JPH09213987A - Field-effect type photoelectric energy converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase an electric field in a semiconductor in the vicinity of a ferroelectric, and to inhibit the recombination of an electron-hole pair generated by light by forming a comb-shaped electrode and a ferroelectric layer on a hydrogenated amorphous silicon layer. SOLUTION: A lower electrode 32 is formed onto a substrate 31, a p-type hydrogenated amorphous silicon layer 33, an i-type hydrogenated amorphous silicon layer 34 and an n-type hydrogenated amorphous silicon layer 35 are growm successively on the lower electrode 32. The hydrogenated amorphous silicon layers may also have n-i-p structure, and the hydrogenated amorphous silicon layers excepting the uppermost layer 35 may also have only i-p structure and i-n structure. Comb-shaped electrodes 36 are formed onto the n-type hydrogenated amorphous layers 35, and a ferroelectric layer 37 is grown on the electrodes 36. A transparent conductive film 38 as an upper electrode is formed onto a surface. According to such constitition, an electric field is induced to the hydrogenated amorphous silicon layer by the spontaneous polarization effect of the ferroelectric layer. Consequently, the recombination of electrons and holes is inhibited by the increase of the electric field induced by the spontaneous polarization effect of a ferroelectric.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric energy conversion device for converting light energy into electric energy, and more particularly to a solar cell and a semiconductor photosensor.

[0002]

2. Description of the Related Art There are two types of semiconductor elements that convert light energy into electric energy, one that uses an amorphous material such as hydrogenated amorphous silicon and one that uses a crystalline material such as silicon or gallium arsenide. is there. As shown in FIG. 9, a solar cell and an optical sensor using hydrogenated amorphous silicon have an upper transparent electrode 2 formed on a substrate 1 and a p-type hydrogenated amorphous silicon formed on the upper transparent electrode 2. 3, i-type (without adding impurities) hydrogenated amorphous silicon 4, and n-type hydrogenated amorphous silicon 5
Are continuously formed, and the lower electrode 6 is further formed. Therefore, the electric field generated by the pin junction of the p-type hydrogenated amorphous silicon 3, the i-type hydrogenated amorphous silicon 4, and the n-type hydrogenated amorphous silicon 5 is used to separate electron-hole pairs. I was trying to do it. However, hydrogenated amorphous silicon has a problem that valence electrons cannot be efficiently controlled due to a large number of crystal defects and a large electric field cannot be obtained.

If a sufficient electric field is not obtained, electron-hole pairs generated by light energy are recombined by the time they reach the electrode and converted into thermal energy, so that they cannot be taken out as electrical energy. Further, the deterioration of the characteristics with the recombination (Stebler-Ronski effect) is also a big problem. On the other hand, in the case of a solar cell and an optical sensor using a crystalline semiconductor, the conventional typical element is shown in FIG.
It has a structure as shown in. That is, the electrode 11 is formed below the p (or n) type silicon substrate 12, the n (or p) type diffusion layer 13 is formed above it, and the upper electrode is formed on the n (or p) type diffusion layer 13. Electrode 1 as
4 are arranged. Therefore, p-type semiconductor and n
An electric field is formed at the junction interface by joining the type semiconductors, and the electron-hole pairs generated by the light energy are separated by this electric field and taken out as electric energy.

However, in order to form a pn junction, it is necessary to diffuse a large amount of impurities (in this figure, donors) from the surface, which shortens the minority carrier lifetime and reduces the energy conversion efficiency due to recombination. there were. In order to solve this problem, P. Van Ha
Len et al. developed an element that does not require an impurity diffusion layer.
[P. Van Halen et al. , IEEE
transactions on Electron D
devices, ED-25, 507 (1978). ].

A cross section of this device is shown in FIG. That is, a p-type silicon substrate 22 is formed on the lower electrode 21, and an ultrathin (20 to 30 Å) oxide (SiO ₂ ) layer (not shown) is formed on the surface of the p-type silicon substrate 22. A metal grid (comb-shaped electrode) is formed, and the n-type inversion layer 23 is formed at the Si interface in contact with SiO ₂ . A silicon oxide film (SiO ₂ film) or titanium oxide (Ti
The O ₂ ) film 25 may be formed. In this device,
Instead of diffusing impurities to form a junction, the Schottky effect based on the difference between the work function of the metal and the Fermi energy level of p-Si causes the semiconductor surface to be inverted to the opposite conductivity type to form an electric field.

However, this element structure is also not in practical use because it is difficult to form an electric field sufficient to invert the semiconductor surface. The same effect can be achieved by an MIS structure in which a metal having a work function different from that of silicon is entirely grown on the surface of the insulating film, but the amount of incident light is reduced by reflection and absorption by the metal. This method is less preferred.

[0007]

As described above, the conventional solar cell (optical sensor) is not technically satisfactory. The present invention, in view of the above situation,
Due to the spontaneous polarization effect of the ferroelectric substance, the electric field in the semiconductor near the ferroelectric substance is increased, and the recombination of electron-hole pairs generated by light is suppressed, and as a result, the conversion efficiency of light energy into electric energy is increased. It is an object of the present invention to provide a field effect photoelectric energy conversion device capable of improving the above.

[0008]

In order to achieve the above object, the present invention provides (A) a photoelectric energy conversion device for converting light energy into electric energy, which is formed on the lower electrode.
-I-n or n-ip junction, or p-i or n-
a hydrogenated amorphous silicon layer having an i-junction, a comb-shaped electrode and a ferroelectric layer formed on the hydrogenated amorphous silicon layer,
An upper electrode is provided, and an electric field is induced in the hydrogenated amorphous silicon layer by the spontaneous polarization effect of the ferroelectric layer.

(B) In a photoelectric energy conversion device for converting light energy into electric energy, a p (or n) type silicon substrate formed on a lower electrode and a p (or n) type silicon substrate are formed. An n (or p) type inversion layer, a comb-shaped electrode and a ferroelectric layer formed on the n (or p) type inversion layer, and an upper electrode, the spontaneous polarization effect of the ferroelectric layer. Is to induce an electric field in the semiconductor layer having the pn junction.

(C) In the field effect photoelectric energy conversion device according to (1) or (2), an insulator such as silicon oxide, silicon nitride or cerium oxide is inserted between the ferroelectric layer and the lower layer. It was done like this. (D) In the field effect photoelectric energy conversion device according to (1) or (2) above, the output signal is transferred to a CCD (C
The transfer is performed by the charge coupled device).

With the above structure, when used as a solar cell, the conversion efficiency is improved, so that more output can be obtained from the cells having the same area. Further, when used as an optical sensor, the conversion efficiency is improved, so that the sensitivity of light detection is improved, and the area of the device can be reduced by the improvement of the sensitivity, and the integration degree can be improved.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a field effect solar cell using hydrogenated amorphous silicon showing a first embodiment of the present invention, and FIG. 1 (a) is a diagram showing the case of its pin junction. FIG. 1 (b) is a diagram showing a case where a metal is used for the substrate in the p-i or n-i junction.

As shown in this figure, a lower electrode 32 is formed on a substrate 31 such as glass or plastic, and a p-type hydrogenated amorphous silicon layer 33 and an i-type hydrogenated amorphous silicon layer are formed on the lower electrode 32. 34 and the n-type hydrogenated amorphous silicon layer 35 are sequentially subjected to plasma CV.
Grow by method D. If the substrate 31 is glass,
If the lower electrode 32 is also transparent, light may naturally be introduced from the lower surface. When a metal is used as the substrate 31, it can be shared with the lower electrode 32.

As shown in FIG. 1A, the hydrogenated amorphous silicon layer is provided with an nip structure.
It may have an in structure. In addition, as shown in FIG.
A sufficient electric field can be obtained by the field effect even if the uppermost layer 35 is omitted and only the ip structure or the in structure is used. Next, a comb-shaped electrode 36 is formed on the n-type hydrogenated amorphous silicon layer 35, and a ferroelectric layer 37 is grown on this. Ferroelectric materials include barium titanate (BaTiO ₃ ) and PZT (PbZrx).
Many materials such as T _{1 1-X} O ₃ ) are known and can be easily formed by a sputtering method, a vacuum evaporation method, a pulse laser deposition method, or the like. Further, a transparent conductive film 38 (metal film) as an upper electrode is formed on the surface.

The solar cell using the hydrogenated amorphous silicon thus obtained was tested by the device simulator "MEDI".
The characteristics were calculated using CI ”with and without the use of a ferroelectric. The conditions for the calculation are summarized in Table 1.

[0016]

[Table 1]

[0017] In other words, (1) mobility, in the case of electronic 2cm ² / V · sec, in the case of Hall 1cm ² / V ·
sec, (2) life is 7 nsec for electrons, 7 nsec for holes, and (3) mobility gap is 1.
5eV, (4) light intensity is 4 × 10 ¹⁷ photons /
sec · cm ² , (5) absorption length is 0.2 micro
n, (6) Software used is two-dimensional device simulator MEDCI, (7) Comb-shaped electrode spacing is 30 μm,
(8) The amorphous silicon film thickness is 2 μm, (9) n-type impurity concentration is 5 × 10 ¹⁶ cm ⁻³ , and (10) p-type impurity concentration is
It is 5 × 10 ¹⁶ cm ⁻³ .

FIG. 2 shows the recombination rate of electrons and holes in the solar cell without the conventional ferroelectric layer, and FIG. 3 shows the recombination rate in the solar cell with the ferroelectric layer of the present invention. The recombination rates of electrons and holes are shown respectively. That is, in FIGS. 2 and 3, the X-axis is the vertical cross-sectional direction of the solar cell, the Y-axis is the horizontal cross-sectional direction of the solar cell, and the Z-axis is the log electron-hole recombination velocity [absolute value] (cm ^{− 3} · sec ⁻¹ ) is shown.

FIG. 4 is a current-voltage characteristic diagram of the conventional solar cell and the solar cell of the present invention, where the vertical axis represents the current (10 ⁻⁹ A / μm).
m), the horizontal axis represents voltage (V). In this figure, the curve a is the solar cell without the conventional ferroelectric layer,
Curve b shows the respective current-voltage characteristics of the solar cell having the ferroelectric layer of the present invention.

FIG. 5 is an output-load characteristic diagram of the conventional solar cell and the solar cell of the present invention, where the vertical axis represents power (10 ⁻³ W /
cm ² ), and the horizontal axis represents the load (Ω-cm ² ). In this figure, the curve a shows the current-voltage characteristics of the solar cell without the conventional ferroelectric layer, and the curve b shows the current-voltage characteristics of the solar cell with the ferroelectric layer of the present invention.

As is clear from these calculation results, the recombination rate of electrons and holes is suppressed by the increase of the electric field induced by the spontaneous polarization effect of the ferroelectric substance, and the output of electrical energy is improved. You can see that Although the solar cell is assumed in the calculation example of this embodiment, the solar cell and the photosensor have the same basic structure. Therefore, it goes without saying that a similar improvement can be seen when this technique is used as an optical sensor.

FIG. 6 is a sectional view of a field effect solar cell using crystalline silicon according to the second embodiment of the present invention. As shown in this figure, a p-type silicon substrate 42 having an electrode 41 attached to the bottom thereof
Comb-shaped electrodes 43 and 44 formed by combining a metal with the n-type portion 43 formed by donor implantation are arranged on the top. The ferroelectric layer 45 is formed on the other surface. Further, the upper electrode 38 is formed thereon. This electrode is removed by etching after polarization of the ferroelectric layer. However, in the case of a transparent electrode, it may be left as it is, and an antireflection effect can be expected. That is, this example has almost the same structure as hydrogenated amorphous silicon except that a bulk crystal is used instead of the hydrogenated amorphous silicon shown in the first example.

FIG. 7 is a sectional view of a field effect solar cell using hydrogenated amorphous (a) or crystalline silicon (b) showing a third embodiment of the present invention. The same parts as those in the first embodiment [hydrogenated amorphous solar cell (FIG. 1)] are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, an insulating layer 3 made of silicon oxide, silicon nitride, cerium oxide or the like is provided between the ferroelectric layer 37 and the n-type hydrogenated amorphous silicon layer 35.
9 is different from that of the first embodiment, and the other points are the same.

With this structure, almost the same effect as in the first embodiment can be obtained, and the recombination on the semiconductor surface can be suppressed. The electrode for polarizing the ferroelectric material is removed by etching after polarizing the ferroelectric material, but ITO (Indium Ti) is used.
When a transparent electrode such as n oxide) is used, it may be left on the ferroelectric layer 37 without etching.

FIG. 8 is a sectional view of a two-dimensional image sensor in which a hydrogenated amorphous silicon solar cell according to a fourth embodiment of the present invention is laminated on a CCD. As shown in this figure, a p-type silicon substrate 51 has a storage diode 52 and a C
CD53 is formed and the transfer gate electrode 5 corresponding to these is formed.
4 and the CCD gate 55 are formed. An insulating layer 56 is formed, and a lower electrode 57 that contacts the storage diode 52 is formed. An n-type hydrogenated amorphous silicon layer 58, an i-type hydrogenated amorphous silicon layer 59, and a p-type hydrogenated amorphous silicon layer 60 are sequentially grown on the lower electrode 57 by the plasma CVD method. A ferroelectric layer 61 is formed on the p-type hydrogenated amorphous silicon layer 60.

With this configuration, the signals (electrons) efficiently collected by the upper photosensor are stored in the storage diode 52 formed in the lower p-type silicon substrate 51,
When a positive voltage is applied to the transfer gate electrode 54, the CCD
It is transferred to the CCD 53 by the gate 55. This signal is transmitted through the CCD 53 to an amplifier (not shown).

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0028]

As described above, according to the present invention, the following effects can be obtained. (1) When used as a solar cell, since the conversion efficiency is improved, more output can be obtained from cells having the same area.

(2) Since recombination of photogenerated carriers is suppressed, photodegradation of the hydrogenated amorphous solar cell is reduced and reliability is improved. (3) When used as an optical sensor, the conversion efficiency is improved, and thus the sensitivity of light detection is improved. (4) When used as an optical sensor, the area of the device can be reduced and the degree of integration can be improved due to the improvement in sensitivity.

(5) Further, since the ferroelectric layer can be grown at a low cost, the manufacturing cost hardly increases.

[Brief description of drawings]

FIG. 1 is a sectional view of a field effect solar cell using hydrogenated amorphous silicon showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a recombination rate of electrons and holes in a solar cell without a conventional ferroelectric layer.

FIG. 3 is a diagram showing a recombination rate of electrons and holes in a solar cell having a ferroelectric layer of the present invention.

FIG. 4 is a diagram showing current-voltage characteristics of a conventional solar cell and the solar cell of the present invention.

FIG. 5 is a diagram showing output-load characteristics of a conventional solar cell and a solar cell of the present invention.

FIG. 6 is a sectional view of a field effect solar cell using crystalline silicon according to a second embodiment of the present invention.

FIG. 7 is a hydrogenated amorphous material (a) showing a third embodiment of the present invention.
Alternatively, it is a cross-sectional view of a field effect solar cell using crystalline silicon (b).

FIG. 8 is a sectional view of a two-dimensional image sensor in which a field effect solar cell using hydrogenated amorphous silicon according to a fourth embodiment of the present invention is laminated on a CCD.

FIG. 9 is a cross-sectional view of a conventional solar cell using hydrogen amorphous silicon.

FIG. 10 is a cross-sectional view of a conventional solar cell using a crystalline semiconductor.

FIG. 11 is a cross-sectional view of a solar cell in which a conventional impurity diffusion layer is unnecessary.

[Explanation of symbols]

 31 substrate 32, 41, 57 lower electrode 33, 60 p-type hydrogenated amorphous silicon layer 34, 59 i-type hydrogenated amorphous silicon layer 35, 58 n-type hydrogenated amorphous silicon layer 36, 44 comb type Electrodes 37, 45, 61 Ferroelectric layer 38 Upper electrode 39 Insulator layer 42, 51 p-type silicon substrate 43 n-type silicon layer 52 Storage diode 53 CCD 54 Transfer gate electrode 55 CCD gate 56 Insulation layer

Claims (8)

[Claims] 1. A photoelectric energy conversion device for converting light energy into electric energy, comprising: (a) a hydrogenated amorphous silicon layer formed on a lower electrode; and (b) on the hydrogenated amorphous silicon layer. An electric field that induces an electric field in the hydrogenated amorphous silicon layer by the spontaneous polarization effect of the ferroelectric layer, and (c) an upper electrode. Effect type photoelectric energy converter. 2. A photoelectric energy conversion device for converting light energy into electric energy, comprising: (a) a p (or n) type silicon substrate having a lower electrode formed on the back surface; and (b) formed on the silicon substrate. an n (or p) type injecting layer and a metal-layered comb-shaped electrode; (c) a ferroelectric layer formed on the upper surface of the silicon substrate and the comb-shaped electrode; and (d) an upper electrode. e) A field-effect photoelectric energy conversion device in which an inversion layer is induced above the silicon substrate (in the vicinity of the interface) by the spontaneous polarization effect of the ferroelectric layer to form a pn junction. 3. The field effect photoelectric energy conversion device according to claim 1, wherein an insulator such as silicon oxide, silicon nitride, or cerium oxide is inserted between the ferroelectric layer and an underlying layer. Energy conversion device. 4. The field effect photoelectric energy conversion device according to claim 1, wherein the output signal is transferred by a CCD. 5. The field effect photoelectric energy conversion device according to claim 1, wherein the oxide transparent conductive film is used as the upper electrode. 6. The field effect photoelectric energy conversion device according to claim 1, wherein an electric field is applied to the upper and lower electrodes to polarize the dielectric, and then the upper electrode is removed by etching. Converter. 7. The field effect photoelectric energy conversion device according to claim 1, 3, 5 or 6, wherein the hydrogenated amorphous silicon layer has the same p-i-type as a normal amorphous silicon solar cell.
A field effect photoelectric energy conversion device having an n or n-i-p junction structure. 8. The field-effect photoelectric energy conversion device according to claim 1, 3, 5 or 6, wherein the hydrogenated amorphous silicon layer has pi or n- in a state where the ferroelectric substance is not polarized.
A field effect photoelectric energy conversion device having an i-junction structure.