JP2743779B2 - Photodiode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodiode, and more particularly to a photovoltaic photodiode.

[0002]

2. Description of the Related Art A first example of a conventional photodiode is as follows.
As shown in FIG. 5, a p-type amorphous silicon (hereinafter abbreviated as a-Si) film 41 and an a-Si film 40 serving as a photoelectric conversion semiconductor film are formed on an insulating substrate (not shown) such as a glass substrate. , An n-type a-Si film 42 are sequentially deposited and laminated, and then patterned to form a p-type a-Si film 41 serving as an electrode for preventing injection of electrons into the a-Si film 40;
N-type aS serving as an electrode for preventing injection of holes into the film 40
A photovoltaic photodiode having a structure in which the a-Si film 40 for photoelectric conversion is sandwiched between the i film 42 and the i film 42 from both sides.

In this photodiode, a p-type a-
When a voltage is applied between the n-type a-Si film 42 and the n-type a-Si film 42 so that the charge is injected between the two electrodes, electrons and holes that can move freely are prevented. A non-existent depletion layer is formed in the a-Si film 40. When a sufficient voltage is applied, the entire region of the a-Si film 40 is depleted. When the light 43 enters the a-Si film 40, an electric field exists in the depletion layer, so that the electrons and holes generated by the light 43 are respectively converted into the n-type a-Si film 4.
2. It can move toward the p-type a-Si film 41.
When such charge transfer occurs in the a-Si film 40, an optical signal is generated in an external electronic circuit connected to the p-type a-Si film 41 or the n-type a-Si film 42.
In a photovoltaic photodiode, an optical signal higher than the charge generated by light cannot be obtained, that is, the quantum efficiency does not exceed 1.

As shown in FIG. 6, a second example of a conventional photodiode is formed on each of two opposing sides of an a-Si layer 10 formed on an insulating substrate (not shown) and patterned in a rectangular shape. The n-type a-Si layers 12a and 12b for preventing injection of holes into the a-Si layer 10 are formed to constitute a photoconductive photodiode.

Here, when a voltage is applied between the n-type a-Si layers 12a and 12b, when light 43 is not incident, a-S
Since the depletion layer spreads in the i-film 10 and becomes a high resistance state,
The current flowing through the diode is small. When the light 43 is incident, the conductivity of the a-Si film 10 increases, the injection of electrons from the n-type a-Si layer connected to the minus side is promoted, and a large current flows through the diode. As described above, the quantum efficiency of the photoconductive photodiode can take a value of about 10 to 100.

[0006] As a third example of a conventional photodiode, Japanese Journal of Applied Physics is available.
Applied Physics, January 1993,
There is an electron multiplying photodiode described in Vol. 32, pp. L39-L41, and as shown in FIG.
Intrinsic aS having an amorphous SiC layer 31 formed on the lower surface
A p-type a-Si layer 33 and an intrinsic a-Si layer 3 on the i-layer 32
It has a multilayer structure in which a 4, n-type a-Si layer 35, a silicon nitride film 36, and an aluminum electrode 37 are sequentially laminated.
It has an electric field intensity distribution as shown by a curve 38 in FIG.

This electric field intensity distribution is equivalent to that of a reach-through type electron multiplying photodiode formed of ordinary crystalline Si, and electrons generated by light absorbed by the intrinsic a-Si layer 32 are converted to intrinsic a-Si. Upon reaching the layer 34, the high electric field present therein causes an avalanche of electrons. Therefore, the quantum efficiency of the electron multiplying photodiode exceeds 1.

[0008]

The above-described conventional photodiode has a problem that a plurality of film forming steps are required to realize the multilayer structure of the first example, and the manufacturing process becomes complicated. The photoconductive photodiode of the second example has a problem that the followability to the time change of the light intensity is inferior to that of the photovoltaic photodiode.

Further, in order to realize an electron multiplying photodiode using an a-Si-based material, there is a problem that a multilayer structure of a plurality of materials is required, and a complicated and sophisticated manufacturing process is required.

An object of the present invention is to provide a high-performance photodiode with a simple configuration.

[0011]

According to a first aspect of the present invention, a first photodiode is formed by forming a rectangular semiconductor film for photoelectric conversion on an insulating substrate and forming one of two opposing sides of the semiconductor film. A minus-side electrode for preventing injection of electrons into the semiconductor film; a plus-side electrode formed on the other of the two opposite sides to prevent injection of holes into the semiconductor film; A region holding fixed space charge formed in parallel with the minus side electrode and the plus side electrode in the semiconductor film intermediate with the electrode.

According to a second photodiode of the present invention, a rectangular semiconductor film for photoelectric conversion is formed on an insulating substrate, and electrons are transferred to the semiconductor film by forming the semiconductor film on two opposing sides of the semiconductor film. A negative electrode for preventing injection (or a positive electrode for preventing injection of holes into the semiconductor film)
And an island-shaped plus-side electrode (or minus-side electrode) disposed in parallel with the minus-side electrode (or plus-side electrode) on the semiconductor film between two opposed minus-side electrodes (or plus-side electrodes). And

[0013]

Next, the present invention will be described with reference to the drawings.

FIGS. 1A and 1B are a perspective view showing a first embodiment of the present invention and a diagram showing an electric field intensity distribution in a diode.

As shown in FIG. 1A, an a-Si layer 10 is deposited on an insulating substrate (not shown) such as a glass substrate by a CVD method and patterned to form a rectangular semiconductor film for photoelectric conversion. To form Next, boron is selectively introduced into one of the opposing sides of the a-Si layer 10 by a photolithography technique and an ion implantation method to form a p-type a electrode serving as an electrode for preventing injection of electrons into the a-Si layer 10. -Si layer 11 is formed, and phosphorus is selectively introduced into the other opposite side to form a-S
n-type a- serving as an electrode for preventing injection of holes into i-layer 10
An Si layer 12 is formed. Further, the p-type a-Si layer 11 and the n-type a-S
A low-concentration p-type a-Si layer 13 is formed in a strip shape in parallel with the i-layer 12 to form a lateral photodiode.

Generally, when a fixed amount of fixed space charge exists in a photoelectric conversion film, an external voltage proportional to the square of the length of the photoelectric conversion film is applied to deplete the entire region of the photoelectric conversion film. There is a need to.

As shown in FIG. 1B, a p-type a-
When the Si layer 13 is not formed, the electric field strength in the photodiode becomes maximum at the interface A between the p-type a-Si layer 11 and the a-Si layer 10 as shown by a curve 21, and the n-type a-
It decreases linearly as it approaches the Si layer 12. This inclination is proportional to the fixed space charge density in the a-Si layer 10.
For example, when a DC voltage is applied, about 1 × 10
^Since a fixed fixed space charge of ¹⁵ cm ^-3 exists, it is necessary to apply a voltage of at least 75 V to deplete a diode having a distance between electrodes of 10 μm. Therefore, it is difficult to deplete a long lateral photovoltaic photodiode at a low voltage.

Therefore, as in this embodiment, the p-type a-S
When the i-layer 13 is formed, since a negative fixed space charge exists in the p-type a-Si layer 13, the realized electric field distribution is as shown in a curve 22 in the p-type a-Si layer 13. Is inverted, and the applied voltage value is obtained by integrating these electric field intensity distributions. Since the areas enclosed by the curves 21 and 22 and the x axis are equal, it can be seen that the same voltage is applied. That is, the low electric field region near the n-type a-Si layer 12 of this embodiment is small.

FIGS. 2A and 2B are a perspective view showing a second embodiment of the present invention and a view showing an electric field intensity distribution in a diode.

As shown in FIG. 2A, p-type a-Si layers 11a and 11b are provided on both sides of a rectangular a-Si layer 10 formed in the same process as in the first embodiment. The island-shaped n-type a-Si layer 14 is formed on the intermediate a-Si layer 10 by being arranged in parallel with the p-type a-Si layers 11a and 11b.

Here, the n-type a-Si layer 1 formed in an island shape
4 are p-type a-Si formed in a belt shape.
The layer 11 is reached. Since the two electrodes have different areas, the density of the lines of electric force, that is, the electric field becomes strong near the island-shaped electrode having a small area. This is the effect of the geometric electric field control. In practice, the electric field near the p-type a-Si layer 11 is strengthened by the effect of the fixed space charge in the a-Si layer 10 described above. In the configuration of FIG. 2A, the effect of the geometric electric field control and the effect of the fixed space charge in the a-Si layer 10 cancel each other. The realized electric field intensity distribution is represented by a curve 23 in FIG.
As shown in FIG. 5, it can be seen that the electric field intensity increases near the island-shaped n-type a-Si layer 14 and the attenuation of the electric field due to fixed space charges in the a-Si layer 10 can be reversed.

FIGS. 3A and 3B are a perspective view showing a third embodiment of the present invention and a diagram showing an electric field intensity distribution in a diode.

As shown in FIG. 3A, a p-type a-Si layer 11 is formed on one opposite side of a rectangular a-Si layer 10 formed in the same process as in the first embodiment. An n-type a-Si layer 12 is formed on the other opposite side, and a strip-shaped low-concentration n is formed in the a-Si layer 10 near the p-type a-Si layer 11 in parallel with the p-type a-Si layer 11. Since the type a-Si layer 15 is formed, as shown in FIG. 3B, the electric field intensity distribution in the diode is such that a high electric field is obtained near the p-type a-Si layer 11 as shown by a curve 24. Can be.

FIGS. 4A and 4B are a perspective view showing a fourth embodiment of the present invention and a view showing an electric field intensity distribution in a diode.

As shown in FIG. 4A, strip-shaped n-type a-Si layers 12a, 12a are formed on two opposing sides of a rectangular a-Si layer 10 formed in the same process as in the first embodiment. 12b are formed, and an island-shaped p-type a-Si layer 16 is formed in the intermediate a-Si layer 10 by being arranged in parallel with the n-type a-Si layers 12a and 12b.

As shown by the curve 25 in FIG. 4B, the electric field strength distribution in the diode is such that the effect of the fixed space charge on the electric field and the geometrical effect reinforce each other, and the island-shaped p-type a-
A high electric field is obtained near the Si layer 15.

[0027]

As described above, according to the present invention, the influence of fixed space charge in the semiconductor film can be offset by the low-concentration p-type a-Si layer formed in the semiconductor film for photoelectric conversion in a strip shape. In addition, the electric field can be geometrically enhanced by the p-type a-Si layer formed in the shape of an island, the effect of fixed space charge in the semiconductor film can be offset, and the depletion layer can be formed at low voltage. Has the effect of becoming

A structure in which the effect of the fixed space charge in the semiconductor film is enhanced by the effect of the fixed space charge in the low-concentration n-type a-Si layer similarly formed in a belt shape and the geometric effect by the island-shaped electrode. Has an effect that an electron multiplying photodiode having a simple structure can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention and a diagram showing an electric field intensity distribution in a diode.

FIG. 2 is a perspective view showing a second embodiment of the present invention and a diagram showing an electric field intensity distribution in a diode.

FIG. 3 is a perspective view showing a third embodiment of the present invention and a diagram showing an electric field intensity distribution in a diode.

FIG. 4 is a perspective view showing a fourth embodiment of the present invention and a view showing an electric field intensity distribution in a diode.

FIG. 5 is a perspective view showing a first example of a conventional photodiode.

FIG. 6 is a perspective view showing a second example of a conventional photodiode.

FIG. 7 is a perspective view showing a third example of a conventional photodiode and a diagram showing an electric field intensity distribution in the diode.

[Explanation of symbols]

10,40 a-Si film 11,11a, 11b, 13,15,16,33,41
p-type a-Si layer 12, 12a, 12b, 14, 35, 42 n-type a-Si layer
Si layer 31 Amorphous SiC layer 32, 34 Intrinsic a-Si layer 36 Silicon nitride film 37 Aluminum electrode 43 Light

Claims (2)

(57) [Claims] A semiconductor film for photoelectric conversion formed in a rectangular shape on an insulating substrate; a negative electrode formed on one of two opposing sides of the semiconductor film to prevent injection of electrons into the semiconductor film; , formed on the other two sides the opposed and a positive electrode that blocks injection of holes into the semiconductor film,
The same plane as the minus side electrode and the plus side electrode is provided on the semiconductor film between the minus side electrode and the plus side electrode.
And a region for holding the fixing space charges formed in the upper, La
Photodiode characterized by being of the teleral type . 2. A semiconductor film for photoelectric conversion formed in a rectangular shape on an insulating substrate, and a negative electrode (2) formed on each of two opposite sides of the semiconductor film to prevent injection of electrons into the semiconductor film. Alternatively, the minus-side electrode (or plus-side electrode) may be provided on the semiconductor film between the two opposed minus-side electrodes (or plus-side electrodes) that prevent injection of holes into the semiconductor film. A) a lateral-type photodiode having an island-like positive electrode (or negative electrode) disposed on the same plane as in (1).