JPH0551194B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an image storage device made of a semiconductor. (Prior Art) The present invention aims to provide a structure of an image storage device that stores image information input as an optical signal, continues to output it as an optical signal, and can be erased as necessary. No such device existed. However, although the objective is different from the present invention, there is a conventional example having a similar structure: H. Beneking: “Full solid state image converter based
on integration of phototransistors and
LEDs”, IEEE Electron Dev.Lett., vol.EDL−
2, pp. 99-100 (1981). FIG. 6 shows a cross-sectional structure of this conventional example. In the figure, a phototransistor 4 is composed of an n-Ga _0.5 Al _0.5 emitter 1, a p-GaAs base 2, and an n-GaAs collector 3, an n-Ga _0.65 Al _0.35 As first cladding 5, and an n-Ga _0.68 The Al _0.32 active layer 6 and the p-Ga _0.6 Al _0.4 second cladding 7 constitute a light emitting device 8 . A light absorption layer 9 is provided between the phototransistor 4 and the light emitting element 8, and the phototransistor 4 does not receive light emitted from the light emitting element 8. In this device, when infrared light 10 is incident on the phototransistor 4, the light emitting element 8 emits visible light 11, and by integrating this into an array, image conversion from infrared to visible light is possible. It is said that the equipment will be available. Since the purpose of this conventional example is infrared-visible image conversion, it does not have a particular function of storing images. (Problems to be Solved by the Invention) The present invention attempts to add an image storage function by modifying the structure of the conventional example. That is, the present invention aims to provide an image storage device that stores image information input as an optical signal, continues to output it as an optical signal, and can be erased as necessary. (Means for Solving the Problems) An image storage device of the present invention includes a double heterostructure light emitting element and a phototransistor capable of receiving light emitted from the light emitting element, and the collector of the phototransistor and the A structural unit is an optical memory element in which a first cladding of the same conductivity type as the collector of the light emitting element is electrically connected, and a plurality of the optical memory elements are arranged on a plane while being electrically and optically insulated from each other. , the second cladding of the light emitting element and the emitter of the phototransistor are electrically connected to each other between the optical storage elements. Here, optically insulating the optical memory elements from each other means that the light emitted from the light emitting elements included in each optical memory element is blocked between the optical memory elements, and is not received by the phototransistor included in the adjacent optical memory element. That means. That is, a light shielding member that is electrically insulating and opaque to light emitted from the light emitting elements is provided between adjacent optical storage elements. (Function) The image storage device of the present invention has an optical storage element composed of a pair of light emitting elements and a phototransistor connected in series as a structural unit. This optical storage element can take two states, on and off, for the same bias voltage state due to optical positive feedback from the light emitting element to the phototransistor. That is, if a bias voltage is applied to the optical storage element in a state where no input light is incident on the phototransistor, no current flows and the light emitting element does not emit light because the phototransistor is in a high resistance state. This is the off state. On the other hand, once input light is incident on the phototransistor, a current flows through the phototransistor and the light emitting element emits light. This is the on state, and this state is maintained even if no input light is input. This is the operating principle of an optical storage element, and it stores information that the incident light was incident. In order to erase this memory, it is sufficient to once return the bias voltage to 0. An image storage device can be obtained by arranging a plurality of these optical storage elements on a plane, but what is important here is that each element is insulated not only electrically but also optically. This is because when another optical storage element receives light emitted from an adjacent optical storage element, it is turned on, and all the optical storage elements are turned on in a chained manner. Note that since the bias voltage is the same in both the on and off states, it is sufficient to apply the same voltage to each optical storage element and set the total applied voltage to 0 only when erasing memory. (Embodiment) FIG. 1 is a perspective view of an embodiment of the image storage device of the present invention, in which optical storage elements 12 are arranged in an array on a plane to constitute the image storage device. In FIG. 1, the optical storage elements 12 are arranged in a 4×4 array, but in reality, they have a more dense array configuration in order to increase the resolution. Each optical storage element is electrically and optically insulated by the isolation region 13, but its upper and lower surfaces are biased with a common voltage by first and second transparent electrodes 14 and 15. The internal structure of the optical memory element will be described below with reference to FIG. FIG. 2 is a sectional view of a main part of the optical memory element. In the figure, a phototransistor 19 is composed of an n-Al _0.5 Ga _0.6 As emitter 16, a p-GaAs base 17, and an n-Al _0.5 Ga _0.5 AS collector 18. Further, a light emitting device 23 is composed of an n-Al _0.5 Ga _0.5 first clad 20, an n-Al _0.3 Ga _0.7 active layer 21, and a p-Al _0.5 Ga _0.5 second clad 22. The light emitting element 23 in this case is a double heterostructure light emitting diode. The collector 18 of the phototransistor 19 and the first cladding 20 of the light emitting element 23 are electrically connected, and feedback light 24 from the active layer 21 of the light emitting element 23 is absorbed and received by the base 17 of the phototransistor 19. Ru. The optical memory element is constructed with the above structure, but
It is electrically and optically insulated from adjacent optical storage elements by a semi-insulating GaAs region 13. That is, of the light emitted from the light emitting element 23, the light other than the output light 25 extracted to the top surface and the aforementioned feedback light 24 are absorbed by the GaAs isolation region 13, so that the phototransistor of the adjacent optical memory element No emitted light is received. Further, the second cladding 22 of the light emitting element 23 and the emitter 16 of the phototransistor 19 are wired to adjacent optical memory elements through first and second transparent electrodes 14 and 15, respectively, and are identical to each other in all optical memory elements. A bias voltage of 1 is applied. Next, the operating principle of the optical memory element will be explained using FIG. 3. Figure 3 shows the voltage-current characteristics of the optical memory element, and for the same bias voltage, A,
There are two states of B. State A (off state) occurs when a bias voltage is applied when the input light 26 to the phototransistor in FIG. 2 is not incident. That is, since the phototransistor is in a high resistance state, no current flows through the optical storage element, and therefore the light emitting element also does not emit light. Here, when the input light 26 is incident on the phototransistor, the phototransistor has a low resistance, current flows to the optical storage element, and the light emitting element emits light. That is, it transitions to state B (on state). In state B, the light emitted from the light emitting element enters the phototransistor as feedback light 24, so state B is maintained even if no external light is incident. In addition, in state B, the output light 25 from the light emitting element is
It is emitted to the outside as. In order to return the state of B to the state of A, it is sufficient to temporarily set the bias voltage to 0. According to the above operating principle, the optical memory element stores input light and continues to emit it as output light, and can erase the memory as necessary. Therefore, images can be stored by arranging these optical storage elements in an array. In this case, each optical storage element functions as a pixel and stores an image, and various methods of operation can be considered. FIG. 4 is a schematic perspective view showing an example of the operation method, in which the pattern of the original drawing is transferred. In this example, the bias voltage of the image storage device 27 is once set to 0 to erase the memory, and then input light is irradiated through the original image 28. As a result, the optical storage elements in the transparent parts of the original image 28 are turned on, and the optical storage elements in the opaque parts of the original image remain in the off state, so that the pattern of the original image is stored. This stored image pattern is maintained even if the irradiation of light through the original image 28 is stopped, but can be erased by setting the bias voltage to zero. Next, FIG. 5 shows another operating system. this is,
Images are stored by scanning a laser beam. The memory of the image storage device 27 is also erased first. Next, the laser beam 29 scans the optical memory element, which is a pixel. At this time, by turning the laser beam on and off, the image storage device 2
Image patterns are stored in 7. This method can be applied not only as an image pattern storage method but also as a data serial-to-parallel conversion method. In other words, it converts optical serial data into two-dimensional parallel data, and is considered to be extremely useful as an elemental technology for optical computers. (Effects of the Invention) As explained above, according to the present invention, it is possible to obtain an image storage device that stores image information input as an optical signal, continues to output it as an optical signal, and can be erased as necessary. can. Conventionally, such a device does not exist, and its application fields are very wide. It is also believed to become a basic elemental technology for optical computers.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the image storage device of the present invention, FIG. 2 is a sectional view of a main part of an optical storage element, and FIG. 3 is a voltage diagram for explaining the operating principle of the optical storage element.
4 is a schematic perspective view showing an example of an operating method, FIG. 5 is a diagram showing another operating method, and FIG. 6 is a diagram showing a cross-sectional structure of a conventional example. 12... Optical recording element, 13... Separation area, 14
...First transparent electrode, 15... Second transparent electrode, 16
... Emitter, 17 ... Base, 18 ... Collector, 19 ... Phototransistor, 20 ... First
Clad, 21...Active layer, 22...Second clad, 23...Light emitting element.

Claims (1)

[Scope of Claims] 1. A light-emitting element having a double hetero structure and a phototransistor capable of receiving light emitted from the light-emitting element, the collector of the phototransistor and the collector of the light-emitting element having the same conductivity type. The second cladding of the light emitting element and the photo storage element are arranged as a structural unit, and a plurality of the optical storage elements are electrically and optically insulated from each other and arranged on a plane. The emitters of the transistors are electrically connected to each other between the optical memory elements, and the light emitted from the light emitting element included in each of the optical memory elements is blocked between the optical memory elements, and the light emitted from the light emitting element included in each of the optical memory elements is blocked between the adjacent optical memory elements. An image storage device characterized in that no light is received by the phototransistor included in the image storage device.