JPS6246991B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a field effect photodetector having high quantum efficiency and high gain in a long wavelength band.

Conventionally, only long-wavelength photodetectors that utilize photoconduction phenomena have been used. In other words, the operating principle of this photodetector is that, as shown in Figure 1, trapped electrons E _T trapped in deep levels in the semiconductor crystal
When light is incident, the impurity level L on the valence band _B1 side is photoexcited to the conduction band _B2 , and the excited free electrons E _F
was used as a carrier to extract current to an external circuit.

However, with this type of photodetector, no gain can be obtained in principle, and when using this type of photodetector, it is necessary to use a preamplifier after the photodetector.

In order to solve the above-mentioned drawbacks, the present invention proposes a novel photodetector that can amplify a negative photoconduction signal generated at the time of optical input to a large amplitude by introducing an electric field effect on the semiconductor surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The field-effect photodetector of the present invention will be explained below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention, 1
is a semi-insulating Si crystal substrate made by thermally diffusing A, which is a deep impurity in Si crystal, at 1000°C for 1 hour. In this case, Mn and Ni can also be used as deep impurities. 2 is an n ⁺ region prepared by adding n-type impurities at a high concentration from the surface of the Si crystal 1;
Reference numerals 3 and 4 forming the source and drain electrode formation regions of the field-effect photodetector of the present invention are drain and source electrodes, respectively, and are provided as ohmic contacts. 8 is a channel region, and a thermal oxide film 6 is formed on the channel region, and a conductive gate metal 7 is formed by vapor deposition of Au. In order to improve the light transmittance, the gate metal 7 is made to have a transmittance of more than semi-transparent, for example, about 50%. 5 is an electrode of the gate metal 7.

The element constituting the photodetector manufactured as described above is structurally substantially an FET, and from a normally off state, a drain voltage V _D1 is applied to the drain electrode 3, the source electrode 4 is grounded, and the gate is By applying a gate voltage V _g to the electrode 5, a drain current _ID can be caused to flow.

The operation of the field effect photodetector according to the present invention will be explained below with reference to FIG. In an n-channel FET consisting of a semi-insulating Si crystal substrate 1 with deep impurities (e.g. Au acceptor level 11),
The electric field due to the positive gate voltage applied through the insulator 10 generates a negative space charge 13, and channel electrons 15 flow. When light irradiation is not performed, the width 16 of the space charge region is determined by the gate voltage, impurity density, etc., and the channel current value is also determined thereby. Therefore, when an FET with this structure is irradiated with light of an appropriate wavelength, electrons are excited from the valence band as shown in 12, and a space charge 14 is newly generated which is proportional to the trapping cross section of the impurity and the amount of light. By equivalently converting the amount of space charge 14 into an increase W in the width of the space charge region, it can be expressed as a variation in the threshold voltage of the FET in the light irradiation state. The threshold voltage increases in accordance with the increase 17 in the space charge region width, and if the gate voltage is kept constant, the channel electrons 15 tend to decrease. 18 indicates a region where no space charge is generated.

Further, to explain the operation of the present invention with reference to FIG. 3, the light incident on the gate metal 7 has a wavelength of 1.3 μm.
The power was 0.05mW. When this infrared light was tapped and incident on a sample, it was found that the drain current _ID , which had been flowing at a magnitude of about 100 μA, was reduced to about half, to 50 μA, when the light was incident. This is what is called negative photoconduction.
However, it has become clear that in the element that makes up this photodetector, this negative photoconduction reaches more than 100 times the value normally obtained.

Further, FIG. 4 shows the amplification degree M of the negative photoconduction characteristic with respect to the gate voltage V _g . The threshold voltage from the drain current characteristics of the elements that make up this photodetector is 1.5V.
It will be understood that the amplification occurs in the range of gate voltage>threshold voltage.

According to the field-effect photodetector of the present invention configured as described above, (1) Since a deep level in the semiconductor crystal is used, it can be used for light detection from infrared to far-infrared.

(2) It is possible to obtain an amplification factor of 100 times or more due to the electric field effect, and there is no need to install a preamplifier for use.

(3) It has high practicality because it can operate in a low voltage region with a drain voltage of 5 V or less and a gate voltage of 5 V or less. (4) By selecting a combination of impurities, the detrap response speed when the light is turned off can be increased. Achieve significant effects such as:

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the operating principle of a conventional photodetector, Fig. 2 is an explanatory diagram of a field-effect photodetector, and Fig. 3a,
b and FIG. 4 show the same characteristic diagram, and FIG. 5 shows an explanatory diagram. 1...Semi-insulating crystal substrate, 2...n ⁺ region, 3
...Drain electrode, 4...Source electrode, 5...Gate electrode, 6...Thermal oxide film, 7...Gate metal,
8... Channel area.

Claims (1)

[Claims] 1. A source region and a drain region are formed by doping n-type impurities at a high concentration from the surface on a deeply doped Si crystal substrate, and an ohmic contact is formed in each of the source region and the drain region, A thermal oxide film is provided on the channel region sandwiched between the source and drain regions, and a conductive gate metal is provided on the thermal oxide film, which exhibits a transmittance of at least semi-transparency to light. A field-effect photodetector characterized by: