JPH02162776A - Photosensor - Google Patents

Abstract

PURPOSE:To improve a photosensor of this design in sensitivity to measuring light rays of short wavelength and to easily modify it in a spectrum sensitive property by a method wherein the measuring light rays are converted through a spectrum sensitive property set by a control means and a photocurrent flowing through a bias electrode is outputted. CONSTITUTION:As the width of P-type layers 21 and 22 is set small enough, depletion layers occurred between the layers 21 and 22 and a silicon substrate 20 are brought into contact with each other to form a zonal depletion layer 35 when a bias voltage EB is made large. In this case, when a channel 36 is formed above the zonal depletion layer 35 by regulating a control voltage EC further, the zonal depletion layer 35 is made to move equivalently downward, so that measuring light ML of short wavelength is made to attenuate before it reaches to the zonal depletion layer 35 and only the optical energy of the measuring light ML of comparatively long wavelength is trapped in the zonal depletion layer 35 and detected as a photocurrent ic.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a photo sensor that receives measurement light and converts it into an electrical signal, and in particular, it is designed to be able to change the conversion characteristics and to convert it into an electric signal. The present invention relates to a photosensor improved to improve side sensitivity.

<Prior Art> FIG. 5 is a vertical cross-sectional view showing an outline of the configuration of a conventional photosensor.

Reference numeral 10 denotes a lightly doped N-type silicon substrate, on which a heavily doped P-type layer 12 is formed, including a light-receiving surface 11 that receives measurement light M L.

An oxide film (S10z) 13 is formed as a transparent interlayer film on the silicon substrate 10 and the P type [12].

Furthermore, on this oxide film 13, a passivation wA14 such as PSG (phosphor glass layer) is applied except for the light receiving surface 11.
covered with. The P-type layer 12 is connected to an electrode 15, and a load resistance RL is connected between the electrode 15 and the silicon substrate 10.
It is reverse biased from power supply E via. In this state, there is a depletion layer 16 between the Pm layer 12 and the silicon substrate 10.
is formed.

With the above configuration, the silicon substrate 1
When the measurement light ML is applied to the depletion layer 16 formed in the
A photocurrent 1 corresponding to the measurement light ML is caused to flow.

<Problem to be solved by the invention> However, such conventional photosensors have problems with the bonding thickness due to the relationship with the light absorption coefficient! It is known that a shallow junction with a small value improves the sensitivity on the short wavelength side, so attempts have been made to improve the sensitivity on the short wavelength side with a shallow junction. There are limitations due to defects, etc.

Furthermore, on the short wavelength side, the measurement light ML enters the silicon substrate 10 and is absorbed immediately, so the sensitive depletion layer 16
The measurement light ML cannot penetrate up to this point, which is disadvantageous for improving the sensitivity on the short wavelength side from a structural point of view.

Means for Solving the Problems> In order to solve the above problems, the present invention provides a silicon substrate containing a low concentration of impurities, and a light-receiving surface for receiving measurement light placed on the silicon substrate. A pair of high-concentration bias electrodes formed by implantation, a transparent electrode formed on the light-receiving surface of the silicon substrate, a bias means for holding the bias electrodes at a reverse bias with respect to the silicon substrate, and and a control means for controlling the potential of the transparent electrode, and converts the measurement light according to the spectral sensitivity characteristics set by the control means, and outputs a photocurrent flowing through the bias electrode.

Even when light is incident on the light-receiving surface of the silicon substrate, a depletion layer is formed on the surface, which improves the sensitivity to short-wavelength measurement light, and furthermore, by controlling the potential of the transparent electrode, spectroscopic Sensitivity characteristics can be easily changed.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal sectional view showing the configuration of one embodiment of the present invention.

N-type silicon substrate 20 lightly doped with impurities
A heavily doped P-type layer 21,22 is formed over the . The width between these P-type Jii21 and 22 is W
This serves as a light receiving surface 23. Further, a heavily doped N-type layer 24 is formed on the upper surface of the silicon substrate 20.

These surfaces are thermally oxidized IB! 25, the light receiving surface 23
A transparent electrode 26 is formed on the top of the thermally oxidized WA 25 corresponding to . These thermal oxide films 25 and transparent type &26 are designed to reduce optical effects such as interference and absorption.

An oxide tl! (S t 02 ) 27 is formed as an interlayer film on the transparent "j:b41i 26 and the thermal oxide film 25, and a passivation film 28 such as PSG is further formed on this.
is formed.

These oxidized WA 27 and passivation WA 28 are opened to the transparent Th electrode 26, and an opening 29 with a diameter d is formed, and an aluminum electrode 30 is further bonded to the P-type layers 21 and 22 and the N-type layer 24, respectively. .31.32 is the thermal oxide film 25, oxidized fi! 27, and are bonded via a passivation film 28.

Also, the aluminum t-pole 3 connected to the transparent electrode 26
3 are bonded via an oxide film 27 and a passivation film 28.

A bias voltage EB is applied to the P-type layer 21.22 with a weak reverse bias through the load resistor RL and the electrode 30.31 with respect to the silicon substrate 20. Further, a control voltage EC is applied to the transparent electrode 26 via a limiting resistor RC and an electrode 33.

With the above configuration, as shown in FIG. 2, a depletion layer 34 is formed on the light receiving surface 23 by reverse bias using the control voltage EC.

Therefore, when the second measurement light ML enters the light-receiving surface 23 through the aperture 29, short wavelengths are immediately absorbed by the depletion layer 34 formed on the very surface of the light-receiving surface 23 and efficiently detected as photocurrent tc. Ru.

FIG. 3 is an explanatory diagram showing another operation of the embodiment shown in FIG. 1.

Since the width W of the P-type layers 21 and 22 is selected to be sufficiently small, when the bias voltage E is increased, each P-type layer 21.2
The depletion layer formed between 2 and the silicon substrate 20 forms a contact zone depletion layer 35 as shown in FIG. In this case, if a channel 36 is formed above the zone depletion layer 35 by further adjusting the control voltage EC, the zone depletion layer 35 will equivalently move downward, and the The wavelength is this zone depletion j
The measurement light M is attenuated before reaching ii35 and has a relatively long wavelength.
Only the light energy of L is captured by the zone depletion layer 35 and detected as a photocurrent i (H).

FIG. 4 is a characteristic diagram showing the relationship between the wavelength of measurement light and the relative sensitivity S according to the present invention.

The horizontal axis shows the wavelength λ (nm) of the measurement light Mt, and the vertical axis shows the relative sensitivity S. Curve C1 has the characteristics shown in FIG. 1, curve C2 has the characteristics shown in FIG. 5, and curve C3 3 shows the characteristics when the zone depletion layer is moved, respectively.

As can be seen from the characteristics below, according to the present invention, the relative sensitivity S on the short wavelength side can be adjusted by adjusting the control voltage Ec.
Since it is possible to change the range of S, the spectral characteristics for the measurement light ML can be changed.

<Effects of the Invention> As specifically explained above in conjunction with the examples, according to the present invention, the relative sensitivity on the short wavelength side can be improved and the potential of the transparent electrode provided on the light receiving surface can be adjusted. Accordingly, the spectral sensitivity characteristics with respect to the measurement light can be changed. Furthermore, since impurities and the like are not diffused into the light-receiving surface, there are few crystal defects that occur during the manufacturing process, and dark current can be extremely reduced.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing the configuration of one embodiment of the present invention, and FIG.
The figures are explanatory diagrams explaining the operation of the embodiment shown in Fig. 1, and Fig. 3.
The figures are explanatory diagrams showing other operations of the embodiment shown in Fig. 1;
The figure is a characteristic diagram showing the relationship between the wavelength of measurement light and the relative sensitivity S according to the present invention, and FIG. 5 is a longitudinal cross-sectional view showing the configuration of a conventional photosensor. 10... Silicon substrate, 11... Light receiving surface, 12...
・P-type layer, 14... Passivation film, 16... Depletion layer, 20... Silicon substrate, 21.22... P-type layer, 23... Light-receiving surface, 24... N-type layer , 26...
Transparent electrode, 28... Passivation film, 29... Open [1 part, 34... Depletion layer, 35... Zone depletion layer,
36... Channel, ML... Measurement light, EC... Control voltage. True 1 figure 2 figure 34 poor class

Claims (1)

[Claims] A silicon substrate containing a low concentration of impurities, a pair of high concentration bias electrodes formed by implanting impurities on this silicon substrate with a light receiving surface for receiving measurement light sandwiched therebetween, and a transparent electrode formed on the silicon substrate; bias means for maintaining the bias electrode at a reverse bias with respect to the silicon substrate; and control means for controlling the potential of the transparent electrode with respect to the silicon substrate; A photosensor characterized in that it converts light according to spectral sensitivity characteristics set by the control means and outputs a photocurrent flowing through the bias electrode.