JPS5825283A - Photodetector - 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 This invention relates to a photodetecting device in which the active region is made of amorphous silicon.

Photovoltaic devices, including light sensing devices, are capable of converting light, particularly sunlight, into electrical energy. A problem in the field of photovoltaic devices is that the cost of producing electrical energy with these devices is generally too high to be competitive with other means of generating electrical energy.

One of the most expensive aspects of manufacturing a photovoltaic device is the semiconductor material of its active region. Typically, photovoltaic devices require a thick single crystal active layer of approximately 20 μm or more in order to absorb sufficient light. Naturally, as the amount of semiconductor material required increases, the cost of the photodetector also increases. Therefore, it is highly desired in the semiconductor field to obtain a material for the active region of a semiconductor device that exhibits photovoltaic properties and reduces the cost of a photodetector or photovoltaic device.

The semiconductor device used in the photodetection device of the invention has a semiconductor junction and an active region of amorphous silicon, for example produced by a glow discharge in silane.

A detailed explanation will be given below with reference to the drawings.

Before explaining the photodetector of the present invention, a Schottky barrier type photovoltaic device shown in FIG. 1 will be explained as a reference. The photovoltaic device 10 shown in FIG. 1 has a substrate 12 of a material that can make ohmic contact with amorphous silicon deposited by glow discharge and has good electrical conductivity. Typical materials for substrate 12 are metals such as aluminum, antimony, stainless steel, or heavily doped N-type single or polycrystalline silicon. An active region 1 of amorphous silicon is formed on the surface of a substrate 12.
4 is provided. By active region is meant the region in which electron-hole pairs are generated and captured as current in the photovoltaic device.

Amorphous materials are materials that do not have long-range order in their lattice periodicity. Amorphous silicon formed by glow discharge in silane (SiH4) has only short-range order of less than 20A. The amorphous silicon in the active region 14 is formed by glow discharge in silane and has a density of about 10-7
It has a carrier lifetime of more than seconds, the average localized state density in the width of the forbidden band is 10 or less, and to-3
It has an electron and hole mobility of more than cz'V·sec. Active region 14 is approximately 1' to 3 .mu.m thick or less.

A metal layer 16 is disposed on the surface of the active region 14 on the side opposite to the substrate 12 with a boundary 18 in between. metal layer 16
are made from highly conductive metallic materials such as oak, gold, platinum, palladium or chromium, which are translucent to sunlight. The metal layer 16 can be made of a single layer or a multilayer metal layer. If metal layer 16 is made of multiple metal layers, for example, the first layer over active region 14 is made of platinum to obtain a large Schottky barrier height, and the second layer above the first platinum layer is made of high conductivity. It can be made from gold or silver from dots.

Since this metal layer 16 is a metal such as gold, platinum, palladium, or chromium, it needs to be about 100 mm thick to be translucent to sunlight.

A grid electrode 24 is provided on the surface of the metal layer 16 opposite to the boundary.
is located. Typically, this grid electrode 24 is made of a highly conductive metal. For purposes of describing the present invention, the grid electrode has two sets of grid lines, each set of grid lines being substantially parallel to each other, and each set of grid lines intersecting another set of grid lines. For convenience of explanation, the grid lines are shown intersecting at right angles. shall be taken as a thing.

Since sunlight impinging on the grid electrode 24 may be reflected outward from the active region 14, the grid electrode 24
occupies only a small area on the surface of metal layer 16. The grid electrode 24 serves to uniformly capture current from the metal range 16. The grid electrode 24 also ensures that the series resistance of the device IO is low when operated as part of a circuit. However, it appears that only one set of grid lines is sufficient for uniform current capture.

An antireflection layer 20 is provided on and around the grid electrode 24 .
is formed on the surface of the metal layer 16 opposite the boundary 18 that is not occupied by the metal layer 16 . The antireflection layer 20 has an entrance surface 22 onto which sunlight rays 26 are incident. As is well known in the art, the amount of solar radiation 26 that passes through the metal layer 16 and impinges on the active region 14 is determined by where λ is the wavelength of the light incident on the entrance surface 22 and n is the appropriate value of the antireflection layer 20. The refractive index can be increased by forming the antireflection layer 20 to a thickness equal to λ/4n. In effect, antireflection layer 20 reduces the amount of light reflected from device 10. Antireflective layers are typically made of dielectric materials such as zinc sulfide.

It is well known in the field of semiconductor devices that surface barrier junctions, generally known as Schottky barriers, are formed by contacting certain metals with certain semiconductors. In the photovoltaic device shown in FIG. 1, a Schottky barrier is formed at boundary 18 by contacting metal layer 16 with active region 14 . The Schottky barrier extends from the boundary into the active region 14 and creates an electric field of space charges, called a depletion region, in the semiconductor material. In the photovoltaic device 10 of FIG. 1, it is desirable for the depletion layer region to extend across the width of the active region 14 between the boundary and the substrate 12. When the depletion layer region extends across the entire width of the active region 14,
Carriers generated in any part of the active region 14 by absorbing sunlight 26 are absorbed by the substrate 1 due to the electric field in the depletion layer region.
2 or the metal layer 16. Substrate 12 serves as one of the electrodes for active region M14. If the depletion region does not extend into a portion of the active region 14, carriers generated in the non-depletion region of the active region 14 will not be swept toward the electrode by the electric field. Carriers generated in the non-depletion region of active region I4 must diffuse toward either the electrode or the depletion region in order to be captured. Furthermore, the non-depleted region increases the series resistance when extracting current from the device, and this series resistance reduces the efficiency of the device.

The amorphous silicon of the active region 14 formed by glow discharge in silane has ideal characteristics as an active region of a photovoltaic device. The carrier lifetime in amorphous silicon formed by snow ivy or vapor deposition is 1O-11.
On the other hand, the carrier lifetime in amorphous silicon formed by glow discharge in silane is about 1O-7 seconds.
More than seconds. Since the mobility of electrons and holes in amorphous silicon due to glow discharge is 1O-3 (yl/v·sec or more), a large current trapping efficiency can be obtained.

The light absorption characteristic of amorphous silicon due to glow discharge is 400
It has better light absorption characteristics than single crystal silicon in the visible light range of 0 to 7,000 people. FIG. 2 shows that amorphous silicon has a larger absorption coefficient in the visible light region than single crystal silicon. This means that even if the active region 14 of amorphous silicon formed by glow discharge is reduced to one tenth of that of single bond j9' silicon O, the same level of light absorption can be obtained in the visible light region. Therefore, even if the active region 14 is made as thin as 1 μm or less, good device efficiency can be obtained.

Furthermore, the average localized state density within the forbidden band width of amorphous silicon due to glow discharge is approximately 10"/am3 or less. The average localized state density of amorphous silicon due to glow discharge is approximately 10"/am3 or less. Increasing the temperature and increasing the purity of the silane used to form amorphous silicon decreases the average localized state density of amorphous silicon produced by this glow discharge compared to that of amorphous silicon formed by other means. In other words, in amorphous silicon made by sputtering or vapor deposition, the average localized state density is 1o”/
art! -eV or more. What is important about the average local state density within the forbidden band width □ is that it is inversely proportional to the square of the depletion region width. Since the density of states of amorphous silicon due to glow discharge is relatively low, a depletion layer width of about 1 μm can be obtained. Furthermore, it is also important with respect to the average local density of states that the carrier lifetime is inversely proportional to the average density of states. From this point of view, it is necessary to reaffirm that the carrier life of amorphous silicon formed by glow discharge is longer than that of amorphous silicon formed by the other methods mentioned above.

FIG. 3 shows a glow discharge device 30 suitable for manufacturing the photovoltaic device 10 and the photodetector device of the present invention as described below. The glow discharge device 30 includes a vacuum chamber 3 delimited by a vacuum pelger 34, usually made of glass material.
I have an i. Inside the vacuum chamber 32 are an anode 36;
A heating plate 3 is placed facing away from this. The anode 36 is made of a highly conductive metal material such as platinum and is in the form of a screen or coil. The heating plate 38 is a ceramic frame surrounding a heating coil powered by a current source 40 outside the vacuum chamber 32.

A first outlet 44 of the vacuum chamber 32 is connected to a diffusion pump, a second outlet 46 is connected to a mechanical pump, and a third outlet is connected to a gas supply of a system that provides various gas sources used in the glow discharge process. . Although the second outlet was stated to be connected to a diffusion pump, it is believed that the diffusion pump is not necessary for pumping down the system.

To make the photovoltaic device 10, a substrate 12 made of, for example, aluminum is placed on a heating plate 38 and connected to a power source 42.
Connect to the negative terminal of Anode 36 connects to the positive terminal of power supply 42 . The power source 42 may be either direct current or alternating current.

Operating power supply 42 in this manner creates a potential difference between anode 36 and substrate 120, which in direct current operation essentially acts as a cathode.

The vacuum chamber 32 is heated to about 0.5 to 1. The substrate 12 is heated to a temperature in the D- range of 150° C. to 400° C. by evacuation to a vacuum level of Ox 10′ Torr and powering the heating coil of the heating plate 38.

Next, put Shiran (SyuH4) in the photo space 32 at 0.1-30
Supply up to Torr pressure. As a result, the substrate temperature is 200
℃ to 500℃. Substrate 12 and active region 1
To ensure ohmic contact between 4 and 4, the active area 14 is 35
It must be deposited on the substrate 12 at a temperature above 0.degree. C. to form a eutectic alloy between the aluminum substrate 12 and the amorphous silicon active region 14.

Power supply 42 is energized to generate a glow discharge between anode 36 and substrate 12 and deposit active region 14 of amorphous silicon on the surface of substrate 12 . In order to deposit the active region 14, the potential difference between the anode 36 and the substrate 12 must be such that the current density on the surface of the substrate 12 is in the range of 0.3 to 3.0 mA/V. 'The deposition rate of amorphous silicon increases with silane vapor pressure and current density. When the above conditions are set, 1 μm of amorphous silicon is deposited in less than 5 minutes.

Once the glow discharge occurs, electrons are emitted from the substrate 12, which bombard the silane molecules (SiH4) causing ionization and dissociation of the molecules. Silicone* > 7!
: Since silicon hydride such as SIH+ is positively charged, it is attracted to the substrate 12, which is the cathode, and silicon is thereby deposited on the substrate 12. The board temperature is 35
After the deposition of the amorphous silicon, the wafer consisting of the substrate 12 and the active region 14 is placed in a well-known vapor deposition apparatus, and the active region 1
4, a metal region 16 is deposited on top of the metal region 16. Similarly, a grid electrode 24 and an antireflection layer 20 are deposited over metal region 16 by well known vapor deposition and masking techniques. This entire process can be performed in a single system capable of both glow discharge and deposition.

Fabrication of the photovoltaic device IO is completed by connecting electrode wires (not shown) to the substrate 12 and grid electrode 24 for connection to external circuitry.

FIG. 4 shows a photodetecting device 1 according to a first embodiment of the present invention.
10 is shown. The photodetector 110 is an active region 11 of amorphous silicon formed by glow discharge in silane, for example.
I have 4. an active region 114Fi, a first doped layer l13, a second doped layer 115 opposite to the first doped layer 113 at a certain distance;
and the second doped layer 113, 115 and in contact with each other. Intrinsic layer 11
'7 is not doped.

The first and second doped layers 113, 115 are of opposite conductivity type. For convenience of explanation, it is assumed that the 20th doped layer 115 is of N-type conductivity, and that the first doped layer 113 is of P-type conductivity.

The first and second doped layers 113 and 115 are doped with electrically active impurities to a high concentration of 10'19/, , s or more. Usually, the N-type second doped layer 115 contains phosphorus,
The P-type first dog layer 113 is doped with boron.

A sunlight-transmitting electrode 128 is provided on the surface of the first doped layer 113 opposite to the second doped layer 115 . Transparent electrode 128 has an incident surface 129 on the opposite side from first doped layer 113 . Transmissive electrode 128 may be transparent or translucent to sunlight and can capture the electrical current generated in active region 114. Sunlight rays 126 enter this device 110 at an entrance surface 129 . The solar transparent electrode 128 can be made of a single layer of a material such as indium tin oxide or tin oxide, both of which are transparent to solar radiation and have high electrical conductivity. Transmissive electrode 12
8 can also be made of a thin film of metal about 100 mm thick, such as gold, antimony, or platinum, which is translucent to sunlight. When the transparent electrode 128 is made of a metal thin film, the first
It is desirable to form the antireflection layer described in the embodiment above on the incident surface 129 of the electrode 12[3 to reduce reflection of sunlight #126. Furthermore, the electrode 128 can also have a multilayer structure in which a commercially available indium tin oxide layer is stacked on a glass material layer. In that case, the indium tin oxide is in close contact with the first doped region 113.

The surface resistance of the electrode 12B on the first doped layer 113 is about 1
OQ/l] or more, the active area 1
In order to capture the current generated in photovoltaic device 14, it is desirable to form a grid-type contact on first doped layer 113 similar to photovoltaic device 10 of FIG. 1 described above.

An electrode 127 is arranged on the surface of the second doped layer 115 opposite to the transparent electrode 128. Electrode 127 is made of a material with suitable conductivity, such as aluminum, chromium, or antimony.

As described for the Schottky barrier type photovoltaic device shown in FIG. 1, the absorption coefficient of amorphous silicon due to glow discharge is larger than that of single crystal silicon in the visible light region. Therefore, a thin amorphous silicon layer may be sufficient even when sufficient sunlight is absorbed. Typically, the thickness of the amorphous silicon intrinsic region is about 1-3 μm or less, while the thickness of the first and second doped layers 113, 115 are each several hundred nanometers.

As is well known to those skilled in the art of PIN photovoltaic devices, by matching the Fermi levels of layers 113, 115 and ll'i', a negative space charge is created in the first doped layer 113. , a positive space charge is generated in the second doped layer 115 and a depletion layer region is formed in the intrinsic layer 11'/. The depth to which the electric field in the depletion region extends into the intrinsic layer 117 is a function of the average localized state density within the width of the forbidden band, as described with respect to the apparatus of FIG. Furthermore, from the explanation regarding the photovoltaic device IO, the depletion layer region is the intrinsic layer 11.
It can be seen that it extends over the entire width of the film, ie, a thickness of about 1-3 μm or less. Therefore, carriers generated in the intrinsic layer 11'7 by absorbing sunlight are swept away by the electric field in the depletion layer region and captured as a current.

In fabricating the photodetector 110, it is assumed that the transparent electrode 12B is a layer of commercially available indium tin oxide formed on a layer of glass material. Electrode 12B is placed on the hot plate of apparatus 30 shown in FIG. The glass layer of the electrode 12B is in close contact with the heating plate 3.

Device 30 is then prepared for depositing a first doped layer 113 of P type on the indium tin oxide layer of electrode 128 .

The vacuum chamber 32 was evacuated to a degree of vacuum of about 1 O-6 Torr, and then silane containing KO95~5% diborane (B2H6) was added.
That is, diborane is 0.5 to 0.5 of the silane-diborane mixture.
5%) is fed into the vacuum chamber 32 to a pressure of 0.1 to 1.0 Torr. Meanwhile, the electrode 128 is 200
Raise the temperature to between 500°C and 500°C.

A glow discharge is carried out on the electrode 12B in the vacuum chamber 32 for about 1-2 seconds with a current density of about 0.5 mA/cn to deposit the first doped layer 113 several hundred thick.

Next, the vacuum chamber 32 is once evacuated using the mechanical pump 46.

Once the vacuum in the vacuum chamber returns to 1 O-6)-oles, silane is fed into the vacuum chamber 32 to a pressure of O11-3 Torr.

Here again o, 3 mAA! on the first doped layer 113! I
A glow discharge is carried out for 1 to 5 minutes with a current density of I~3.0 mA/c++l to deposit an intrinsic layer 11 with a thickness of approximately 1 .mu.m.

Next, approximately 0.1, t, O% of phosphine (RH3) is supplied into the vacuum chamber 32 as a doping gas. As a result, the phosphine is 04-
t, constitutes O%. 0.3m4/ on the intrinsic layer 117
A glow discharge is performed with a current density of cd4, OmA/cIIN, and a twentieth N-type doped layer 115 with a thickness of several hundred layers is deposited on the surface of the intrinsic layer 117.

Although phosphine and diborane are mentioned as doping gases for the first and second doped layers 113, 115, other suitable doping gases known in the art may be used.

Electrode 127 is then deposited on the surface of second doped layer 115 using well known vapor deposition methods. The final step in manufacturing the photodetector 110 is to connect the electrode 127 to an external circuit.
and connecting wiring (not shown) to the electrode 128.

FIG. 5 shows a photodetecting device 21o according to a second embodiment of the present invention. Photosensing device 210 has an amorphous silicon substrate 211 formed by glow discharge in silane mixed with a suitable doping gas. The base body 211 is l
A first doped layer 252 of conductivity type, and a P-N layer in this layer.
A second doped layer 2 of opposite conductivity type that contacts via a junction 256
I have 54. For convenience of explanation, the first doped layer 25
2 is of P type, and the second doped layer 254 is of −N type. Both the first and second doped layers 252, 254 are the active region 214 of the photodetector 210. The substrate 211 has a thirtieth doped layer 258 on the surface opposite the P-N junction 256 of the second doped layer 254 . The third doped layer 258 is of the same conductivity type as the second doped layer 254 but has a higher doping concentration than the second doped layer 254. Therefore, the third doped region 258 is N
+ type. Thirtieth doped layer 258 serves to make an ohmic contact to active region 214.

On the surface of the third doped layer 258 opposite the P-N junction 256, an electrode 227 identical to the electrode 12 of the first embodiment is provided.
is formed. A solar radiation transparent electrode 228 having a solar radiation incident surface 229 is connected to the P-N of the first doped layer 252.
It is located on the surface opposite junction 256. Sunlight 256 enters device 210 at entrance surface 229 . The sunlight-transmitting electrode 228 is the same as the sunlight-transmitting electrode 12B in the second embodiment.

To explain the operation of the light detection device 21○, the sunlight rays 226
is incident on the entrance surface 229 of the device 210, and the sunlight 2
26 is absorbed in active region 214, generating electron-hole pairs. These carriers diffuse toward the P-N junction 256 and reach the space charge electric field of the P-N junction 256 before recombining, where they are trapped and become the current in the device 210.

The method of manufacturing the device 210 will be described. First, as in the case of the device 110, it is assumed that the transparent electrode 228 has an indium tin oxide layer provided on a glass material layer. The electrode 228 is placed on the heating plate 38 of the apparatus 30 such that the glass material layer is in intimate contact with the heating plate 38.

The apparatus is then prepared for depositing a first doped layer 252 over the indium tin oxide layer of the transparent electrode 228.

Vacuum chamber 32 is evacuated to a vacuum of about 10')-liters and then a total of silane containing about 1-5% diborane is fed into vacuum chamber 32 to a pressure of 0.1-1.0 Torr. Between the electrodes 22
8 raises the temperature to 200°C to 500°C.

A glow discharge is performed in the vacuum chamber 32 for about 1-2 seconds with a current density of about 0.5 mA/ctd on the surface of the electrode 228, and the first doped layer 252 is several hundred thick.
to be coated with.

Next, the vacuum chamber 32 is evacuated with a mechanical pump 46,
When the vacuum level is about 10'), the vacuum level is about 0. Silane containing O1% nophosphine is fed into vacuum vessel 32 to 0.1-3 torr (7) IE power. First doped layer 2520
o on the surface, smx/c++f~3. Glow discharge is performed for about 1 to 30 minutes at a current density of OmA/mA, and
A doped layer 254 is deposited to a thickness in the range of 1 to 20 μm.

Phosphine is then fed into the vacuum chamber 32 so that it is in a mixture with 0.5% silane. Here, again on the second doped layer 2Ei, o, sm*/cd~3
, Om A/c/, and a glow discharge is carried out with a current density of Om A/c/ to deposit the third doped layer 258 to a thickness of several hundred layers.

Electrode 227 is then formed on third doped layer 258 by well-known vapor deposition methods. The device 210 is manufactured using electrode 2.
Wiring (not shown) is connected to the transparent electrode 27 and the transparent electrode 228 to complete the process.

In the photodetecting devices of the first and second embodiments of the invention, the electrodes 12'7.227 reflect unabsorbed solar radiation back into the respective active regions 14.114.214, thereby reducing the absorption of the radiation. Efficiency can be improved.

In the embodiment of the present invention, the light transmitting electrodes 12B, 228
It should be noted that the is the support for each device.

The two embodiments of the present invention have been mainly described as photovoltaic devices that receive sunlight and convert it into electrical energy, but the photodetector of the present invention is a photodetector with high frequency response; That is, it is clear that it can be used as a device that responds to radiant energy. It has been found that when the active region is amorphous silicon formed by glow discharge in silane, the photodetector has a high frequency response of 10 MHz or higher.

The photodetecting device 110 of the first embodiment of the present invention is a PIN structure, and its spectral response can be matched to human visibility. Adjusting the spectral response of the photodetector 110 to the luminous sensitivity is achieved by adjusting the thickness and doping impurity concentration of either the P-type doped layer 113 or the second doped layer 115, and the thickness of the intrinsic layer 11F. This is done by changing. As an example, the spectral response of device 110 has a P-type head area of 5 atomic percent.
It is made to have a boron acceptor impurity concentration of about 500 μm, while an intrinsic layer thickness of about 0.3 μm approaches human visual sensitivity.

By using glow discharge amorphous silicon in the active region of a photodetector, it is possible to create a device with a thinner active region than a device using single-crystal silicon with the same basic structure. Furthermore, devices using amorphous silicon with glow discharge can absorb light to the same extent as single-crystal silicon photodetectors with active regions ten times thicker.

Therefore, a particular advantage of the present invention as a photovoltaic or light sensing device is that the use of thin active regions allows for reduced manufacturing costs. Furthermore, since the present invention as a photodetecting device can be manufactured at a lower temperature than a device using a single crystal, less energy is required to manufacture the device of the present invention, and it is also suitable for photovoltaic devices such as single crystal solar cells. In comparison, it is possible to manufacture a photovoltaic device with a large area, which reduces the cost of the device.

For example, it has been found that a semiconductor device with an active region of amorphous silicon generated by glow discharge in silane has a rectifying effect in the dark state. As an example, the Schottky barrier type semiconductor device 1o of FIG. 1, which has an N-type single crystal silicon substrate 12, a gold metal region 16, and has removed the grating electrode 24 and the antireflection layer 20, is in a reverse bias state of 10.4V. In contrast, in a forward bias state of +0.4V, the current rectification characteristic was such that a current 104 times larger was allowed to flow. Although embodiments of the invention have been described in terms of photodetector or photovoltaic devices, they can also be operated as current rectifiers.

However, in that case, as is well known to engineers in this field,
Some modifications, such as removing the grid electrode and anti-reflection layer, make it highly desirable as a rectifier. The photodetector of the present invention has a potential barrier formed by a PN junction or a PIN junction.

When the photodetector of the present invention has amorphous silicon formed by glow discharge in silane as the active region, it works well as a photodetector or the current rectifier described above.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a Schottky barrier type photovoltaic device shown as a reference for explaining the photodetecting device according to the present invention. FIG. 2 shows a comparison of the absorption coefficient of amorphous silicon due to glow discharge with respect to single crystal silicon in the visible light region. FIG. 3 is a simplified illustration of an apparatus for forming amorphous silicon by glow discharge in silane. FIG. 4 is a sectional view of a first embodiment of a photodetecting device according to the present invention. FIG. 5 is a sectional view of a second embodiment of a photodetecting device according to the invention. 110.210...Semiconductor device, 114.214-...
Active region of amorphous silicon, 12F, 22F・Electrode, 128.228...Light transmission electrode, 113.115・
...Doped layer, l17... Intrinsic layer. Patent Applicant: RCSNY Corporate Information: Satoshi Shimizu and 2 others Answers 1
Tubo 2 1-1-1

Claims (1)

[Claims] Carrier life of Hto7 seconds or more, 10! '/am3 or less, the average localized state density within the forbidden band width, and 1O-3
The active body of amorphous silicon has an electron and hole mobility of d/v·sec or more, and the active body of amorphous silicon has a semiconductor contact therein. B. A photosensing device having electrical contacts to regions of the active body on either side of the semiconductor junctions.