JPH10270790A - Surface-emitting laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a contact resistance that occupies the large part of an element resistance by forming a specific number of trenches at a contact layer that is the lowest layer of an upper semiconductor multilayer film for allowing an electrode to contact the surrounding of the bottom part of a mesa. SOLUTION: An n-type semiconductor multilayer reflecting film is formed on a n-type GaAs substrate and further a clad layer 3, an active layer 4, a clad layer 5, a contact layer 7 for forming an electrode, and a p-type semiconductor multilayer reflecting film 6 are formed. Then, a p-type semiconductor multilayer reflection film 6 is etched up to the upper surface of the contact layer 7, for example, by a reactive ion beam etching, thus forming a mesa. Then, a beam exposure resist is formed around the mesa, a pattern is formed by a beam exposure, and at least one trench 30 is formed by etching. Then, a p-type electrode 23 in a shape for covering the mesa is formed and further a plating pad 24 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A conventional surface emitting laser has a high resistance p.
Current can be injected from the contact layer bypassing the reflective semiconductor multilayer film, and the sheet resistance in the lateral direction is increased by increasing the thickness of the layer to 5 / 4λ, which is five times the normal value. Was known to do.

FIG. 4 shows a cross-sectional structure of a conventional vertical cavity surface emitting laser, which is an example of a surface emitting laser, and FIG. 5 is a process flow diagram of the surface emitting laser. The structure will be described below according to the manufacturing method. On the n-type GaAs substrate 1, when the wavelength in the medium is λ, Ga having a thickness of ４λ
An n-type semiconductor multilayer reflective film 2 is formed by alternately stacking As layers and AlAs layers having a thickness of 積 層 λ. N-type Al
_0.3 Ga _0.7 As clad layer 3, i-In _0.2 Ga _0.8
An As layer 4 and a p-type Al _0.3 Ga _0.7 As clad layer 5 are grown, and then a １ ／ λ-thick AlAs layer starting from the AlAs layer and a １ ／ λ-thick GaAs layer are stacked. The semiconductor multilayer reflective film 6 is sequentially grown. At this time, in order to reduce the electric resistance of the device, the thickness of the GaAs layer closest to the active layer in the lowermost layer among the AlAs / GaAs layers constituting the p-type semiconductor multilayer reflective film is set to be as thick as 5 / 4λ. And a contact layer 7 for forming an electrode later. The surface emitting laser substrate 15 is manufactured as described above. These growths are performed by a method such as molecular beam epitaxy (MBE).

[0004] Unlike the vertical cavity surface emitting laser, such a vertical cavity surface emitting laser has a direction in which light propagates perpendicular to the active layer, so that the length of a region having a gain is the thickness of the active layer. Therefore, the region where light is amplified is short, and it is necessary to increase the optical reflectance of the semiconductor multilayer reflective film in order to amplify the light in the element enough to cause laser oscillation. Therefore, as the semiconductor multilayer reflective films 2 and 6, two kinds of substances having a large difference in refractive index, here, AlAs and GaAs are used. These substances having a large difference in the refractive index generally have a large difference in the band gap, and a potential barrier is generated at a discontinuous portion of the band at the interface, which hinders the traveling of the carrier and increases the electric resistance. Since carriers in the p-type semiconductor are holes whose effective mass is larger than that of electrons, the increase in electric resistance is larger than that in the n-type semiconductor. Therefore, in order to lower the device resistance, it is effective to inject current from the side bypassing the p-type semiconductor multilayer reflective film. One example is Kurihara et al. -1 tec
hnical digest TuB1-2).

Therefore, an element process capable of injecting current from the side is performed as shown in FIG. First, a photoresist film is formed as an etching mask on the surface emitting laser substrate 15, and the photoresist 16 is patterned into an element shape (6 μm square) by using a lithography process (FIG. 5).
(B)). Thereafter, the p-type semiconductor multilayer reflective film 6 is etched to the upper surface of the contact layer 7 by means such as reactive ion beam etching 17 using chlorine gas (FIG. 5B) to form a mesa 20 (FIG. c)). Next, using the same photolithography process, the surface emitting laser substrate 15
Is further etched to the n-type semiconductor multilayer reflective film 2, and an n-type electrode 22 is formed on the etched bottom surface using a metal such as AuGeNi (FIG. 5 (d)). Heat treatment such as flash alloy is performed. Further, after applying a photoresist on the entire surface, an opening having a size of about 10 μm □ is formed on the element by a photolithography process. After an AuZn film is formed on the entire surface, a p-type electrode 23 having a shape covering the mesa is formed by a lift-off process (FIG. 5E). Further, a plating pad 24 serving as an electrode pad and a mask for ion implantation is formed on the p-type electrode 23 and the n-type electrode 22 by the following method. After forming a Ti / Au film 25 on the entire surface (FIG. 5 (f)), a resist mask 26 having an opening at a portion to be plated is formed by photolithography (FIG. 5 (g)). At this time, the p-type electrode portion has an opening having the same size as the p-type electrode 23 manufactured earlier, and the n-type electrode portion has a size smaller than the size of the groove etched at the time of forming the n-type electrode in order to avoid damage due to ion implantation. Is also an opening that is about 5 μm larger on one side. Thereafter, a plating pad 24 plated with gold by electrolytic plating is formed (FIG. 5 (h)), and then the photoresist mask 26 is removed, and Ti
The / Au film 25 is etched by dry etching using argon gas or ion milling, and the Ti / Au film 25 used as an electrode during plating is peeled off. Since the thickness of the plating pad 24 is large, it remains in a self-aligned manner after the etching of the Ti / Au film 25. Using the plating pad 24 thus formed as a mask, ion implantation 27 is performed on the entire surface (FIG. 5 (i)) to form a high resistance region 28 for current confinement (FIG. 5 (i)). The ion implantation conditions are such that the ion species is proton (H ⁺ ), the implantation energy is 100 keV, and the dose is 5 × 10 ¹⁴ cm ⁻² . This ion implantation makes it possible to confine the current at the depth of the active layer. In this implantation energy region, since the energy is relatively small, the resistance is increased not only to the depth of the active layer but also to the outermost surface. It does not change.
Finally, the substrate is mirror-polished and, if necessary, a non-reflective coating is applied to the back surface.

The current is injected mainly from the periphery of the mesa of the p-type electrode 23, and is confined by the high resistance region 28 by ion implantation from the surface to the depth of the active layer.

[0007]

In the above-described surface emitting laser, current can be injected from the contact layer by bypassing the p-type semiconductor multilayer reflective film having high resistance, and the sheet resistance in the lateral direction can be reduced. The thickness of the layer is 5/4 of the usual 5 times.
Setting to λ contributed to a reduction in resistance. But,
The current is injected from the periphery of the mesa because of the high resistance of the mesa. The area of the current is small, and accordingly, the contact resistance of the electrode is large. If the electrode is enlarged and the area around the mesa is increased, the contact resistance will be reduced.
Accordingly, the size of the ion implantation mask must be increased. In this case, the amount of current injected into portions other than the lower portion of the mesa becomes relatively large, resulting in a large current loss and a decrease in luminous efficiency.

In addition, since the contact layer is close to the active region, the doping concentration is kept low in order to suppress the light absorption loss, and in order to avoid the deterioration of the active layer and the semiconductor multilayer reflection film, a flash alloy or the like is used. Since no heat treatment is performed, the contact resistance is large and the film has Schottky characteristics. From the above factors, the resistance of the p-type electrode portion accounts for nearly 70% of the element resistance. Since the resistance of the p-type electrode is large, not only does the applied voltage rise and power consumption increases, but also because the part is close to the active layer, if heat is generated by the resistance, the differential quantum efficiency also decreases, and the luminous efficiency also decreases. Was.

An object of the present invention is to provide a surface emitting laser having a low electric resistance which solves the above-mentioned problems.

[0010]

SUMMARY OF THE INVENTION The present invention is as follows. 1. An upper semiconductor multilayer reflective film, an intermediate layer including an active layer,
A lower semiconductor multilayer reflective film, a high resistance region for current constriction, and an upper semiconductor multilayer film formed by etching the upper semiconductor multilayer film while leaving a lowermost layer of the multilayer film, covering the entire mesa surface and the periphery of the mesa bottom; And a surface emitting laser having an electrode provided so as to be able to inject current by bypassing the upper semiconductor multilayer film, wherein the contact is the lowermost layer of the upper semiconductor multilayer film with which the electrode comes into contact around the bottom of the mesa. A surface emitting laser comprising at least one trench formed in a layer. 2. The lower semiconductor multilayer reflective film is an n-type semiconductor multilayer reflective film formed on an n-type GaAs substrate, and the intermediate layer is an n-type Al _0.3 Ga formed on the lower semiconductor multilayer reflective film.
_{A 0.7} As clad layer, an i-In _0.2 Ga _0.8 As active layer, a p-type Al _0.3 Ga _0.7 As clad layer, and the upper semiconductor multilayer reflective film is a p-type semiconductor multilayer reflective film formed on the intermediate layer. 2. The surface emitting laser according to the above 1, wherein 3. An upper semiconductor multilayer reflective film, an intermediate layer including an active layer,
A lower semiconductor multilayer reflective film, a high resistance region for current constriction, and an upper semiconductor multilayer film formed by etching the upper semiconductor multilayer film while leaving a lowermost layer of the multilayer film, covering the entire mesa surface and the periphery of the mesa bottom; And a method of manufacturing a surface emitting laser having an electrode provided so as to allow current injection to bypass the upper semiconductor multilayer film, wherein the lowermost layer of the upper semiconductor multilayer film contacted by the electrode near the bottom of the mesa Forming at least one trench in the contact layer. 4. The lower semiconductor multilayer reflective film is an n-type semiconductor multilayer reflective film formed on an n-type GaAs substrate, and the intermediate layer is an n-type Al _0.3 Ga formed on the lower semiconductor multilayer reflective film.
_{A 0.7} As clad layer, an i-In _0.2 Ga _0.8 As active layer, a p-type Al _0.3 Ga _0.7 As clad layer, and the upper semiconductor multilayer reflective film is a p-type semiconductor multilayer reflective film formed on the intermediate layer. 4. The method for manufacturing a surface emitting laser according to claim 3, wherein:

According to the surface emitting laser of the present invention, the contact area is increased by the area of the side surface of the groove by forming the groove in the contact layer portion in contact with the electrode covering the mesa, and the contact resistance is reduced by the increased area. Only reduced. Therefore, the element resistance is greatly reduced. As described above, the driving voltage is reduced by the surface emitting laser by reducing the element resistance without reducing the light emission efficiency, and a surface emitting laser that can be driven at, for example, a CMOS level can be obtained.

[0012]

Embodiments of the present invention will be described with reference to the following examples.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following embodiment, the same material and dimensions as those described in the above-mentioned prior art are provided with a trench which is a feature of the present invention. Therefore, in the following figure,
The reference numerals (numbers) of the parts having the same functions as in FIGS. 4 and 5 are the same.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an enlarged view of an electrode portion of the device, and FIG.
Is a structural diagram of the present device, and FIG. 3 is a process flow diagram of the present device. The structure will be described below according to the manufacturing method.

Assuming that the wavelength in the medium is λ, the GaAs layer having a thickness of １ ／ λ and the １ ／ λ
To form an n-type semiconductor multilayer reflective film 2 in which AlAs layers each having a thickness of 3 nm are alternately stacked. On top of this, n-type Al _0.3 Ga _0.7 As
Clad layer 3, i-In _0.2 Ga _0.8 As layer (active layer)
4. growing a p-type Al _0.3 Ga _0.7 As clad layer 5;
Next, a 1 / 4λ thick A starting from the AlAs layer
A p-type semiconductor multilayer reflective film 6 in which an lAs layer and a GaAs layer having a thickness of 1 / 4λ are laminated is sequentially grown. At this time, in order to reduce the electric resistance of the element, the thickness of the lowermost GaAs layer closest to the active layer 4 among the AlAs / GaAs layers constituting the p-type semiconductor multilayer reflective film is set to be as thick as 5 / 4λ. Then, a contact layer 7 for forming an electrode later is formed. The surface emitting laser substrate 15 is manufactured as described above. These growths are performed by a method such as molecular beam epitaxy (MBE).

Next, using the above-mentioned substrate 15 (FIG. 3A), an element process capable of injecting current from the side is performed according to FIG. 3 as follows. First, a photoresist film is formed as an etching mask on the surface emitting laser substrate 15, and the photoresist 16 is patterned into an element shape (6 μm square) using a lithography process (FIG. 3).
(B)). Thereafter, the p-type semiconductor multilayer reflective film 6 is etched to the upper surface of the contact layer 7 by means such as reactive ion beam etching 17 using chlorine gas (FIG. 3B) to form a mesa 20 (FIG. c)). Next, using the same photolithography process, the surface emitting laser substrate 15
Is further etched to the n-type semiconductor multilayer reflective film 2, and an n-type electrode 22 is formed on the etched bottom surface using a metal such as AuGeNi (FIG. 3 (d)). Heat treatment such as flash alloy is performed.

After that, the photoresist mask is removed using an O ₂ asher and organic cleaning, and electron beam exposure (E
B) A resist 29 is applied to the entire surface, and is exposed to an electron beam (E).
B) Two rows of concentric patterns having a width of 0.5 μm are formed on the periphery of the mesa by using 31 (FIG. 3E). The EB
Using a resist as a mask, a 0.5
Etching is performed to a depth of μm to form a trench 30.

In general, when fabricating a mesa-type light-emitting device, a surface in contact with electrode 23 and contact layer 7 (corresponding to a in FIG. 1)
About 30% of one side of the mesa is appropriate, usually about 2 μm, and the entire width of the trench (integration of the width of each trench) is about 1/2. The width of the trench cannot be made extremely narrow due to etching and electrode forming techniques, and therefore the number of trenches is naturally limited to about 1 to 10. The depth of the trench is meaningless if it is shallow,
At 0.1 μm or more, the upper limit is up to the thickness of the contact layer.

After the trench is formed, the EB resist is removed, and in order to remove the damaged layer on the surface, wet etching is performed to a depth of about 10 nm from the surface with a hydrogen peroxide solution of phosphoric acid. Furthermore, after applying photoresist on the entire surface,
10 μm on the device by photolithography process
An opening having a size of about □ is formed. AuZn on top
After the film is formed on the entire surface, a p-type electrode 23 having a shape covering the mesa is formed by a lift-off process (FIG. 3F). At this time, a treatment such as vapor deposition is performed with the substrate tilted appropriately so that the AuZn film is formed on the side wall of the trench. Further, a plating pad 24 serving as an electrode pad and a mask for ion implantation is formed on the p-type electrode 23 and the n-type electrode 22 by the following method. After a Ti / Au film 25 is formed on the entire surface (FIG. 3G), a resist mask 26 having an opening in a portion to be plated is formed by photolithography (FIG. 3H). At this time, the p-type electrode portion has an opening having the same size as the p-type electrode 23 manufactured earlier, and the n-type electrode portion has a size smaller than the size of the groove etched at the time of forming the n-type electrode in order to avoid damage due to ion implantation. 5μ on one side
The opening is about m larger. Thereafter, a plating pad 24 plated with gold by electrolytic plating is formed (FIG. 3).
(I)) The photoresist mask 26 is removed, the entire surface of the Ti / Au film 25 is etched by dry etching or ion milling using argon gas or the like, and the Ti / Au film 25 used as an electrode during plating is peeled off. I do.
Since the plating pad 24 is thick, the Ti / Au film 25
Remains in a self-aligned manner after etching.

The plating pad 24 thus formed
Is used as a mask to perform ion implantation 27 on the entire surface (FIG. 3
(J)), a high resistance region 28 for current constriction is formed (FIG. 3 (j)). The ion implantation conditions are such that the ion species is proton (H ⁺ ), the implantation energy is 100 keV, and the dose is 5 × 10 ¹⁴ cm ⁻² . This ion implantation makes it possible to confine the current at the depth of the active layer. In this implantation energy region, since the energy is relatively small, the resistance increases not only to the depth of the active layer but also to the outermost surface,
Since the p-type electrode and the n-type electrode are covered with the ion implantation mask, the resistance does not increase. Finally, the substrate is mirror-polished and, if necessary, a non-reflective coating is applied to the back surface. The current is injected mainly from the periphery of the mesa of the p-type electrode 23, and is confined from the surface to the depth of the active layer by the high resistance region 28 by ion implantation.

The electric resistance of the surface emitting laser of the present invention obtained in this manner is twice as large as that of the case where the contact area between the p-type electrode and the contact layer is not formed as described above. Therefore, it was reduced to about 1/2.

[0022]

As described above, according to the present invention,
The contact resistance occupying most of the element resistance can be greatly reduced, and the reduction of the element resistance and the reduction of the driving voltage can be achieved. By using the present invention, for example, a surface emitting laser which can be driven at a CMOS level with a low resistance is realized.

[Brief description of the drawings]

FIG. 1 is an enlarged view of an electrode portion of an element of the present invention.

FIG. 2 is a structural view of an element of the present invention.

FIG. 3 is a process flow chart of the device of the present invention.

FIG. 4 is a cross-sectional view of a conventional device.

FIG. 5 is a process flow diagram of a conventional device.

[Explanation of symbols]

Reference Signs List 1 n-type GaAs substrate 2 n-type semiconductor multilayer reflective film 3 n-type Al _0.3 Ga _0.7 As clad layer 4 In _0.2 Ga _0.8 As active layer 5 p-type Al _0.3 Ga _0.7 As clad layer 6 p-type semiconductor multilayer reflective film 7 contact layer Reference Signs List 15 surface emitting laser substrate 16 photoresist 17 reactive ion beam etching 20 mesa 22 n-type electrode 23 p-type electrode 24 plating pad 25 Ti / Au film 26 resist mask 27 ion implantation 28 high resistance region 29 EB resist 30 trench 31 electron beam exposure

Claims (4)

[Claims] 1. An upper semiconductor multilayer reflection film, an intermediate layer including an active layer, a lower semiconductor multilayer reflection film, a high resistance region for current confinement, and an upper semiconductor multilayer film leaving a lowermost layer of the multilayer film. Forming a mesa by etching at a surface, covering the entire surface of the mesa and the periphery of the bottom of the mesa, and having an electrode provided so as to allow current injection to bypass the upper semiconductor multilayer film. A surface emitting laser, wherein at least one trench is formed in a contact layer, which is the lowermost layer of the upper semiconductor multilayer film in contact with the electrode around the bottom of the mesa. 2. The method according to claim 1, wherein the lower semiconductor multilayer reflective film is made of n-type GaAs.
An n-type semiconductor multilayer reflective film formed on a substrate, wherein an intermediate layer is an n-type Al _0.3 Ga _0.7 As clad layer formed on the lower semiconductor multilayer reflective film, i-In _0.2 Ga
_{A 0.8} As active layer, a p-type Al _0.3 Ga _0.7 As clad layer, and an upper semiconductor multilayer reflective film formed on the intermediate layer.
2. A reflective semiconductor multilayer film.
A surface emitting laser according to claim 1. 3. An upper semiconductor multilayer reflective film, an intermediate layer including an active layer, a lower semiconductor multilayer reflective film, a high-resistance region for current confinement, and an upper semiconductor multilayer film leaving a lowermost layer of the multilayer film. Forming a mesa by etching with an electrode, and covering the entire surface of the mesa and the periphery of the bottom of the mesa, and having an electrode provided so as to allow current injection to bypass the upper semiconductor multilayer film. 3. The method for manufacturing a surface emitting laser according to claim 1, wherein at least one trench is formed in a contact layer which is a lowermost layer of the upper semiconductor multilayer film in contact with the electrode around the bottom of the mesa. 4. The method according to claim 1, wherein the lower semiconductor multilayer reflective film is made of n-type GaAs.
An n-type semiconductor multilayer reflective film formed on a substrate, wherein an intermediate layer is an n-type Al _0.3 Ga _0.7 As clad layer formed on the lower semiconductor multilayer reflective film, i-In _0.2 Ga
_{A 0.8} As active layer, a p-type Al _0.3 Ga _0.7 As clad layer, and an upper semiconductor multilayer reflective film formed on the intermediate layer.
4. A reflective semiconductor multilayer film.
3. The method for manufacturing a surface emitting laser according to item 1.