JPH07235188A - Optical memory using impurity level in semiconductor fine particles - Google Patents

Abstract

PURPOSE:To form an optical memory on a semiconductor substrate by utilizing an electron transition between impurities in a semiconductor by forming fine particles made of the semiconductor of a different type in the semiconductor. CONSTITUTION:AlSb 51 is used as a host crystal, and AlGaSb 52 having a large Al composition is used as fine particles. The AlGaSb 52 is grown on a semiconductor substrate made of like GaAs. The AlGaAs 52 is operated as a buffer or a barrier layer. A stress between the substrate and a grown structure can be preferably alleviated when an AlSb 52/GaSb superlattice, etc., is inserted between the GaAs and the AlGaSb 52 or the AlGaSb 52 is thickly stacked. After its surface is terminated with S or Se in the GaAs/AlGaSb, semiconductor fine particles are formed by a liquid-like epitaxy method. An Inks fine particle structure can be formed on the AlGaSb 52 by the same principle. The formed structure is embedded in a semiconductor by growing the AlGaSb. Thus, an optical memory can be formed on the substrate, input/output can be controlled only by a light. Multiplexing of one feature of the memory can be realized by altering a fine particle size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION Although it is expected that an optical computer will be realized, the present invention relates to an optical memory device which is closely related to the optical computer. In particular, the fact that reading and writing are performed by using lights of different wavelengths, The feature of the optical device is that it utilizes a deep impurity level which has been thought to be "one hundred harms and no interest".

[0002]

2. Description of the Related Art An optical memory is a storage element whose input and output are made of light instead of ordinary electricity. That is, it is an element which records digital or analog information by light and can be taken out when necessary. There are various types of optical memory devices, but if semiconductors are used as the material, they can be manufactured on semiconductor substrates using highly advanced growth and process technologies, and existing semiconductor lasers and photodetectors, and eventually electronic devices, can be used. It has the advantage that it can be integrated with circuits.

[0003]

Most of the optical memories currently in use only read destructively written information like a CD-ROM, and in order to enable writing, a magneto-optical device is used. It is necessary to use a medium other than light, such as a disc. In addition, although proposals have been made to use the hole burning effect of organic molecules and the like, the problems have been postponed in the future in terms of coupling with semiconductor elements, development into OEIC, and the like.

The problems to be solved by the present invention are (1) input / output control can be performed only by light, (2) semiconductor structure forming technology can be used because it can be formed on a semiconductor substrate, and (3) ) Easy coupling with an optical element, and (4) future developability.

[0005]

In order to solve the above problems, a first invention of the present invention is to provide a semiconductor as a host,
An optical memory is characterized in that fine particles made of different kinds of semiconductors are formed and the electron level in the fine particles and the electronic transition between impurities in the fine particles or the host semiconductor are utilized.

According to a second aspect of the invention, in a semiconductor which is a host,
Fine particles made of different kinds of semiconductors are formed, and NPPC (Ne
gative Persistent Photo-C
and a valence band between the conduction band and the valence band in the fine particles, in which writing is performed by using electronic transition between a conduction band of the fine particle semiconductor and an impurity level in the host semiconductor. The optical memory is characterized in that reading is performed using transition.

According to a third aspect of the present invention, in a semiconductor which is a host,
An optical memory in which fine particles made of different kinds of semiconductors are formed and a DX center is used, and writing is performed by using electronic transition between an impurity level in the fine particle semiconductor and a conduction band in the fine particle semiconductor, and a quantum well of the fine particle semiconductor. The optical memory is characterized in that reading is performed by using a transition between quantum levels in the inside.

A fourth aspect of the invention is to add a semiconductor, which is a host, to
Fine particles made of different kinds of semiconductors are formed, and PPC (Per
silent Photo-Condition
y) is an optical memory that utilizes the electronic transition between the valence band of the fine particle semiconductor and the impurity level in the host semiconductor for writing, and uses the transition between the quantum levels in the valence band of the fine particle. Alternatively, the optical memory is characterized in that reading is performed by using interband transition between the valence band and the conduction band in the fine particles.

[0009]

Operation: An example of the present invention, AlGaSb / InAs
NPPC (Negative Persi)
sentence Photo-Conditionity)
An optical memory using is described. The sample structure is shown in Figure 1.
Shown in.

AlGaSb and In with deep impurity levels
In the heterojunction system of As, when irradiated with light at a low temperature,
The electron concentration in the nAs channel decreases, and unless the system is brought into an equilibrium state due to temperature rise, etc., it continues forever.
The NPPC phenomenon can be seen. The details of NPPC are not known, but the electrons in the InAs well are
After the energy corresponding to the energy difference (conduction band discontinuity value) between the nAs conduction band and the AlGaSb conduction band is given to the barrier layer, the energy is emitted, and then it is trapped by a deep impurity in the barrier layer. Conceivable. Therefore, it is possible to write information by changing the electron concentration in the conduction band of InAs fine particles by irradiating with light corresponding to this conduction band discontinuity value (FIG. 2).

On the other hand, considering light absorption between bands in InAs fine particles, when electrons completely occupy the first quantum level of the conduction band in InAs fine particles, conduction band quantum level-valence band. No light absorption between them (that is, band-to-band transition in InAs fine particles) occurs, and absorption occurs when it is not occupied. Therefore, reading can be performed using this principle. FIG. 3 corresponds to reading in the state (0) in which no information is written, and FIG. 4 corresponds to reading in the state (1) in which information is written. The electron-hole pair generated by the band-to-band excitation disappears due to recombination, and is considered to have no influence on the next reading.

Next, an optical memory using the DX center will be described.

As an example, consider the AlGaSb / AlSb system, but any material may be used as long as the DX center is present in the host and the electrons are confined in the fine particles. The structure is shown in FIG.

It is known that an impurity level called a DX center is formed by doping impurities such as Te into AlGaSb having a large Al composition.
Although the origin of the DX center has not been clarified at this stage, it is known that it is one of the properties of the impurity itself, rather than the compound defect mentioned in the early stage of the research. DX
The center is known to have a bistable shallow level and a large activation energy between both levels. Which level is stable depends on the position of the Fermi level. When cooled to a low temperature, thermal electron transfer disappears.

First, consider the case where electrons are present in the DX center in the initial state. When irradiated with light having an optical activation energy or more, the electrons in the DX center are excited to the bistable shallow level. This is a write operation (Fig. 6).

Next, the read operation will be described. An electron excited to a shallow level is easily excited to the conduction band (first quantum level) at a finite temperature. Therefore, light absorption occurs due to the transition from the first quantum level to the second quantum level. By detecting the attenuation of the incident light due to this absorption, it is possible to read the information as to whether or not the electron exists in the first quantum level. FIG. 7 corresponds to reading in the state (0) in which no information is written, and FIG. 8 corresponds to reading in the state (1) in which information is written.

Next, another example of the present invention, Al _x Ga
_{1-x Sb / Al y Ga} 1-y Sb (x> 0.5, y <0.
5) PPC (Persistent Ph) seen in the system
An optical memory using the auto-conductivity will be described. The sample structure is shown in FIG.

Al _x Ga _1-x with deep impurity levels
The _{Sb / Al y Ga 1-y} Sb heterojunction systems, at low temperature,
When light is irradiated, the hole concentration in the Al _y Ga _{1 -y} Sb channel increases, and a PPC phenomenon of holes is observed, which continues forever unless the system is brought into an equilibrium state due to a temperature rise or the like. For PPC, but it is not known that the detailed, Al _y Ga _1-y Sb valence electrons of the electron band in is, Al _y
After the energy is given by the energy corresponding to the energy difference (transition energy) between the valence band of Ga _1-y Sb and the conduction band of Al _x Ga _1-x Sb, the barrier appears after the energy is released into the conduction band of the barrier layer. It is considered that holes are permanently generated in the valence band of Al _y Ga _{1 -y} Sb because they are trapped by deep impurities in the layer and the reverse process does not occur at low temperature. Therefore, by irradiating with light corresponding to this transition energy, Al _y Ga
Information can be written by changing the hole concentration in the valence band of _1-y Sb particles (FIG. 10).

On the other hand, considering the light absorption between sub-bands in Al _y Ga _{1 -y} Sb fine particles, holes are Al _y
When the Ga _{1 -y} Sb fine particles do not exist in the first quantum level of the valence band, the optical absorption between the first quantum level and the second quantum level (that is, the intersubband transition in the fine particles) is Does not happen,
Absorption occurs only when holes are present. Therefore, reading can be performed using this principle. FIG. 11 corresponds to the reading in the state (1) where the information is written, and FIG. 12 corresponds to the reading in the state (0) where the information is not written. It is considered that the holes excited by the intersubband excitation relax the energy and do not affect the next reading.

In addition, GaSb band-to-band transition can be used for reading. With light having an energy corresponding to this transition, PPC does not occur, and thus nondestructive read-out is possible. Now, when there is no hole in the first quantum level in the fine particles, the band-to-band transition occurs when light having energy corresponding to the band-to-band transition of the fine particles is incident. That is, light is absorbed (FIG. 13). On the other hand, when holes satisfy the first quantum level, transition does not occur,
Therefore, the incident light goes out without being absorbed (FIG. 14). Assuming that the state in which PPC has occurred is the state (1) in which information is written, FIG. 13 shows (0) and FIG. 14 shows (1).

As described above, a semiconductor optical memory can be manufactured by using a fine particle system with deep impurities. The reason for using fine particles is that the energy levels of carriers are completely discrete and that information is not lost due to diffusion or the like (that is, electrons are completely confined).

Recently, a fine particle forming technique has been developed, and it is possible to form particles having a fairly uniform size. In the case of fine particles, the quantum level can be changed by changing the size, so that the memory can be multiplexed.

[0023]

【Example】

(Embodiment 1) An embodiment of the optical memory of the present invention using an AlGaSb / InAs system will be described (the structural diagram is FIG. 1). AlGaSb is grown on a semiconductor substrate such as GaAs. This AlGaSb functions as a buffer and as a barrier layer. The stress between the substrate and the growth structure may be relaxed by inserting an AlSb / GaSb superlattice or the like between GaAs and AlGaSb and by stacking AlGaSb thicker. As for the composition of Al _x Ga _{1 -x} Sb, it is easier to form a deep impurity level when using x> 0.2. Recently, GaAs / AlGaAs
It has been reported that semiconductor fine particles can be formed by a method called liquid epitaxy after terminating the surface with S or Se in the system, but I on AlGaSb can be formed by the same principle.
It is also possible to form an nAs fine particle structure. The formed fine particle structure is formed by further growing AlGaSb,
It is embedded inside the semiconductor, and the structure finally becomes as shown in FIG. Size can be controlled, but 10nm
To a degree. At this time, the fine particles are broken during normal growth, but the shape of the fine particles can be preserved by performing low temperature MEE growth or the like. AlGaS in the vicinity of InAs fine particles
If Te or the like is doped into b, a deep level can be formed.

When this sample is cooled to about 100 K, NPPC occurs. That is, AlGaSb and InA
When light corresponding to the discontinuity of the conduction band with s (about 1 eV) is incident, the InAs fine particles are depleted. Whether or not it has been depleted can be determined by putting in light of about 0.5 eV corresponding to the band-to-band transition in the InAs fine particles and observing its absorption.

Example 2 Next, AlSb / AlGaS
An embodiment of the optical memory of the present invention using the b-system will be described (the structural diagram is FIG. 5). AlSb as host crystal
And AlGaSb having a large Al composition is used as the fine particles. The particle forming method and the embedding method thereof are
This is the same as described in the aSb / InAs system part.

The sample is cooled to a low temperature of about 100K. When a light of about 1 eV corresponding to the optical activation energy of DX level-shallow level in fine particles is incident on this sample, a shallow level is formed and a large thermal activation energy (about 0.4 eV). Therefore, it will not return to the DX center. on the other hand,
Since the shallow level is easily activated, electrons are excited in the conduction band (first quantum level). Whether or not this electron exists is determined by the light (about 0.1e) corresponding to the energy difference between the quantum levels.
V) can be detected.

(Embodiment 3) Next, an embodiment of the optical memory of the present invention using the AlSb / GaSb system (x = 1, y = 0) will be described (the structural diagram is FIG. 9). AlSb is grown on a semiconductor substrate such as GaAs. This AlSb is
It acts as a buffer and as a barrier layer. GaSb
The stress between the substrate and the growth structure may be relaxed by inserting an AlSb / GaSb superlattice or the like between the AlSb and AlSb, or by stacking the AlSb thicker. If it is used only as a buffer, AlGaSb may be more difficult to be oxidized. The GaSb fine particle structure formed on AlSb is embedded in the semiconductor by further growing AlSb, and finally the structure shown in FIG. 9 is obtained. The size can be controlled, but it should be about 10 nm. At this time, the fine particles are broken during normal growth, but the shape of the fine particles can be preserved by performing low temperature MEE growth or the like.

When this sample is cooled to about 100 K, PPC occurs. That is, the conduction band of AlSb and Ga
When light corresponding to the energy difference (about 1 eV) from the valence band of Sb is made incident, holes are generated in the GaSb fine particles. The light corresponding to the energy difference between the first quantum level and the second quantum level of the GaSb fine particles or the light having the energy corresponding to the band gap of the fine particles is incident on the GaSb fine particles to write in GaSb. Information can be detected.

[0029]

According to the present invention, writing and reading are facilitated due to the discrete nature of the energy of fine particles.
Also, the memory density is improved. Writing is optical excitation 28,
Readout is performed by observing light absorption having energy between quantum levels in the valence band or light absorption having transition energy between bands.

The greatest effect of the present invention is that an optical memory can be formed on a semiconductor substrate. That is,
Highly advanced semiconductor growth and process technology can be used as it is, and it can be grown on the same substrate as the laser and light receiving element, and monolithic integration is possible in the future. Further, according to the present invention, input / output control can be performed only by light, and by varying the particle size, multiplexing, which is one of the features of the optical memory, can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of an optical memory of the present invention using NPPC.

2 is a band diagram showing a write operation of the optical memory of FIG. 1. FIG.

3 is a band diagram showing a "0" read operation of the optical memory of FIG.

4 is a band diagram showing a "1" read operation of the optical memory of FIG.

FIG. 5 is a sectional view showing a structure of an optical memory of the present invention using a DX center.

6 is a band diagram showing a write operation of the optical memory of FIG.

7 is a band diagram showing a "0" read operation of the optical memory of FIG.

8 is a band diagram showing a "1" read operation of the optical memory of FIG.

FIG. 9 is a sectional view showing a structure of an optical memory of the present invention using PCC.

10 is a band diagram showing a write operation of the optical memory of FIG.

11 is a band diagram showing a "1" read operation of the optical memory of FIG.

12 is a band diagram showing a "0" read operation of the optical memory of FIG.

FIG. 13 is a band diagram showing a “0” read operation of the optical memory when the GaSb transition between bands is used for reading.

FIG. 14 is a band diagram showing a “1” read operation of the optical memory when the GaSb band-to-band transition is used for reading.

[Explanation of symbols]

11, 13, 52 AlGaSb 12 InAs fine particles 21 Conduction band of AlGaSb 22 Valence band of AlGaSb 23 Valence band of InAs 25 Deep impurity level 26, 106 First quantum level 27, 107 Second quantum level 28 , 108 Photoexcitation 29 Electron capture 210, 64 Electron 211 Deep impurity level 111, 121 ΔE (energy difference between first quantum level and second quantum level) 31 ΔE (conduction band first quantum level and valence band) Energy difference from the summit) 32, 41, 112, 122, 132, 142 Incident light with energy of ΔE 33 Transition process from forbidden valence band to first level 114 First level to second level Transition process 42 to transmitted light that is attenuated by the process of 43 34 Unattenuated transmitted light 43 Excitation from valence band to first level (prohibited 51 AlSb 61 conduction band of AlSb 62 first quantum level of conduction band of AlGaSb 63 DX level 65 photoexcitation process 66 shallow level 67 thermal excitation process from shallow level to quantum level 71, 81 AlGaSb well The transition process from the first quantum level to the second quantum level in the inside 72 71 The process of incident light 73 71 having energy equivalent to the process transition of 71 71 The process of 71 71 that does not occur and is not absorbed 74 Second of AlGaSb Quantum level 82 81 Transmitted light 91, 93 Al _x Ga _1-x Sb 92 Al _y Ga _1-y Sb fine particles 101 attenuated by absorption accompanying incident light 83 81 having energy corresponding to transition process the valence band of the Al _x Ga _1-x conduction band 102 of Sb Al _x Ga _1-x Sb in the valence band 103 Al _y Ga _1-y conduction band 104 of Sb Al _y Ga _1-y Sb 105 deep level 109 hole 1010 electron trapped in deep level 113, 123, 133, 143 transmitted light 124 prohibited transition process from the first level to the second level 131, 141 ΔE (conduction band Energy difference between one quantum level and first valence band quantum level: energy required for band-to-band transition) 134 Inter-band transition process in fine particles 144 Inter-band transition process in forbidden fine particles

Claims (4)

[Claims] 1. An optical memory in which fine particles made of a different kind of semiconductor are formed in a semiconductor which is a host, and electron transition between the electron level in the fine particles and impurities in the fine particles or the host semiconductor is utilized. 2. Fine particles made of different kinds of semiconductors are formed in a semiconductor which is a host, and NPPC (Negative) is formed.
Persistent Photo-Conducti
an optical memory utilizing the electron transfer between the conduction band of the fine particle semiconductor and the impurity level in the host semiconductor, and writing between the conduction band and the valence band in the fine particle. An optical memory characterized in that reading is performed using transitions. 3. An optical memory in which fine particles made of different kinds of semiconductors are formed in a semiconductor which is a host and a DX center is used, which is between an impurity level in the fine particle semiconductor and a conduction band in the fine particle semiconductor. An optical memory characterized in that writing is performed by using electron transition and reading is performed by using transition between quantum levels in a quantum well of the fine particle semiconductor. 4. A PPC (Persistent) is formed by forming fine particles of a different semiconductor in a semiconductor that is a host.
An optical memory using Photo-Conductivity), wherein writing is performed by using an electronic transition between a valence band of the fine particle semiconductor and an impurity level in the host semiconductor, and a quantum level in the valence band of the fine particle is written. The optical memory is characterized in that reading is performed by using inter-transition or by using inter-band transition between valence band and conduction band in the fine particles.