JPS6262022B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heterojunction photoconductive element having spatially different spectral sensitivities. Single-tube color cameras and single-chip color cameras use a method that converts red (R), green (G), and blue (B) light signals into electrical signals and extracts them from a single element. There is. In this type of system, an organic or inorganic filter is placed in front of the photoconductive element and color selection is performed by spatially changing the spectral transmittance, but this filter has a high loss of light and , there is a problem that it is expensive. The present invention provides a photoconductive element that can directly perform color selection by utilizing the difference in photoconductive spectral sensitivity of heterojunction elements without using the above-mentioned filter. FIG. 1 shows the structure of a heterojunction photoconductive element for explaining the principle of the present invention. 1, 2 in the figure
are semiconductor layers having resistances of R ₁ and R ₂ and bandgap widths of Eg ₁ and Eg _2, respectively, and the respective materials and dimensions and shapes are such that they have the relationships R ₁ ≪ R ₂ and Eg ₁ > Eg ₂ . has been selected. 4 is a transparent electrode formed on the semiconductor layer 1, and 5 is an electrode formed on the semiconductor layer 2. Consider the case where light 3 is incident on this element through the transparent electrode 4 from the side of the semiconductor layer 1 where the forbidden band width is large. At this time, when a voltage is applied to the element, the voltage is applied to the semiconductor layer 2, which has substantially a higher resistance than the semiconductor layer 1, and the semiconductor layer 2 becomes a sensitive layer, and the spectral sensitivity of the photocurrent becomes as shown in FIG. The short wavelength limit of the spectral sensitivity is determined by the wavelength λ ₁ corresponding to the bandgap Eg ₁ of the semiconductor layer 1 on the incident side. When the thickness is sufficiently thick and there is little photoconductivity due to impurities, the long wavelength limit is determined by the wavelength λ ₂ corresponding to the forbidden band width Eg ₂ of the semiconductor layer 2, which is a sensitive layer. This can be explained as follows. Light with a wavelength shorter than wavelength _λ1 is absorbed by the semiconductor layer 1, generating electron-hole pairs, but since there is little or no electric field in the semiconductor layer 1, electron-hole recombination occurs and contributes to the photocurrent. do not. Of the light with a wavelength longer than λ1 that is transmitted without being absorbed by the semiconductor layer ₁ , the light with a wavelength shorter than _λ2 is absorbed by the semiconductor layer 2, generating electron-hole pairs, and an electric field is applied to the semiconductor layer 2. Therefore, it is detected as a photocurrent from the semiconductor layer 2. Utilizing this property, if a material having arbitrary forbidden band widths Eg ₁ and Eg ₂ is selected as the material constituting the heterojunction, the spectral sensitivity can be controlled arbitrarily. Therefore, by spatially arranging a plurality of heterojunction elements made of a certain material, or a plurality of heterojunction elements each made of different materials, in a strip or island shape, light having different spectral sensitivities can be produced. A conductive element can be obtained. The photoconductive element of the present invention includes a first semiconductor that absorbs blue light among visible light and transmits insulating light and red light, a second semiconductor that absorbs blue light and green light and transmits red light, and a second semiconductor that absorbs blue light and green light and transmits red light. A photoconductor is formed on a substrate, and includes at least as a component a third semiconductor that absorbs the entire area, and the first, second, and third semiconductors have higher resistances in that order, and the second semiconductor has a higher resistance than the other. A first semiconductor and a third semiconductor are formed on the entire surface of the substrate, and a first semiconductor and a third semiconductor are formed in an island shape or a band shape, and a portion of the first, second, and third semiconductors are in contact with each other. stacked, the second semiconductor of the first semiconductor
Alternatively, the visible light is allowed to enter from the surface side not in contact with the third semiconductor. When a photoconductive element is used in a color camera or the like, a semiconductor material having a forbidden band width Eg such that the spectral sensitivity is in the visible range may be selected. For example, the relative sensitivity of the ideal imaging characteristics of the NTSC system required for a color camera is:
It is specified as shown in Figure 3. Third
Since it is actually impossible to have negative imaging characteristics in the figure, the negative part may be omitted,
Measures such as slightly deforming are usually used.
Therefore, in order for the photoconductive element of the present invention to have the three primary color RGB decomposition characteristics of the spectral sensitivity shown in FIG. As a semiconductor that has a width and determines the long wavelength limit,
A material having a forbidden band width at a wavelength longer than 400 nm may be used. Examples of such materials having a spectral intensity in the visible light region include - group compounds and - group compounds such as GaP. Example 1 FIG. 4 is a plan view of a photoconductive element according to this example, and FIG. 5 is a sectional view thereof. The photoconductive element of this example is manufactured by the steps shown below.
ZnS 10 is formed as a buffer layer over the entire surface of the glass substrate 8 having a transparent electrode 9 to a thickness of 0.05 μm. On top of that, as shown in Figures 4 and 5, CdS6 as the first semiconductor is placed in a strip shape with a width of 50 μm and a pitch of 50 μm.
Form a thickness of 0.05 μm. Furthermore, CdSe7 as a third semiconductor is placed on top of this in a crosswise manner with a width of 50 μm.
Form a strip with a pitch of 50 μm and a thickness of 1.0 μm. Finally, ZnTe 11 as a second semiconductor is formed to a thickness of 1.0 μm over the entire surface. Using this photoconductor as an image pickup tube target, light is incident from the substrate 8 side, scanned with an electron beam, and the signals from the semiconductor are processed to obtain color-separated signals. Note that the resistance is highest in the order of CdS6, CdSe7, and ZnTe11, and ZnS10 is the smallest and is not necessarily a buffer layer for improving the crystallinity of the upper three layers. FIG. 11 shows the spectral sensitivity characteristics of each of the above semiconductor layers. The device thus formed is divided into four types of lamination regions A, B, C, and D shown in FIGS. 4 and 5. The spectral sensitivities of these four regions are shown in the table below based on the relationship between the heterojunction shown in FIG. 5 and the characteristics and resistance shown in FIG. 11. In addition, G is green, R is red,
B indicates blue. FIG. 6 is a diagram showing this.

[Table] In this way, by forming different junctions by combining semiconductor layers, it is possible to form photoconductive elements with locally different spectral sensitivities, and by processing the resulting photocurrent, R, G, It is possible to obtain a signal corresponding to Embodiment 2 A photoconductive element having regions having three different spectral sensitivities shown in FIG. 7 can be configured to have the spectral sensitivities of those regions as shown in FIG. 8 as follows. first,
Cd ₀ . ₃ Zn ₀ . ₇ Te 12 is deposited on the Au electrode 17 deposited on the substrate in an island shape as shown in FIG.
is formed with a thickness of 1 μm. CdS _0.5 and Se _{0.5 13} as a second semiconductor having almost the same spectral sensitivity _{characteristics} as ZnTe are formed thereon to a thickness of 1 μm (FIG. 9B). Furthermore, as shown in FIG.
m form. Finally, as a buffer layer for electrode formation.
ZnS _{0 . 4} Se ₀ .
16c... is formed by vapor deposition into an island shape as shown in FIG. 9(e). In this example as well, the resistance increases in the order of the first, second, and third layers, and the buffer layer 15 is the smallest, and this layer 15 is not necessarily required. FIG. 10 shows a cross-sectional view taken along the line B-B' of the photoconductive element produced in FIG. 9E, corresponding to E, F, and G in FIG. 7.
The electrodes 17 and 16 are connected to the scanning element using minute wire bonding or the like on each semitransparent electrode 16.
When voltages are sequentially applied between 16a, 16b, and 16c, the color signal shown in FIG. 8 is obtained. As described above, according to the present invention, it is possible to change the combination of materials of the heterojunction depending on the location. Therefore, it is possible to form a photoconductive element having regions with locally different spectral sensitivities. By using this element, without using a filter,
Color sorting becomes possible. Compared to the method of forming R, G, and B three-color filters and then layering a photoconductor that is sensitive to the entire visible light range, it takes two times (three times if electrodes are included) for semiconductors.
It can be created with few steps. It becomes possible to exhibit the excellent feature that the multilayer film semiconductor layer can be composed of three layers like an interference filter.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the configuration of an example of a heterojunction photoconductive element for explaining the principle of the present invention, Fig. 2 is a spectral characteristic diagram of an example of a heterojunction photoconductive element, and Fig. 3 is a diagram of an NTSC color camera. A diagram showing ideal imaging characteristics, FIG. 4 is a plan view of a photoelectric conversion element in which two materials are formed in a cross shape, which is an embodiment of the present invention.
Figure 5 is a sectional view taken along line A-A' in Figure 4, Figure 6 is a diagram showing the spectral sensitivity of the area corresponding to Figures 4 and 5, and Figure 7 is a diagram showing the spatial sensitivity distribution of Example 2. 8 are spectral sensitivity diagrams corresponding to Example 2, FIG. 9 A to E are plan views showing the order of fabrication of the photoelectric conversion element of Example 2, and FIG. 10 is B of FIG. 9 E. -B' line cross-sectional view and FIG. 11 are spectral characteristic diagrams of each semiconductor. 6...CdS, 7...CdSe, 8...Glass substrate, 9...Transparent electrode, 11...ZnTe.

Claims (1)

[Claims] 1 A first semiconductor that absorbs blue light among visible light and transmits green and red light, a second semiconductor that absorbs blue and green light and transmits red light, and a third semiconductor that absorbs the entire range of visible light. A photoconductor including a semiconductor at least as a component is formed on a substrate, and the first, second, and third semiconductors have a larger resistance in that order,
The second semiconductor is formed on the entire surface of the substrate, the first semiconductor and the third semiconductor are formed in an island shape or a band shape on the substrate, and one of the first, second, and third semiconductors is formed on the substrate. The photoconductive element is characterized in that the parts are stacked in contact with each other, and the visible light is incident from a side of the first semiconductor that is not in contact with the second or third semiconductor.