JPH0366178A - Optoelectric transducer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a photoelectric conversion element that converts light into an electrical signal, and in particular to a photoelectric conversion element that achieves high sensitivity by using charge multiplication in an amorphous semiconductor. It relates to a conversion element.

[Prior art] Video information systems, optical communications, and optical communications that use light as a medium for information signals.
In other industrial and consumer fields, photoelectric conversion elements that convert optical signals into electrical signals are one of the most important and fundamental components, and many of them have already been put into practical use.

In general, photoelectric conversion elements are required to have high sensitivity.

Among these, avalanche photodiodes (hereinafter referred to as APDs), which amplify photogenerated carriers by impact ionization, have high gain and fast response speed, and are therefore promising candidates for photoelectric conversion elements that meet these requirements. Many APDs have already been put into practical use, especially as photodetectors in optical communication systems, and are also used in other fields, such as -dimensional image sensors, two-dimensional image sensors with stacked photodetectors, and photoconductive image pickup tubes. Application to electrophotographic photoreceptors, etc., is also strongly desired.

Most of the materials used to create such APDs are crystalline semiconductors, particularly materials mainly composed of SL of the RV group and GaAs5InP of the II-V group. Creating an APD using a crystalline semiconductor material generally requires a high-temperature, ultra-high vacuum manufacturing process, so it is not suitable for stacking on existing circuit elements or for increasing the area. In addition, Ga, As, and the like are highly toxic materials and are problematic to handle industrially.

Therefore, it is desired to realize an APD using an amorphous semiconductor material, which is industrially inexpensive, can be produced at low temperatures, and is suitable for stacking on existing circuits and increasing the area.

Conventionally, as a method for realizing APD using an amorphous semiconductor, a charge injection blocking structure is formed using an amorphous semiconductor mainly composed of Se, and avalanche multiplication occurs within the amorphous semiconductor to amplify the signal. method (Television Society Technical Report 1987 Vol. 10, pages 1-6), hydrogen and halogen (
For example, a method of signal multiplication by forming a p+πpnn" junction in an amorphous semiconductor mainly composed of SL containing fluorine, chlorine) and causing avalanche multiplication in the pn junction depletion layer (Japanese Unexamined Patent Publication No. 55-95953 (No. Publication), or an amorphous semiconductor mainly composed of a compound of Si and C containing at least one of hydrogen and halogen elements, with many layers in which the composition ratio of SL and C is continuously varied in the film thickness direction. A method has been proposed (Japanese Patent Application Laid-Open No. 63-233574) in which signal multiplication is carried out by stacking layers to increase the electron multiplication factor to cause avalanche multiplication.

[Problems to be Solved by the Invention] In the prior art method using avalanche multiplication in amorphous Se or avalanche multiplication at the pn junction of amorphous SL, the thermal There were stability issues.

That is, in the former case, the amorphous material itself has poor heat resistance, and the characteristics deteriorate significantly when operated for a long time or left in a high-temperature environment for a long time. Furthermore, in the latter case, the dark current increases significantly at temperatures above about room temperature, making it impossible to apply a high enough electric field to obtain a sufficient multiplication factor.

In addition, in the latter case, since there are many recombination centers at the pn junction interface, the depletion layer does not expand much and a sufficient multiplication factor cannot be obtained.

In the conventional technique described above, which uses avalanche multiplication in a multilayer structure of layers with varying composition ratios of Si and C, although consideration is given to thermal stability, SL and C
In addition to the difficulty in the manufacturing method of continuously changing the composition ratio of SL and C, the dark current increases significantly due to the presence of many recombination centers in the compound of SL and C. It was not possible to apply a high enough electric field.

In other words, in order to carry out charge multiplication such as impact ionization in a semiconductor, a sufficiently high level of energy must be required so that free carriers can acquire the energy necessary to cause impact ionization within their mean free path. An electric field must be applied, but in a simple pin structure of amorphous Si, there are many recombination centers such as dangling bonds, so
When a large reverse bias voltage is applied to cause charge multiplication such as impact ionization, the dark current increases significantly, making it impossible to obtain realistic device performance.

The purpose of the present invention is to eliminate the problems of the above-mentioned conventional techniques, and to provide high sensitivity, good photoresponse characteristics, excellent heat resistance, easy fabrication, and the ability to stack on existing circuits. An object of the present invention is to provide an amorphous semiconductor photoelectric conversion element that can be expanded in area.

[Means and actions for solving the problem] Recently, a-3e
It has been reported that avalanche multiplication occurs in (amorphous Se) under a high electric field of 10'V/cm or more (Y, Takasaki et al.: 1988
MR3Spring Meeting Symposia
um) oThis is interesting not only from the practical standpoint of developing amorphous semiconductor devices with new functions, but also because it provides information on carrier transport phenomena under high electric fields. From this perspective, we have a-3L (
In order to explore the possibility that a similar phenomenon may occur in amorphous Si (amorphous Si), we are investigating the reverse polarity photocurrent characteristics of a-3L photodiodes. The present invention has been made based on such considerations.

The photoelectric conversion element of the present invention is a pin type photoelectric conversion element in which the i-layer is composed of an amorphous SL, in which an amorphous Si nitride layer is provided between a p-type semiconductor layer and an n-type semiconductor layer, and the The present invention is characterized in that when a reverse bias voltage is applied to the photoelectric conversion element, an electric field is concentrated on the amorphous Si nitride layer and/or the vicinity of the amorphous Si nitride layer to perform charge amplification.

In the photoelectric conversion device of the present invention, amorphous Si nitride having more insulating properties is provided inside or adjacent to the amorphous Si layer constituting the device, and an electric field is concentrated near the amorphous Si nitride. Since charge is multiplied efficiently, there is no need to apply a high electric field to the entire device, and a significant increase in dark current due to application of a large reverse bias voltage can be avoided.

The operation of the photoelectric conversion element of the present invention will be explained in detail below using the drawings.

As shown in FIG. 1(a), a p-type amorphous Si carbide layer 1 which is a p-type semiconductor layer, an amorphous nitride SL layer 2, an amorphous Sii layer which is an i-type semiconductor layer, A transparent electrode is formed at one end of a photoelectric conversion element formed by sequentially laminating n-type microcrystals 5il14, which are n-type semiconductor layers, and a metal electrode is formed at the other end. When a reverse bias voltage is applied to the electrodes at both ends, amorphous nitride 5i
A high electric field is concentrated in the amorphous SL layer near Jll and the amorphous Si nitride layer.

Among the electrons and holes generated in the amorphous Si carbide layer by light irradiation, electrons are injected into the conduction band of the amorphous nitride SL layer by tunneling or diffusion due to the high electric field. Subsequently, the electrons injected into the conduction band of the amorphous Si nitride layer are accelerated by the above-mentioned high electric field, resulting in charge multiplication due to impact ionization. That is, it is possible to realize a highly sensitive photoelectric conversion element that multiplies charges generated by light irradiation inside the element.

In the present invention, by providing the amorphous nitride SL layer inside or adjacent to the amorphous Si layer, the electric field can be concentrated only in a part of the photoelectric conversion element, and the charge can be efficiently increased by impact ionization. It is important to produce double effect, and the above-mentioned photomultiplying effect may occur in the amorphous nitride SL layer, the amorphous Si layer near the amorphous nitride Si layer, or both at the same time. good.

Furthermore, the position where the amorphous Si nitride layer is provided is between the p-type amorphous Si layer and the amorphous SL layer, inside the amorphous SL layer, or between the n-type mechanical crystal SL layer and the amorphous SL layer. It may be between the p-type amorphous SL layer and the amorphous Si layer shown above, or inside the amorphous Si layer shown in FIG. 1(b). It is desirable that

In the photoelectric conversion element of the present invention shown in FIG.
Electrons and/or holes accumulate at both ends of the L layer, further increasing the electric field concentrated in the amorphous nitride SL layer and the amorphous SL layer near the amorphous nitride Si layer, which are dissimilar layers, and thus , the charge multiplication effect further increases.

As mentioned above, various materials can be used in principle for the heterogeneous layer such as amorphous Si nitride inserted into the amorphous Si, but there are some materials that are relatively good with the amorphous SL layer. It is desirable to use an amorphous Si nitride layer that can form an interface and relatively easily control the energy gap and the position of the band edge of the conduction band (electron affinity), as well as concentrate the electric field and obtain an efficient multiplication effect. , and in order to flow a sufficient current at a low applied voltage, it is more desirable to use an amorphous Si nitride layer having a composition such that the energy gap is about 2.4 eV.

Furthermore, the layer thickness of the above amorphous Si layer is amorphous nitride SL
It is determined by the position where the layer is provided, the applied voltage and multiplication factor necessary to realize the required function as a photoelectric conversion element, the layer thickness of the amorphous Si layer, etc. It is preferable that the applied voltage is several tens of volts at most, and in order to make the charge multiplied at this applied voltage travel efficiently through the amorphous Si and take it out as a signal charge with good response, it is necessary to Since the thickness of the layer is preferably approximately lum, in such a case, the thickness of the amorphous nitrided SL layer may be greater than 100 Å, preferably 200 Å to 500 Å.

Moreover, as the p-type semiconductor layer of the photoelectric conversion element of the present invention,
When the above-mentioned heterogeneous layer has the function of blocking charge injection from the electrode and is provided in contact with the p-type semiconductor layer,
It is clear from the operating principle of the photoelectric conversion element of the present invention that materials other than the above-mentioned amorphous Si carbide layer can be appropriately used as long as they have a photoelectric conversion function.

Similarly, it is clear that materials other than the above-mentioned microcrystalline Si layer can also be used for the n-type semiconductor layer as appropriate.

In addition, as a manufacturing method for creating this device, deposition methods are generally effective, and vapor deposition methods, chemical vapor deposition (CVD), etc.
D) method, vapor phase epitaxy method, sputtering method, molecular beam epitaxy method, etc. can be used. Among these, it is particularly preferable that the amorphous semiconductor layer be formed by a glow discharge method using a capacitively coupled deposited film forming apparatus. This method requires a creation temperature of 3
Because the temperature is around 00°C, it can be easily stacked on semiconductor devices on which integrated circuits and the like have already been formed, and different types of semiconductor layers can be easily created by simply changing the ingredients of the raw material gas. It has characteristics such as being able to use materials that are low in pollution and industrially, and being able to easily form a film over a large area. , can solve all the conventional problems.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) The prepared sample was a-3iN with an optical gap of 2.4 eV at the p/i interface of a p-1-n a-3L solar cell structure.
(Amorphous nitride SL) layer is inserted. Also, u
The thickness of the ndoped a-Si layer is 1 μm.

A sectional view of a device according to a first embodiment of the present invention is shown in FIG. 2(a).

This device was created by the following operations.

First, a transparent electrode 102 made of ITO/5no2 was formed using a vapor deposition apparatus on a 7059 glass substrate 1011 manufactured by Corning, and etched so that the electrode had a predetermined shape.

Next, the substrate was placed on the anode electrode of a capacitively coupled deposited film forming apparatus, the inside of the deposition chamber was evacuated to about 10-' Torr, and the substrate was heated to about 300° C. with a heater. After the substrate reaches a predetermined temperature, silane gas SiSiH4100se diluted to 10% with 2 in hydrogen gas and methane gas CH410 sec are introduced into the deposition chamber. After confirming that the internal pressure of the deposition chamber reached the predetermined pressure of approximately 0.3 Torr, high-frequency power (13,56 MHz) 0.5 W/
cm'' was put into the deposition chamber.Glow discharge was performed for a predetermined period of time, and 200 layers of blocking layer and light-receiving layer 103 made of amorphous p-type Si film were deposited.

After that, in the same procedure as for the blocking layer and the light-receiving layer 103, silane gas Si diluted to 10% with 2 in hydrogen gas was added.
H<100 sccm and ammonia gas NH35se
cm and amorphous nitride SL[104 diluted to 10% with 2 in hydrogen gas SiH42 with 100 sec of amorphous Si layer 105 diluted with 2 in hydrogen gas to 10% Silane gas 5iH
4100sec and phosphine gas PHa 10sc
500 microcrystalline n-type Si layers 106 were sequentially deposited from 50 cm to 10 cm.

Finally, an AI layer 107 is deposited as an electrode, and the A1 layer 1
07, microcrystalline n-type Si layer 106, amorphous Si layer 105,
Amorphous nitride SL layer 104 and amorphous carbide SL layer 10
3 was etched into a predetermined shape.

When the band gap of each semiconductor layer was optically measured, the amorphous p-type Si film layer had a band gap of 2. OeV, 2.4 eV for amorphous Si nitride layer, 1.8 eV for amorphous Si layer,
The microcrystalline n-type Si layer had a voltage of 1.9 eV.

Light with a wavelength of 460 nm (light intensity 2.36 x 1
0"photons/s-em") was irradiated from the p-layer side and the photocurrent was measured. FIG. 2(b) shows a-3iN
The J-V (direct current voltage) characteristics when the film thickness of the (amorphous Si nitride) layer is varied from 0 to 500 layers are a-
The results showed that when 3iN was inserted, the quantum efficiency exceeded 1, and the rate of increase in current also increased as the thickness increased.

That is, at an applied voltage of 30 V, the multiplication factor is about 2 times, and
At an applied voltage of 40 V, a multiplication factor of approximately 4 times was obtained.

Moreover, the ratio of signal current to dark current was obtained by more than two orders of magnitude.

Furthermore, when the light response speed was measured by blinking the light irradiated onto the photoelectric conversion element of this example, a rise response speed of about 2 m5ec was obtained as shown in FIG. 2(c).

Further, even when this was operated continuously for a long time at 80° C., no change in characteristics occurred.

Furthermore, the thickness of the amorphous Si nitride layer was 200 in the above example, but by changing the deposition time, the thickness was increased to 5.
Even if the number of participants was 0.00, the same effect as in the above example was obtained as shown in FIG. 2(b). Furthermore, when the thickness of the amorphous Si nitride layer was set to 100 layers, which is thinner than the 200 layers in the above example, a sufficient multiplication effect could not be obtained as shown in FIG. 2(b).

(Example 2) A second embodiment of the invention is shown in FIG. 3(a).

This device was created by the following operations.

First, a transparent electrode 202 made of ITO/5nOa was formed using a vapor deposition apparatus on a 7059 glass substrate 20L manufactured by Corning, and etched so that the electrode had a predetermined shape.

Next, the substrate was placed on the anode electrode of a capacitively coupled deposited film forming apparatus, the inside of the deposition chamber was evacuated to about 10-' Torr, and the substrate was heated to about 300° C. with a heater. After the substrate reached a predetermined temperature, silane gas SiH<101005e diluted to io% with hydrogen gas and methane gas CI410eccm were introduced into the deposition chamber.The internal pressure of the deposition chamber became a predetermined pressure of about 0.3 Torr. After checking, high frequency power (13,56MHz) 0゜5W/
cm" was placed in the deposition chamber. Glow discharge was performed for a predetermined period of time to deposit 200 blocking layers and light-receiving layers 203 made of amorphous p-type Si carbide.

5 After that, silane gas 5iH diluted to 10% with 2 in hydrogen gas was added in the same manner as the blocking layer and light receiving layer 203.
From 4100 sec to 5000 sec, the amorphous Si layer 204 was diluted to 10% with silane gas SiH in hydrogen gas.
<100 sccm and ammonia gas NH.

The amorphous Si nitride layer 205 from 5 sec.
From 4100 sccm to 500 sccm, silane gas SiH diluted to 10% with 2 in hydrogen gas
< 100 sec and phosphine gas PHs 10
Five hundred microcrystalline n-type silicon layers 207 were sequentially deposited from eccm.

Finally, the A1 layer 208 is deposited as an electrode, and the A1 layer 208 is deposited as an electrode.
08, microcrystalline n-type Si layer 207, amorphous SL layer 206,
Amorphous nitrided SL layer 205, amorphous SL layer 204, and amorphous Si carbide layer 203 were each etched into predetermined shapes.

The band gap of each semiconductor layer was optically measured, and the amorphous p-plasticized t-layer had a band gap of 2. OeV, 2.4 eV for the amorphous Si nitride layer, 1.8 eV for the amorphous Si layer,
The microcrystalline 6 crystal n-type Si layer had a voltage of 1.9 eV.

The photoelectric conversion element of this example has a wavelength of 660 nm and a light intensity of 7.
When we irradiated it with light of 6 x 10-'W/cm" and measured the DC current-voltage characteristics, we obtained the characteristics shown in Figure 3 (b). That is, at an applied voltage of 30 V, the A multiplication factor of approximately 4 times was obtained at an applied voltage of 40 V.

Moreover, the ratio of signal current to dark current was obtained by more than two orders of magnitude.

Further, when the photoresponse speed was measured by blinking the light irradiated to the photoelectric conversion element of this example, a rise response speed of about 50 μsec was obtained as shown in FIG. 3(c).

Further, even when this was operated continuously for a long time at 80° C., no change in characteristics occurred.

[Effects of the Invention] As is clear from the above, the present invention has high sensitivity, good photoresponsiveness, excellent heat resistance, is easy to create, can be laminated on existing circuits, and has a large area. It is possible to obtain an amorphous semiconductor photoelectric conversion element that can also be converted into

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are schematic energy band diagrams of the photoelectric conversion element of the present invention. FIG. 2(a) is a schematic diagram of the device configuration of the first embodiment of the present invention, and FIG. 2(b) shows the thickness of the a-3iN layer of 0-50.
DC current voltage (
FIG. 2(c) is a characteristic diagram showing the photoresponsiveness when the light irradiated to the photoelectric conversion element is blinked. FIG. 3(a) is a schematic diagram of the element configuration of the second embodiment of the present invention, and FIG. 3(b) is a diagram showing the direct current voltage (
J-V) characteristic diagram, FIG. 3(c) is a characteristic diagram showing the photoresponsiveness when the light irradiated to the photoelectric conversion element was blinked. 1.103,203...Amorphous Si carbide layer 2.104
, 205...Amorphous nitride 31 layer 3.3', 1
05,204,206...Amorphous Si layer

Claims (2)

[Claims] (1) In a pin-type photoelectric conversion element in which the i-layer is made of amorphous Si, an amorphous Si nitride layer is provided between a p-type semiconductor layer and an n-type semiconductor layer, and this amorphous Si nitride layer When a reverse bias voltage is applied to the photoelectric conversion element having the above, an electric field is concentrated in the amorphous Si nitride layer and/or in the vicinity of the amorphous Si nitride layer to perform charge amplification. conversion element. (2) The thickness of the amorphous Si nitride layer is 200 Å or more,
2. The photoelectric conversion element according to claim 1, wherein the photoelectric conversion element has a thickness of 00 Å or less.