JPH0559596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an interdigital surface emitting laser oscillation device in which the threshold gain of injection current is reduced.

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

(Problem to be solved by the invention) This conventional surface-emitting laser oscillation device has the great advantage that the optical resonator can be shortened compared to a laser oscillation device in which the optical resonator is formed along the direction of the bonded surface. . However, since the resonator is shortened, it is necessary to increase the threshold injection current density, which has the disadvantage of increasing the operating current density of the laser.

Possible means for solving this drawback include a method of making the active layer a multilayer structure to equivalently thicken the active layer, and a method of increasing the reflectance of the mirror electrode to reduce loss due to stimulated emission. However, with the above-mentioned method, it is difficult to inject current into the active layer of a multilayer structure.For example, in the method of injecting current using a tunnel junction, heat generation occurs at the tunnel junction, and the number of active layers is large. This has the disadvantage that current cannot be injected. Furthermore, in order to increase the reflectance of the reflective surface of the resonator, it is difficult to obtain a sufficiently satisfactory reflectance as long as a mirror electrode in which the electrode and the reflective surface are integrally structured is used.

Furthermore, a surface-emitting laser oscillator has been proposed in which the thickness direction of the film on the substrate is a simple n-type isohetero structure, and a pn junction is formed in the direction perpendicular to the film by selectively diffusing Zn on some sides. ing. but,
In this laser oscillation device, a pn junction is formed on the side periphery of the circular active region, so minority carriers are not injected sufficiently to the center of the circular active region.
A non-uniform laser beam is generated, making it impossible to obtain a circular laser beam with an axially symmetrical structure.Also, when forming an ultra-thin active layer with a quantum well structure, misalignment occurs in the active layer due to diffusion of Zn, etc. There are also disadvantages such as the occurrence of

(Means for Solving the Problems) An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a surface emitting laser oscillation device that can reduce the threshold gain of the injection current, reduce the operating current density, and generate a uniformly distributed laser beam. This is what we provide.

A surface emitting laser oscillation device according to the present invention has a pn A resonator is formed in a direction perpendicular to the pn junction, and a semiconductor region of one conductivity type and a carrier injection semiconductor region of the opposite conductivity type are formed on the side of the resonator to constitute a current path. , formed between the one conductivity type semiconductor active layer and the opposite conductivity type semiconductor layer.
The diffusion potential of the pn junction formed between the opposite conductivity type semiconductor layer and the one conductivity type semiconductor region and the one conductivity type semiconductor active layer and the opposite conductivity type carrier injection semiconductor region It is formed
The one conductivity type semiconductor region, the one conductivity type active layer,
A current path is formed through a semiconductor layer of an opposite conductivity type and a carrier injection region of an opposite conductivity type, so that minority carriers are uniformly injected over the entire surface of the pn junction extending in a direction perpendicular to the resonator direction. It is characterized by having the following configuration.

(Function) A first semiconductor layer of one conductivity type formed on a substrate and a second semiconductor layer formed on this first semiconductor layer and constituting an active layer.
By setting the diffusion potential between the semiconductor layer and the first semiconductor layer to be lower than the diffusion potential between the fourth semiconductor layer and the first semiconductor layer formed to surround the active layer,
The carrier is injected into the active layer through a pn junction formed at the interface between the first semiconductor layer and the second semiconductor layer (active layer). As a result, carriers can be injected into the active layer through the pn junction extending in a direction perpendicular to the direction in which the resonator extends, and uniformly distributed laser light can be emitted. Moreover, since the area of the pn junction into which the carrier is injected can be increased, it can be
It is also possible to further reduce the resistance during operation compared to conventional laser devices in which a pn junction is formed.

(Example) FIGS. 1 to 3 show the configuration of an example of a surface emitting laser oscillation device according to the present invention, and FIG.
~E are diagrammatic cross-sectional views sequentially showing the manufacturing process, the second
The figure is a diagrammatic sectional view showing the configuration when completed, and FIG. 3 is an external view as well. In this example, an interdigital surface emitting laser oscillation device having an active layer with a multilayer structure will be described. n-type or semi-insulating GaAs
Metal organic chemical vapor deposition (MOCVD) is applied on the substrate 1.
The n-type GaAlAs cladding layer 11 and p
Several tens of pairs of GaAs active layers 12 are grown alternately, and hetero pn junctions are successively formed in parallel with the substrate 10 to form a multilayered active layer. Thereafter, for example, a SiO ₂ layer 13 is sputtered on the portion constituting the cylindrical mesa, and then the cylindrical mesa is formed by reactive ion etching (RIE) or the like.

Next, a p-type GaAlAs layer 14 is embedded and grown around the cylindrical mesa. This p-type GaAlAs layer 14 functions as a p-type carrier supply region. Thereafter, P ⁺ −
A GaAs cap layer 15 is formed.

Next, a region is formed that will act as an n-type carrier injection region. First, a SiO ₂ layer is partially formed on the cap layer 15, and then the portions where SiO ₂ is not formed are removed by etching by RIE or the like.

Next, an n-type GaAlAs layer is buried and grown in the etched portion to form an n-type GaAlAs layer 17 which acts as an n-type carrier injection region. Afterwards, SiO ₂ layers 13 and 16 are removed.

Next, an n-side electrode 18 made of Au/Ge is provided on the end face of the n-type GaAlAs layer 17, and a p-type GaAlAs
Also on the cap layer 15 formed on the layer 14, AU/
A p-side electrode 19 made of Zn/Au is formed. Further, a portion of the substrate 10 where the cylindrical mesa is formed is removed by etching to form an opening for emitting laser light, and a reflecting mirror 20 made of a dielectric multilayer film or a metal film is formed on the bottom and inner peripheral surface of this opening. At the same time, a reflecting mirror 21 is also formed on the upper end surface of the cylindrical mesa to form an optical resonator.

Next, the operation will be explained. In this example, n-type
The diffusion potential between the GaAlAs layer 11 and the p-type GaAlAs active layer 12 is the same as that between the n-type GaAlAs layer 11 and the p-type GaAlAs
14 so that it is smaller than the diffusion potential. By setting conditions like this,
Most of the electrons injected into the n-type GaAlAs layer 11 are formed between it and the p-type GaAs active layer 12.
It will be injected into the active layer 12 via the pn junction. GaAs constituting the active layer 12 in this example
Since the forbidden band width of 11 is smaller than that of GaAlAs formed around it, a double heterostructure can be formed, and the n-type GaAlAs layer 11 to p-type GaAs
The carrier can be efficiently injected into the active layer. When a positive voltage is applied to the p-side electrode 19 and a negative voltage is applied to the n-side electrode 18 to supply a forward current, the n-type electrode 18, the n-type GaAlAs layer 17, and each n-type that acts as a carrier injection region GaAlAs layer 11, n-type GaAAs layer 11, p-type GaAs active layer 12, and each p-type GaAs active layer 12 through each pn junction.
Electrons, which are minority carriers, are injected into the active layer 12, causing the active layer 12 to enter a population inversion state, leading to oscillation. At this time, the optical resonator is constructed between reflecting mirrors 20 and 21, and the laser beam is transmitted through the reflecting mirror 21 and emitted in the direction of arrow a. As a result, a carrier is injected into the active layer 12 through the pn junction extending in a direction perpendicular to the direction of laser light emission, making it possible to emit an axisymmetric laser beam with uniform energy distribution and a circular cross section. can.

Note that electrons are also directly injected from the n-type GaAlAs layer 17 to the p-type GaAs active layer 12 via the pn junction on the side of the active layer 12, but since the area ratio of the pn junction surface is small, most of the electrons are It is implanted into the active layer 12 through the junction between the n-type GaAlAs cladding layer 11 and the p-type GaAs active layer 12.

The current path is indicated by 22. The current is p-side electrode 1
9, cap layer 15, p-type GaAlAs layer 14, each p
GaAs active layer 12, pn junction on both sides, n type
It flows through the GaAlAs cladding layer 11, the n-type GaAlAs layer 17, and the n-side electrode 18. Therefore, the n-type GaAlAs layer 17 provided on the side of the resonator is a semiconductor region constituting a carrier injection semiconductor region;
The p-type GaAlAs layer 14 acts as a semiconductor region constituting a current path.

FIG. 4 is a diagrammatic cross-sectional view showing the configuration of a modified example of the surface emitting laser oscillation device according to the present invention. In this example, the active layer has a one-layer structure, and only p-type regions forming current paths are provided on the sides of the resonator.
An n-type GaAlAs cladding layer 31 acting as a carrier injection region on an n-type GaAs substrate 30, a p-type
GaAs active layer 32 and n-type GaAlAs cladding layer 3
The p-type GaAs active layer 32 and the n-type GaAlAs layer 33 are partially etched by RIE or the like to form a cylindrical mesa, and the p-type GaAlAs layer 34 constituting a current path is formed around the cylindrical mesa. Embed and grow. Further, a cap layer 35, a SiO ₂ layer 36, and a p-side electrode 37 are sequentially formed on the p-type GaAlAs layer 34. N-type GaAlAs cladding layer 33 of cylindrical mesa
A reflecting mirror 38 is formed on the substrate 30, and an opening for emitting laser light is provided in the substrate 30, and a reflecting mirror 39 is also formed on the bottom surface and inner peripheral surface of this opening. Furthermore, an n-side electrode 40 is formed on the opposite surface of the substrate 30.
When a forward current is supplied between the p-side electrode 37 and the n-side electrode 40, electrons are injected into the active layer 32 through the n-type GaAlAs layer 31 and the p-n junction between the n-type GaAlAs layer 31 and the p-type GaAs active layer 32. and light emission occurs. 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. The current is p-side electrode 3
7, p-type GaAlAs layer 34, p-type GaAs active layer 32,
p-n junction, n-type GaAlAs cladding layer 31, n-type
It flows through the GaAs substrate 30 and the n-side electrode 40.
Therefore, the substrate 30 and the n-type GaAlAs cladding layer 3
1 acts as a carrier injection semiconductor region, and the p-type GaAlAs layers 34 provided on both sides of the resonator act as semiconductor regions forming a current path. As a result, pn perpendicular to the laser beam emission direction
Since a carrier is injected into the active layer 32 through the junction, an axially symmetric circular laser beam with uniform energy distribution can be emitted.

Even with a 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, making it possible to further increase the reflectance of the reflecting mirror, thereby increasing the threshold gain. can be reduced. In this example, the n-type GaAlAs cladding layer 33 is replaced with the p-type.
It may also be composed of a GaAlAs layer.

FIG. 5 is a diagrammatic sectional view showing the configuration of another modification of the surface emitting laser oscillation device according to the present invention. In this example, the configuration has two active layers, and the n-type
An n-type GaAlAs cladding layer 51 on the GaAs substrate 50,
A first p-type GaAs active layer 52, an n-type GaAlAs cladding layer 53 acting as a carrier injection region, a second p-type GaAs active layer 54, and an n-type GaAlAs cladding layer 55 acting as a carrier injection region are formed. A mirror electrode 56 serving as an n-side electrode is provided on the GaAlAs cladding layer 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 constituting a current path is formed on the side of the optical resonator, and a cap layer 59, a SiO ₂ layer 60, and a p-side electrode 61 are sequentially formed on this p-type GaAlAs layer 58. An n-side electrode 62 is formed on the opposite side. P-side electrode 61, n-side electrode 62 and mirror electrode 56
When a forward current is supplied between the first active layer 5 and
Electrons are injected into the second active layer 54 through the n-type GaAlAs layer 55 and the p-n junction, and electrons are injected into the second active layer 54 through the n-type GaAlAs layer 55 and the p-n junction. A resonator is formed between them, and laser light is emitted in the direction of arrow a. The current path at this time is indicated by reference numeral 63. If the semiconductor region that forms the current path is provided on the side of the resonator as in this example, the pn
The first and second active layers 52 and 54 via a bond.
A carrier can be injected into the laser beam, and a laser beam with uniform energy distribution can be emitted. Note that in this example, the first and second active layers 52 and 54
The n-type GaAlAs layer 53 formed between the p-type
It can also be a GaAlAs layer.

The present invention is not limited to the above-described embodiments, and can be modified and modified in many ways. For example, although GaAlAs/GaAs-based semiconductors are used in the above embodiments, the present invention is not limited to these semiconductor materials, and it is possible to use combinations of various semiconductor materials that can appropriately set the difference in diffusion potential. For example, the same effect can be obtained by using a GaInAs/InP semiconductor. In particular, the above-mentioned lateral junction method (Transverse Junction) has a remarkable advantage compared to the fact that it is difficult to apply to this quaternary semiconductor.

Further, the surface emitting laser oscillation device according to the present invention can also be applied to a multilayer stripe type laser oscillation device.

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

(1) Extends in a direction perpendicular to the laser beam emission direction
Since the structure is such that a carrier is injected into the active layer through a p-n junction, a circular axisymmetric laser beam with a uniform energy distribution in the cross section can be emitted.

(2) Since the structure is such that a carrier injection region is formed on the side of the optical resonator and the carrier is diffused into the low resistance cladding layer and then injected into each active layer, the carrier is uniformly and injected into each active layer. The carrier can be uniformly injected, thereby making it possible to equivalently thicken the active layer and reduce the threshold injection current.

(3) Since the electrode and the reflecting mirror are separated, it is possible to simultaneously obtain good ohmic characteristics and a reflective film with high reflectance, and it is possible to significantly reduce the threshold gain required for oscillation.

(4) Unlike conventional DFB/DBR lasers, different types of 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 a DBR laser can be easily manufactured.

(5) Since the resonator is formed perpendicular to the p-n junction surface, the optical resonator length can be shortened.
Single mode becomes easier.

Note that the effects (1) and (3) above cannot be obtained with the lateral joining method, and are remarkable effects of the present invention.

[Brief explanation of drawings]

1A to 1E are diagrammatic cross-sectional views sequentially showing the manufacturing process of a surface emitting laser oscillation device according to the present invention;
The figure is a diagrammatic sectional view showing the configuration of an example of the surface emitting laser oscillation device according to the present invention, FIG. 3 is an external view showing the configuration of an example of the surface emitting laser oscillation device according to the present invention, and FIGS. 4 and 5 is a diagrammatic cross-sectional view showing the configuration of a modified example of the surface emitting laser oscillation device according to the present invention,
FIG. 6 is a diagrammatic cross-sectional view showing the configuration of a conventional surface emitting laser oscillation device. 10, 30, 50...Substrate, 11, 31, 51
...n-type GaAlAs cladding layer, 12, 32, 5
2,54...p-type GaAs active layer, 13,16,3
6,60...SiO ₂ layer, 14,34,58...p
type GaAlAs layer, 15, 35, 59... cap layer, 17... n type GaAlAs layer, 18, 40, 62
... n-side electrode, 19, 37, 61 ... p-side electrode,
20, 21, 38, 39, 57...Reflector, 2
2, 41, 63... Current path, 56... Mirror electrode.

Claims (1)

[Claims] 1 At least one semiconductor active layer 12 of one conductivity type
and at least two opposite conductivity type semiconductor layers 11 are stacked such that the active layer 12 is sandwiched between the opposite conductivity type semiconductor layers 11 to form a pn junction.
A semiconductor region 14 of one conductivity type and a carrier injection semiconductor region 1 of the opposite conductivity type form a resonator in a direction perpendicular to the junction and constitute a current path on the side of this resonator.
7 and formed between the one conductivity type semiconductor active layer 12 and the opposite conductivity type semiconductor layer 11.
The diffusion potential of the junction is the opposite conductivity type semiconductor layer 11.
and one conductivity type semiconductor region 14.
Diffusion potential of p-n junction and one conductivity type semiconductor active layer 1
2 and the opposite conductivity type carrier injection semiconductor region 17, the diffusion potential of the pn junction formed between the one conductivity type semiconductor region 1
4. One conductivity type active layer 12, opposite conductivity type semiconductor layer 1
1, and a current path passing through the carrier injection region 17 of the opposite conductivity type, so that minority carriers are uniformly injected over the entire surface of the pn junction extending in a direction perpendicular to the resonator direction. A surface emitting laser oscillation device characterized by: