JPH0797691B2 - Optical bistable semiconductor device - Google Patents

Description

The present invention relates to an optical logic device used for optical information processing and the like.

(Prior Art) In recent years, digital information processing utilizing the high parallelism of light has attracted attention. For this purpose, it is necessary to develop a so-called surface-type logic element that controls light two-dimensionally. An optical bistable element is one of the most important ones. Conventionally, the structure shown in FIG. 3 has been applied to the Applied Physics Letters (Applid Physi
cs Letters) Volume 45, page 13 (1984) Mirror (Mile
r, DAB) etc. A quantum well layer 31 in which thin films of GaAs and GaAlAs are alternately laminated is applied to a pin structure sandwiched between cladding layers 32 and 33 of GaAlAs whose conductivity types are p-type and n-type, respectively, via a large resistance 21.
When the input light is weak, the energy of the light is different from the energy of the excitons of the quantum well, so the absorption is small. When the light becomes strong, the photocurrent generated by the absorption of the light flows,
Due to the voltage drop across the resistance, the electric field strength applied to the quantum well decreases, the energy of excitons changes, and absorption of light increases. Therefore, the photocurrent further increases and the voltage drop across the resistance increases. Optical bistability is realized by such positive feedback. This optical bistable element has a not type characteristic in which the transmission intensity decreases as the light intensity increases.

(Problems to be Solved by the Invention) In the above-described optical bistable element, since the change in the absorption coefficient of the quantum well is used, the planar type element that does not have a sufficient light absorption length is turned on. You cannot increase the off-state output ratio. Further, since absorption occurs even in the on state, there is a disadvantage that loss in the on state increases if the length of the element that absorbs light is increased and the output in the off state is decreased.

An object of the present invention is to provide a surface-type optical bistable device which has a small loss in an on state and can have a large on / off ratio.

(Means for Solving the Problems) The optical bistable semiconductor device of the present invention is a Fabry-Perot resonator having two mutually parallel reflecting mirrors, and a first conductivity type first semiconductor layer inside the Fabry-Perot resonator. It has a semiconductor multi-layer structure consisting of an active layer of an intrinsic semiconductor multi-quantum well structure and a second semiconductor layer of the second conductivity type, and electrodes sandwiching the semiconductor multi-layer structure are connected to a voltage source via a resistor. , The resonance energy of the Fabry-Perot resonator in the state where no voltage is applied to the semiconductor multilayer structure is lower than the exciton energy of the multiple quantum well structure when there is no electric field, and the signal light is in the above state. The light having the resonance energy of the Fabry-Perot resonator is used.

(Function) In the present invention, the energy of light resonating in the Fabry-Perot resonator in the state where the voltage source is not connected is more than the energy of excitons of the multiple quantum well structure of the active layer when no electric field is applied. Is also on the low energy side. The energy of the light used as the signal light is the energy of the light that resonates with the Fabry-Perot resonator when this voltage source is not connected.

When light is not incident, the voltage from the voltage source is applied to the multiple quantum well structure as it is, so the energy of excitons shifts to the low energy side, and the refractive index for signal light is when the electric field is not applied to the multiple quantum well structure. Greater than Therefore, the resonance energy of the Fabry-Perot resonator is deviated, and the light transmittance is small. Since most of the light is reflected at this time, the light intensity entering the Fabry-Perot resonator is small and the light is absorbed in the multiple quantum well structure at a small rate.

When the intensity of incident light increases, photocurrent due to absorption causes a voltage drop due to resistance, and the electric field applied to the multiple quantum well structure decreases. For this reason, the exciton energy shifts to the high energy side, the refractive index for the signal light decreases, and the resonance energy of the Fabry-Perot resonator approaches the energy of the signal light. The transmittance of signal light is increased.
At the same time, the intensity of light entering the Fabry-Perot resonator increases, so that the proportion of light absorbed in the multiple quantum well structure increases and the photocurrent further increases.

Optical bistability is realized by the above positive feedback. Whereas the conventional technique utilizes the change of the absorption coefficient due to the electric field of the multi-quantum well structure, the optical bistability of the present invention utilizes the change of the refractive index, which is used for the excellent transmission of the Fabry-Perot resonator. Since it is combined with the characteristics, it is possible to realize a surface-type optical bistable device which has a small loss in the ON state and can have a large ON / OFF ratio.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention. n-type
N-type Al _0.4 Ga _0.6 As contact layer 12 on GaAs substrate 11
A buffer layer 13 having a thickness of 2 μm and made of undoped Al _0.4 Ga _0.6 As
Undoped GaAs well layers 141 and 1 with thicknesses of 50 nm and 10 nm.
A multi-quantum well layer 14 in which five barrier layers 142 of undoped Al _0.4 Ga _0.6 As having a thickness of 0 nm are alternately laminated, undoped Al
A buffer layer 15 of _0.4 Ga _0.6 As having a thickness of 50 nm and p-type-As _0.4 Ga
A contact layer 16 of _0.6 As is sequentially laminated with a thickness of 2 μm, and the substrate 11 in the light incident portion is removed by etching. Further, reflecting mirrors 17 and 18 having a reflectance of 98% by a dielectric multilayer film, an n-side electrode 19 and a p-side electrode 20 are formed on the incident side and the emitting side. 100
Connect to power supply 22 through kΩ resistor 21. The power supply voltage is 2.4V.

The input / output characteristics of this embodiment are shown in FIG. The Fabry-Perot resonator resonates with 1.45 eV light when the electric field is zero. The solid line is transmitted light and the broken line is reflected light. Input light intensity Pin is 0.2
At 4 mW, the transmitted light transits from the off state to the on state,
It has hysteresis that transitions from the ON state to the OFF state at 5 mW. The reflected light exhibits the opposite hysteresis characteristic.
The intensity ratio between on-state and off-state is about 9: 1 for transmitted light and about 4: 1 for reflected light at Pin = 0.24mW. Conventionally, the transmitted light is, for example, 2.5: 1. Since a Fabry-Perot resonance modulator is used for the light control mechanism, a large on / off ratio can be obtained. Also, the extinction ratio was improved by 3 dB. In addition, the optical power required to make a transition from the off state to the on state was 0.67 mW in an experimental example such as a mirror having the same load resistance, which is about 1/3.

(Effect of the invention) To summarize the effect of the present invention, the loss in the ON state is small,
A surface-type optical bistable device capable of increasing the on / off ratio can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure,
11 is a substrate, 12 is a contact layer, 13 is a buffer layer, 14 is a multiple quantum well layer, 15 is a buffer layer, 16 is a contact layer, 1
Reference numerals 7 and 18 are reflecting mirrors, 19 is an n-side electrode, and 20 is a p-side electrode. 14
1 is a well layer and 142 is a barrier layer. Also, 21 is a resistance,
22 is a power supply. FIG. 2 is a diagram showing the input / output characteristics of this embodiment. The horizontal axis represents the intensity of the input light and the vertical axis represents the intensity of the output light. The solid line is transmitted light and the broken line is reflected light. FIG. 3 is a structural diagram showing an example of a conventional technique. Reference numeral 31 is a quantum well layer, and 32 and 33 are clad layers.

Claims (1)

[Claims] 1. A first semiconductor layer of a first conductivity type inside a Fabry-Perot resonator composed of two mutually parallel reflecting mirrors, and an active layer composed of an intrinsic semiconductor multiple quantum well structure.
A semiconductor multi-layer structure including a second semiconductor layer of a second conductivity type, the electrodes sandwiching the semiconductor multi-layer structure are connected to a voltage source via a resistor, and no voltage is applied to the semiconductor multi-layer structure. The resonance energy of the Fabry-Perot resonator in the state is lower than the exciton energy of the multiple quantum well structure in the absence of electric field, and the light of the resonance energy of the Fabry-Perot resonator in the state is used as the signal light. An optical bistable semiconductor device characterized by.