JPH0553164A - Optical flip-flop element - Google Patents

Abstract

PURPOSE:To stably execute the operation by a simple optical system by allowing the (i) layer of an optical modulator to have a characteristic by which an attenuation characteristic of light is varied by the output voltage of a phototransistor, and also, allowing a multilayer reflecting film to have a characteristic by which a part of light transmits through. CONSTITUTION:An (i) layer 26a of an optical modulator 28a is constituted of an i-MQW (multiple well) layer, therefore, it has such a characteristic that transitivity of light is changed when an output voltage of a phototransistor 24a is varied. Also, an n-DBR(distributed Bragg reflector) layer 25a forms a multilayer reflecting film by forming semiconductor layers whose reflection factors are different to a laminated structure, and has such a quality as a part of light which transmits through the (i) layer 26a is allowed to pass through. Therefore, when the output voltage of the phototransistor 24a of a master side is varied, light transitivity in the (i) layer 26a is varied, a part of light which passes through the (i) layer 26a passes through an (n) layer 25a and reaches the phototransistor 24a and is amplified and becomes a set state, and it becomes a reset state in the same way on a slave side, as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical flip-flop element driven and controlled by an optical signal.

[0002]

2. Description of the Related Art Development of an optical flip-flop is desired as a key device for optical signal processing and optical information processing. As a conventional device of this type, for example, reference [Apli
edPhysics Letters Volume 52 141
As shown in "Page 9", two multi-well (MQW) pin type optical modulators formed on the same semiconductor substrate are connected in series by external electrodes, and a constant voltage power source is connected to both ends thereof. "Symmetric seed (S-SEED)" having a function of changing the transmitted light of the light irradiated to the second pin type optical modulator according to the optical input intensity of the first pin type optical modulator. An element called a is proposed.

In this device, light having a wavelength near the exciton absorption peak generated by the quantum confined Stark effect (QCSE) is used, and transmitted light biased with a constant intensity can be controlled by input light having the same wavelength. it can. The configuration and characteristics will be described with reference to FIG.

In FIG. 8, p-AlGaAs layers 1a, i
A first M composed of an MQW layer 2a and an n-DBR (Distributed Bragg Reflector) layer 3a.
A diode 4a having a QW-pin structure (hereinafter referred to as a diode) is connected to an i-AlGaAs insulating layer 5 via an i-AlGaAs insulating layer 5.
-Laminated on the GaAs substrate 6. Also, the insulating layer 5
A second pin structure diode 4b having the same structure as the diode 4a is formed on the right side of the n-DBR layer 3a and the p-A layer.
The 1 GaAs layer 1b is connected by the electrode 7.

Now, the set light 8 incident on the diode 4a, the read light 9, and the reflected light of the read light 9a are output light 1
0, the reset light 11 incident on the transistor 4b, the read light 9b, and the reflected light of the read light 9b are output light 10b.
Then, the flip-flop characteristic shown in FIG. 9 is obtained.

[0006]

However, since such a conventional device uses the bistability due to the negative current-voltage characteristic of the pin structure generated by the light near the exciton absorption, the operating wavelength is set to the exciton absorption peak. It is necessary to set it, the extinction ratio of the light modulator is low, and the loss is large.

When the read light is constantly applied, the gain between the output light 10a and the set light 8 or between the output light 10b and the reset light 11 is small. 10b must be incident with the set light 8 or the reset light 11 shifted in time. Therefore, the optical system becomes complicated and the processing speed becomes slow.

The present invention has been made in view of such a situation. Between the output light 10a and the set light 8 or between the output light 10b and the reset light 11, the high extinction ratio and the high response speed are maintained. The optical flip-flop element which has a large gain and operates stably with a simple optical system.

[0009]

In order to solve such a problem, the present invention provides a p-type collector for a phototransistor.
In an optical flip-flop element in which a semiconductor device having a structure in which n layers of an in-structure optical modulator are in contact is a master side, and a slave semiconductor device having the same structure is connected in series to the semiconductor device, the i layer of the optical modulator is an output of a phototransistor. The n-layer of the optical modulator has a multi-layered reflective film and part of the light transmitted through the i-layer is transmitted.

[0010]

When the output voltage of the phototransistor on the master side changes, the light transmittance in the i layer of the optical modulator changes, and a part of the light passing through the i layer passes through the n layer to reach the phototransistor and is amplified. It becomes a state. When the output voltage of the phototransistor on the slave side changes, the reset state is similarly established.

[0011]

First, the structure of the device of the present invention, its operating principle and characteristics, the layer structure of the device, and the optical flip-flop characteristics will be described in this order.

FIG. 1 is a cross-sectional view of the device of the present invention, in which an npn is formed on a semi-insulating semiconductor substrate (a semiconductor substrate which is not doped and is hereinafter referred to as a semiconductor substrate) 20.
Structure of emitter 21a, base 22a, collector 23a
And a phototransistor 24a are formed. Then, the n-DBR layer 26, i-MQ
This is a structure in which an MQW-pin modulator (hereinafter referred to as an optical modulator) 28a including a W layer 26a and a p layer 27a is laminated.

That is, a pin-structured optical modulator 28a is formed on the collector 23a of the phototransistor 24a in contact with its n-layer, and this is referred to as a master side semiconductor device 30a, and a slave having the same structure as the slave side is formed on the right side of the semiconductor substrate 20. The side semiconductor device 30b is formed. The i layer 26a of the optical modulator has a characteristic that the light transmittance changes when the output voltage of the phototransistor 24a changes because the i layer 26a is formed of the i-MQW layer. Also,
The n-DBR layer forms a multilayer reflective film by stacking semiconductor layers having different reflectances, and has a property of passing a part of light transmitted through the i layer 26a.

The surface side of the optical modulator 28a, that is, the p layer 2
A ring-shaped electrode 29a shown by diagonal lines is formed on the upper side of 7a, and the right side portion thereof is grounded. The left side portion is connected to the electrode 32a formed on the emitter 21a of the phototransistor 24a by the connection line 33a. Further, the electrode 31a is formed on the n-DBR layer 25a of the optical modulator 28a, the electrode 32a is formed on the emitter 21a of the phototransistor 24a, and the electrode 30 is formed.
a and the electrode 32a are connected by the connection wire 33a.

When the voltage of plus Vb is supplied to the electrode 32b of the semiconductor device 30b, the phototransistor 24b and the phototransistor 24a are biased in the quasi-direction, and the optical modulators 28b and 28a are biased in the reverse direction.

The set light 34 is incident on the phototransistor 24a from the semiconductor substrate 20 side, and the output light 35 is extracted as reflected light of the hold light 36 applied to the optical modulator 28a. Further, the reset light 37 enters the phototransistor 24b from the semiconductor substrate 20 side, and the output light 38
Is extracted as reflected light of the hold light 39 with which the light modulator 28b is irradiated.

In order to increase the contrast, antireflection coating layers 40a and 40b are formed on the surface side of the optical modulators 28a and 28b, that is, on the surface of the p layer 27a to suppress reflection on the surfaces. Although not shown in the figure, the lower surface of the semiconductor substrate 20 is also antireflection coated. Further, in FIG. 1, a structure in which the conductivity of each layer is completely inverted is possible, and an optical modulator, D
A structure in which BR and a phototransistor are laminated in this order is also possible.

In order to explain the operation principle of the device of the present invention, first, the operation principle of the MQW-pin type optical modulator is shown in FIG.
Will be explained. FIG. 2A shows a change in absorption spectrum in the i layer when a reverse bias voltage V is applied to the optical modulator having the MWQ-pin structure. Due to the quantum confined Stark effect (QCSE), the excitation absorption peak appearing near the absorption edge shifts to the long wavelength side as the voltage V increases.

Due to this effect, the absorption dip in the reflection spectrum (when the n layer has the DBR structure) is also shown in FIG.
As shown in (b), the wavelength shifts to the long wavelength side as the reverse bias voltage V increases. Here, at zero bias (V = 0)
FIG. 2C shows the voltage dependence of the optical output intensity Po and the absorption coefficient α at the exciton absorption wavelength λ1 of. The light output intensity Po decreases to a certain value as the voltage increases, and vice versa.

FIG. 3A shows an equivalent circuit of the first semiconductor element, which is composed of the phototransistor 24a and the optical modulator 28a, in the flip-flop element shown in FIG. The hold light 36 enters the optical modulator 28a, and the set light 34 enters the phototransistor 24a. Figure 1
At the light modulator 24, the transmitted light 41 of the hold light 36 from the DBR layer 25a to the phototransistor 24a is Pt.
The reverse bias voltage supplied to a is V, the absorption coefficient is α, D
When the reflectance of the BR layer 33a is R, the relationship is represented by the following equation.

Pt = (1-R) · Ph · exp {−α (V) L}

In FIG. 3B, the current-voltage curves of the optical modulator 28a and the phototransistor 24a in the case where the set light 34 is zero and only the hold light 36 is incident, and the current-voltage curves of the phototransistor 24a are both combined by a dotted line. It is shown by a solid line. The hold light 36 is in the case of being set on the longer wavelength side (λ1 in FIG. 2) than the exciton peak wavelength at the time of zero bias. Figure 2
As seen in (c), since the absorption coefficient increases as the voltage increases, the leakage light to the phototransistor 24a decreases as the voltage increases. That is, the overall characteristic shows a negative resistance in which the current decreases as the voltage increases, indicating that there is an amplifying action.

FIG. 4 (a) shows an equivalent circuit of the flip-flop element shown in FIG. FIG. 4B shows current-voltage curves when there is no set light, when the set light above the threshold is incident, when there is no reset light, and when the reset light above the threshold is incident. In this case, the hold lights 36 and 39 are always irradiated with a constant light.

The operating point when the intensity of the set light 34 and the reset light 37 is zero is stable at either point a or point b, and the previous operating point is retained. Next, the characteristic of the set light is shown in FIG.
Move to the upper side of (b). When the characteristic indicated by the dotted line is reached, the characteristic of the reset light is turned off and the characteristic of the set light intersect at the point c, but when the characteristic of the set light further rises, the stable point rapidly moves to the point a.

As a result, a small voltage close to zero is supplied to the optical modulator 28a, and a large voltage close to the reverse bias voltage is supplied to the optical modulator 28b. At that time, the output light intensity 35 is very large, and the output light intensity 38 is very small. Even after the set light 34 is blocked, the operating point is still a, so that the intensity of each output light 35 is maintained.

Assuming that the phototransistor 24b is initially in the reset state, the phototransistor 24b is on and the phototransistor 24a is off. Therefore, a large bias is supplied to the optical modulator 28a, and almost no voltage is supplied to the optical modulator 28b. From this, i of the optical modulator 28b
The absorption coefficient of the MQW layer 26b becomes small, and the hold light 3
9 is reflected by the n-DBR layer 25b and strong output light 38 is obtained.

On the other hand, since the optical modulator 28a is the opposite, the absorption coefficient in the i-MQW layer 26a becomes high and n-D.
The output light 35 reflected and returned by the BR layer 25a becomes very small. On the other hand, when the set light equal to or more than the threshold is supplied, the operation reverse to that described above is performed, the output light 35 becomes large and the output light 38 becomes small. In this state, the light leaking through the multilayer reflective film 33a causes the phototransistor 24a to reach the phototransistor 24a. Since the generated voltage is amplified, it exhibits a latching action and is held.

When the reset light 37 above the threshold is incident, the operating point moves from a to b. In this case, since the voltage applied to each optical modulator is inverted, the output light intensity is also inverted and reset. This state is maintained even after the reset light 37 is blocked. The input / output characteristics at this time are shown in FIG. As shown in FIG. 5, the output light 35 is set to the bright state and the output light 38 is set to the dark state by the incidence of the set light, and the output light intensity is inverted by the incidence of the reset light 37. Further, it can be seen that the output light intensity is maintained even after the set light 34 or the reset light 37 is blocked.

By changing the set light and the reset light in this way, the amount of light absorbed in the i-MQW layer 26a changes, and the amount of light reflected and output by the multilayer reflective film changes. Therefore, if the hold light 36 has a large energy, the reflected light 35 also has a large energy when the i-MQW layer 26a has a small absorption. Even if the set of the hold light 36 is large, the energy of the set light 34 and the reset 37 may be small. For this reason,
This device can control a large amount of energy with a small amount of energy, and as a result, it has a photoenhancing side effect.

Next, a specific example will be described. Figure 6 is Ga
It is sectional drawing of an element at the time of using As / AlGaAs. Semi-insulating AlGaAs substrate 101 (thickness 350μ
m) on top of three components, namely p-GaAs cap layer 108 (thickness 0.1 μm), p-Al _0.3 Ga _0.7 A
s clad layer 107 (thickness 0.5 μm), undoped G
aAs well layer (thickness 10 nm) and undoped Al _0.3 G
a i-MQW layer 106, n-AlAs having a structure in which obstacle layers (thickness 3 nm) of a _0.7 As are alternately laminated for 310 cycles
Layer (thickness 71.5 nm) and n-Al _0.3 Ga _0.7 As layer (thickness 62.9 nm) are alternately laminated for 7 periods to form an n-DBR (Distributed Bragg Reflector) layer 105. An optical modulator 120 having a reflection mode MQWpin structure having a laminated structure, and n-G
aAS collector layer 104 (thickness 4 μm), p-GaAs
Base layer 103 (thickness 0.25 μm), n-Al _0.3 G
A phototransistor 121 composed of an a _0.7 As layer (thickness: 0.5 μm) was formed by the molecular epitaxial growth method. Be and Si were used as the p-type and n-type dopants, respectively.

This wafer was processed as shown in FIG. AuZnNi was used as the p-type electrode 109, and AuGeNi was used as the n-type electrode 113. The SiO ₂ thin film 116 is i-
It is for protecting the MQW layer 106. A non-reflective coating layer 114 is provided to obtain high contrast. Cr / Au connection line 1 between two semiconductor elements
12 to connect.

FIG. 7 shows the response characteristics of the device of this embodiment measured under a hold light energy of 1 mw. It has an optical amplification function that the output light intensity is larger than the intensity of the set light 34 or the reset light 37, and has a high contrast of 20 dB or more. Also, the rise time was as high as 20 ns for each semiconductor element sample of 100 μm type.

The embodiment described above is based on GaAs / AlGaA.
Although the optical memory is configured by s, it is not limited to this.
InGaAs / InP, InAlAs / InGaAs,
It can also be applied to other material systems such as GaAs / InGaAs.

[0034]

As described above, according to the optical flip-flop element of the present invention, the photo-transistor side effect and the high on-time characteristic, which are characteristics of the phototransistor, are utilized, and the low input strength and high speed are achieved. It becomes possible to operate an optical flip-flop. Further, since the flip-flop according to the present invention has a large extinction ratio, it is very promising as an optical signal processing element.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an element of the present invention.

FIG. 2 is a graph showing characteristics of an optical modulator.

FIG. 3 is a diagram showing an equivalent circuit of a master side device or a slave side device and its characteristics.

FIG. 4 is a diagram showing an equivalent circuit of a flip-flop element and its characteristics.

FIG. 5 is a graph showing a response characteristic of a flip-flop element.

FIG. 6 is a sectional view showing a structure of an embodiment of an optical flip-flop element.

7 is a graph showing the response characteristics of the device shown in FIG.

FIG. 8 is a sectional view showing an example of a conventional device.

9 is a graph showing characteristics of the device of FIG.

[Explanation of symbols]

 20 semiconductor substrate 24a, 24b phototransistor 25a, 25b n-DBR layer 26a, 26b i-MQW layer 27a, 27b p layer 28a, 28b optical modulator 29a, 29b electrode 30a, 30b semiconductor device electrode 31a, 31b electrode 32a, 32b Electrode 34 Set light 35, 38 Output light 36, 39 Hold light 37 Reset light

Claims (1)

[Claims] 1. A semiconductor device having a structure in which a phototransistor having a pin structure of a phototransistor is vertically stacked with a multilayer reflection film sandwiched therebetween is defined as a master side, and a slave side semiconductor device having the same structure is connected in series to the semiconductor device. In the flip-flop element, the phototransistor is connected in parallel with the optical modulator, the phototransistor is driven as a forward bias and the optical modulator is driven as a reverse bias, and the i layer of the optical modulator is an output of the phototransistor. An optical flip-flop element having a characteristic that a light attenuation characteristic changes according to a voltage change, and the multilayer reflective film has a characteristic that a part of light is transmitted.