JPH11261153A - Surface emitting semiconductor laser and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid deteriorating the element by a means such that at least a part has a protrudent resonator and opening at the top face of the resonator and an embedded metal layer of a specified melting point or less is formed to closely contact a top electrode continuously formed along the resonator and an insulation film surface. SOLUTION: A main heating source for the surface emitting semiconductor laser having a protrudent resonator structure is the Joule heat of the resistance of an n-type semiconductor multilayer reflection layer 106 or a contact resistance of a p-type contact layer 107 and top electrode 110. These heat sources exist mainly at a resonator protrusion 108. By embedding the resonator protrusion 108 in a good thermal-conductivity embedding layer 112, the embedding layer 112 acts as a heat sink to accelerate the heat radiation of the resonator protrusion 108, thereby lowering the temp. of the resonator and thus the deterioration of the element can be avoided. To closely imbed the resonator protrusion 108, the heat treating temp. is set so as not to exceed 400 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-emitting type semiconductor laser which emits a laser beam in a direction perpendicular to a substrate.

[0002]

2. Description of the Related Art A conventional surface emitting semiconductor laser is disclosed in IEE, Journal of Quantum Electronics, Vol. 27, No. 6, 1991.
Year) pages 1332 to 1346 [IEEE Jou
rnal of QuantumElectronic
s, vol. 27, no. 6 pp1332-1346
(1991)], Jack L. It is summarized in detail and systematically in a commentary article by Jewel et al.

[0003] In general, the main factor that limits the output of a semiconductor laser or impairs its reliability is a rise in temperature due to heat generation during element driving. As one method of suppressing a temperature rise, a method of increasing heat dissipation is generally used. A semiconductor laser device is formed on a compound semiconductor substrate. However, heat dissipation to the substrate side cannot be expected much because the compound semiconductor has low thermal conductivity. Therefore, in the case of the edge emitting type semiconductor laser, a method of increasing heat radiation by directly contacting an element forming portion with a heat sink has become a common means.

However, in the case of the surface emitting type semiconductor laser of the surface emitting type, since the laser is emitted to the surface of the substrate on which the element is formed, a heat sink cannot be brought into direct contact with the element, so that the heat radiation is difficult. I had it.

In order to solve this problem, for example, Japanese Patent Application Laid-Open
According to the description of Japanese Patent No. 283796, an electrode having a heat sink function is provided. It is considered that the main heat source in the surface emitting semiconductor laser having such a protruding resonator structure is Joule heat due to the resistance of the p-type semiconductor multilayer reflective layer or the contact resistance between the p-type contact layer and the upper electrode. Can be These heat sources mainly exist on the resonator protrusions. For this reason, by embedding the periphery of the resonator protruding portion in close contact with a metal having excellent heat conduction, heat dissipation can be increased and the element temperature can be significantly reduced.

In order to emit a laser beam from the surface, only the periphery of the cavity projection must be buried with metal, and the top surface of the cavity projection having the laser emission portion must be formed so as not to be covered with metal. In the above-described method, a metal is deposited only on an exposed metal portion by using a plating method, so that the laser emission port on the upper surface of the resonator protrusion is secured while embedding the metal around the resonator.

[0007]

In order to deposit a metal only on an exposed metal portion by using a plating method as in the above-described method, an electrolytic plating method must be used. However, since the treatment in the electrolytic solution is necessary, there is a possibility that the semiconductor element may be contaminated with impurities. In addition, there is a problem in that a current flows through the element, thereby deteriorating the characteristics of the element.

An object of the present invention is to provide a surface emitting semiconductor laser having a high laser output and high reliability by realizing a heat sink structure capable of emitting light from the surface by a simple method not including a step of deteriorating the element. To provide.

[0009]

According to the present invention, there is provided a surface emitting laser having a resonator having at least a portion having a projecting resonator, and having an opening on an upper surface of the resonator. And a buried layer made of a metal having a melting point of 400 ° C. or less formed so as to be in close contact with the upper electrode. The buried layer is preferably a metal or an alloy that forms a solid solution with gold. An electrode pad made of gold is provided on a part of the surface of the buried layer. Further, the resonator is characterized in that the inclination angle of the side surface of the projection is 90 ° or less, and more desirably 60 ° or less. Further, the insulating film is formed so as not to cover at least a side surface of the resonator.

According to a method of manufacturing a surface emitting semiconductor laser of the present invention, a step of forming at least a part of a resonator in a projection shape, and a step of forming an insulating film covering at least a substrate surface excluding an upper surface of the resonator. Forming an upper electrode having an opening on the upper surface of the resonator projection; and depositing a buried metal having a melting point of 400 ° C. or less on the surface of the substrate except for at least the opening and a range of 1 μm in the vicinity thereof. The method is characterized by including a step of forming a buried layer by performing a heat treatment at a temperature equal to or higher than the melting point of the buried metal. The area of the buried metal is larger than the area of the upper electrode. Further, it is preferable that the volume of the buried metal is larger than the volume obtained by multiplying the area of the upper electrode by the height of the resonator projection. Further, the step of forming the buried layer by performing the heat treatment is performed in an atmosphere of a reducing gas or an inert gas. Further, it is desirable to perform a step of performing a plasma cleaning process prior to the step of forming the buried layer by performing the heat treatment.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a sectional view schematically showing a surface emitting semiconductor laser according to the present invention. This surface-emitting type semiconductor laser comprises an n-type GaAs substrate 101, an n-type semiconductor multilayer reflection layer 102, an n-type cladding layer 103, an active layer 104, a p-type cladding layer 105, a p-type semiconductor multilayer reflection layer 106, and a p-type semiconductor multilayer reflection layer 106. The mold contact layer 107 is sequentially laminated. Then, the cavity projection 108 is formed by etching the p-type cladding layer 105 halfway through the p-type contact layer 107 and the p-type semiconductor multilayer reflective layer 106 to form a projection. By forming the resonator projections 108, the injected current does not spread, the reactive current can be suppressed, and efficient laser oscillation can be achieved. An insulating film 109 made of a SiO ₂ film is formed around the resonator projection 108.
And an upper electrode 110 composed of two layers of a Ti film and an Au film. The insulating film 109 is formed so as to cover at least the surface of the p-type cladding layer 105.
Since the thermal conductivity of SiO _2, which is a material of No. 09, is small, the resonator protrusions 108 are preferably not hampered with heat radiation.
It is desirable not to touch the side. The upper electrode 110 is formed continuously along the insulating film 109, the side surface of the resonator projection 108, and the surface of the p-type contact layer 107. Further, the upper electrode 110 has a laser emission port 111 on the upper surface of the resonator projection 108. The laser emission port is an opening on the upper surface of the resonator projection 108 of the upper electrode 110,
From here, laser light is emitted to the front surface side of the substrate. Then, the resonator projection 108 is brought into close contact with the surface of the upper electrode 110.
Buried layer 112 is formed so as to bury the periphery of. This buried layer 112 functions as a heat sink. Further, an Au electrode pad 113 is formed on the surface of the buried layer 112 so as not to block the laser emission port 111, and AuGe, N
A lower electrode 114 made of i and Au is formed.

Here, the n-type semiconductor multilayer reflective layer 102
30 pairs of lAs and Al _0.15 Ga _0.85 As are alternately stacked and have a reflectivity of 99.9% or more with respect to the laser oscillation wavelength. The p-type semiconductor multilayer reflective layer 106 is composed of AlAs and Al
Twenty-five pairs of _0.15 Ga _0.85 As are alternately stacked and have a reflectance of 99.6% or more with respect to the laser oscillation wavelength. Active layer 10
Reference numeral 4 denotes a multiple quantum well active layer including three GaAs well layers and an Al _0.3 Ga _0.7 As barrier layer stacked so as to sandwich the well layers. The p-type contact layer 107 is made of a GaAs layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ or more. AuS having a melting point of 280 ° C.
An n alloy is used. As the buried layer, a metal having a melting point of 400 ° C. or less such as Sn, In, SnIn, PbSn, and AuSi can be used in addition to AuSn. In the present invention, a heat treatment step at a temperature equal to or higher than the melting point is required in order to bury the resonator protrusions with good adhesion by melting the metal.
If this temperature exceeds 400 ° C., unexpected diffusion of dopants and the like may occur. This temperature is preferably as low as possible, and more preferably a metal having a melting point of 300 ° C. or less is used. The thickness of the buried layer 112 is preferably as large as possible from the viewpoint of the effect as a heat sink, and is desirably formed to a thickness equal to or higher than the height of the resonator projection 108.

The main heat source in the surface emitting type semiconductor laser having the projecting resonator structure is the resistance of the p-type semiconductor multilayer reflective layer 106 or the p-type contact layer 107 and the upper electrode 110.
These heat sources are mainly present in the resonator protrusions 108. By embedding the periphery of the resonator protrusion 108 with the buried layer 112 having good thermal conductivity, the buried layer 112 is formed.
Acts as a heat sink, radiating heat from the resonator projections 108 and lowering the temperature of the resonator. Furthermore, the structure in which the insulating film 109 having low thermal conductivity is not formed on the side surface of the resonator protrusion 108 can further enhance the heat sink function without hindering heat radiation from the resonator protrusion 108 to the buried layer 112.

According to the present invention, this resonator projection 108
By closely covering the periphery with the buried layer 112 having excellent heat conduction, heat dissipation was enhanced, and the element temperature during driving could be greatly reduced. As a result, a significant increase in laser output and improvement in reliability were realized. (Manufacturing method) Next, a manufacturing method will be described with reference to FIGS. First, as shown in FIG.
1 and an n-type semiconductor multilayer reflective layer 102 and an n-type clad layer 1
03, an active layer 104, a p-type cladding layer 105, a p-type semiconductor multilayer reflective layer 106, and a p-type contact layer 107 are sequentially epitaxially grown by metal organic chemical vapor deposition. Se was used as an n-type dopant, and Zn was used as a p-type dopant. Then, a photoresist is applied to the surface, and a resist mask is formed in the shape of the resonator by a photolithographic method. Here, an arbitrary shape such as a circle, a rectangle, and a stripe can be selected as the shape of the resist mask.

Next, as shown in FIG. 3, using the resist mask as a mask, etching is performed by reactive ion beam etching or the like halfway through the p-type cladding layer 105 to form a resonator projection 108, and the resist mask is removed. After that, thermal CVD using monosilane as a raw material, for example, a SiO ₂ film as an insulating film 109 on the surface excluding the resonator protrusions 108
It is formed by a method. Here, the p-type cladding layer 105
Was etched about 5 μm halfway through, but may be etched to any depth.

Next, as shown in FIG. 4, a laser emission port 111 is provided on the upper surface of the cavity protrusion, and the upper electrode 110 is continuously formed along the side surface of the cavity protrusion 108 and the surface of the insulating layer 109.
To form As a method for depositing, 0.1 μm of Ti and 0.1 μm of Au are sequentially laminated on the substrate surface by the sputter deposition method, and then a part of the upper surface of the resonator protrusion 108 and the upper surface of the insulating film 109 are dry-etched using argon gas. Some Ti and Au were removed. At this time, the upper electrode 110
Was formed such that its area was smaller than the area of the insulating layer 109, that is, a region where the insulating layer 109 was exposed was provided for a reason described later. The Ti layer used as the material of the upper electrode 110 is a material that can make ohmic contact with a compound semiconductor. In addition, an AuGe alloy is used for an n-type compound semiconductor, and an AuZn is used for a p-type compound semiconductor. An alloy or the like can be used. Au formed on the outermost surface did not form an oxide film and was selected as a material having excellent wettability with a buried layer described later. This is because if an oxide film is formed on the surface of the upper electrode 110, it may cause poor filling.

Next, as shown in FIG. 5, a buried metal 115 is deposited on the upper electrode 110 by using a lift-off method so that at least the laser emission port 111 is exposed. The buried metal 115 is the same as the buried layer 112 in FIG. 1 in material, but is different in shape and function, so a different name is used here. Here, an AuSn alloy was used as the material of the buried metal 115. In addition, Sn, In, Sn
In alloy, PbSn alloy, AuSi alloy, etc. have a melting point of 40
A metal having a temperature of 0 ° C. or less can be used. The buried metal 115 becomes a buried layer by being melted and deformed by a heat treatment later. However, in order to completely bury the periphery of the resonator protrusion 108, the thickness of the buried metal 115 is reduced by the thickness of the resonator protrusion 108. It is preferable that the height is equal to or higher than the height. However, if the thickness of the buried metal 115 is too large, lift-off becomes extremely difficult, so the limit is about 4 μm. When the height of the resonator projection 108 exceeds 4 μm, the area of the buried metal 115 is
By making the area larger than 0, the thickness of the buried layer after melting can be increased as described later, and sufficient burying becomes possible. More preferably embedded metal 115
Is made to be 105% or more of the area of the upper electrode 110. Furthermore, if the volume of the buried metal 115 is equal to or greater than the volume obtained by multiplying the area of the upper electrode 110 by the height of the resonator projection 108, the resonator projection 10
8 can be almost embedded. More preferably, the volume of the buried metal 115 is at least 105% of the volume obtained by multiplying the area of the upper electrode 110 by the height of the resonator projection 108. Here, the thickness of the buried metal 115 is 4 μm.
The area of the buried metal 115 was set to be 125% of the area of the upper electrode 110. Further, in such a lift-off method of the metal film, burrs and the like may be generated at the edge portion. Not be.

Then, in order to clean the exposed surface of the upper electrode 110, the substrate surface was subjected to argon plasma cleaning. This makes it possible to completely remove the dirt such as organic substances on the exposed surface of the upper electrode 110, thereby facilitating the formation of the buried layer.

Next, as shown in FIG. 6, when the buried metal is melted by applying a heat treatment, the buried layer 112 is formed by flowing and deforming so as to be in close contact with the upper electrode 110 around the resonator projection 108, and then cooled and solidified. Is done. As a heat treatment method, first, the substrate was placed in an atmosphere in which a mixed gas of argon and hydrogen, which is a reducing gas, was substituted, and heated at a temperature of 300 ° C. slightly higher than the melting point of the AuSn alloy for one minute. The molten buried metal flows because of good wettability to the upper electrode, and the gap between the cavity protrusion and the buried metal at the time of deposition of the buried metal is automatically filled, and the periphery of the cavity protrusion is completely adhered. Can be embedded.

The reason why the area of the buried metal is larger than the area of the upper electrode 110 is to increase the thickness of the buried layer 112 and to provide a driving force for the flow when the buried metal is melted. The liquefied embedded metal has very poor wettability to the insulating film. Therefore, the buried metal on the insulating film is repelled when melted and recedes, and automatically gathers on the upper electrode. As a result, the volume or thickness of the buried metal on the upper electrode increases, and the driving force for flow also increases. In the case of this embodiment, since the area of the buried metal 115 is formed to be 125% of the area of the upper electrode 110,
The buried metal 115 deposited first at 4 μm formed the buried layer 112 having a thickness of about 5 μm after melting, and the cavity protrusion 108 having a height of 5 μm was almost completely buried. Further, the effect of smoothing the surface of the solidified buried layer 112 was also obtained.

The close contact between the upper electrode and the buried layer occurs due to mutual good wettability. On the other hand, the wettability of the buried layer with respect to the semiconductor is small, so that the laser emission port 111 where the p-type contact layer 107 is exposed is embedded in the buried layer. It is secured without being covered by 112. Also, the buried metal 115
The burrs generated at the edge of the metal are also melted and disappear. However, the end of the laser emission port 111 and the buried metal 11
When the edge of No. 5 is 1 μm or less, the buried layer 112 may very rarely cover the laser emission port 111 after the heat treatment. Therefore, it is desirable that the distance between the end of the laser emission port 111 and the edge of the embedded metal 115 is 1 μm or more.

By performing the heat treatment in a reducing gas atmosphere,
Occurrence of an oxide film on the surface of the molten buried metal is suppressed, and more excellent fluidity is obtained, whereby poor burying can be suppressed. Here, a mixed gas of argon and hydrogen is used as the reducing gas as the atmosphere gas, but a hydrogen gas may be used. Further, an inert gas may be used. Inert gas here refers to helium, neon, argon, krypton,
It is a rare gas such as xenon or a gas with low reactivity such as nitrogen.

In this way, it is possible to form the buried metal 112 which has a sufficient thickness, closely adheres to the periphery of the resonator projection 108 without any gap, and has excellent heat dissipation. Resonator projection 10
If the height of 8 and the deposition thickness are made uniform, flattening can be achieved. Since the heat treatment temperature is a relatively low temperature of 400 ° C. or less, atomic diffusion hardly occurs, and there is no fear of element deterioration.
In our experiments, heat treatment at over 400 ° C. caused unexpected diffusion of dopants and metal atoms of the upper electrode, resulting in a significant decrease in laser oscillation performance.

Then, as shown in FIG. 7, an Au electrode pad 113 is formed on the surface of the buried layer 112 so as not to cover the laser emission port, and finally, AuGe, Ni,
By depositing the lower electrode 114 on which Au is laminated, a surface-emitting type semiconductor laser is completed.

As described above, according to the method for manufacturing a surface emitting semiconductor laser of the present invention, the buried metal is heated and melted at a temperature equal to or higher than the melting point, so that the periphery of the cavity projection can be buried in a close contact. By embedding in a self-aligned manner due to the good wettability of the embedded metal and the upper electrode, a surface-emitting type semiconductor laser with an embedded layer can be created very easily without requiring high alignment accuracy when patterning and depositing the embedded metal. Was.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. The active layer 104 is made of InGaAs, GaAs, or AlGaAs according to the oscillation wavelength of the surface emitting semiconductor laser.
s, GaInP, AlGaInP, InGaAsP, Z
nSe, ZnS, GaN, AlGaN, InN, InG
A single layer or a quantum well layer made of any one of aN can be used, and the present invention can be implemented even if the p-type and the n-type of the conductivity type of the semiconductor are switched.

[Embodiment 2] Next, a second embodiment of the present invention will be described. FIG. 8 is a sectional view schematically showing a surface emitting semiconductor laser according to a second embodiment of the present invention. This surface-emitting type semiconductor laser differs from the first embodiment in that an Al oxide layer utilizing natural oxidation of an AlAs layer is used as a current confinement structure.

Hereinafter, this will be described in detail with reference to FIG. This surface-emitting type semiconductor laser includes an n-type GaAs substrate 201, an n-type semiconductor multilayer reflective layer 202 and an n-type cladding layer 203.
, An active layer 204, a p-type cladding layer 205, a current confinement layer 215, a p-type semiconductor multilayer reflective layer 206, and a p-type contact layer 207 are sequentially laminated. Then, the cavity projection 208 is formed by etching the p-type cladding layer 205 halfway through the p-type contact layer 207, the p-type semiconductor multilayer reflective layer 206, and the current confinement layer 215 to form a projection.

An insulating film 209 made of a SiO ₂ film and an upper electrode 210 made of two layers of a Ti film and an Au film are formed around the resonator projection 208. The insulating film 209 is formed so as to cover the surface of the p-type cladding layer 205 except for the resonator protrusion 208 (formed so as not to cover the side surface of the resonator protrusion 208), and the upper electrode 210 is formed of the insulating film 209. And side surface of resonator projection 208 and p-type contact layer 2
07 are formed continuously along the surface. Further, the upper electrode 210 has a laser emission port 211 on the upper surface of the resonator projection 208. The buried layer 2 is formed around the resonator projection 208 so as to be in close contact with the surface of the upper electrode 210.
12 are further formed, and an Au electrode pad 213 is formed on the surface of the buried layer 212 so as not to block the laser emission port 211, and AuGe, Ni,
A lower electrode 214 made of Au is formed.

Here, the n-type semiconductor multilayer reflective layer 202 is made of A
30 pairs of lAs and Al _0.15 Ga _0.85 As are alternately stacked and have a reflectivity of 99.9% or more with respect to the laser oscillation wavelength. The p-type semiconductor multilayer reflective layer 206 is made of Al _0.9 Ga _0.1 As.
And 30 pairs of Al _0.15 Ga _0.85 As are alternately stacked and have a reflectance of 99.5% or more with respect to the laser oscillation wavelength. The active layer 204 is a multiple quantum well active layer composed of three GaAs well layers and an Al _0.3 Ga _0.7 As barrier layer stacked so as to sandwich them. p-type contact layer 207
Is composed of a GaAs layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ or more. The upper electrode 210 is formed of a Ti thin film and an Au thin film.
A layer that is in contact with the buried layer 212 has A
u is facing. The burying layer 212 has a melting point of 280 ° C.
And a thickness exceeding the height of the resonator projection 208. AuS as buried layer
In addition to n, metals having a melting point of 400 ° C. or less, such as Sn, In, SnIn, PbSn, and AuSi, can be used.

The current confinement layer 215 comprises an AlAs layer 216 and an Al oxide layer 217 formed so as to surround the periphery thereof. The Al oxide layer 217 is formed of an AlAs layer 216.
Is naturally oxidized from the side face of the resonator projection 208. As a well-known method, for example, a method is known in which a resonator projection is formed so that at least the AlAs layer is exposed, and a heat treatment at about 400 ° C. is performed in a steam atmosphere. The AlAs layer 216 initiates an oxidation reaction from the exposed portion on the side surface of the resonator projection 208 to the inside, and gradually becomes oxidized Al oxide.
Layer 217 is replaced. As a result, the AlAs layer 21
6 is surrounded without interruption by the Al oxide layer 217. The current injected from the upper electrode is blocked because the Al oxide layer 217 is an insulator, and the cavity protrusion 208
Flows through the AlAs layer 216 which is a conductor located at the center of the resonator so as to concentrate on the center of the resonator projection 208. Thus, the current confinement layer 215 functions as a horizontal current confinement structure. The injected current is applied to the cavity protrusion 2
By concentrating at the center of 08, the reactive current is greatly suppressed as compared with a simple protruding resonator structure, and a reduction in threshold current and an improvement in laser output can be expected.

However, the current confinement structure using the Al oxide layer also has a large problem in terms of heat radiation. Al oxide layer is A
Since the thermal resistance is about 5 to 10 times as large as that of the lAs layer, heat radiation of the resonator projection to the substrate side is hindered, and a temperature rise during driving is caused. The main heat source in the surface-emitting type semiconductor laser having the protruding resonator structure is considered to be Joule heat due to the resistance of the p-type semiconductor multilayer reflective layer or the contact resistance between the p-type contact layer and the upper electrode. These heat sources mainly exist on the resonator protrusions. The current confinement layer must be formed on the resonator protrusion for convenience in manufacturing method. Since the current confinement layer loses the current confinement effect when it is separated from the active layer, it must be formed near the base of the resonator protrusion. I can't. By arranging the current confinement layer having a high thermal resistance at the base of the resonator projection, the resonator projection is easily thermally isolated, and the driving temperature is higher than that of the projection resonator structure having no current confinement layer. It leads to a rise. As a result, a laser output may not be obtained as expected. There was also a major problem in reliability, which is particularly susceptible to heat.

When the present invention is applied, the resonator projections 208
Since the buried layer 212 having good thermal conductivity can be formed in close contact with the surrounding area, the heat generated in the resonator projection 208 is released to the buried layer 212, thereby greatly improving the heat radiation. As a result, the device temperature during driving could be greatly reduced, and a remarkable increase in laser output and improvement in reliability were obtained. Therefore, when the present invention is applied to the protruding resonator structure using the Al oxide layer as the current confinement layer, current confinement and heat radiation, which have not been possible in the past, can be achieved at the same time, which is extremely effective.

Third Embodiment Next, a third embodiment of the present invention will be described. FIG. 9 is a sectional view schematically showing a surface emitting semiconductor laser according to a third embodiment of the present invention. This surface-emitting type semiconductor laser differs from the first embodiment in that the inclination angle θ of the side surface of the resonator projection 308 is formed smaller than 90 °. By reducing the inclination angle θ in this manner, poor adhesion between the buried layer and the resonator projection can be further reduced.

The details will be described below with reference to FIG. This surface-emitting type semiconductor laser includes an n-type semiconductor multilayer reflective layer 302 and an n-type clad layer 303 on an n-type GaAs substrate 301.
And an active layer 304, a p-type cladding layer 305, a p-type semiconductor multilayer reflective layer 306, and a p-type contact layer 307 are sequentially stacked. Then, the resonator projection 3 is etched into a projection shape halfway through the p-type cladding layer 305 via the p-type contact layer 307 and the p-type semiconductor multilayer reflective layer 306.
08 is formed. Here, the inclination angle θ of the side surface of the resonator projection 308 is set to 60 °.

An insulating film 309 made of an SiO ₂ film, an upper electrode 310 made of three layers of a Cr film, an AuZn film and an Au film are formed around the resonator projection 308. The insulating film 309 is formed of the p-type cladding layer 3 except for the resonator protrusion 308.
The upper electrode 310 is formed so as to cover the surface of the insulating film 309, the side surface of the resonator protrusion 308, and the surface of the p-type contact layer 307. Further, the upper electrode 310 has a laser emission port 311 on the upper surface of the resonator projection 308. A buried layer 312 is formed around the cavity protrusion 308 so as to be in close contact with the surface of the upper electrode 310, and the Au electrode pad 31 is formed on the buried layer 312 so as not to block the laser emission port 311.
3 is formed, and AuGe, N is formed on the back surface of the n-type semiconductor substrate.
A lower electrode 314 made of i and Au is formed.

Here, the n-type semiconductor multilayer reflective layer 302 is made of A
30 pairs of lAs and Al _0.15 Ga _0.85 As are alternately stacked and have a reflectivity of 99.9% or more with respect to the laser oscillation wavelength. The p-type semiconductor multilayer reflective layer 306 is made of Al _0.9 Ga _0.1 As.
And 30 pairs of Al _0.15 Ga _0.85 As are alternately stacked and have a reflectance of 99.5% or more with respect to the laser oscillation wavelength. The active layer 304 is a multiple quantum well active layer composed of three GaAs well layers and an Al _0.3 Ga _0.7 As barrier layer sandwiched therebetween. p-type contact layer 307
Is composed of a GaAs layer having a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ or more. The upper electrode 310 is made of a thin film of Ti and a thin film of Au.
A layer that is in contact with the buried layer 212 has A
u is facing. The burying layer 312 has a melting point of 280 ° C.
And a thickness exceeding the height of the resonator projection 308. AuS as buried layer
In addition to n, metals having a melting point of 400 ° C. or less, such as Sn, In, SnIn, PbSn, and AuSi, can be used.

When forming the resonator protrusion, the inclination angle θ of the side surface
Is set to 90 ° or less in order to obtain better adhesion between the buried layer and the side surface of the resonator projection. If the inclination angle θ of the side surface of the resonator projection is too large, the thickness of the upper electrode on the side surface is insufficient, so that a uniform Au surface is not formed and the wettability with the molten embedded metal deteriorates. Then, problems such as the progress of the buried metal stopping at the boundary between the side surface and the bottom surface of the resonator protrusion and the generation of a void occur, and the resonator protrusion cannot be buried. According to our experiments, when the inclination angle θ was larger than 90 °, the generation of voids could not be avoided. On the other hand, when the inclination angle θ is 90
As the angle becomes smaller than 0 °, the frequency of voids and poor adhesion decreases, and at a tilt angle of 60 °, voids and poor adhesion can be almost completely suppressed and good embedding can be realized. In addition, when the inclination angle θ is reduced, the area of the side surface of the resonator increases, so that the effect of improving the heat radiation property can be obtained.

According to the present invention, the element temperature during driving can be greatly reduced by forming a metal having excellent heat conduction on the resonator projections with good adhesion. As a result, a significant increase in laser output and improvement in reliability were realized.

[0040]

As described above, according to the present invention, a metal having a low melting point is used as an embedding material, and it is possible to embed the cavity projection by melting and thereby to embed the material in a very simple manner with good adhesion. As a result, the heat radiation is dramatically improved, the rise in the element temperature during driving can be suppressed, the laser output can be improved, and the reliability can be further improved. It is particularly effective when applied to a surface emitting semiconductor laser having a current confinement layer using an Al oxide layer.

Further, according to the manufacturing method of the present invention, since the buried layer is automatically buried in the cavity protrusion by melting, the patterning for depositing the buried metal does not require high alignment precision, and is extremely simple. Embedding with high adhesion can be realized. There is no gap between the periphery of the resonator projection and the buried layer. The burrs and the like at the edge portions, which are likely to be generated during patterning, are eliminated by melting, and burying with high flatness can be realized. Also 40
By using a metal having a relatively low melting point of 0 ° C. or less, the temperature of the heat treatment can be kept low, there is no fear of atomic diffusion due to heat, and the device can be formed without a step of deteriorating the element.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a surface emitting semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a sectional view illustrating a manufacturing process of the surface emitting semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a sectional view showing a manufacturing process of the surface emitting semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a manufacturing process of the surface emitting semiconductor laser according to the first embodiment of the present invention.

FIG. 5 is a sectional view showing a manufacturing process of the surface emitting semiconductor laser according to the first embodiment of the present invention.

FIG. 6 is a sectional view showing a manufacturing process of the surface emitting semiconductor laser according to the first embodiment of the present invention.

FIG. 7 is a sectional view showing a manufacturing process of the surface emitting semiconductor laser according to the first embodiment of the present invention.

FIG. 8 is a sectional view showing a surface emitting semiconductor laser according to a second embodiment of the present invention.

FIG. 9 is a sectional view showing a surface emitting semiconductor laser according to a third embodiment of the present invention.

[Explanation of symbols]

 101, 201, 301 n-type GaAs substrate 102, 202, 302 n-type semiconductor multilayer reflective layer 103, 203, 303 n-type cladding layer 104, 204, 304 active layer 105, 205, 305 p-type cladding layer 106, 206, 306 p-type semiconductor multilayer reflective layer 107, 207, 307 p-type contact layer 108, 208, 308 resonator projection 109, 209, 309 insulating film 110, 210, 310 upper electrode 111, 211, 311 laser emission port 112, 212, 312 buried layer 113,213,313 electrode pad 114,214,314 lower electrode 115 buried metal 215 current confinement layer 216 AlAs layer 217 Al oxide layer

Claims (11)

[Claims] 1. A vertical cavity surface emitting semiconductor laser having at least a part of a resonator having a protruding shape, wherein: an insulating film covering at least a substrate surface excluding an upper surface of the resonator; An upper electrode having an opening and continuously formed along the surface of the resonator and the insulating film; and a buried layer made of a metal having a melting point of 400 ° C. or less and formed to be in close contact with the upper electrode. A surface-emitting type semiconductor laser characterized by the above-mentioned. 2. A surface emitting semiconductor laser according to claim 1, wherein said buried layer is an alloy forming a solid solution with gold. 3. A surface emitting semiconductor laser according to claim 1, further comprising an electrode pad made of gold on a part of the surface of said buried layer. 4. A surface-emitting type semiconductor laser according to claim 1, wherein said resonator has an inclination angle of 90 ° or less on a side surface of said projection. 5. The surface-emitting type semiconductor laser according to claim 1, wherein the inclination angle of the side surface of the projection is 60 degrees or less. 6. A surface-emitting type semiconductor laser according to claim 1, wherein said insulating film is formed so as not to cover at least a side surface of said projection of said resonator. 7. A method for manufacturing a vertical cavity surface emitting semiconductor laser having a resonator having at least a part of a protrusion, wherein at least a part of the resonator is formed in a protrusion, and at least the resonator is formed. Forming an insulating film covering the surface of the substrate except for the upper surface of the substrate, forming an upper electrode having an opening on the upper surface of the resonator projection, and forming the upper electrode on the surface of the substrate excluding at least the opening and a 1 μm area in the vicinity thereof. Melting point 4
A method for manufacturing a surface-emitting type semiconductor laser, comprising: a step of depositing a buried metal at a temperature of not higher than 00 ° C .; and a step of forming a buried layer by performing a heat treatment at a temperature not lower than the melting point of the buried metal. 8. The method according to claim 7, wherein the area of the buried metal is larger than the area of the upper electrode. 9. A surface-emitting type semiconductor laser according to claim 8, wherein a volume of said buried metal is larger than a volume obtained by multiplying an area of said upper electrode by a height of said resonator projection. Method. 10. A surface-emitting type semiconductor laser according to claim 7, wherein the step of performing the heat treatment to form the buried layer is performed in an atmosphere of an inert gas or a reducing gas. Manufacturing method. 11. The method according to claim 7, wherein
A method of manufacturing a surface-emitting type semiconductor laser, comprising a step of performing a plasma cleaning process prior to the step of performing the heat treatment to form a buried layer.