JPS6328502B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to semiconductor devices, and in particular to devices for converting electromagnetic radiation into electrical signals.

The invention can be advantageously used in a variety of optoelectronic systems, such as those that convert optical images into suitable electrical signals.

The demand for optical signal processing systems is increasing in various research and engineering fields. A key element in these systems is a device that converts radiation into electrical signals. The use of solid state converters results in processing systems that are smaller and generally lower in cost. In some cases simpler constructions can be achieved.

Known devices for converting electromagnetic radiation into electrical signals (see U.S. Pat. No. 4,016,586 Cl. 357-2, 1977) include:
Two interconnected bands with different widths of band gaps forming forbidden contacts for charge carriers of one sign.
one semiconductor layer and two electrodes, one located on the side of the free surface of the semiconductor layer with a wide bandgap and the other located on the side of the free surface of the semiconductor layer with a narrow bandgap. ing. However, in this known device, even if the structure of the material forming the semiconductor layer with a wide bandgap allows the formation of charge carrier trapping sites, certain factors may prevent other types of charge carriers from entering the semiconductor layer with a wide bandgap. This results in unhindered dark injection for charge carriers of the type, so that it exhibits forbidden contact only for one type of charge carrier. As a result, the charge pattern, or image record, formed by light injection becomes flattened and exhibits defects that prevent recording of the spatial structure of the optical signal.

The object of the invention is to provide a device for converting electromagnetic radiation into electrical signals, which makes it possible to significantly improve the quality of recording the spatial structure of optical signals.

The purpose is to arrange two semiconductor layers with different widths of band gaps which are interconnected and form a forbidden contact for charge carriers of one sign, and one with a wider band gap placed on the side of the free surface of the semiconductor layer. comprising two electrodes, one of which is arranged on the side of the free surface of the semiconductor layer, the other with a narrow bandgap, and according to the invention the semiconductor layer with a wide bandgap is connected to charge carriers of the other sign. This is also accomplished by means of devices for converting electromagnetic radiation into electrical signals, which are manufactured from materials of construction that can exhibit forbidden contact.

Preferably, the structure of the material forming the semiconductor layer with a wide bandgap makes it possible to form charge carrier trapping sites in addition to exhibiting forbidden contacts for charge carriers of both signs.

Preferably, the material structurally capable of exhibiting forbidden contacts to charge carriers of both signs and forming charge carrier trapping sites represents compensated zinc selenide with a degree of compensation close to 100%. .

The concentration of charge carrier trapping sites in the material forming the semiconductor layer with a wide bandgap is 10 ¹¹
It is advantageous to exceed cm ^-2 .

Preferably, the wide bandgap semiconductor layer has a thickness of 5 microns or less.

It is also advantageous for the device according to the invention to include at least one main dielectric layer connected to the semiconductor having a wide bandgap.

Preferably, in some cases, the main dielectric layer is
Additional connections are made to the semiconductor layer with a narrow bandgap.

Advantageously, the device according to the invention includes at least one additional dielectric layer arranged between the electrode and the free surface of the semiconductor layer with a wide bandgap.

Also, the thickness of the main and additional dielectric layers should be
It is advantageous to set it to 10000 Å.

From a technical point of view, it is expedient if the electrode arranged on the side of the free surface of the semiconductor layer with a wide bandgap is a point electrode arranged to allow its movement.

This point electrode may represent a mercury probe.

The present invention has the advantage that the spatial structure of an optical signal can be converted into a well-defined charge pattern, which greatly improves the quality of optical image recording.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The device for converting electromagnetic radiation into electrical signals consists of a semiconductor layer 1 (Fig. 1) having a wide bandgap 2 (the energy bands are shown in Fig. 2) and a thickness of less than 5 microns (Fig. 1) and a narrow band gap 2 (the energy bands are shown in Fig. 2). a semiconductor layer 3 having a band gap 4 (FIG. 2);
Made of compensated zinc selenide with a degree of compensation close to 100%. The structure of the material, which allows the formation of forbidden contacts for charge carriers of both signs and the formation of charge carrier trapping sites, consists of approximately equal amounts of positively charged donors 5 and negatively charged acceptors 6.
(hereinafter referred to as charge trapping sites 5 and 6) in FIGS. 1 and 2. These form forbidden contacts to charge carriers of both signs and are able to capture electrons 7 and holes 8, respectively. a translucent electrode 9 forming non-ohmic contact with the material of layer 1;
are arranged on the side of the free surface of layer 1, while electrode 10, forming ohmic contact with the material of layer 3, is arranged on the side of the free surface of layer 3. Connected in series to the device are a bias power supply 11 and a load 12 which generates a video signal at output 13 when reading out the recorded electromagnetic radiation 14 (hereinafter referred to as optical signal 14) from electrode 9.

FIG. 2 also shows the valence bands 15, 16 and conduction bands 17, 18 of layers 1, 3 and the Fermi levels of electrodes 9, 10.

In another embodiment of the invention, the device for converting electromagnetic radiation into electrical signals comprises a dielectric layer 21 (FIG. 3) located between electrode 9 and layer 1.

In yet another embodiment of the invention, a device for converting electromagnetic radiation into electrical signals includes a dielectric layer 22 (FIG. 4) disposed between layers 1 and 3.

In a further embodiment of the invention, a device for converting electromagnetic radiation into an electrical signal is arranged between electrodes 9 and layers 1 and 1 and 3, respectively.
two dielectric layers 23 and 24 (FIG. 5).

In another preferred embodiment of the invention, the device for converting electromagnetic radiation into electrical signals comprises mercury probes 25 arranged on the sides of layer 1 and acting as electrodes.
(Figure 6) is used.

A sinusoidal voltage generator 26 connects the probe 25 and the source 11.
connected to.

FIG. 7 shows the band gap 27, valence band 28 and conduction band 29 of the dielectric layer 21 (FIG. 3). The band gap 2 is an additional trapping site 30 formed by adding impurities, for example.
including. The concentrations of all sites 5, 6 and 30 are
More than 10 ¹¹ cm ^-2 . Valence band 1 of layer 3 (Figure 3)
6 shows an electron 31 (seventh
Figure) is shown.

The energy band diagram in FIG.
The band gap 32, valence band 33, and conduction band 34 in Figure) are shown.

Below the Fermi level 19 in FIG.
An electron 35 is shown captured by one of the capture sites 30 in bandgap 2 of layer 1 of FIG. 4 as 4 is being recorded.

The energy band in FIG. 9 corresponds to the dielectric layer 2 in FIG.
Band gaps 36, 37, valence bands 38, 39, and conduction bands 40, 41 of No. 3 and 24 are shown, respectively. Holes 42 are shown in the layer 15 of the valence band 15.
, while the conduction band 17 is located at the acquisition site 30 of the band gap 2 when the optical signal 14 is being recorded.
contains electrons that are captured by

The operation of the device according to the invention for converting electromagnetic radiation into electrical signals will now be described.

In FIGS. 1 and 2 the photons carrying the optical signal 14 are absorbed, for example, in the electrode 9 and, depending on the polarity of the electrical bias supplied by the source 11, are transferred to the conductor 17 of layer 1 or to the valence electrons. Emission of electrons 7 or holes 8 into the band 15 is made possible. “What is light emission?
The ejection of free charge carriers, i.e. electrons or holes, from one layer to another by the effect of incident radiation, which is similar to the photoemission of electrons from the photocathode into the vacuum of the phototube. is similar to Now, the photo-emitted electrons 7 or holes 8 are captured by the capture sites 5 or 6, respectively. Charges are therefore formed in layer 1 along the surface of layer 1, the surface density of which corresponds to the spatial structure of the optical signal projected onto the device,
This state indicates that the optical signal 14 has been recorded.

The electrostatic field established by this charge is applied to layer 3, so that a corresponding charge pattern is formed within layer 3. For example, if we measure the photovoltage at different points on the surface of layer 3 disposed on the side of layer 1, its value will depend on the charge pattern formed in layer 3 and thus the recorded optical signal 14. would correspond to the spatial structure of This makes it possible to read the recorded optical information. In order for a capture site to be charged to the level required to be clearly read within the desired time interval, the concentration of the capture site must exceed ¹⁰ cm ^-2 if the intensity of the optical signal is maintained within reasonable limits. Must be.

The photovoltaic force (video signal) connects the surface of layer 3 to electrode 9.
is measured in layer 3 by scanning with a focused light beam (not shown) from the side. The electron energy in this beam is smaller than the width of bandgap 2 of layer 1 and is smaller than the width of bandgap 4 of layer 3.
should be larger than the width of the This video signal is developed across load 12 and is taken at output 13.

The above process will now be described in more detail with a focus on the reading process.

When the image to be recorded is projected onto the semi-transparent electrode 9, the semiconductor layer 1 with a wide bandgap is formed.
, causing a photoemission of electrons into the electron beams, which are captured by the capture sites 5 . The greater the intensity of the radiation recorded in the image projected onto the device, the greater the density of negative charge captured by the capture site. A charge pattern corresponding to the image to be recorded is thus formed in the semiconductor layer 1 with a wide bandgap.

The recorded image in the form of a charge pattern is read out by a narrow beam of light that scans the surface of the device.
The video signal is developed across a load resistor 12 inserted into an electrical circuit in series with the device (this is similar to an image tube using an electron beam instead of a light beam).

As previously mentioned, the photon energy of the reading beam must be higher than the width of the narrow layer 3 bandgap, but should not exceed the width of the wide layer 1 bandgap 2. The read radiation (beam) passes through the translucent electrode 9 and the wide band gap layer 1 and is absorbed into the narrow band gap layer 3 near the interface with this layer 1, generating electron-hole pairs. . If the charge density in the wide bandgap layer 1 (corresponding to the bright area of the image) at the time of irradiation with the scanning beam is 0 in the same area of the device.
If the electron-hole pairs are Occurs within 12 days. The value of this signal in the linear region is proportional to the voltage drop in the narrow bandgap semiconductor layer 3, ie to the density of the charges accumulated in layer 1, and thus to the local intensity of the recorded image.

When the reading beam scans a dark region of the recorded image, the electrons and holes generated by the reading beam are No photovoltaic signal is generated because the pairs do not separate and recombine without generating photovoltaic force.

The reading light beam scanning the surface of the device as described above generates a video signal at the load resistor 12. When the amplified video signal is applied to the brightness electrode of the image pickup tube, the image recorded on the screen of the video monitoring device can be reproduced by synchronizing the electron beam scanning it with the scanning of the reading light beam. It is possible. If necessary, the video signal can be sent to a computer for processing.

According to the invention, the long-wave boundary for recording the optical signal 14 is the Fermi level 19 (FIG. 2) and the electron 7
is determined by the energy barrier between the Fermi level 19 and the top of the valence band 15 for the hole 8, between the bottom of the conduction band 17 for the hole 8 and the top of the valence band 15 for the hole 8.

The recording of the optical signal 14 from the electrode 9 by the optical emission of electrons 7 and holes 8 is as described above.

A similar process occurs by optical emission of electrons or holes from the valence band 16 or conduction band 18 of layer 3 when recording optical information.

The smaller the thickness of layer 1, the greater the effect of the electrostatic field on charges trapped by sites 5 and 6 when a charge pattern is formed in layer 3. Conversion sensitivity is therefore increased. Preferably, the layer thickness should be limited to a maximum of 1 to 5 microns.

According to the invention, dielectric layer 21 of FIG. 3 prevents shunting of video signals when microholes are formed in layer 1.

The electrons 31 shown in FIG. 7 are photoemitted from the valence band 16 of layer 3 of FIG. 3 onto a trapping site.

Please refer to FIGS. 3 and 7. layers 1 and 21
The energy barrier between the bottoms of conduction bands 17 and 29 (FIG. 3) and the tops of valence bands 15 and 28 prohibits free flow of charge carriers through layer 1 and prevents charge capture by trapping sites 30. Since the probability is increased, the conversion sensitivity is increased. These energy barriers are in any case the band gap 2 of layer 21.
Since the width of band gap 7 is much larger than the width of band gap 2 of layer 1, it is always formed.

Please refer to FIGS. 4 and 8. The free flow of charge carriers through layer 1 occurs between band gaps 2 and 32 and between the bottoms of conduction bands 17, 34 and the tops of valence bands 15, 33 of layer 1 and the desired energy location of dielectric layer 22. by providing an appropriate energy ratio between In this way, electrons 35 are emitted onto the capture site 30 .

Please refer to FIGS. 5 and 9. The provision of two dielectric layers 23 and 24 makes it possible to simultaneously restrict the free flow of electrons 43 and holes 42 through layer 1. In this case, the long-wave boundary for recording the optical signal 14 is determined by the width of the bandgap 2 of layer 1.

Photon absorption produces electrons 43 and holes 42,
These are separated by external electric fields and captured by capture sites 30.

According to the invention, energy barriers are formed (barrier for electrons 43 and barrier for holes 42)
acts in pairs. These are a pair of barriers, namely layer 1
a barrier between the conduction band 17 of the dielectric layer 23 and the bottom of the conduction band 40 of the dielectric layer 23, and a barrier between the valence band 15 of layer 1 and the top of the valence band 39 of the dielectric layer 24, as well as another pair of Barrier, i.e. conduction band 17 of layer 1 and dielectric layer 2
4 and the barrier between the bottom of the conduction band 41 of layer 1 and the top of the valence band 38 of layer 1 and dielectric layer 23.

The operation of the apparatus shown in FIGS. 3 to 5 is the same as the reading procedure of the apparatus shown in FIG. 1 with respect to reading the recorded image.

To explain the flow of the read current, the ohmic read photocurrent flows only in the semiconductor layer 3 having a narrow bandgap. This current is caused by the bias current generated in the wide bandgap semiconductor layer 1 in the structure of FIG. 1, in layers 1 and 21 in the structure of FIG. The layers 1 and 24 are then short-circuited via the respective bias currents generated. The analog of the converter operating in readout mode is a photodiode in series with a capacitor. 1st, 3rd, 4th and 5th
In the transducer embodiment shown, no ohmic current flows in the wide bandgap semiconductor layer 1 during reading, so that the information written in the layer is not erased.

The dielectric layer 21 and the fifth layer shown in FIGS. 3 and 4
The width of the bandgap of dielectric layers 23 and 24 shown in the figure is greater than the width of the bandgap of layer 1;
For this reason, these dielectric layers are transparent to the reading light. In the devices shown in FIGS. 4 and 5, the thickness of the dielectric layer between the wide band gap semiconductor layer 1 and the narrow band gap semiconductor layer 3 is determined by the effect of the charges trapped in layer 1. The electric field induced within is undisturbed and a video signal is formed as the recorded image is read out.

In the apparatus shown in FIGS. 3-5, images are recorded as described with respect to the apparatus shown in FIG. Furthermore, in the case of the device of FIG. 3, by using optical emission of electrons and holes from the semiconductor layer 3 with a narrow bandgap to the semiconductor layer 1 with a wide bandgap, and in the case of the devices of FIGS. The data can be recorded by using light emission of electrons and holes from electrode 9 to layer 1 and absorption of light by layer 1, as shown in FIGS. 8 and 9.

When the operating area of the semiconductor layer 1 is large, the sixth
A mercury probe 25 is moved along the free surface of the layer 1 as shown by using a known mechanism (not shown). The use of probe 25 partially reduces the large capacity of the device to shunt the video signal. According to the invention, the mercury probe 2
5 eliminates 100% of shunts over the entire area of layer 1 when micropores are present.
A sinusoidal voltage generator 26 provides an alternating current that flows through the device and the load 12 and, if the load is properly selected, has a value corresponding to the charge pattern formed in the layer 3 (the value of photovoltaic power). (same as ) dynamic capacity can be measured and the information recorded thereby can be read.

The operation of the apparatus will be explained in more detail in FIG. 6 as follows.

The operation during the recording stage is similar to the apparatus of FIGS. 3 and 5.

Readings are taken by scanning a mercury probe across the surface of the device and measuring the capacitance of the area where the probe is located at any given time. A sinusoidal voltage generator 26 is placed in series with the device and load resistor 12 to measure the capacitance. The load resistor 12 is made small so that the current flowing through the load can be measured with respect to the value of the local capacitance of the device.

It is known that the capacitance of structures consisting of a semiconductor substrate and a high resistance layer, such as metal-dielectric-semiconductor structures, varies depending on the applied voltage and the charging state of the structure. By measuring the capacitance of a local area of the device, it is therefore possible to record the level of local density of charge stored in layer 1 and thus the level of local illumination of the recorded image. Generating the video signal requires continuous scanning of the mercury probe over the entire area of the device.

[Brief explanation of the drawing]

1 is a functional diagram of a device for converting electromagnetic radiation into electrical signals according to the invention, schematically showing the structure of the material forming the semiconductor layer with a wide bandgap; FIG. FIG. 3 is a functional diagram of a device for converting electromagnetic radiation into electrical signals according to the invention with a dielectric layer on the free surface of a semiconductor layer with a wide bandgap. 4 is a functional diagram of a device for converting electromagnetic radiation into electrical signals according to the invention with one dielectric layer arranged between semiconductor layers, and FIG. 5 is a functional diagram of a device according to the invention with two dielectric layers. FIG. 6 is a functional diagram of a device for converting electromagnetic radiation into an electrical signal according to the present invention having a mercury probe; FIG. 8 is an energy band diagram of the structure of FIG. 3, and FIG. 9 is an energy band diagram of the structure of FIG. 4. DESCRIPTION OF SYMBOLS 1... Semiconductor layer, 2... Band gap of layer 1, 3... Semiconductor layer, 4... Band gap of layer 3, 5... Donor capture site, 6... Acceptor capture site, 7... Electron, 8... hole, 9,10
... Electrode, 11 ... Bias power supply, 12 ... Load for video signal generation, 13 ... Output of device, 14 ...
...Optical signal, 15... Valence band of layer 1, 16... Valence band of layer 3, 17... Conduction band of layer 1, 18...
Conduction band of layer 3, 19, 20...Fermi level, 2
1, 22, 23, 24...dielectric layer, 25...mercury probe, 26...sine wave voltage generator, 27...
...Band gap of layer 21, 28...Valence band of layer 21, 29...Conduction band of layer 21, 30...Tracking site, 31...Electron, 32...Band gap of layer 22, 33...Band gap of layer 22 Valence band, 34...
Conduction band of layer 22, 35... electron, 36... layer 23
band gap, 37... band gap of layer 24, 38... valence band of layer 23, 39... layer 2
Valence band of 4, 40... Conduction band of layer 23, 41...
...Conduction band of layer 24, 42...hole, 43...electron.

Claims (1)

Claims: 1. Two interconnected semiconductor layers (1 and 3) with band gaps (2 and 4) of different widths forming forbidden contacts for charge carriers of one sign; Two electrodes (9 and 1) are arranged on the side of the free surface of the semiconductor layer 1 with a wide bandgap 2 of
0) and in which the material of one semiconductor layer 1 with said wide bandgap 2 presents a forbidden contact for charge carriers of the other sign and attempts to convert. forming charge carrier trapping sites 5, 6, 30 capable of trapping charges created in said one semiconductor layer 1 by light emission that changes the photoconductivity of said one semiconductor layer 1 depending on the intensity of electromagnetic radiation applied to said one semiconductor layer 1; A device for converting electromagnetic radiation into an electrical signal, characterized in that the material is capable of converting electromagnetic radiation into an electrical signal. 2. Device for converting electromagnetic radiation into electrical signals according to claim 1, wherein the material of one semiconductor layer 1 with a wide bandgap 2 is compensated zinc selenide with a compensation factor close to 100%. 3. Device according to claim 1 or 2, wherein the concentration of charge carrier trapping sites 5, 6, 30 in the material of the semiconductor layer 1 with wide bandgap 2 exceeds 10 ¹¹ cm ^-2 . 4. Device according to any one of claims 1 to 3, characterized in that the thickness of the semiconductor layer 1 with the wide bandgap 2 is less than 5 microns. 5. Two interconnected semiconductor layers (1 and 3) with band gaps (2 and 4) of different widths forming forbidden contacts for charge carriers of one sign, and one with a wide band gap 2. Two electrodes ( 9 and 1
0) and at least one dielectric layer (21 or 22 or 23, 24) connected to one semiconductor layer 1 having said wide bandgap 2. , the material of said one semiconductor layer 1 presents a forbidden contact for charge carriers of the other sign, and the photoconductivity of said one semiconductor layer 1 depends on the intensity of the electromagnetic radiation to be converted. converting electromagnetic radiation into electrical signals, characterized in that it is a material capable of forming charge carrier trapping sites 5, 6, 30 capable of trapping charges created in said one semiconductor layer 1 by light emission that changes the electromagnetic radiation; device to do. 6. Device according to claim 5, in which a dielectric layer (22 or 24) is connected between both semiconductor layers. 7 One electrode 9 and wide band gap 2
A dielectric layer 23 is provided between one semiconductor layer 1 having a
6. The device according to claim 5, wherein: 8 Dielectric layers 21, 22, 23, 24 are 50 to 50
Claim 5 having a thickness of 10000 Å
8. The device according to any one of items 7 to 7. 9. Device according to claim 7, in which the electrode 9 arranged on one semiconductor layer 1 with the wide bandgap 2 is a movable point electrode. 10. The device according to claim 9, wherein the point electrode is a mercury probe 25.