsenide around a low resistance region 14A made of aluminum arsenide (AlAs), and the current is confined only in the low resistance region 14A. It has come to be. A region of the active layer 13 corresponding to the low resistance region 14A is a light emitting region. The second multilayer reflective film 15 is a DBR mirror having a multilayer structure made of, for example, a p-type AlGaAs mixed crystal.

  The groove 20 separates the mesa region 10 and the external region 30. In order to form the high resistance region 14B by oxidation of aluminum arsenide in the manufacturing process described later, the groove 20 preferably has a depth that allows the current confinement layer 14 to be completely exposed.

  The external region 30 has the same layer configuration as the mesa region 10. However, the current confinement layer 14 has only the high resistance region 14B in which aluminum arsenide is oxidized.

  The bridge girder 40 connects the groove 20 and the external region 30 and prevents the mesa region 10 from being peeled from the substrate 11 due to thermal stress in the manufacturing process. In the present embodiment, for example, two bridge beams 40 are provided at intervals of 180 degrees, the diameter of the mesa region 10 is about 46 nm, and the width of the bridge beam 40 is about 20 nm. In addition, the space | interval, the number, or shape of the bridge girder part 40 is not limited, You may provide in spiral form instead of radial form. The layer structure of the bridge girder 40 is the same as that of the external region 30.

On the second multilayer reflective film 15, an etching stop layer 16 and a contact layer 17 are sequentially stacked. The etching stop layer 16 is for etching the contact layer 17 in the manufacturing method described later, and is formed in the mesa region 10, the external region 30, and the bridge girder 40. The etching stop layer 16 is preferably made of a material that can ensure an etching selectivity with the contact layer 17 described later, for example, Al _x Ga _1-x As mixed crystal (0 <x <0.8). The thickness t of the etching stop layer 16 in the stacking direction (hereinafter simply referred to as “thickness”) is as follows. The refractive index of the etching stop layer 16 is N (stop) and the oscillation wavelength of the surface emitting laser is λ. It is preferable to follow the following formula (1) so that no reflection occurs.

t = n * λ / {4 * N (stop)} (n is a natural number) (1)

  The contact layer 17 is formed in the mesa region 10 while avoiding the outer region 30 and the bridge girder 40. Since the contact layer 17 has a higher impurity concentration and lower resistance than the other layers, the current easily spreads in the lateral direction. However, the contact layer 17 and the bridge girder 40 are not provided in the bridge girder 40. It is possible to reliably suppress the leakage of current to the external region 30 via the.

  The contact layer 17 is preferably made of, for example, p-type gallium arsenide. In a normal surface emitting laser, the AlGaAs mixed crystal layer having a small aluminum composition of the second multilayer reflective film 15 has a role as a contact layer, but the contact layer 17 is made of p-type gallium arsenide containing no aluminum. This is because the contact resistance of the p-side electrode can be lowered as compared with the case of a normal surface emitting laser.

  Further, the contact layer 17 preferably has an opening 17A for extracting light generated in the active layer 13. This is because light is absorbed by the contact layer 17 made of gallium arsenide when the oscillation wavelength of the surface emitting laser is 850 nm or less, but the absorption of light can be eliminated by providing the opening 17A.

  A p-side electrode 18 is formed on the contact layer 17. Since the p-side electrode 18 is formed in a continuous shape from the contact layer 17 to the external region 30 through the bridge girder 40, there is no step and there is no possibility of disconnection. On the other hand, an n-side electrode 19 is formed on the back side of the substrate 11.

  This semiconductor laser can be manufactured, for example, as follows.

  First, as shown in FIG. 4, an aluminum arsenide layer 14C that becomes an n-side multilayer reflection film 12, an active layer 13, and a current confinement layer 14 by crystal growth, for example, on a substrate 11 made of the above-described material, and a p-side multilayer reflection. A film 15, an etching stop layer 16 and a contact layer 17 are grown sequentially.

  After the contact layer 17 is grown, a mask (not shown) made of a resist is selectively formed on the contact layer 17. Next, the contact layer 17 is selectively removed by etching using this mask and the etching stop layer 16, thereby leaving the contact layer 17 at a position where the mesa region 10 is to be formed as shown in FIG. 5. At this time, the opening 17A is also formed. As an etchant for the contact layer 17, a material that etches the gallium arsenide of the contact layer 17 and is difficult to etch the AlGaAs mixed crystal of the etching stop layer 16, for example, ammonia water or a mixture of hydrogen peroxide water and water. Can be used. 5 to 7 show a cross section taken along line II-II in FIG.

  After the contact layer 17 is etched, the etching stop layer 16, the second multilayer reflective film 15, the aluminum arsenide layer 14C and the active layer 13 are selectively removed as shown in FIG. A groove 20 is formed on the outer side to separate the mesa region 10 and the outer region 30. At this time, the bridge girder 40 (see FIG. 1) is also formed.

  After forming the groove 20 and the bridge girder 40, the aluminum arsenide 14C exposed to the groove 20 is oxidized by heating, for example, in water vapor as shown in FIG. Oxidation proceeds in an annular shape from the periphery of the aluminum arsenide layer 14C toward the center, so that by stopping the oxidation at an appropriate time, an annular high resistance region 14B is formed, and the central unoxidized portion Becomes the low-resistance region 14A. Thereby, the current confinement layer 14 having the low resistance region 14A and the high resistance region 14B is formed.

  After forming the current confinement layer 14, an insulating film 50 made of the above-described material is formed as shown in FIG. Subsequently, similarly as shown in FIG. 2, an n-side electrode 19 is formed on the back side of the substrate 11, an opening is formed in the insulating film 50, and a p-side electrode 18 is formed on the contact layer 17. Thereby, the surface emitting laser shown in FIGS. 1 to 3 is completed.

  In this surface emitting laser, when a predetermined voltage is applied between the n-side electrode 19 and the p-side electrode 18, the drive current supplied from the p-side electrode 18 is current-confined by the current confinement layer 14. Light is emitted by being injected into the active layer 13 and electron-hole recombination. This light is reflected by the first multilayer reflective film 12 and the second multilayer reflective film 15, reciprocates between them to generate laser oscillation, and is emitted to the outside as a laser beam from the opening 17A. Here, since the contact layer 17 is formed in the mesa region 10 while avoiding the external region 30 and the bridge girder 40, it is possible to suppress current from leaking to the external region 30 via the contact layer 17 and the bridge girder 40. Is done.

  As described above, in this embodiment, the contact layer 17 is not formed in the bridge girder 40, and thus, it is possible to suppress the leakage current from diffusing from the contact layer 17 to the external region 30 through the bridge girder 40 with a simple configuration. be able to. Therefore, it is possible to reduce the oscillation threshold of the laser and improve the light emission efficiency.

  In the present embodiment, the etching stop layer 16 and the contact layer 17 are sequentially formed on the second multilayer reflective film 15, and the contact layer 17 is left at the position where the mesa region 10 is to be formed. Since the groove 20 and the bridge girder 40 are formed on the outer side of 17, a complicated ion implantation step is unnecessary, and the surface emitting laser of the present invention can be easily manufactured.

  Furthermore, specific examples of the present invention will be described.

A surface emitting laser was manufactured in the same manner as in the above embodiment. When the threshold current I _th and the quantum efficiency η of the obtained surface emitting laser were examined, the threshold current I _th was 2.2 mA and the quantum efficiency η was 0.33 W / A.

As a comparative example to this example, a surface emitting laser was fabricated in the same manner as in this example, except that the contact layer 17 was not etched. Also in this comparative example, when the threshold current I _th and the quantum efficiency η were examined, the threshold current I _th was 3.5 mA and the quantum efficiency η was 0.2 W / A.

Thus, according to this embodiment, the threshold current I _th can be reduced to about two thirds and the quantum efficiency η can be increased by about 1.6 times compared to the comparative example. That is, it has been found that if the contact layer 17 is provided while avoiding the external region 30 and the bridge girder 40, diffusion of leakage current can be suppressed and characteristics can be improved.

  While the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made. For example, the material and thickness of each layer, the film formation method, and the film formation conditions described in the above embodiment are not limited, and other materials and thicknesses may be used. It is good also as conditions.

  In the above embodiment, the configuration of the surface emitting laser has been specifically described. However, it is not necessary to provide all the layers, and other layers may be further provided.

  The present invention can be applied not only to a single surface emitting laser but also to a laser array in which surface emitting lasers are integrated, or a device in which surface emitting lasers and other devices such as photodiodes are integrated.

  The surface emitting laser according to the present invention can be applied to, for example, a light source for optical fiber communication or optical wiring, a light source for a laser printer, or an optical disc.

It is a perspective view showing the structure of the surface emitting laser which concerns on one embodiment of this invention. It is sectional drawing along the II-II line of FIG. It is sectional drawing along the III-III line of FIG. It is sectional drawing showing the manufacturing method of the surface emitting laser shown in FIG. 1 in order of a process. FIG. 5 is a cross-sectional view illustrating a process following FIG. 4. FIG. 6 is a cross-sectional view illustrating a process following FIG. 5. FIG. 7 is a cross-sectional view illustrating a process following FIG. 6.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Mesa region, 11 ... Substrate, 12 ... N-side multilayer reflective film, 13 ... Active layer, 14 ... Current confinement layer, 14A ... Low resistance region, 14B ... High resistance region, 14C ... Aluminum arsenide layer, 15 ... p Side multilayer reflective film, 16 ... etching stop layer, 17 ... contact layer, 18 ... p-side electrode, 19 ... n-side electrode, 20 ... groove, 30 ... external region, 40 ... bridge girder

Claims (13)

A mesa region in which a first multilayer reflective film, an active layer, and a second multilayer reflective film are sequentially laminated on a substrate;
An outer region surrounding the mesa region across a groove;
A bridge girder provided in the groove and connecting the mesa region and the external region;
A surface emitting laser comprising: a contact layer formed in the mesa region while avoiding the external region and the bridge girder. The surface emitting laser according to claim 1, further comprising an electrode having a continuous shape from the contact layer to the outer region through the bridge girder. The surface emitting laser according to claim 1, wherein the contact layer is made of gallium arsenide (GaAs). The surface emitting laser according to claim 1, wherein the contact layer has an opening through which light generated in the active layer is extracted. The surface emitting laser according to claim 1, further comprising an etching stop layer between the second multilayer reflective film and the contact layer. The surface-emitting laser according to claim 5, wherein the etching stop layer is made of Al _x Ga _1-x As (0 <x <0.8). The surface emitting laser according to claim 1, wherein the mesa region includes a current confinement layer between the active layer and the second multilayer reflective film. Forming a first multilayer reflective film, an active layer, and a second multilayer reflective film in order on a substrate;
Forming an etching stop layer and a contact layer in order on the second multilayer reflective film;
Selectively removing the contact layer by etching using the etching stop layer to leave the contact layer at a planned formation position of a mesa region;
Forming a groove separating the mesa region and the external region outside the contact layer, and forming a bridge girder connecting the mesa region and the external region in the groove. Manufacturing method of light emitting laser. The method of manufacturing a surface emitting laser according to claim 8, comprising a step of forming an electrode having a continuous shape from the contact layer to the outer region through the bridge girder. The surface emitting laser manufacturing method according to claim 8, wherein the contact layer is made of gallium arsenide (GaAs). 9. The method of manufacturing a surface emitting laser according to claim 8, wherein the contact layer is left at a position where the mesa region is to be formed, and an opening for extracting light generated in the active layer is formed in the contact layer. . The method of manufacturing a surface emitting laser according to claim 8, wherein the etching stop layer is made of Al _x Ga _1-x As mixed crystal (0 <x <0.8). An aluminum arsenide (AlAs) layer is formed between the active layer and the second multilayer reflective film, and a current confinement layer is formed by oxidizing the aluminum arsenide layer exposed in the groove. A method for manufacturing a surface emitting laser according to claim 8.

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