JPH03276138A - Optical bistable element and its driving method - Google Patents

Abstract

PURPOSE:To obtain an optical bistable element of high ON/OFF ratio by providing a negative resistance element connected in series to a pin diode with a multiple quantum well structure, which is formed with the layer-built structure of a barrier layer and a well layer, between a p-type layer and an n-type layer. CONSTITUTION:A multiple quantum well structure pin diode 11, a resonance tunnel type multiple quantum well structure negative resistance element 12, and a variable voltage power source 13 are connected in series. The pin diode 11 and the resonance tunnel type multiple quantum negative resistance element 12 are so connected that their polarities are opposite. The variable voltage source 13 is so connected that the pin structure diode 11 is biased backward. Input light 14 is made incident on an i-type layer of the pin diode 11 in the perpendicular direction. Thus, the optical bistable element of high ON/OFF ratio is realized. Relations between the light input and the light output can be logically inverted to AND and NAND by the set voltage of the variable voltage power source 13.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical bistable device that produces two different stable states of output light for the same optical input intensity.

(Prior Art) So-called optical computing, such as optical logic operations and optical information processing, is attracting attention as a future calculation method due to the characteristics of light, such as its high speed and parallelism. In order to perform this optical computing, various optical components are required, and many proposals have been made, among which an optical bistable element is cited as one of the high-speed components.

Conventionally, various materials including dielectrics have been used as materials for the above-mentioned elements, but semiconductor materials have been chosen for their compatibility with lasers and detectors.
), Volume 24, Page 1, (1988), optical bistable devices have been proposed.

The configuration and operating principle of a conventional device will be briefly explained with reference to the drawings. As shown in FIG. 2, its element structure consists of a pin diode 21 and a negative resistance element 22 connected in series.
The connection is made such that the direction of the photocurrent generated in the pin diode 21 and the current direction of the negative resistance element 22 coincide. Here, the pin diode 2 has two layers with n-type conductivity and an i
and an n layer having n-type conductivity, while a double barrier resonant tunnel diode is used as the negative resistance element 22. 2 layers of pin diode optical input 2
4 generates a photocurrent and generates optical output 25 in the n layer, and by changing the externally applied voltage, 1
The transmittance of light in the layer changes. A constant voltage power supply 23 (voltage ■) is connected to both ends of the bistable element.

Figure 3(a) shows the current-voltage curve of the PIN diode in accordance with the current-voltage characteristic (solid line) of the part that combines the double-barrier resonant tunneling diode and constant voltage power supply in the optical bistable device shown in Figure 2. (dashed line). Also, Figure 3 (
b) shows the optical input/output characteristics of the optical bistable element. When light with near exciton absorption energy is incident on the pin diode, a photocurrent rph is generated. As shown in FIG. 3(a), as the incident light intensity increases, Ip
When h exceeds the peak current value rp, the operating point is 33a in the figure.
There is a sudden change from 34a to 34a. At this time, the voltage drop across the double-barrier resonant tunneling diode increases rapidly (
■p→■pp), the applied voltage across the pln diode decreases rapidly (■.-Vp→■o-~'pp)
. As a result, the light transmittance of the i-layer increases rapidly due to the quantum-confined Stark effect or the Franz Kjeldysch effect. At the time of 2, the optical output intensity of the pin diode increases rapidly from 33b to 34b as shown in FIG. 3(b). Conversely, when Iph decreases and reaches the Halley current value ■ν, the operating point changes from 38a to 39 in 11U(a).
Changes to a.

At this time, the voltage applied to the double barrier resonant tunneling diode increases rapidly. Therefore, the light output intensity is 3 in Figure 3(b).
It rapidly decreases from 8b to 39b. With the above operating principle, two different optical output intensities are obtained at the optical input intensity corresponding to Iph (Iv<Iph<Ip).

(Problem B to be Solved by the Invention) By the way, the above-mentioned optical bistable element has a drawback that the on-off ratio R (=L, , /L, 2), which is a basic characteristic, is small. R is the voltage change Δ of the negative resistance element at I=ip
The larger Vp (-Vpp -Vp) becomes, the larger it becomes.

The reason why R is small is that a normal double-barrier resonant tunnel diode is assumed as the negative resistance element, so Δ■2 is 1.
This is because it is as small as a layer.

Furthermore, the above-mentioned optical bistable device could only perform AND-type logic. An object of the present invention is to solve the above-mentioned problems, to realize an optical bistable device with a large on-off ratio, and to make it possible to invert AND-type and NAND-type logic with the same device.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an optical bistable element composed of a photovoltaic force, a pin diode for optical modulation, a negative resistance element, and a voltage source. (1) The negative resistance element has a resonant tunneling multiple quantum well structure, and is further characterized in that the semiconductor layer serving as the well layer is doped with an impurity having a conductivity type.

The differences from the conventional technology are as follows.

a. By using a resonant tunneling multiple quantum well structure as a negative resistance element, Δ■2 becomes large to 5 or more, and an optical bistable element with a large on-off ratio can be realized.

b. By doping a semiconductor layer serving as a well layer of a negative resistance element having a resonant tunneling multi-quantum well structure with an impurity having a conductivity type, an optical bistable element capable of operating at room temperature can be realized.

(2) In the above element, by using a variable voltage power source as the voltage source, the logic can be inverted between AND type and NAND type depending on the set voltage amount.

The present invention will be described in detail below with reference to the drawings.

(Example) FIG. 4 shows a cross-sectional view of an example of a negative resistance element having a resonant tunneling multiple quantum well structure. This consists of an n-type 1nP substrate 41, an n-type 1nAIAs semiconductor layer 42, an undoped InAlAs layer 43a serving as a barrier layer, and an InAlAs layer 43a serving as a well layer.
Multiple quantum well layer 43 in which GaAs layers 43b are alternately laminated
, and a P-type InAlAs semiconductor layer 44.

In addition, the n-electrode 45 formed of the AuGeNi layer and the ^uZn
An n-electrode 46 made of a Ni layer is provided. 33b
The InGaAs layer of the well layer may be an undoped layer according to claim 1, or an n-type layer or an n-type layer according to claim 2.

The current-voltage characteristics (solid line) of this device at room temperature are
As shown in the figure. - For example, the number of quantum wells is 50, and the I of the well layer is
nAIAs are undoped. Negative resistance characteristics with an extremely large value of Δ■ of approximately 5V were obtained. This Δ■
The value of can be freely adjusted by changing the number of quantum wells. In the figure, the current-voltage characteristics of the double-barrier resonant transistor are also shown by broken lines, and by introducing a quantum well structure, ΔV can be increased and the on-off ratio R can be improved.

Further, similar results can be obtained when the InAlAs well layer is doped to be n-type or p-type.

FIG. 6 shows the photon energy dependence of the absorption coefficient of a multi-quantum well structure pin diode using the reverse bias voltage applied to the diode as a parameter. The diode has a structure in which an n-type InAlAs semiconductor layer, an i-layer with a multi-quantum well structure, and a p-type 1nAIAs semiconductor layer are stacked on an n-type 1nP substrate.
It has a structure in which 50 cycles of AlAs layers (7 angstroms thick) and InAlAs layers (50 angstroms thick) are stacked alternately. As the voltage increases, the absorption peak shifts to the lower energy side.

FIG. 1 shows an equivalent circuit of an optical bistable device according to the present invention. Multiple quantum well structure pin diode 11
and resonant tunneling multi-quantum well structure negative resistance element 12
and a variable voltage power supply 13 are connected in series. pin
The diode 11 and the resonant tunneling multi-quantum well negative resistance element 12 are connected so that their polarities are opposite to each other. The variable voltage power supply 13 is a pin structure diode 11
is connected so that it is reverse biased.

The optical input/output characteristics of this optical bistable device are as follows.

Exciton peak wavelength at no bias (1.50μm)
FIG. 7 shows the optical input/output characteristics when the optical bistable element is operated with a 1.52 μm light source on the longer wavelength side. This operating wavelength is set at the position indicated by the arrow ■ in FIG. 6. Figure 7 (a) shows the case where the voltage of the variable voltage power supply is set to 5■ constant and bistable operation is performed between points B and A in Figure 6, and Figure 7 (b) shows the variable voltage power supply. This is a case where bistable operation is performed between point 0 and point B in FIG. 6 with the voltage constant at 12V. In (a), an AND-type bistable operation is obtained, and in (b), a NAND-type bistable operation is obtained, and the logic can be reversed depending on the bias conditions. Furthermore, even when the amount of voltage is constant, a similar logic inversion can be achieved by changing the operating wavelength.

The operating range in which optical bistable characteristics can be obtained is the wavelength range in which the absorption coefficient changes depending on the reverse bias voltage applied to the pin diode. For example, when a voltage change as shown in FIG. 6 occurs, the operating wavelength range will be between arrows (1) and (2), and optical bistable changes will be obtained over a very wide range.

Further, in this optical bistable element, the light intensity at which switching occurs can be freely set by the peak of the negative resistance element and the Halley current value. Since the peak and valley current values of this negative resistance element are proportional to the element area, the switching light intensity can be freely changed depending on the element area of the negative resistance element. For example, it is possible to reduce the switching light intensity by reducing the area of the negative resistance element.

The optical bistable element shown in FIG. 1 is of a vertical light incidence type in which light is incident perpendicularly to the i-layer of a pin diode, but a waveguide type in which light is incident in parallel to the i-layer is also possible. In this case, a larger on-off ratio can be obtained than in the vertical light incidence type.

FIG. 8 shows a cross-sectional view of a monolithically integrated optical bistable device. This is an n-type InP substrate 81
, n-type 1nAIAs semiconductor layer 82, InAlAs layer 83
One layer 83 having a multi-quantum well structure in which A and InGaAs layers 83b are alternately laminated, a p-type 1nAIAs semiconductor layer 84, an undoped InAlAs layer 85a serving as a barrier layer, and an n-type doped InGaAsJW 85b serving as a well layer are alternately laminated. Multiple quantum well layer 85, n-type n^IAs layer 86
It is equipped with Here, 82 to 84 are pin diodes,
84 to 86 form negative resistance elements. In addition, a polyimide film 87, an n-electrode 88 formed of an AuGeNi layer,
A Ti/Au deposited film 89 is provided. As mentioned above, the portion of the negative resistance element is made small in order to match the photocurrent of the pin diode and the peak current of the negative resistance element. In order to match the peak current of this device, the negative resistance element portion is kept small. The same optical input/output characteristics as shown in FIG. 7 can be obtained with this element as well.

(Effects of the Invention) As described above, the present invention can provide an optical bistable element with a large on-off ratio and capable of operating at room temperature. Note that this device has the advantage of having a large degree of freedom in operating wavelength and being able to freely change the switching light intensity. Furthermore, this device has an unprecedented feature in that logic can be inverted with the same device depending on bias conditions and wavelength conditions. Since the device of the present invention can be made monolithic, it is also suitable for large-scale integration. From the above, the present invention allows complex optical information processing to be performed with high reliability.

[Brief explanation of drawings]

Fig. 1 shows an equivalent circuit of the device of the present invention, Fig. 2 shows a conventional optical bistable device, and Fig. 3 shows the operating principle of the conventional optical bistable device.
is the current of the combination of negative resistance element and constant voltage source ~
(b) shows the optical input/output characteristics of the optical bistable device, FIG. 4 is a cross-sectional view of the negative resistance element used in the device of the present invention, and FIG. 5 shows the resonant tunneling multi-quantum well. Type negative resistance element (
Figure 6 shows the photon energy dependence of the absorption coefficient of a multi-quantum well structure pin diode with reverse bias voltage as a parameter. Figure 7 shows the optical input intensity vs. optical output intensity characteristics of the device of the present invention; (a) shows the case when 5 µ is applied as a bias from the variable voltage power source, and (b) shows the case when 12 V is applied from the variable voltage power source. 8 is a cross-sectional view of the monolithic structure of the device of the present invention. 11...Multi-quantum well structure pin diode 12...
- Resonant tunnel type multiple quantum well structure negative resistance element 13... Variable voltage power supply 14... Input light 15... Output light 21... Pin diode 22... Double barrier type resonant tunnel diode (DB −
RTD) 23... Constant voltage power supply 24... Input light 25... Output light 31 a ~ 39 a + 31 a ~ 39 b −
...Operating point 41...N-type InP substrate 42...N-type InAlAs semiconductor layer 43...Multiple quantum well layer 43a...Undoped InAlAs layer (barrier layer) 4
3 b -1nGaAs layer (well layer) 44-P type! nA
lAs semiconductor layer 45-n electrode (AuGeNi layer) 46-n electrode (AuZnNi layer) 81...n-type InP substrate 82''-n-type 1nAIAs semiconductor layer 83...multiple quantum well layer 83a.'' InAlAs layer 83 b ・-InGaAs layer 84 - p-type 1n AIAs semiconductor layer 85...Multiple quantum well layer 85a...Undoped InAlAs layer 85 b ・n
Type-doped InGaAs layer 86 - n-type 1n AIAs layer 87...polyimide film 88, n-electrode (AuGeNi layer) 89... film deposited on Ti/8U

Claims (1)

[Claims] 1. In an optical bistable element that is configured by a series connection of a pin diode and a negative resistance element and produces stable states of two different output light intensities for the same optical input intensity, the pin A diode is formed of a layer with p-type conductivity (p-layer), a layer with high resistance and electrical insulation (i-layer), and a layer with n-type conductivity (n-layer). Alternatively, a photocurrent is generated by light input from the n-layer to the i-layer, and the transmittance of light in the i-layer changes by changing the voltage applied to both ends of the photocurrent.
It has a function of modulating the intensity of light output emitted to the layer side, and the negative resistance element has a multi-quantum well structure formed of a stacked structure of a barrier layer and a well layer between the p layer and the n layer. An optical bistable element characterized in that the bistable element is operated by connecting a voltage source to both ends of the bistable element. 2. In an optical bistable element that is composed of a series connection of a pin diode and a negative resistance element and produces two stable states of different output light intensities for the same optical input intensity, the pin diode has p-type conductivity. (p layer), a layer with high resistance and electrical insulation (i layer), and a layer with n-type conductivity (n layer). The optical input generates a photocurrent, and by changing the voltage applied to both ends of the photocurrent, the transmittance of light in the i-layer changes, modulating the intensity of the optical output emitted to the n-layer side or p-layer side. The negative resistance element has a multi-quantum well structure formed of a stacked structure of a barrier layer and a well layer between a p-layer and an n-layer, and a well layer of the multi-quantum well structure. An optical bistable element doped with an impurity having a conductivity type, and operated by connecting a voltage source to both ends of the bistable element. 3. The device according to claim 1 or 2, wherein the voltage source is a variable voltage power source, and the relationship between the optical input and the optical output can be logically inverted between an AND type and a NAND type depending on a set voltage amount. A method for driving optical bistable devices.