JP2005251852A - Vertical resonator type surface emitting laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical resonator type surface emitting laser that can emit laser light which is further narrowed in irradiating angle. <P>SOLUTION: The vertical resonator type surface emitting laser 100 contains a substrate 101, a pair of mirrors 102 and 104 provided above the substrate 101, and an active layer 103 provided between the mirrors 102 and 104. The laser 100 also contains refractive-index matching layers 120 and 122 formed adjacently to the active layer 103. The refractive-index matching layers 120 and 122 have refractive-index changing areas at least in their portions. The refractive-index changing areas have refractive indexes between the refractive indexes of the active layer 103 and mirrors 102 and 104, and the refractive indexes change toward the mirrors 102 and 104 from the active layer 103 so that differences between the refractive indexes and those of the mirrors 102 and 104 may decrease. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a vertical cavity surface emitting laser.

  A surface emitting laser is a laser that emits laser light perpendicular to a substrate, is easier to handle than an end-face laser, and has a circular radiation pattern, and is expected as a light source for various sensors and optical communications. Yes. When a surface emitting laser is used for various sensors or optical communication, it may be desirable to obtain a laser beam having a radiation pattern with a narrow radiation angle.

  An object of the present invention is to provide a vertical cavity surface emitting laser capable of emitting laser light having a narrower emission angle.

The vertical cavity surface emitting laser according to the present invention is
A substrate,
A pair of mirrors provided above the substrate;
An active layer provided between the pair of mirrors;
A refractive index matching layer formed adjacent to the active layer,
The refractive index matching layer has a refractive index changing region at least in part,
The refractive index changing region has a refractive index between the refractive index of the active layer and the refractive index of the mirror, and the refractive index difference from the mirror decreases from the active layer toward the mirror. The refractive index changes as follows.

  According to the vertical cavity surface emitting laser of the present invention, the refraction angle of the emitted laser light can be made smaller and the radiation angle can be made narrower.

  That is, light has a characteristic of being refracted at interfaces having different refractive indexes, and the refraction angle increases as the difference in refractive index between the interfaces increases. The vertical cavity surface emitting laser according to the present invention can reduce the refractive index difference at the interface between the active layer and the mirror by providing a refractive index matching layer between the active layer and the mirror. The refraction angle of the emitted laser light can be reduced. Therefore, the radiation angle of the emitted laser light can be made narrower.

  In the vertical cavity surface emitting laser according to the present invention, the refractive index matching layer may be a confinement layer.

  In the vertical cavity surface emitting laser according to the present invention, the refractive index can be continuously changed in the refractive index changing region.

  According to the vertical cavity surface emitting laser according to the present invention, the refractive index difference between the mirror and the active layer can be further reduced by continuously changing the refractive index in the refractive index changing region.

  In the vertical cavity surface emitting laser according to the present invention, the refractive index of the refractive index changing region may change stepwise.

  In the vertical cavity surface emitting laser according to the present invention, the refractive index matching layer as a whole may be the refractive index changing region.

  Since the refractive index matching layer as a whole is a refractive index changing region, the refractive index can be changed in a wide region in the stacking direction compared to the case where a part is a refractive index changing region. The refractive index difference can be relaxed.

  In the vertical cavity surface emitting laser according to the present invention, the refractive index of the refractive index matching layer may be continuous with the refractive index of the active layer on the adjacent surfaces of the refractive index matching layer and the active layer. it can.

  The refractive index of the refractive index matching layer is continuous with the refractive index of the active layer on the adjacent surface of the refractive index matching layer and the active layer, thereby reducing the refractive index difference at the interface between the active layer and the refractive index matching layer. can do.

In the vertical cavity surface emitting laser according to the present invention, the refractive index matching layer and the mirror are adjacent to each other,
The refractive index of the refractive index matching layer may be continuous with the refractive index of the mirror at adjacent surfaces of the refractive index matching layer and the mirror.

  Since the refractive index of the refractive index matching layer is continuous with the refractive index of the mirror at the adjacent surface of the refractive index matching layer and the mirror, the refractive index difference at the interface between the refractive index matching layer and the mirror can be reduced. it can.

In the vertical cavity surface emitting laser according to the present invention, the mirror is a multilayer reflective film having a plurality of layers,
At least one of the plurality of layers is a mirror refractive index matching layer whose refractive index changes,
The mirror refractive index matching layer may change its refractive index from the mirror refractive index matching layer toward another adjacent layer so that a difference in refractive index from the other layer decreases.

  Thereby, since the difference in refractive index between the mirror layers can be relaxed, the radiation angle of the laser beam can be made narrower.

In the vertical cavity surface emitting laser according to the present invention, the refractive index change region is an AlGaAs layer,
The refractive index can be changed by changing the Al composition ratio in the refractive index changing region.

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

1. Device structure 1-1. Overall Structure FIG. 1 is a plan view schematically showing a vertical cavity surface emitting laser 100 according to the present embodiment to which the present invention is applied, and FIG. 2 is a cross-sectional view taken along line AA in FIG. It is.

  As shown in FIGS. 1 and 2, the vertical cavity surface emitting laser 100 of the present embodiment includes a semiconductor substrate (GaAs substrate in the present embodiment) 101 and a vertical resonator formed on the semiconductor substrate 101. (Hereinafter referred to as “resonator”) 140, first electrode 107, and second electrode 109. The resonator 140 includes a first mirror 102, an n-type confinement layer 122, an active layer 103, a p-type confinement layer 120, and a second mirror 104.

  Next, each component of the vertical cavity surface emitting laser 100 will be described.

  The first mirror 102 and the second mirror 104 are, for example, distributed Bragg reflection type mirrors (DBR) made of a semiconductor multilayer film. The active layer 103 includes a first barrier layer 1032, a well layer 1034, and a second barrier layer 1036 (see FIG. 3). The first barrier layer 1032 and the second barrier layer 1036 are made of AlGaAs, and the well layer 1034 is made of GaAs. The active layer 103 has a quantum well structure (a single quantum well or a multiple quantum well). The second mirror 104 is made p-type by doping with C, Zn, Mg, or the like, for example, and the first mirror 102 is made n-type by doping with Si, Se, or the like, for example. Yes. Therefore, a pin diode is formed by the second mirror 104, the active layer 103 not doped with impurities, and the first mirror 102.

  Details of the p-type confinement layer 120 and the n-type confinement layer 122, and the first mirror 102 and the second mirror 104 will be described later.

  The second mirror 104, the p-type confinement layer 120, the active layer 103, and a part of the n-type confinement layer 122 constitute a columnar semiconductor deposited body (hereinafter referred to as “columnar portion”) 130. The side surface of the columnar portion 130 is covered with a buried insulating layer 106.

  An insulating layer 105 functioning as a current confinement layer may be formed in a region close to the p-type confinement layer 120 among the layers constituting the columnar portion 130. The insulating layer 105 can have a ring shape along the periphery of the columnar portion 130. The current confinement insulating layer 105 is made of, for example, aluminum oxide.

  In the vertical cavity surface emitting laser 100 according to the present embodiment, the buried insulating layer 106 is formed so as to cover the side surface of the columnar portion 130. As the resin constituting the embedded insulating layer 106, for example, a polyimide resin, a fluorine resin, an acrylic resin, an epoxy resin, or the like can be used. In particular, from the viewpoint of ease of processing and insulation, a polyimide resin or a fluorine resin can be used. A resin is desirable.

  A first electrode 107 is formed on the columnar part 130 and the buried insulating layer 106. The opening on the columnar portion 130 in the first electrode 107 serves as a laser beam emission surface 108. The first electrode 107 is made of, for example, a laminated film of an alloy of Au and Zn and Au. Further, a second electrode 109 is formed on the back surface of the semiconductor substrate 101. The second electrode 109 is made of, for example, a laminated film of an alloy of Au and Ge and Au. That is, in the vertical cavity surface emitting laser 100 shown in FIGS. 1 and 2, the first electrode 107 is joined to the second mirror 104 and the second electrode 109 is joined to the semiconductor substrate 101 on the columnar portion 130. ing. Current is injected into the active layer 103 by the first electrode 107 and the second electrode 109.

  The materials for forming the first and second electrodes 107 and 109 are not limited to those described above. For example, Cr, Metals such as Ti, Ni, Au, or Pt, and alloys thereof can be used.

  1-2. Next, details of the pair of mirrors and the confinement layer, which are characteristic parts of the present invention, will be described with reference to FIGS.

  FIG. 3 shows the first mirror 102, the n-type confinement layer 122, the active layer 103, the p-type confinement layer 120, and the second mirror 104 from the portion indicated by the symbol B in FIG. FIG. FIG. 4 is a diagram showing an outline of the refractive index in the stacking direction of the portion B in FIG.

  Here, the mirror and the confinement layer are made of, for example, AlGaAs, and the refractive index can be changed by changing the Al composition ratio.

1-2-1. Mirror The first mirror 102 and the second mirror 104 are multilayer reflective films having a plurality of films. The first mirror 102 includes a first mirror refractive index matching layer 1030, an n-type Al _0.9 Ga _0.1 As layer 1022, a second mirror refractive index matching layer 1026, an n-type Al _0.15 Ga _0.85 As layer 1024, and a third mirror. And a mirror refractive index matching layer 1028. Hereinafter, description will be made in order from the lower layer.

The first mirror refractive index matching layer 1030 is formed between the n-type Al _0.9 Ga _0.1 As layer 1022 which is the lowermost layer of the first mirror 102 and the semiconductor substrate 101 (GaAs substrate).

As shown in FIG. 4, the first mirror refractive index matching layer 1030 is formed so that the refractive index is continuous on the adjacent surface to the semiconductor substrate 101 and the adjacent surface to the n-type Al _0.9 Ga _0.1 As layer 1022. Has been. The first mirror refractive index matching layer 1030 is formed such that the refractive index continuously decreases from the semiconductor substrate 101 toward the n-type Al _0.9 Ga _0.1 As layer 1022.

  Here, the decrease in the refractive index may be a linear decrease, or may be a curvilinear decrease such as a quadratic function or a triangular function curve. In the illustrated example, the refractive index of the first mirror refractive index matching layer 1030 continuously decreases, but may decrease stepwise.

As described above, since the first mirror refractive index matching layer 1030 is made of AlGaAs, the refractive index can be changed by changing the Al composition ratio. In order to change the refractive index as described above, the Al composition ratio of the first mirror refractive index matching layer 1030 is changed upward from the Al composition ratio of the semiconductor substrate 101 by the n-type Al _0.9 Ga _0.1 As layer 1022. It is set so as to continuously increase up to the Al composition ratio.

As described above, the vertical cavity surface emitting laser 100 has a refractive index between the semiconductor substrate 101 and the n-type Al _0.9 Ga _0.1 As layer 1022 as compared with the case where the first mirror refractive index matching layer 1030 is not provided. Since the discontinuity can be reduced, the radiation angle of the laser light can be reduced.

The second mirror refractive index matching layer 1026 is formed between the n-type Al _0.9 Ga _0.1 As layer 1022 and the n-type Al _0.15 Ga _0.85 As layer 1024.

As shown in FIG. 4, the second mirror refractive index matching layer 1026 has a refractive index on the adjacent surface to the n-type Al _0.9 Ga _0.1 As layer 1022 and the adjacent surface to the n-type Al _0.15 Ga _0.85 As layer 1024. It is formed to be continuous. The second mirror refractive index matching layer 1026 is formed so that the refractive index continuously increases from the n-type Al _0.9 Ga _0.1 As layer 1022 toward the n-type Al _0.15 Ga _0.85 As layer 1024.

  Here, the increase in the refractive index may be a linear increase, or may be a curvilinear increase such as a quadratic function or a triangular function curve. In the example shown in the drawing, the refractive index of the second mirror refractive index matching layer 1026 increases continuously, but may increase stepwise.

As described above, since the second mirror refractive index matching layer 1026 is made of AlGaAs, the refractive index can be changed by changing the Al composition ratio. In order to change the refractive index as described above, the Al composition ratio of the second mirror refractive index matching layer 1026 is changed from the n-type Al _0.9 Ga _0.1 As layer 1022 to the n-type Al _0.15 Ga _0.85 As layer 1024. It is set to decrease continuously.

The third mirror refractive index matching layer 1028 is formed between the n-type Al _0.15 Ga _0.85 As layer 1024 and the n-type Al _0.9 Ga _0.1 As layer 1022.

The third mirror refractive index matching layer 1028 is formed so that the refractive index is continuous on the adjacent surface to the n-type Al _0.15 Ga _0.85 As layer 1024 and the adjacent surface to the n-type Al _0.9 Ga _0.1 As layer 1022. Has been. The third mirror refractive index matching layer 1028 is formed so that the refractive index continuously decreases from the n-type Al _0.15 Ga _0.85 As layer 1024 toward the n-type Al _0.9 Ga _0.1 As layer 1022.

  Here, the decrease in the refractive index may be a linear decrease, or may be a curvilinear decrease such as a quadratic function or a triangular function curve. In the example shown in the figure, the refractive index of the third mirror refractive index matching layer 1028 continuously decreases, but may decrease stepwise.

As described above, since the third mirror refractive index matching layer 1028 is made of AlGaAs, the refractive index can be changed by changing the Al composition ratio. In order to change the refractive index as described above, the Al composition ratio of the third mirror refractive index matching layer 1028 is changed from the n-type Al _0.15 Ga _0.85 As layer 1024 to the n-type Al _0.9 Ga _0.1 As layer 1022. It is set to increase continuously.

As described above, the first mirror 102 has the first mirror refractive index matching layer 1030 in the lowermost layer, and the n-type Al _0.9 Ga _0.1 As layer 1022, the second mirror refractive index matching layer 1026, and n For example, 40 pairs of the layer 1020 in which the type Al _0.15 Ga _0.85 As layer 1024 and the third mirror refractive index matching layer 1028 are stacked are stacked.

As described above, the vertical cavity surface emitting laser 100 according to the present embodiment includes the second mirror refractive index matching layer 1026 and the third mirror refractive index matching layer 1028, so that the n-type Al _0.15 Ga _{0.85 is provided.} The refractive index difference at the interface between the As layer 1024 and the n-type Al _0.9 Ga _0.1 As layer 1022 is relaxed. On the other hand, light has a characteristic of being refracted at interfaces having different refractive indexes. Therefore, the vertical cavity surface emitting laser 100 according to the present embodiment has a vertical cavity type as compared with the case where the second mirror refractive index matching layer 1026 and the third mirror refractive index matching layer 1028 are not provided. The refraction angle of the laser light emitted from the surface emitting laser 100 can be made smaller, and the emission angle can be made narrower.

  The second mirror 104 is different from the n-type doped first mirror 102 in that it does not have the first mirror refractive index matching layer 1030 adjacent to the semiconductor substrate 101 and is p-type doped. However, since it has the same mirror refractive index matching layer as the first mirror 102 between layers and has the same periodic structure, the description is omitted.

1-2-2. Confinement Layer Next, the n-type confinement layer 122 and the p-type confinement layer 120 will be described.

  First, the n-type confinement layer 122 will be described. The n-type confinement layer 122 is formed between the first mirror 102 and the active layer 103. As shown in FIG. 4, the n-type confinement layer 122 has a refractive index between the refractive index of the active layer 103 and the refractive index of the first mirror 102. In addition, the refractive index of the n-type confinement layer 122 changes from the active layer 103 toward the first mirror 102 so that the difference in refractive index from the first mirror 102 decreases.

Specifically, as shown in FIG. 3, an n-type Al _0.9 Ga _0.1 As layer 1022 is provided on the uppermost layer of the first mirror 102, and a first barrier layer 1032 is provided on the lowermost layer of the active layer 103. It has been. As for the refractive index, as shown in FIG. 4, the n-type confinement layer 122 has a continuous refractive index on the adjacent surface to the n-type Al _0.9 Ga _0.1 As layer 1022 and the adjacent surface to the first barrier layer 1032. is there. Further, the refractive index changes so that the refractive index difference from the n-type Al _0.9 Ga _0.1 As layer 1022 continuously decreases from the first barrier layer 1032 toward the n-type Al _0.9 Ga _0.1 As layer 1022. As shown in FIG. 4, since the refractive index of the first barrier layer 1032 is higher than that of the n-type Al _0.9 Ga _0.1 As layer 1022, the refractive index of the n-type confinement layer 122 is directed upward. Increase continuously.

  Here, the increase in the refractive index may be a linear increase, or may be a curvilinear increase such as a quadratic function or a triangular function curve. In the illustrated example, the refractive index of the n-type confinement layer 122 increases continuously, but may increase stepwise.

As described above, since the third mirror refractive index matching layer 1028 is made of AlGaAs, the refractive index can be changed by changing the Al composition ratio. As described above, in order to change the refractive index, the Al composition ratio of the n-type confinement layer 122 is continuously decreased from the n-type Al _0.9 Ga _0.1 As layer 1022 toward the first barrier layer 1032. Is set.

  Next, the p-type confinement layer 120 will be described. As shown in FIG. 3, the p-type confinement layer 120 is formed between the active layer 103 and the second mirror 104 and has a refractive index between the active layer 103 and the second mirror 104. As shown in FIG. 4, the refractive index of the p-type confinement layer 120 changes from the second mirror 104 toward the active layer 103 so that the refractive index difference from the active layer 103 decreases.

Specifically, as shown in FIG. 3, a second barrier layer 1036 is provided on the uppermost layer of the active layer 103, and a p-type Al _0.9 Ga _0.1 As layer 1042 is provided on the lowermost layer of the second mirror 104. It has been. As for the refractive index, as shown in FIG. 4, the p-type confinement layer 120 has a continuous refractive index on the adjacent surface to the second barrier layer 1036 and the adjacent surface to the p-type Al _0.9 Ga _0.1 As layer 1042. is there. The p-type confinement layer 120 changes in refractive index from the p-type Al _0.9 Ga _0.1 As layer 1042 toward the second barrier layer 1036 so that the difference in refractive index from the second barrier layer 1036 decreases. As shown in FIG. 4, since the refractive index of the p-type Al _0.9 Ga _0.1 As layer 1042 is lower than the refractive index of the second barrier layer 1036, the refractive index of the p-type confinement layer 120 is upward. It decreases continuously.

  Here, the decrease in the refractive index may be a linear decrease, or may be a curvilinear decrease such as a quadratic function or a triangular function curve. In the example shown in the figure, the refractive index of the p-type confinement layer 120 continuously decreases, but may decrease stepwise.

  Note that the composition and the number of layers of the first mirror 102, the n-type confinement layer 122, the active layer 103, the p-type confinement layer 120, and the second mirror 104 are not limited to this.

2. Operation and Effect of Device A general operation of the vertical cavity surface emitting laser 100 according to the present embodiment will be described below. The following method for driving the vertical cavity surface emitting laser 100 is an example, and various modifications can be made without departing from the spirit of the present invention.

  First, when a forward voltage is applied to the pin diode between the first electrode 107 and the second electrode 109, recombination of electrons and holes occurs in the active layer 103, and light emission due to such recombination occurs. Stimulated emission occurs when the generated light reciprocates between the second mirror 104 and the first mirror 102, and the light intensity is amplified. When the optical gain exceeds the optical loss, laser oscillation occurs, and laser light is emitted in a direction perpendicular to the semiconductor substrate 101 from the emission surface 108 on the upper surface of the columnar portion 130.

  The vertical cavity surface emitting laser 100 has the following characteristics. Laser light has the property of being refracted at interfaces having different refractive indexes, and the refraction angle increases as the difference in refractive index between the interfaces increases. Since the vertical cavity surface emitting laser 100 according to the present embodiment has an n-type confinement layer 122 as shown in FIGS. 3 and 4, it is between the first mirror 102 and the active layer 103. The refractive index changes continuously. Therefore, compared with the case where the n-type confinement layer 122 is not provided, the refractive index difference between the interfaces is small, and thus the refraction angle is small. Therefore, it is possible to prevent the radiation angle of the laser light emitted from the vertical cavity surface emitting laser 100 from being widened.

  For the p-type confinement layer 120 between the active layer 103 and the second mirror 104, the same effect as that of the n-type confinement layer 122 is obtained.

  Further, by providing a mirror refractive index matching layer on the first mirror 102 and the second mirror 104, a difference in refractive index between layers constituting the mirror can be reduced. Therefore, it is possible to prevent the radiation angle of the laser light from becoming wider.

3. Device Manufacturing Method Next, an example of a method for manufacturing the vertical cavity surface emitting laser 100 according to the present embodiment to which the present invention is applied will be described with reference to FIGS. 5 to 8 are cross-sectional views schematically showing the manufacturing process of the vertical cavity surface emitting laser 100 of the present embodiment shown in FIGS. 1 to 3, corresponding to the cross sections shown in FIG. Yes.

(1) First, a semiconductor multilayer film 150 is formed on the surface of a semiconductor substrate 101 made of n-type GaAs by epitaxial growth while modulating the composition, as shown in FIG. Here, the semiconductor multilayer film 150 is composed of a first mirror 102, an n-type confinement layer 122, a GaAs well layer 1034, and an Al _0.3 Ga _0.7 As barrier layer, and includes an active structure including a quantum well structure composed of three layers. It consists of a layer 103, a p-type confinement layer 120, and a second mirror 104. By laminating these layers on the semiconductor substrate 101 in order, the semiconductor multilayer film 150 is formed.

The first mirror 102 has, for example, a first mirror refractive index matching layer 1030 in the lowermost layer, and an n-type Al _0.9 Ga _0.1 As layer 1022, a second mirror refractive index matching layer 1026, and an n-type Al _0.15 Ga on the top. _{This is} a 40-pair multilayer reflective film in which _0.85 As layer 1024 and third mirror refractive index matching layer 1028 are periodically stacked as one pair.

Similar to the first mirror 102, the second mirror 104 has 25 pairs of multilayer reflections having two types of mirror index matching layers between a p-type Al _0.9 Ga _0.1 As layer and a p-type Al _0.15 Ga _0.85 As layer. It is a membrane.

  The p-type confinement layer 120 and the n-type confinement layer 122 are formed by epitaxially growing the supply amount of Al continuously.

  When the second mirror 104 is grown, at least one layer in the vicinity of the p-type confinement layer 120 can be formed on an AlAs layer or an AlGaAs layer that is oxidized later and becomes the insulating layer 105 for electrode confinement. The AlGaAs layer serving as the insulating layer 105 has an Al composition of 0.95 or more. Further, it is desirable that the outermost layer of the second mirror 104 has a high carrier density and facilitates ohmic contact with the electrode (first electrode 107).

  The temperature at which the epitaxial growth is performed is appropriately determined depending on the growth method and raw material, the type of the semiconductor substrate 101, or the type, thickness, and carrier density of the semiconductor multilayer film 150 to be formed. Preferably there is. Further, the time required for performing the epitaxial growth is also appropriately determined in the same manner as the temperature. In addition, as a method for epitaxial growth, a metal-organic vapor phase epitaxy (MOVPE) method, an MBE (Molecular Beam Epitaxy) method, an LPE (Liquid Phase Epitaxy) method, or the like can be used.

  Subsequently, a resist layer R100 having a predetermined pattern is formed as shown in FIG. 5 by applying a resist on the semiconductor multilayer film 150 and then patterning the resist by a lithography method. The resist layer R100 is formed above the region where the columnar portion 130 (see FIGS. 1 and 2) is to be formed. Next, using this resist layer R100 as a mask, the second mirror 104, the p-type confinement layer 120, the active layer 103, and a part of the n-type confinement layer 122 are etched by, for example, a dry etching method. As shown, a columnar semiconductor deposited body (columnar portion) 130 is formed. Thereafter, the resist layer R100 is removed.

  Subsequently, as shown in FIG. 7, the Al composition in the second mirror 104 is changed by introducing the semiconductor substrate 101 on which the columnar portion 130 is formed by the above process into a steam atmosphere of about 400 ° C., for example. A high layer (a layer having an Al composition of 0.95 or more) is oxidized from the side surface to form an insulating layer 105 for current confinement. The oxidation rate depends on the furnace temperature, the amount of steam supplied, the Al composition of the layer to be oxidized and the film thickness.

  (2) Next, as shown in FIG. 8, the buried insulating layer 106 surrounding the columnar portion 130, that is, a part of the first mirror 102, the p-type confinement layer 120, the active layer 103, and the n-type confinement layer 122 is formed. Form.

  Here, a case where polyimide resin is used as a material for forming the buried insulating layer 106 is described. First, a precursor (polyimide precursor) is applied onto the semiconductor substrate 101 having the columnar portion 130 using, for example, a spin coating method to form a precursor layer. At this time, the precursor layer is formed to have a thickness greater than the height of the columnar section 130. As a method for forming the precursor layer, known techniques such as a dipping method, a spray coating method, and a droplet discharge method can be used in addition to the spin coating method described above.

  Next, the semiconductor substrate 101 is heated using, for example, a hot plate to remove the solvent, and then placed in a furnace at, for example, about 350 ° C. to imidize the precursor layer, thereby almost completely curing polyimide. A resin layer is formed. Subsequently, as shown in FIG. 8, the upper surface 130 a of the columnar part 130 is exposed, and the buried insulating layer 106 is formed. As a method for exposing the upper surface 130a of the columnar section 130, a CMP method, a dry etching method, a wet etching method, or the like can be used. Alternatively, the buried insulating layer 106 can be formed using a photosensitive resin. The buried insulating layer 106 can be patterned by lithography or the like as necessary.

  (3) Next, a process of forming the first electrode 107, the second electrode 109, and the laser beam emission surface 108 (see FIG. 2) for injecting current into the active layer 103 will be described.

  First, before forming the first electrode 107 and the second electrode 109, the exposed upper surfaces of the columnar portion 130 and the semiconductor substrate 101 are cleaned using a plasma treatment method or the like as necessary. Thereby, an element having more stable characteristics can be formed. Next, as shown in FIG. 2, for example, a laminated film of, for example, an alloy of Au and Zn and Au is formed on the upper surface of the buried insulating layer 106 and the columnar portion 130 by, for example, vacuum deposition, and then the columnar portion is formed by lift-off method. A portion where the laminated film is not formed is formed on the upper surface of 130. This portion becomes the emission surface 108. In the above process, a dry etching method or a wet etching method can be used instead of the lift-off method.

  Further, a laminated film of, for example, an alloy of Au and Ge and Au is formed on the exposed surface of the semiconductor substrate 101 by, for example, a vacuum deposition method. Next, annealing is performed. The annealing temperature depends on the electrode material. In the case of the electrode material used in the present embodiment, it is usually performed at around 400 ° C. Through the above steps, the first electrode 107 and the second electrode 109 are formed.

  Through the above process, the vertical cavity surface emitting laser 100 shown in FIGS. 1 and 2 is obtained.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments and can take various forms. For example, in the above-described embodiment of the present invention, the n-type confinement layer 122 and the p-type confinement layer 120 are the refractive index changing region where the refractive index changes. A part of the p-type confinement layer 120 may be a refractive index changing region.

1 is a plan view of a vertical cavity surface emitting laser according to the present embodiment. Sectional drawing of the vertical cavity surface emitting laser shown in FIG. FIG. 3 is an enlarged view of a portion B of the vertical cavity surface emitting laser shown in FIG. 2. Schematic of the refractive index in the lamination direction of a vertical cavity surface emitting laser. Sectional drawing which shows the manufacturing method of the vertical cavity surface emitting laser which concerns on this Embodiment. Sectional drawing which shows the manufacturing method of the vertical cavity surface emitting laser which concerns on this Embodiment. Sectional drawing which shows the manufacturing method of the vertical cavity surface emitting laser which concerns on this Embodiment. Sectional drawing which shows the manufacturing method of the vertical cavity surface emitting laser which concerns on this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Vertical cavity surface emitting laser, 101 Semiconductor substrate, 102 1st mirror, 103 Active layer, 104 2nd mirror, 105 Insulating layer, 106 Embedded insulating layer, 107 1st electrode, 108 Output surface, 109 2nd electrode, 120 p-type confinement layer, 122 n-type confinement layer

Claims (9)

A substrate,
A pair of mirrors provided above the substrate;
An active layer provided between the pair of mirrors;
A refractive index matching layer formed adjacent to the active layer;
Including
The refractive index matching layer has a refractive index changing region at least in part,
The refractive index changing region has a refractive index between the refractive index of the active layer and the refractive index of the mirror, and the refractive index difference from the mirror decreases from the active layer toward the mirror. A vertical cavity surface emitting laser whose refractive index changes as described above. In claim 1,
The vertical cavity surface emitting laser, wherein the refractive index matching layer is a confinement layer. In claim 1 or 2,
The refractive index changing region is a vertical cavity surface emitting laser in which the refractive index continuously changes. In claim 1 or 2,
The refractive index changing region is a vertical cavity surface emitting laser in which the refractive index changes stepwise. In any of claims 1 to 4,
The refractive index matching layer is a vertical cavity surface emitting laser, the entirety of which constitutes the refractive index changing region. In any of claims 1 to 5,
A vertical cavity surface emitting laser in which a refractive index of the refractive index matching layer is continuous with a refractive index of the active layer on adjacent surfaces of the refractive index matching layer and the active layer. In any one of Claims 1 thru | or 6.
The refractive index matching layer and the mirror are adjacent to each other,
A vertical cavity surface emitting laser in which a refractive index of the refractive index matching layer is continuous with a refractive index of the mirror on an adjacent surface of the refractive index matching layer and the mirror. In any one of Claims 1 thru | or 7,
The mirror is a multilayer reflective film having a plurality of layers,
At least one of the plurality of layers is a mirror refractive index matching layer whose refractive index changes,
The mirror refractive index matching layer is a vertical cavity surface emitting light whose refractive index changes from the mirror refractive index matching layer toward another adjacent layer so that a difference in refractive index from the other layer decreases. laser. In any of claims 1 to 8,
The refractive index changing region is composed of an AlGaAs layer,
A vertical cavity surface emitting laser that changes a refractive index by changing an Al composition ratio in the refractive index changing region.

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