Photodetector

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a light receiving element, and more particularly to a light receiving element having a photodiode structure.

【0002】

[Conventional technology]

The brightness detector is used for detecting the presence or absence of light, measuring the intensity of light, measuring electric power, and the like. In particular, in a brightness detector used for measuring the intensity of light using a photodetector such as CdS or Si, the wavelength selectivity is uniquely determined by the nature of the CdS or the structure of the Si photodetector, so that the wavelength selectivity is uniquely determined with respect to the incident light. Wavelength selectivity cannot be freely selected.

【0003】

[Problems to be Solved by the Invention]

With a conventional photodetector, the wavelength selectivity for incident light cannot be freely selected, and the wavelength selectivity does not accurately match the visibility curve. Therefore, there is a gap between the brightness detection output of the photodetector and the human sense, and it is difficult to obtain a brightness detector with satisfactory performance.

【0004】

The present invention provides a light receiving element that makes it easy to match the detection output with the luminous efficiency because it is easy to select the wavelength selectivity in view of the problem of the conventional brightness detector. The purpose is to obtain a high brightness detector.

【0005】

[Means for solving problems]

In order to achieve the above object, the light receiving element of the present invention is formed in a single semiconductor bulk, and is composed of a plurality of pn junctions having different wavelength selectivity for light incident on the light receiving surface of the semiconductor bulk. It is characterized by having a portion and an electrode connected to each semiconductor layer constituting the pn junction.

【0006】

The wavelength selectivity is preferably obtained by arranging the semiconductor layers constituting each junction in a laminated structure, or can be obtained even if the band gaps in each junction are different.

【0007】

It is also a preferred embodiment of the present invention that the light receiving element includes an arithmetic circuit having an input connected to each electrode that extracts a signal current from the photoelectric conversion unit. In this case, in order to accurately match the output of the light receiving element with the relative luminous efficiency, it is preferable to combine the signal currents taken out from each electrode while performing numerical calculation in the arithmetic circuit.

【0008】

[Action]

From each electrode, the light receiving element includes a plurality of pn junctions having different wavelength selectivity for the light incident on the light receiving surface and electrodes connected to the semiconductor layer constituting each of the pn junctions. Since the signal currents to be taken out can be appropriately combined, a light receiving element having a desired wavelength selectivity can be obtained, and a photodetector having a wavelength selectivity that accurately matches the relative sensitivity curve can be obtained.

【0009】

When adopting a configuration in which the semiconductor layers constituting each junction are arranged in a laminated structure, it is easy to make the wavelength selectivity of each junction with respect to the incident light on the light receiving surface different from each other. Further, if a configuration is adopted in which the band gaps in each junction are formed to have different values for each junction, the selectivity for the wavelength of light can be set to a different value in each junction.

【0010】

If a configuration is adopted in which an arithmetic unit is provided in which an input is connected to an electrode connected to each semiconductor layer constituting the pn junction, the wavelength with respect to the incident light on the light receiving surface can be selected by selecting the arithmetic content in the arithmetic unit. A light receiving element having a simple structure that allows easy selection of selectivity can be obtained.

【0011】

[Example]

The present invention will be described in more detail with reference to the drawings. FIG. 1 is a cross-sectional view showing the structure of a light receiving element according to an embodiment of the present invention. In the figure, an n-type epitaxial layer 2 is grown and formed on the upper surface of the p-type substrate 1, and a p-type diffusion layer 3 and an n-type diffusion layer 4 are sequentially formed on the upper surface of the n-type epitaxial layer 2 in a laminated manner. .. Each epitaxial layer and diffusion layer can be formed by a process for forming a bipolar transistor.

【0012】

A transparent protective film 5 is formed over a light receiving surface composed of a main surface of a substrate including a region composed of diffusion layers 3 and 4 and an epitaxial layer 2. At the predetermined positions of the semiconductor layers 1 to 4, the protective film 5 is selectively removed to form contact holes, and electrodes 6 are formed in the respective portions. Each semiconductor layer composed of the substrate 1, the n-type epitaxial layer 2 and the diffusion layers 3 and 4 is connected to a predetermined arithmetic circuit (not shown) via the corresponding electrodes 6.

【0013】

The light-receiving element has a first photodiode PD1 on the junction surface of the n-type diffusion layer 4 and the p-type diffusion layer 3, and the p-type diffusion layer 3 and the n-type epitaxial layer 2 in this order from the light-receiving surface side. A second photodiode PD2 is formed on the joint surface, and a third photodiode PD3 is formed on the joint surface between the n-type epitaxial layer 2 and the p-type substrate 1. With such a configuration, each photodiode has a different depth from the light receiving surface.

【0014】

FIG. 2 is a circuit diagram illustrating a circuit for extracting current from the light receiving element of the above embodiment. In the figure, the photocurrent generated by the photodiode PDn is i_nAnd each electrode is e with the reference code (n) attached to each corresponding semiconductor layer as a subscript._nIt is shown by. In the figure, the electrode e connected to the n-type diffusion layer 4₄And the electrode e connected to the n-type epitaxial layer 2₂Is connected to an arithmetic circuit (not shown) via bipolar transistors Q1 and Q2 whose bases are maintained at predetermined potentials and are in a conductive state, respectively, and the electrode e of the p-type diffusion layer 3₃Is similarly connected to the arithmetic circuit via the bipolar transistor Q3 whose base is maintained at a predetermined potential and is in a conductive state. Electrode e of p-type substrate region 1₁Is directly connected to the arithmetic circuit.

【0015】

With the above configuration, when light is incident on the light receiving element, as shown in FIG. 2, the photocurrents i from the transistors Q1, Q2, and Q3, respectively.₁, I₂+ i₃, I₁+ i₂Is taken out independently and input to the arithmetic circuit. In the arithmetic circuit, i₁And i₁+ i₂From i₂Is also obtained, and this and i₂+ i₃Tokara i₃Is obtained, so in the end, i₁, I₂, And i₃Can be obtained independently. Therefore, by multiplying these by an appropriate numerical value or adding or subtracting them, an arbitrary numerical calculation becomes possible.

【0016】

Generally, in a light receiving element made of a photodiode, the quantum efficiency expressed as the ratio of the number of emitted photoelectrons to the number of incident photons is determined by the depth of the junction surface from the light receiving surface and the wavelength of the incident light. In this case, the longer the wavelength of the incident light, the higher the quantum efficiency at the deeper junction surface. In the bipolar structure photodiode shown in FIG. 1, the depths of the photodiodes PD1, PD2, and PD3 from the light receiving surface are different from each other, and the quantum efficiencies are different according to the wavelength of the incident light.

【0017】

Figure 3 shows the currents i of each of the photodetectors PD1, PD2, and PD3 when the incident light with wavelengths from 400 nm to 800 nm is received on the light receiving surface.₁, I₂, I₃Illustrates the wavelength dependence of the ratio of to the total current. For incident light with a short wavelength, most of it is current i₁As the wavelength gets longer, the current i₂And the ratio of i3 increases. Current i₂The ratio of is maximal between wavelengths of 500 nm and 600 nm, and as the wavelength becomes longer than that, the current i₂As the ratio of₃Will increase.

【0018】

By the way, it is known that the number of photons contained in light of the same intensity is proportional to the wavelength, and in the light receiving element of FIG. 1 in which the current ratio shown in FIG. 3 can be obtained, the photocurrent obtained from the incident light of the same intensity can be obtained. i₁, I₂, I₃Will have the wavelength dependence shown in FIG. The vertical axis in the figure shows the relative ratio, not the absolute value. The dotted line is the luminous efficiency curve (k) shown for comparison with these, and the current curve i.₂The point P selected above is drawn so that it has a peak. Each current i₁, I₂, I₃It can be understood that each has characteristics that are significantly different from the luminous efficiency curve (k).

【0019】

From each current characteristic in Fig. 4, i₃-0.67 × i₁Is calculated to obtain the curve a in FIG. This curve a is a curve that increases almost uniformly with increasing wavelength, and changes from negative to positive between 500 nm and 600 nm. Current i₂By finding the difference between and the absolute value of this curve a and extracting only the positive part thereof, a curve that is particularly close to the luminosity curve (k) is obtained. In Figure 5, i₂-| i₃-0.67 × i₁| Was calculated, and only the curved part whose numerical value was 0 or more was extracted and drawn as the curve b. It can be understood from the figure that the curve b has a wavelength selectivity that accurately approximates the luminous efficiency curve (k).

【0020】

It cannot be said that the characteristics close to the luminosity curve can be obtained by the above calculation for any of the light receiving elements having the configuration shown in FIG. 1, and such characteristics follow the structure obtained by the adopted bipolar process. That is, it depends not only on the depth of the joint surface but also on various process conditions. However, a brightness output having arbitrary wavelength selectivity can be obtained by performing an appropriate numerical calculation on the current value of each obtained photodiode while considering the wavelength dependence of each current. By matching this wavelength selectivity with the wavelength selectivity of the luminous efficiency curve, a brightness detector with high accuracy can be obtained.

【0021】

In the above embodiment, an example is shown in which the wavelength selectivity with respect to the incident light is different at each joint surface according to the depth from the light receiving surface, but instead of such a configuration, the impurity concentration in each epitaxial layer or diffusion layer is changed. By doing so, it is possible to adopt a configuration in which the band gaps of the joint surfaces are different from each other.

【0022】

[Effect of the invention]

As described above, according to the light receiving element of the present invention, the wavelength selectivity for the light incident on the light receiving surface of the photoelectric conversion unit can be arbitrarily selected, so that the brightness can be accurately matched to the human senses. It has a remarkable effect that makes it possible to manufacture a detector.

【0023】

When the semiconductor layers constituting each bonding surface are arranged in a laminated manner so that the wavelength selectivity for light incident on the light receiving surface differs depending on the depth from the light receiving surface, the impurity concentration of each semiconductor layer is determined. The selection can be made uniformly.

【0024】

When the band gaps of the joint surfaces are different from each other and the wavelength selectivity with respect to the light incident on the light receiving surface is different, the arrangement of each diffusion layer has a degree of freedom.

【0025】

When the light receiving element further includes an arithmetic circuit, a photodetector having a desired wavelength selectivity can be obtained depending on the configuration of the arithmetic circuit to be adopted.

[Simple explanation of drawings]

[Figure 1]

The cross-sectional view which shows the structure of the light receiving element of one Example of this invention.

[Figure 2]

The circuit diagram which illustrates the structure of the current extraction circuit in the light receiving element of FIG.

[Fig. 3]

The graph which illustrates the wavelength dependence of the incident light in the current ratio of each photodiode in the light receiving element of FIG.

[Fig. 4]

The graph which shows the relative magnitude of the current value of each photodiode obtained by the incident light of the same intensity.

[Fig. 5]

The graph which shows the wavelength selectivity obtained by calculation from the current characteristic of FIG.

[Explanation of symbols]

1 p type substrate 2 n epitaxial layer 3 p type diffusion layer 4 n type diffusion layer 5 Protective film 6 electrodes Q1 ~ Q3 Bipolar transistor PD1 ~ PD3 photodiode