JPS61222383A - Pickup device for amorphous semiconductor - Google Patents

Abstract

PURPOSE:To realize a pickup device with high sensitivity, low residual image and low dark current by using an amorphous silicon film or a similar amorphous semiconductor film as a photoelectric transducing film and making contact an interface with an electrode with an injection-typed contact and making it perform an amplification function inside. CONSTITUTION:A clear electrode 2 is located on a glass substrate 1 and an n<+> type hydrogenated amorphous silicon layer 3 with <= nearly 1,000Angstrom thickness is attached on the electrode. On the layer 3, a p-type, hydrogen amorphous silicon layer 4 with the thickness of quite thin layer such as several 100Angstrom is attached and furthermore, an i-type hydrogenated amorphous silicon layer 5 with the thickness of several mum is performed. Then, an n<+> typed hydrogenated amorphous silicon layer 6 is provided between the layer 5 and an electrode 7 to perform an ohmic contact. By consisting the device as stated above, the whole element can perform the amplification function as a phototransistor and the sensitivity is improved. Also, by selecting an adequate p-type hydrogenated amorphous silicon layer 4, it is possible to reduce the residual image.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an imaging device using an amorphous semiconductor film in a photoelectric conversion section, and includes a photodetector with high sensitivity, low afterimage, and low dark current; The aim is to provide image pickup tubes, dan-layer type gymnastics image plates, etc.

(Prior art and problems) A photoelectric conversion film for imaging using a conventional photoconductive semiconductor is shown in FIG. High resistance semiconductors, such as selenium (SO) and antimony trisulfide (sb, s, )
Vizien image pickup tubes and electrophotographic photoreceptors are examples of devices that utilize the change in resistance value caused by a photoconductive phenomenon in which a thin film is provided.

These problems include the fact that the dark current cannot be reduced because charge is injected from the electrode (injected contact), that it is difficult to uniformly apply an electric field perpendicular to the photoconductive film, and that the dark current is generated by light within the film. The response time of the photoconductive phenomenon was slow due to the large number of traps that semi-permanently captured charge carriers such as electrons or holes. IE conversion films have been widely used in industrial applications because their sensitivity can be adjusted by applied voltage, they have a certain degree of dynamic wrench in the photosensitivity region, and they can be produced at low cost. In order to eliminate dark current, a structure is used near the interface between the electrode and the photoconductive semiconductor film to prevent charge from being injected from the electrode into the photoconductive film using n-type and p-type semiconductors or similar materials. By applying an electric field uniformly to the photoconductive film and creating a photoconductive film that traps fewer charge carriers (electrons or holes), electron-hole pairs generated by light can be quickly transferred to the anode and cathode sides. A method has been developed in which the afterimage is reduced by separating and accumulating the image.

An example of a blocking contact is shown in Section 8 (8), but in use, a positive voltage is applied to the electrode on the n-type semiconductor 22 side and a negative voltage is applied to the electrode on the p-type conductor 28 side. Holes are prevented from being injected from the electrode into the p-type semiconductor, and electrons from the electrode are prevented from being injected into the p-type semiconductor, and an electric field is generated almost uniformly over the entire central 1-type semiconductor 24 (intrinsic semiconductor region with high resistance). Electrons and holes generated by light in the shaped semiconductor region are attracted by a uniform and strong electric field and are quickly concentrated on opposite electrode sides, resulting in less afterimage and less dark current. Most of the photoconductive image pickup tubes that have been put into practical use recently are of this type.In the photoconductive film mentioned above, the charge carriers of electrons and holes generated by light are quickly separated and mutually separated. It is good that - reaches the electrode in the opposite direction, but there it recombines with electrons or holes of the opposite polarity and disappears.For example, in Figure 8, a positive voltage is applied to the electrode on the n-type semiconductor side. , 1 generated by light
The electrons in the n-type semiconductor region are attracted by the electric field and reach the n-type semiconductor, and the excess electrons that break the thermal equilibrium toughness of the n-type semiconductor region are immediately annihilated at the interface between the n-type semiconductor and the electrode on that side. Therefore, this type of photoconductive film does not have a current gain of 1 or more, that is, the ratio of the number of charges generated by light within the photoconductive film to the number of charges of the photocurrent extracted to the outside of the photoconductive film does not exceed 1. Photoconductive image pickup tubes currently in practical use require an illuminance of several hundred lux or a special configuration or illumination to capture high-quality images.
There is a photoconductive image pickup tube that can be easily used in the ~101 lux range. This is because it is not possible to obtain a current gain that greatly exceeds the above-mentioned current gain l, that is, the sensitivity is not yet sufficient.

(Means for Solving the Problems) An object of the present invention is to eliminate the above-mentioned drawbacks, use an amorphous silicon film or a similar amorphous semiconductor film as a photoelectric conversion film,
The structure of the film was specially devised, and the interface with the electrode was changed to injection type contact, and a phototransistor amplification effect was performed inside the film, increasing the current gain to more than 1 and increasing the photoelectric conversion efficiency. We have realized a photodetector 1 or image sensor that can be used even in the low-light region of 1O lux, and has a high sensitivity that could not be achieved with conventional photoconductive type devices.Moreover, it has a high 8/H, low noise, and is easy to handle. The purpose of the present invention is to provide an amorphous semiconductor imaging device that is as simple as the photoconductive type.

That is, in the amorphous semiconductor imaging device of the present invention, an amorphous semiconductor material is used to construct the photoelectric conversion film of the photoconductive type light receiving element, and n'' of the amorphous semiconductor material is sequentially formed from the direction of light incidence. pin", n"ipn", .

The photoelectric conversion film is made up of any one of p"nip+t p+inp+ stacked layers, and the intermediate p or n layer is an extremely thin layer of approximately 1000λ or less, which is floated from an external power source and generated by the light. changing the potential of the p or n layer with charge carriers (electrons or holes),
A quantum efficiency of 1 that allows a number of charges approximately equal to the number of charge carriers generated in response to the input of light to be extracted as an output photocurrent.
The photoelectric conversion film described above is characterized by configuring the above-mentioned photoelectric conversion film. 1 is a cross-sectional view of a light receiving element using an amorphous silicon (semiconductor) photoelectric conversion film.

A transparent electrode 3 is placed on a glass plate 1, and an n+ type hydrogenated amorphous silicon (n''a-SiH) layer 8 is deposited thereon to a thickness of about 1000λ or less by a green discharge method or a sputtering method. p-swollen hydrogenated amorphous silicon (pa-Si
H) @ 4 is attached in a very thin layer of several hundred λ, and further hydrogenated amorphous silicon (i a
-81H) After layer 5 is overlapped by several μm, n+ type a -
A 5fi1 layer is deposited for ohmic contact with electrode 7.

Light 8 passes through glass plate l and transparent electrode 2 and becomes pa-8iH.
When generating electron-hole pairs in Mt4 or ia-19iHMlB, if a voltage is applied to this semiconductor film from an external power supply 9 such that negative voltage is applied to electrode 2 and positive voltage is applied to electrode 7, the semiconductor film Inside, electrons travel to the electrode 7 side and one hole travels to the transparent electrode 2 side. As a result p a -8iil layer 4
Holes gather in this part and increase the potential of this part (second
In the figure, the solid line shifts to the broken line) p a -81HM deviates from the zero thermal equilibrium state, accumulates excess holes, and increases the potential.
4, electrons are injected from the adjacent n+ a-SiHJllδ, and some of the injected electrons 11, 12, are transmitted through the pa-8iH layer number while the electrons 11 travel toward the ia-811 layer 5. Then, the remaining electrons 18 recombine with the excess holes accumulated in the previous p a -SiHM4, and the remaining electrons 18
-SiH layer 5, and thereafter travels toward electrode 7 due to the electric field applied to the i a -SiH layer. On the other hand, after the remaining electrons 18 reach ia -811I m s, electrons are transferred from the na-8iil layer 8 again to p a -8
11 layer 4 and runs through pa-ail wII4 again. This repetition continues until the accumulated excess holes generated by the light 8 accumulated in the pa-8iil k 4 disappear. Electrons that have reached the electrode 7 due to the electric field are taken out to an external circuit and observed as a photocurrent.

In this way, a photocurrent whose number of charges is greater than the number of electron-hole pairs generated by the light 8 is observed in the external circuit, and a current gain greater than 1 is obtained. FIG. 1 shows a band diagram explaining this operation.

This operation is the transistor amplification effect of the phototransistor itself, and a highly sensitive element that cannot be obtained with a blocking contact type photoconductive film can be obtained. At this time, the larger the ratio of the number of the remaining electrons 18 to the number of the one part electrons 12, the larger the current gain becomes. However, if the number of remaining electrons 18 is too large, the excess holes will remain forever. Therefore, it is necessary to select a suitable p a-8iH layer because it becomes an afterimage and is inconvenient.
A layer with a resistance of 1Ω and a thickness of several hundred people was selected. The thickness of this layer is preferably as thin as possible so as not to cause punch-through due to the applied voltage.

FIG. 8 shows an example of voltage-current characteristics obtained through experiments of the above-mentioned embodiment and the conventional example. B is the characteristic obtained in the SL-SiH element with the conventional blocking structure, and B is the characteristic of the element having the structure of the above example, which can obtain a gain of 10 times or more compared to the conventional one. can.

A structure as shown in FIG. 4, in which the incident direction of light in FIG. 1 is reversed, also operates in a similar manner, and an element meeting the purpose of the present invention can be constructed.

By differentiating the light incident side, the spectral characteristics can be given characteristics. In addition, the polarity of voltage application is also reversed, increasing the degree of freedom in polarity and expanding the applicability. If we replace the effects of things, we can create an element. Therefore, in the above element, the n"pin+ configuration or n"ipn+ configuration can be similarly realized in the p"nip+ configuration or p+inp+ configuration. However, the lifetime of the hole (the time until it recombines as a minority carrier) ) is shorter than the lifetime of electrons, so in a device that uses hole injection, the na-8iH layer must be thinner and less than 500λ to obtain the same current gain.

In hydrogenated amorphous silicon, the diffusion length of electrons or holes is short, and the resistance value is extremely high compared to single crystal silicon, so there is little diffusion of charge carriers in the lateral direction parallel to the film surface, and In Figure 1, p which controls the injection current
Since the a-SiH layer 4 is extremely thin and has a large lateral resistance, the lateral charge conversion charge distribution corresponds to the optical input depending on the location, that is, it has a resolution for imaging, and can be applied as an imaging device. 0 This cannot be achieved with a similar configuration using single crystal silicon. FIG. 5 shows an example in which the a-Sin configuration according to the present invention is applied to an image pickup tube target. Figure 1 or 4 on target
Components having the same function as each layer in the figure are given the same reference numerals. Reference numbers δ, 4, 5, 6 in Figure S are p”a n
*1e The a-5iIf layer corresponds to the 10th layer, but for the 9th layer with reference number 6, a vapor-deposited film of antimony trisulfide (sb, s, ) is used for the special characteristics of the image pickup tube. It is designed to have the same function as the p layer.

The light imaged by the optical lens passes through glass l and transparent electrode 8.
The light passes through the a-SiH layer and generates electron-hole pairs depending on the amount of light. Electrons are accumulated in the na-Sin layer, controlling the potential of this layer and promoting hole injection. As a result, the multiplied holes are accumulated in the sb, s8 layer 6 and read out by an external electron beam 14.

FIG. 6 shows the a-Sin film structure of the present invention applied by laminating it on a solid-state imaging plate. The structure of the solid-state image pickup plate, which is the signal readout section of the image pickup tube, is a MOS type in which charge carriers accumulated between the source and the substrate are switched by a gate and read out from the drain. A COD type in which carriers are sequentially transferred and read out to an external circuit may also be used, and the photoelectric conversion layer of a stacked solid-state imaging plate is replaced with the a-SiH layer structure according to the present invention.

Reference number in Figure 6! , 6, 6, and 4.8 have structures corresponding to transparent electrodes and "e' e pe"+ layers, respectively.

In this case, the n+ layer can be replaced by a very thin silicon nitride film or a silicide such as molybdenum (10) or tampon (Or). a −8 by optical lens system
The optical image formed on the 1H film is multiplied by the same principle as described above, and is accumulated in the storage diode of the solid-state scanning circuit, between the source and substrate in the case of the MOS type, and in the potential well in the case of the 00D type. and read out by sequential scanning. #!
The reason why the glass plate l is omitted in FIG. 6 is that in the case of a solid-state imaging plate, a mechanically strong silicon single crystal scanning substrate 16 or the like is used instead of the above-mentioned one.

Although the above description has been made using an a-SiH layer, this invention is applicable not only to hydrogenated amorphous silicon films but also to other equivalent layer properties such as resistivity and minority charge carrier life. Any other amorphous semiconductor film whose diffusion length and the like can be controlled may be used. For example, I-M
group or IV group semiconductors.

(Effects of the Invention) The present invention is a simple photoconductive type photoelectric conversion element and a light receiving element having a quantum efficiency of 1 or more and an amplification factor.

The principle and operation are similar to a phototransistor, but it is not single crystal but amorphous silicon, n:1! I.J.
L temporary - / 11 Go ν Zeni Materikyu - Emochi Yuichi silk 1 Kan needle length,
It has new features such as being able to be applied to imaging devices by taking advantage of the short lifespan of minority charge carriers, and achieving extremely fast response times. In addition, the degree of amplification can be greatly controlled by the h-node of the applied voltage, making it possible to create a light-receiving element and an imaging device with a large dynamic range.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view in the film thickness direction of an example of a light receiving element using an amorphous silicon photoelectric conversion film according to the present invention, and FIG.
A semiconductor energy band diagram for explaining the photoelectric conversion operation of the photodetector shown in the figure; Figure 8 is a diagram showing a comparison of the experimental results of the embodiment shown in Figure 1 and the conventional example; Figure 4 is the figure shown in Figure 1. FIG. 6 is a cross-sectional view of an image pickup tube target to which the amorphous silicon film structure according to the present invention is applied, and FIG. Converter section cross-sectional view 1 FIGS. 7 and 8 are cross-sectional views in the film thickness direction for explaining a conventional photoelectric conversion device. 1...Glass plate 2...Transparent electrode sn+
or p+ type ice hydrogenated amorphous silicon n+ or pa
-8in) layer 4...p or n type water purple amorphous silicon (p or n a -SiH) Mjj5...1 type hydrogenated amorphous silicon (i & -8iil) layer 6... n+ or p+ type water accumulated amorphous silicon (n+ disturbed p”5L
-SiH) layer 7... Electrode 8... Light 9... External power supply lO... Load resistance 11... p a -
Part of the electrons 12...11 injected into the Sin layer 18-・Remaining electrons 14 of 11...Electron beam 15-・Electron gun Figure 1 Figure 2 Figure 2 Mark I voltage ( V) - Figure 4

Claims (1)

[Claims] 1. In constructing the photoelectric conversion film of the photoconductive type light receiving element, an amorphous semiconductor material is used, and n^+pin^+ of the amorphous semiconductor material is sequentially formed from the direction of light incidence. ,n^+ip
The photoelectric conversion film is composed of any one of n^+, p^+nip^+, p^+inp^+ laminated layers, and the intermediate p or n layer is an extremely thin layer of approximately 1000 Å or less, and this is floated from an external power supply, and the potential of the p or n layer is changed by charge carriers (electrons or holes) generated by the light, and charges greater than or equal to the number of charge carriers generated in response to the input of the light are generated. An amorphous semiconductor imaging device characterized in that the photoelectric conversion film has a quantum efficiency of 1 or more and can be extracted as an output photocurrent. 2. The amorphous semiconductor imaging device according to claim 1, wherein the amorphous semiconductor material is hydrogenated amorphous silicon. 3. One or two layers constituting any one of the laminated layers are produced using a different amorphous semiconductor material from other layers constituting any one of the laminated layers. An amorphous semiconductor imaging device according to claim 1 or 2, wherein: