JPH06302916A - Semiconductor optical element - Google Patents

Abstract

PURPOSE:To provide a semiconductor optical element wherein integration and miniaturization are facilitated and pulse light is generated. CONSTITUTION:When a voltage is applied to an absorption part B having an absorption layer 6 of superlattice structure, the energy gap between two levels increases, and the absorption coefficient to oscillation light becomes small. In the gain part C having an active layer 11, the loss in a resonator becomes small as compared with the gain, and a light oscillates. In the state of light oscillation, the voltage applied to a resistor R connected in series with the absorption part B increases, the voltage applied to the absorption part B decreases, and the absorption coefficient of the absorption layer 6 becomes large. At this time, light absorption in the absorption layer 6 becomes large, the loss in the resonator becomes large as compared with the optical gain of the active layer 11, and light oscillation stops. When light oscillation stops, the voltage applied to the absorption part B increases, the absorption coefficient of the absorption layer 6 becomes small, the loss of the whole resonator becomes smaller than the optical gain of the active layer 11, and the light oscillates. The above process is repeated, and pulse light is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical cavity type semiconductor optical device having an active layer and an absorption layer.

[0002]

2. Description of the Related Art FIG. 8 is a schematic sectional view showing the structure of a conventional laser device which oscillates pulsed light. The laser device shown in the figure has a stripe structure, and a clad layer 52, an active layer 53 made of AlGaAs, a clad layer 54, and a contact layer 55 are laminated in this order on a substrate 51 made of n-GaAs, and on the contact layer 55. Electrode 5 in the center
6 are formed, and electrodes 57, 58 are provided on both sides of the electrode 56 with the electrode 56 interposed therebetween.
Are formed.

In the laser device having such a stripe structure, a voltage is applied to the electrodes 57 and 58 and a reverse bias voltage is applied to the electrode 56, and when an electric current of an appropriate value is passed, carriers become active layers. Injected into 53, the light intensity in the device gradually increases. At this time, part of the light is absorbed in the central portion of the active layer 53 to which the reverse bias voltage is applied by the electrode 56, that is, in the saturable absorption region SA. Therefore, the light density in the device does not reach a level sufficient for laser light oscillation.

When the saturable absorption area SA is saturated, light is no longer absorbed, the light intensity in the device suddenly increases, and the population inversion of carriers occurs in the active layer 53. Oscillates. At this moment, the population inversion disappears due to carrier emission, and the light intensity returns to a weak state in the device. Then, as the light intensity increases again, part of the light is absorbed in the saturable absorption area SA.

In this way, in the above laser device, oscillation and stop of the laser light occur alternately and pulsed light is output. A laser device that outputs pulsed light in this way is
Appl.Phys.Lett.58 (12), 25 March 1991. When an excessive current is applied to such a laser device, the population inversion does not disappear even if carriers are emitted during optical oscillation, and as a result, the oscillation of the laser light does not stop. The pulse light is not output.

[0006]

The laser device is roughly classified into the stripe type and the vertical cavity type, and the vertical cavity type is a type in which light is emitted in the stacking direction of the substrate, the active layer, and the constituent layers such as a reflecting mirror. Is a laser device that oscillates. The stripe type laser device that outputs the pulsed light described above is
There is a problem that the device becomes large in the case of dimensional integration. On the other hand, the vertical cavity type laser device can be miniaturized even if it is two-dimensionally integrated. Such a vertical cavity type laser device which outputs pulsed light in two dimensions can be applied to a clock for an optical computer which oscillates in two dimensions, for example.

The present invention has been made paying attention to the fact that light oscillation and stoppage are repeated by utilizing the absorption bistable characteristic of light in the absorption region, and the integration and miniaturization can be easily performed. An object of the present invention is to provide a semiconductor optical device that can perform and outputs pulsed light.

[0008]

A semiconductor optical device according to a first aspect of the present invention is provided with reflecting mirrors on both sides of an active layer in the stacking direction with an optical gain larger than the absorption loss between the two reflecting mirrors. In the semiconductor optical device for oscillating light, an absorption layer having bistability of absorption coefficient with respect to the light is provided between the both reflecting mirrors.

A semiconductor optical device according to a second invention is characterized in that, in the first invention, the absorption layer has a superlattice structure.

[0010]

In the semiconductor optical device of the present invention, the absorption layer is provided between the reflecting mirrors provided on both sides, and this absorption layer has the bistability of the absorption coefficient, that is, it has two types for the light to be oscillated. A stable state is maintained with absorption coefficients α ₁ and α ₂ . The two stable states will be described below. FIG. 9 is a graph showing the relationship between the oscillating light intensity and the absorption coefficient, where the vertical axis represents the absorption coefficient and the horizontal axis represents the light intensity. From the figure, the light intensity increases in the stable state with a small absorption coefficient α ₁ . As a result,
Transition to a stable state with a large absorption coefficient α ₂ , and the light intensity is L
_It decreases gradually after reaching ₁ . As a result, the state transitions to a stable state with a small absorption coefficient α ₁ , and the light intensity decreases to L _{2 and} then gradually increases. Then, the state again transits to a stable state with a large absorption coefficient α ₂ . Thus, the absorption layer repeats stable states with _two different absorption coefficients α ₁ and α ₂ depending on the light intensity.

In the present invention, the light from the active layer is absorbed by the absorption layer as described above. FIG. 10 is a graph showing the oscillation characteristics of a vertical cavity type semiconductor optical device, in which the vertical axis represents the light intensity and the horizontal axis represents the current value. In the figure, a shows the oscillation light when the absorption loss between the reflecting mirrors is small, that is, when the absorption coefficient is small, and oscillates at a light intensity of L ₂ or more at a current value smaller than I _OP . Further, b shows oscillation light when the absorption coefficient is large, and it oscillates at a light intensity of L ₂ or more at a current value larger than I _OP . By forming the above-mentioned absorption layer in the semiconductor optical device having such oscillation characteristics, when a current I _{OP is} passed through the active layer, light oscillates (L ₁ ) to have a large absorption coefficient α ₂ and the absorption coefficient. When α ₂ is reached, the light oscillation stops (L ₂ ), and when the light oscillation is stopped, the absorption coefficient α ₁ becomes small and the light is emitted. By repeating the oscillation and stop of light in this way, pulsed light is output.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic perspective view of a semiconductor optical device of the present invention. As shown in FIG. 1, the optical semiconductor element M of the present invention has an absorption section B having an absorption layer formed on a rectangular parallelepiped substrate section A, and the absorption layer B has a smaller bottom area than the substrate section A. Are stacked on a corner area of the substrate portion A. Then, a substantially columnar gain portion C having an active layer is laminated on the absorber B on a corner area of the absorber B. Then, the electrodes 17 are provided on the surfaces of the gain portion B and the substrate portion A,
An electrode 16 is formed on the surfaces of the absorbing portion B and the substrate portion A, and an electrode 15 is formed on the surface of the substrate portion A.

2 to 5 are schematic sectional views taken along the line II-II in FIG. 1 showing the process of manufacturing such a semiconductor optical device. The structure of the semiconductor optical device M will be described more specifically below. As shown in FIG. 2, the following layers are sequentially stacked on the substrate 1 made of n-GaAs by the MBE (Molecular Beam Epitaxial) method. Buffer layer 2: n-GaAs DBR3 (Bragg reflector): n-GaAs / AlAs
(59 nm / 73 nm) 20 pairs First clad layer 4: n-Al _x Ga _1-x As Second clad layer 5: Al _x Ga _1-x As Absorption layer 6: GaAs / AlAs (8 nm / 0.49 nm) super lattice structure of 5 pairs third cladding layer _{7: Al x Ga 1-x} As fourth cladding layer _{8: p-Al x Ga 1} -x As first contact layer _{9: p-Al 0.1 Ga 0.9} As (
0.5 μm) Fifth clad layer 10: Al _x Ga _1-x As active layer 11: Al _0.3 Ga _0.7 As / GaAs (7 nm /
9 nm) 3 pairs sixth cladding layer _{12: n-Al x Ga 1} -x As DBR13 ( Bragg reflectors): n-GaAs / AlAs
20 pairs of second contact layer 14: n-GaAs

The uppermost second contact layer 14 thus laminated is removed by photolithography and etching while leaving an area smaller than that of DBR 13 at approximately the center of DBR 13. Then, the fifth cladding layer 1 is formed in a region other than the region of about 2 μm in diameter from which light should be emitted.
Proton irradiation is performed to a depth of 0 to form current block regions D and D.

Next, as shown in FIG. 3, the diameter including the second contact layer 14 is obtained by photolithography and etching to a depth reaching the first contact layer 9.
Leave the 10 μm cylindrical gain part C
3, the sixth cladding layer 12, the active layer 11 and the fifth cladding layer 10 are removed. Next, as shown in FIG. 4, by photolithography and etching to a depth reaching the buffer layer 2, the bottom area is made larger than that of the gain section C, and the absorption section B is formed. Then, as shown in FIG.
An electrode 15 is formed on the buffer layer 2, an electrode 16 is formed on the first contact layer 9, and an electrode 17 is formed on the second contact layer 14.

In the semiconductor optical device M having such a structure, the composition of the active layer 11 is set according to the desired wavelength of the oscillation light. In addition, the superlattice structure has Wannier-Stark localization, and the energy gap between the two levels changes greatly when an electric field is applied and when no electric field is applied, so the light absorption coefficient in the superlattice structure changes significantly. The composition and thickness of the absorption layer 6 having such a superlattice structure are set so that the energy of the oscillated light is between the energy gaps between the two levels depending on the magnitude of the applied voltage to the absorption layer 6.

FIG. 6 is a schematic cross-sectional view in the case where a power source and a resistor are connected to the electrodes of the semiconductor optical device M formed as described above. A power supply is provided between the electrodes 17 and 16, a power supply is provided on the electrode 15 side, a resistance R is provided on the electrode 16 side, and an absorption portion B is provided.
And the resistor R are provided so as to be connected in series. In the surface emitting laser device having such a configuration, a voltage is applied to the absorption portion B to increase the energy gap between two levels of the superlattice structure, and the absorption coefficient for oscillated light is small (α
₁ ) At this time, in the gain portion C into which the current is injected, the gain of the active layer 11 exceeds the loss in the resonator, exceeds the threshold value, and oscillates light.

In the state of oscillating light, the voltage applied to the resistor R increases and the voltage applied to the absorption portion B decreases, and the absorption coefficient of the absorption layer 6 for the oscillated light becomes large (α ₂ ). At this time, the absorption of light in the absorption layer 6 becomes large, the loss in the resonator becomes lower than the gain of the active layer 11, and the oscillation of light is stopped. Absorption part B when the light oscillation is stopped
Voltage increases, the absorption coefficient of the absorption layer 6 decreases (α ₁ ), and the gain of the active layer 11 again exceeds the loss in the resonator to oscillate light. By repeating the above operation, pulsed light is output. FIG. 7 is an explanatory diagram showing the operating characteristics of the oscillated light, where the vertical axis represents the optical output and the horizontal axis represents the time.

As described above, the semiconductor optical device that outputs pulsed light has a circular beam pattern of oscillating light, and since it is a vertical resonator type, it has a high light reflectance, and the gain section C and the absorption section B are high. The light coupling efficiency with is good. Further, as described above, the absorption layer 6 having a superlattice structure increases a variation difference in absorption coefficient and improves the operating characteristics of the oscillated light.

In this embodiment, the semiconductor optical device is described as being formed on an n-type substrate, but the present invention is not limited to this, and it may be formed on a p-type substrate.
Further, the laminated structure and composition of the semiconductor optical device are not limited to those shown above, and may be InGaAs-based,
Any material may be used as long as the absorption coefficient of the absorption layer 6 maintains bistability with respect to oscillation light. Further, in this embodiment, the absorption layer 6
Is formed of a superlattice structure, but the invention is not limited to this, and any composition having a bistable characteristic of absorption coefficient may be used.

Further, although the present embodiment describes the case where the proton irradiation is performed for the current constriction, the present invention is not limited to this, and the current blocking layer having the current constriction function is formed. May be. Further, although the resistor R is connected to the absorbing portion B in the above-mentioned embodiment, the present invention is not limited to this, and may be, for example, a diode.

[0022]

As described above, in the present invention, by providing the vertical resonator type semiconductor optical device with the absorption layer having the bistability of the absorption coefficient for the light to be oscillated,
Light oscillation and stop are alternately performed, and pulsed light is output.
The present invention has excellent effects such as reduction in size by dimensional integration.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a semiconductor optical device of the present invention.

FIG. 2 is a schematic sectional view taken along line II-II of FIG. 1 showing a process for manufacturing the semiconductor optical device of the present invention.

FIG. 3 is a schematic sectional view taken along line II-II of FIG. 1 showing a process of manufacturing the semiconductor optical device of the present invention.

FIG. 4 is a schematic cross-sectional view taken along the line II-II of FIG. 1 showing a process of manufacturing the semiconductor optical device of the present invention.

FIG. 5 is a schematic cross-sectional view taken along the line II-II in FIG. 1, showing a process for manufacturing the semiconductor optical device of the present invention.

FIG. 6 is a schematic cross-sectional view when a power source and a resistor are connected to the electrodes of the semiconductor optical device M of the present invention.

FIG. 7 is an explanatory diagram showing operating characteristics of oscillated light.

FIG. 8 is a schematic cross-sectional view showing the structure of a conventional laser device that outputs pulsed light.

FIG. 9 is a graph showing the relationship between oscillating light intensity and absorption coefficient.

FIG. 10 is a graph showing oscillation characteristics of a vertical cavity type semiconductor optical device.

[Explanation of symbols]

 1 Substrate 3,13 Multilayer Reflector 6 Absorption Layer 11 Active Layer

Claims (2)

[Claims] 1. A semiconductor optical device comprising reflection mirrors on both sides of an active layer sandwiched in the stacking direction, and oscillating light in the stacking direction with an optical gain larger than an absorption loss between the two reflectors. A semiconductor optical device having an absorption layer having bistability of absorption coefficient for the light therebetween. 2. The semiconductor optical device according to claim 1, wherein the absorption layer has a superlattice structure.