JPH0716073B2 - Surface emitting laser oscillator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface emitting laser oscillator in which a threshold gain of an injection current is reduced.

(Prior Art) FIG. 2 is a diagrammatic sectional view showing a configuration of a conventional surface emitting laser oscillator. An n-type GaAlAs cladding layer 2, a p-type GaAs active layer 3 and a p-type GaAlAs layer 4 are sequentially deposited on an n-type GaAs substrate 1 to form a double heterojunction. A mirror surface electrode 5 is formed on the p-type GaAlAs cladding layer 4, and an electrode 6 is formed on the other surface of the GaAs substrate 1. When a forward bias is applied between the mirror surface electrode 5 and the electrode 6 to supply a current above the threshold value, an active region is formed in the p-type GaAs active layer 3 and a Fabry-Perot resonator is formed between the mirror surface electrode 5 and the reflecting mirror 7. Optical resonance is generated along the optical resonance path 8, and laser light is emitted from the reflecting mirror 7 in the direction of arrow a.

(Problems to be Solved by the Invention) This conventional surface emitting laser oscillation device has a great advantage that the optical resonator can be shortened as compared with a laser oscillation device in which an optical resonator is formed along the bonding surface direction. . However, there is a drawback that the operating current density of the laser is increased because it is necessary to increase the threshold injection current density for shortening the resonator.

As a means for solving this drawback, a method in which the active layer has a multi-layer structure and the active layer is equivalently thick, and a method in which the reflectance of the mirror electrode is increased to reduce the loss due to stimulated emission can be considered. However, it is difficult to inject a current into the active layer having a multi-layered structure by the above-mentioned method, and for example, in the method of injecting a current by utilizing a tunnel junction, there is a disadvantage that heat is generated at the tunnel junction. When the number of active layers is large, there is a drawback that current cannot be injected. In addition, it is difficult to obtain a sufficiently satisfactory reflectance even if the reflectance of the reflecting surface of the resonator is increased, as long as a mirror surface electrode in which the electrode and the reflecting surface are integrated is used.

We also proposed a surface emitting laser oscillator in which the film thickness direction on the substrate is just an n-type iso-heterostructure and Zn is selectively diffused laterally to form a pn junction in a direction orthogonal to the film surface. Has been done. However, in this laser oscillator, since the pn junction is formed on the side circumference of the circular active region, the minority carriers are not sufficiently injected to the center of the circular active region, and a non-uniform laser beam is generated. A circular laser beam having an axisymmetric structure cannot be obtained, and in the case of forming an ultrathin active layer having a quantum well structure, there are disadvantages such that the active layer is misaligned due to diffusion of Zn or the like.

(Means for Solving the Problem) An object of the present invention is to eliminate the above-mentioned drawbacks, to reduce a threshold gain of an injection current, to reduce an operating current density, and to generate a uniformly distributed laser beam. It is provided.

The surface emitting laser oscillator according to the present invention is formed on a semiconductor substrate of one conductivity type and has a first semiconductor layer of the same conductivity type and an opposite conductivity type which is formed on a part of the first semiconductor layer and constitutes an active layer. -Shaped second semiconductor layer, and a third semiconductor layer of the same conductivity type that is formed on the second semiconductor layer and forms a clad layer,
A fourth semiconductor layer of opposite conductivity type formed on the first semiconductor layer so as to surround the entire circumferences of the second and third semiconductor layers;
A pn junction formed between the first semiconductor layer and the second semiconductor layer, comprising a first electrode formed on the substrate and a second electrode formed on the fourth semiconductor layer; A resonator is formed in a direction orthogonal to each other, and a small number of carriers are injected into the active layer through the pn junction.

(Function) The diffusion potential between the first-conductivity-type first semiconductor layer formed on the substrate and the second semiconductor layer formed on the first semiconductor layer and forming the active layer is surrounded by the active layer. 4th formed
By setting the diffusion potential between the semiconductor layer and the first semiconductor layer to be smaller than the diffusion potential, the carrier is formed through the pn junction formed at the interface between the first semiconductor layer and the second semiconductor layer (active layer). Is injected into. As a result, the carrier can be injected into the active layer through the pn junction extending in the direction orthogonal to the extending direction of the resonator, and the uniformly distributed laser light can be emitted. Moreover, since the area of the pn junction into which the carrier is injected can be increased, the resistance during operation can be further reduced as compared with the conventional laser device in which the pn junction is formed so as to surround the side surface of the active layer. It will be possible.

(Embodiment) FIG. 1 is a diagrammatic sectional view showing the structure of an example of a surface emitting laser oscillator according to the present invention. In this example, the active layer has a single-layer structure, and only the p-type region forming the current path is provided on the side of the resonator. On the n-type GaAs substrate 30, the n-type GaAlAs cladding layer 31, p which acts as a minority carrier injection region,
P-type GaAs active layer 32 and n-type GaAlAs cladding layer 33 are sequentially deposited, and the p-type GaAs active layer 32 and n-type GaAlAs layer 33 are formed by RIE or the like.
Is partially etched to form a cylindrical mesa, and a p-type GaAlAs layer 34 forming a current path is embedded and grown around the cylindrical mesa. In addition, a cap layer 35, Si on the p-type GaAlAs layer 34
The O ₂ layer 36 and the p-side electrode 37 are sequentially formed. N type of cylindrical mesa
A reflector is formed on the GaAlAs clad layer 33 and the substrate is formed.
An opening for emitting laser light is provided in 30, and a reflecting mirror 39 is also formed on the bottom surface and the inner peripheral surface of this opening. The reflectors 38 and 39 form a resonator. Further, an n-side electrode 40 is formed on the opposite surface of the substrate 30. The diffusion potential between the n-type clad layer 31 and the p-type active layer 32 is
It is set to be lower than the diffusion potential with the GaAlAs layer 34. As a result, the carrier is supplied through the pn junction formed between the clad layer 31 and the active layer 32.
When a forward current is supplied between the p-side electrode 37 and the n-side electrode 40, the n-type GaAlAs layer 31 and the n-type GaAlAs layer 31 and the p-type GaAs active layer
Electrons are injected into the active layer 32 through the pn junction with 32, and light is emitted. Then, an optical resonator is formed between the reflecting mirrors 38 and 39, and laser light is emitted in the direction of arrow a. The current path in this case is indicated by reference numeral 41. Current is p-side electrode 37, p-type GaAlAs layer
34, p-type GaAs active layer 32, pn junction, n-type GaAlAs cladding layer
31, through the n-type GaAs substrate 30 and the n-side electrode 40. Therefore, the substrate 30 and the n-type GaAlAs cladding layer 31 act as a carrier injection semiconductor region, and p-type Ga provided on both sides of the resonator is provided.
The AlAs layer 34 will act as a semiconductor region forming a current path. As a result, it is orthogonal to the laser beam emission direction.
Since the carrier is injected into the active layer 32 through the pn junction,
It is possible to radiate an axially symmetric circular laser beam having a uniform energy distribution.

Even with the configuration in which only the p-type carrier supply region 34 is provided on the side of the resonator as in this example, the reflecting mirror and the electrode can be separated, and the reflectance of the reflecting mirror can be further increased, thereby increasing the threshold gain. Can be reduced. In this example, the n-type GaAlAs clad layer
33 may be composed of a p-type GaAlAs layer.

FIG. 2 is a diagrammatic sectional view showing the configuration of another modification of the surface emitting laser oscillator according to the present invention. In this example, a structure having two active layers is used, and n-type GaAlAs is formed on the n-type GaAs substrate 50.
The clad layer 51, the first p-type GaAs active layer 52, the n-type GaAlAs clad layer 53 acting as a carrier injection region, and the second p-type.
N-type GaAs active layer 54 and n acting as carrier injection region
N-type GaAlAs clad layer is formed by forming the Ga-type GaAlAs clad layer 55
A mirror surface electrode 56 acting as an n-side electrode is provided on 55, and a reflecting mirror 57 is provided on the bottom surface of the opening of the substrate 50 and its inner peripheral surface to form a resonator. Further, a p-type GaAlAs layer 58 forming a current path is formed on the side of the optical resonator, and the p-type GaAlAs layer 58 is formed.
A cap layer 59, a SiO ₂ layer 60, and a p-side electrode 61 are sequentially formed on the upper surface, and an n-side electrode 62 is formed on the opposite side of the substrate 50. p
When a forward current is supplied between the side electrode 61, the n-side electrode 62, and the mirror surface electrode 56, electrons are injected into the first active layer 52 through the n-type GaAlAs layer and the pn junction, and the second active layer. 54 is n-type Ga
Electrons are injected through the AlAs layer 55 and the pn junction, and the mirror surface electrode
A resonator is formed between 56 and the reflecting mirror 57, and laser light is emitted in the direction of arrow a. The current path at this time is indicated by reference numeral 63. When the semiconductor region forming the current path is provided on the side of the resonator as in this example, the carrier is formed in the first and second active layers 52 and 54 through the pn junction with almost no heat generation. Can be injected and laser light with a uniform energy distribution can be emitted. In this example, the n-type GaAl formed between the first and second active layers 52 and 54 is formed.
The As layer 53 may be a p-type GaAlAs layer.

The present invention is not limited to the above-described embodiments, but various modifications and variations are possible. For example, in the example described above,
Although GaAlAs / GaAs-based semiconductors have been described, the semiconductor materials are not limited to these semiconductor materials, and various semiconductor material combinations that can appropriately set the difference in diffusion potential can be used. The same effect can be obtained by using a system semiconductor or the like. In particular, the transverse junction method described above is a significant advantage as compared with the fact that it is difficult to apply to this quaternary semiconductor.

The surface emitting laser oscillator according to the present invention can also be applied to a multilayer stripe laser oscillator.

(Effects of the Invention) The effects of the present invention described above are summarized as follows.

(1) Since the carrier is injected into the active layer through a pn junction extending in a direction orthogonal to the laser light emission direction, a circular axisymmetric laser beam having a uniform energy distribution in the cross section can be emitted.

(2) Since the carrier injection region is formed on the side of the resonator of the optical resonator to diffuse the carrier into the low-resistance clad layer and then the carrier is injected into each active layer, it is possible to uniformly and uniformly Carriers can be uniformly injected, which makes it possible to equivalently thicken the active layer and reduce the threshold injection current.

(3) Since the electrode and the reflecting mirror are separated from each other, good ohmic characteristics and a high reflectance reflecting film can be obtained at the same time, and the threshold gain required for oscillation can be greatly reduced.

(4) Unlike conventional DFB / DBR lasers, different semiconductor layers can be formed directly on the substrate without crystal growth on the diffraction grating, so if the thickness of each layer is set to 1/4 wavelength, DFB or DB
R laser can be easily manufactured.

(5) Since the resonator is formed perpendicularly to the pn junction surface, the optical resonator length can be shortened and the single mode can be easily realized.

The effects (1) and (3) cannot be obtained by the lateral joining method, and are the remarkable effects of the present invention.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an example of a surface emitting laser oscillator according to the present invention, FIG. 2 is a schematic sectional view showing a configuration of a modified example of a surface emitting laser oscillator according to the present invention, and FIG. It is a diagrammatic sectional view showing a configuration of a conventional surface emitting laser oscillator. 30,50 …… Substrate 31,51 …… N-type GaAlAs cladding layer 32,52,54 …… p-type GaAs active layer 36,60 …… SiO ₂ layer 34,58 …… p-type GaAlAs layer 35,59 …… Cap layer 40,62 …… n-side electrode 37,61 …… p-side electrode 38,39,57 …… Reflecting mirror 41,63 …… Current path 56 …… Mirror surface electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-104188 (JP, A) JP-A-53-67391 (JP, A)

Claims (1)

[Claims] 1. A first semiconductor layer of the same conductivity type formed on a semiconductor substrate of one conductivity type, and a second semiconductor layer of the opposite conductivity type formed on a part of the first semiconductor layer to form an active layer. A semiconductor layer, a third semiconductor layer of the same conductivity type formed on the second semiconductor layer and forming a cladding layer, and an opposite formed on the first semiconductor layer so as to surround the second and third semiconductor layers. A fourth semiconductor layer of conductivity type, a first electrode formed on the substrate, and a second electrode formed on the fourth semiconductor layer, wherein the first semiconductor layer and the second semiconductor layer A resonator is formed in a direction orthogonal to the pn junction formed between the first semiconductor layer and the second semiconductor layer, and a diffusion potential generated between the first semiconductor layer and the second semiconductor layer is
It is characterized in that it is set to be smaller than a diffusion potential generated between the first semiconductor layer and the fourth semiconductor layer and a minority carrier is injected into the active layer through the pn junction. Surface emitting laser oscillator.