JPH01179125A - Optical space modulating element - Google Patents

Abstract

PURPOSE:To eliminate the need of a window and a peeling process and to reduce the cost by laminating an andope multiple quantum well layer having exciton absorption and energy being lower than an energy gap of a substrate, on the substrate by a p-i-n structure. CONSTITUTION:On (n) type semiconductor substrate 41 having an energy band gap E2, an (n) layer 31 of a semiconductor, an (i) layer 21 containing a multiple quantum well in which energy E1 of an exciton absorption end is smaller than the energy gap E2 of the substrate 41, and a (p) layer 11 of a semiconductor are laminated successively to a p-i-n structure. Therefore, since the energy E1 of the exciton absorption end of the multiple quantum well layer 21 is lower than the energy band gap E2 of the substrate 41, an output light for passing through the p-i-n structure transmits through substrate 41. Accordingly, a window and a peeling process which are necessary up to the present becomes unnecessary, and the cost of a secondary array can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical spatial modulation element that modulates the intensity of two-dimensional light such as an image using an electrical signal.

[Conventional technology]

Conventionally, GaAs is used as an optical spatial modulator that modulates the intensity of incident light using an electrical signal.
An optical spatial modulator is created by laminating a structure obtained by sandwiching an undoped multiple quantum well consisting of a periodic structure of GaAs layers between a p-GaAs layer and an n-GaAs layer (p-i-n structure). , and a two-dimensional array in which these p-1-n structures are two-dimensionally arranged on a substrate has been fabricated. As a reference for this optical spatial modulation element, Wood (WOOD et al., Electronics
Letters 23.916 (1987)).

FIG. 3 is a cross-sectional view showing the structure of this element, with n −
It has a structure in which an n-GaAs layer 3, an undoped AI GaAs/GaAs multiple quantum well (MQW) layer 2, and a p-GaAs layer 1 are laminated in this order on a GaAs substrate 4. Electrodes 5 and 6 are provided on the upper surface of the p-GaAs layer 1, which is the uppermost layer, and on the bottom surface of the n-GaAs substrate 4, respectively. A reverse bias voltage power source 7 is connected between these electrodes. The structure is such that the substrate 4 is provided with a window 8 for transmitting light.

To explain the operating principle of the optical spatial modulation element constructed in this way, light having an energy equal to the exciton absorption edge in the multi-quantum well layer 2 is incident perpendicularly to the surface of the p-GaAs layer 1. The intensity of this light is changed by a mirror (Miller et al., Phys.
sical Review 832, 1043 (198
5)) Q CS E (Quantua+-
Confined 5tark Effect) is modulated by the voltage applied to the p-1-n structure. That is, if the reverse bias voltage applied to the p-1-n structure is increased, the exciton absorption edge shifts to the lower energy side. As a result, the absorption rate of light in the multi-quantum well layer 2 increases, and the light is emitted through the n-GaAs layer 3 (
The intensity of the output light decreases.

[Problem that the invention seeks to solve]

However, according to such a conventional optical spatial modulator, since the multiple quantum well layer 2 is obtained as a periodic structure of GaAs layers and ^1GaAs layers, the energy of input and output light is
In other words, the energy El of the exciton absorption edge (the energy of the exciton absorption edge when the bias voltage is zero) is as shown in FIG.
(e.g., E 1 =1.45eVS
E2 = 1.37 eV), if there is no window 8, the output light exiting through the n-GaAs layer 3 will be GaA
It is absorbed by the s-substrate 4. For this reason, it is necessary to obtain output light of sufficient intensity (a window 8 is provided on the GaAs substrate 4 for transmitting the output light, and after film growth, the GaAs substrate 4 is
Requires a process to peel off part of the material. Additionally, the moving parts are so thin that they require a transparent epoxy layer to support them. That is, it is necessary to take measures such as reinforcing the peeled portions of the GaAs substrate 4 with a transparent adhesive.

As described above, conventional light spatial modulation elements have two problems: the manufacturing method is difficult and the configuration is complicated, but it is difficult to realize large-scale two-dimensional data processing and precise image processing. The high cost of two-dimensional arrays was unavoidable.

In FIG. 4, the curve shown by a solid line is the absorption characteristic curve of the multi-quantum well layer 2 when the bias voltage is zero, and the curve shown by the broken line is the absorption characteristic curve of the multi-quantum well layer 2 when a reverse bias voltage is applied. The characteristic curve indicated by the -dotted chain line is Ga
The absorption characteristic curve of the As substrate 4 is shown.

[Means for solving problems]

The present invention was made in view of these problems, and includes an undoped multiple quantum well layer having an exciton absorption edge energy lower than the energy gap of the substrate, sandwiched between a p layer and an n layer on a semiconductor substrate. The p-1-n structure obtained in the above is laminated.

[Effect]

Therefore, according to the present invention, since the energy of the exciton absorption edge in the multiple quantum well layer is lower than the energy bandgap of the semiconductor substrate, the output light passing through the p-1-n structure and exiting is directed to the semiconductor substrate. becomes transparent.

〔Example〕

Hereinafter, the spatial light modulation element according to the present invention will be explained in detail.

FIG. 1 is a sectional view showing the structure of one embodiment of this optical spatial modulation element. That is, the energy bandgap E2
On top of the n-type semiconductor substrate 41 having a semiconductor layer 31 . of the same or different semiconductor than the substrate 41 . one layer 21 including a multiple quantum well in which the energy E1 of the exciton absorption edge is smaller than the energy bandgap E2 of the substrate 41; and the substrate 41
It has a structure in which two layers 11 of the same or different semiconductors are laminated in sequence. That is, on the n-type semiconductor substrate 41,
p- obtained by sandwiching the first layer 21 between the second layer 11 and the first layer 31
A 1-n structure is laminated. Electrodes 5 and 6 are provided on the upper surface of the second layer 11, which is the uppermost layer, and on the bottom surface of the substrate 41, and a reverse bias voltage power source 7 is connected between these electrodes.

Next, the operation of the optical spatial modulation element configured as described above will be explained. Now, input light with energy El and a constant intensity is incident perpendicularly to the surface of the second layer 11. The intensity of this light is
When passing through the first layer 21, p-1-
It is modulated by the voltage applied to the n-structure. That is, p
If the reverse bias voltage applied to the -1-n structure is increased, the exciton absorption edge shifts to the lower energy side. As a result, the light absorption rate in the multiple quantum well in the first layer 21 increases, and the intensity of the output light exiting through the first layer 31 decreases. That is, output light with an intensity corresponding to the magnitude of V, which is the reverse bias voltage value, can be obtained.

Here, the energy E1 of the exciton absorption edge of the multiple quantum well in the i-layer 21 is smaller than the energy bandgap E2 of the substrate 41, as shown in FIG.
Output light exiting through 1 may be transmitted through substrate 41 . Therefore, there is no need to provide a window for transmitting the output light on the substrate 41, and the optical spatial modulator can be easily manufactured and its configuration can be simplified. That is, since there is no need to provide a window on the substrate 41, there is no need for a process of peeling off a part of the substrate 41 after film growth, making it possible to easily manufacture the film. Furthermore, in the conventional element, it was necessary to reinforce the part where the substrate was peeled off with a transparent adhesive, but in the element of this embodiment, such reinforcement is not necessary, so the structure is simple.

Therefore, according to the optical spatial modulation element according to this example,
It is now possible to easily arrange the p-1-n structure two-dimensionally on the substrate 41, which increases the cost of two-dimensional arrays that can realize large-scale two-dimensional data processing and precise image processing. It becomes possible to suppress this.

Specifically, for example, the semiconductor substrate is an InP substrate, and the undoped multiple quantum well layer is made of two types of InxGat-J3yP with different Inn composition and As composition y.
By using a periodic structure of +-y layers (O≦X≦1.0≦y≦1), it is possible to obtain a spatial light modulation element similar to that described in the embodiment.

Further, the semiconductor substrate is an InP substrate, and the undoped multiple quantum well layer is an In, Ga+-Js layer (0
≦X≦1) and a periodic structure of InyA 1 +-, As layers (O≦y≦1) with In composition y, it is also possible to obtain the same optical spatial modulation element as explained in the example. .

Below, as specific examples 1 and 2, practical examples of fabrication of this optical spatial modulation element and its performance will be disclosed.

<Specific Example 1> An optical spatial modulation element having the configuration shown below was manufactured using a metal organic vapor phase epitaxial growth method (MOVPE method).

Substrate 41: Se-doped InPS thickness 200 um (absorption edge wavelength approximately 1 μm) 1 layer 31: Se-doped InPS % thickness 1. crmi
Layer 21: Gao, zsIno, ? 5AS6.5
IIP0.50 (75A), InP (50A) alternating layers (
50 cycles) 9 layers 11: Zn-doped InP, 1 μm thick Electrode 5:
Au/Zn, thickness 1500A Electrode 6: Au/Ge/
Ni, thickness 1500A Element shape: diameter 200 μm, element spacing: 100 μm, two-layer, two-array electrode 5 was donut-shaped with an outer diameter of 200 μm and an inner diameter of 100 μm, and electrodes 6 were provided on all parts except the element position (diameter 200 μm). .

Light with a wavelength of 1.3 μm and an intensity of 200 μW was incident on this device. When the voltage between the electrodes 5 and 6 was changed from 0V to 10V, the intensity of the output light was reduced by about two-thirds. The response speed of the element was about 10 ns. All four elements showed equivalent characteristics.

<Specific Example 2> An optical spatial modulation element having the configuration shown below was produced using a molecular beam epitaxial growth method (MBE method).

Substrate 41: Se-doped InP, thickness 200 μm (absorption edge wavelength approximately I11 m) 1 layer 31: Si-doped Ino, 53caO, 4?A
S, thickness 1μm i ji 'l 1: Ino, 53Gao, iJs
(100A), Ino, to sz8 0.4. As
(50^) Alternating layers (50 periods) 9 layers 11: Be-doped Ino, 53caO,a, As layer thickness 1 μm Other configuration: Same as Example 1.

Light with a wavelength of 1.5 μm and an intensity of 200 μW was incident on this device. When the voltage between the electrodes 5 and 6 was changed from Ov to IOV, the intensity of the output light was reduced by about half. The response speed of the element was about 1 ns.

All four elements showed equivalent characteristics.

In each of the above-mentioned examples, an n layer, an i layer, and a p layer were sequentially laminated on an n-type substrate to obtain a p-1-n structure.
p-1-, in which p-layer, i-layer, and n-layer are laminated in order on a p-type substrate
It is also possible to have an n structure. In this case, the connection direction of the reverse bias voltage power source 7 may be reversed, and a negative voltage may be applied to the electrode 5 and a positive voltage may be applied to the electrode 6.

〔Effect of the invention〕

As explained above, according to the spatial light modulation device of the present invention, an undoped multiple quantum well layer having an exciton absorption edge energy lower than the energy gap of this substrate is sandwiched between a p layer and an n layer on a semiconductor substrate. Since the resulting p-1-n structure is stacked, the output light that passes through the p-1-n structure and exits is transmitted through the semiconductor substrate. Therefore, there is no need to provide a window on the substrate for transmitting the output light, and a peeling process is not required, making the fabrication easy. Further, in the conventional element, it was necessary to reinforce the part where the substrate was peeled off with a transparent adhesive, but in the element of the present invention, such reinforcement is not necessary and the structure is simplified.

Therefore, by using the element according to the present invention, it is possible to easily create a two-dimensional array that enables large-scale two-dimensional data processing and precise image processing, and it is possible to suppress the increase in cost of the two-dimensional array. become able to.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of an embodiment of a spatial light modulation element according to the present invention, and FIG. 2 is a characteristic showing the energy dependence of the light absorption coefficient in the substrate and multiple quantum well layer of this spatial light modulation element. 3 are cross-sectional views showing the structure of a conventional optical spatial modulation element, and FIG. 4 is a characteristic diagram showing the energy dependence of the light absorption coefficient in the substrate and multiple quantum well layer of this optical spatial modulation element. 5.6... Electrode, 7... Reverse bias voltage power supply,
11...p layer, 21...i layer, 31...n layer, 4
1... n-type semiconductor substrate. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] In an optical spatial modulation element that modulates the intensity of incident light using an electrical signal, an undoped multiple quantum well layer having an exciton absorption edge energy lower than the energy gap of this substrate is formed on a semiconductor substrate by a p layer and an n layer. p obtained by sandwiching
An optical spatial modulation element formed by stacking -i-n structures.