JPH0274078A - Photodetecting circuit - Google Patents

Abstract

PURPOSE:To enable a photodetecting element to detect even a long wave band, to operate at a zero bias, and to be excellent in mechanical strength by a method wherein a Fermi level of a P-type semiconductor is within a valence electron band, and a Fermi level of an N-type semiconductor is within a conduction band. CONSTITUTION:An N<+> layer 301, which is much doped to enable its Fermi level 304 to be in a conduction band, and a P<+> layer 303 layer, which is also much doped to make its Fermi level 304 belong in a valence electron band, constitute a P-N junction 302. By such a band structure as mentioned above, electrons of the valence electron band of the P<+> layer 303 are made to ooze out to a forbidden band, and the oozed electrons happen to absorb photons with energy smaller than the band gap of a material substance through a photon absorbing mechanism, and a so-called Franz-Kerdische effect grows prominent and a photovoltaic force is generated. By this setup, a photodetecting element of this design is effective against a long wave band, operable at a zero bias, and excellent in mechanical strength.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a photodiode that is effective in long wavelength bands.

[Prior art] Conventionally, photodetectors in long wavelength bands include P-N junction photodiodes using semiconductor materials with a narrow bandgap such as nanoAs, PbS photoconductive elements, and thermocouple type photodiodes. meters were used.

[Problem to be solved by the invention] However, P-
N-junction photodiodes have problems such as the need to use expensive materials and their inability to be used at wavelengths of 2 μm or more.

In addition, since photoconductive elements require a bias voltage to obtain an optical signal, a photocurrent is detected even when there is no optical signal, so-called dark current flows, so they are not suitable for detecting minute amounts of light. .

Furthermore, since the calorimeter is an assembly of extremely thin thermocouples, its mechanical strength is weak, and high-speed measurement is impossible because the signal output is delayed by several hundred rlLS with respect to the optical input due to the thermal lid measurement.

Therefore, the present invention aims to solve these conventional problems and to obtain a photodetecting element that is effective even in a long wavelength band, operates with zero bias, and is mechanically strong.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a combination of a P-type semiconductor and an N-type semiconductor.
In the photodetecting element having a junction with a type semiconductor, the P
The Fermi level of the N-type semiconductor is in a valence band, and the Fermi level of the N-type semiconductor is in a conductor.

[Effect] The present invention will be explained in detail using FIG.

Figure 3 shows the Fermi level [14
Band diagram of a PN junction 502 formed by an NJ sound 501 in which 04 is placed in the conduction band and a P+ layer 503♂ in which the Fermi γ band 04 is placed in the valence band by the same large amount of doping. It is.

Using such a band fIlt structure, the P layer 30
Electrons in the ll1Ii electron band of 5 leak into the forbidden band, and due to the mechanism in which the leaked electrons absorb photons, they also absorb photons with an energy smaller than the band gap of the material, so-called 7 run two. The Keldeitz effect becomes significant and generates a photovoltaic force.

In other words, it becomes a photodetecting element that is sensitive even to long wavelengths.

[Example] An example of the present invention will be described below with reference to the drawings. Fig. 1 is a sectional view of a photodetector element of the present invention.

Figure 1 shows (・) N+ using phosphorus as a dopant.
A 1-doped P+ region 106 is formed on a Si substrate 104 by ion implantation with boron, a 5in2 protective film 102 is formed as a surface protective film by dry thermal oxidation, and then an extraction electrode 101105 is formed.

Figure 2 shows the spectral sensitivity characteristics 2 of the conventional 81 photodiode.
01 and the spectral sensitivity characteristics of the photodetector element 202 of the present invention are shown. Due to the large amount of impurity doping, the impurity level, conduction band, and valence band are degenerated, resulting in a narrow effective band gap (
In addition to the so-called band tilling effect, it has been shown that the conventional 81 photodiode can be used for a wavelength range of 2 μm or more, whereas the conventional 81 photodiode can only be used for a wavelength range of up to 1.1 μm. Ta.

In addition, in terms of absolute sensitivity characteristics, it has approximately 1000 times the sensitivity at a wavelength of 1.5 μm compared to a normal calorimeter-type thermocouple photometer, which is considered essential when using a calorimeter-type thermocouple photometer. There is no need for ultra-precision electronic circuits, and a single general-purpose operational amplifier is sufficient.

In addition, the response time to optical input is within 20 μs,
It operates at extremely high speed as a photodetector element in the long wavelength range.

In this example, a photodetecting element made by doping Sl with phosphorus and boron was explained, but of course this can be applied to compound semiconductors such as GaAs, nP, Zn5e, and 0dTe, as well as 70 mixed crystals, superlattices, and mixed crystals. A superlattice containing mixed crystals may also be used.

Of course, a group 1 substance such as Ge or 5iGe may be used together with a compound semiconductor.

Further, the spectral sensitivity characteristics shown in FIG. 2 can be changed by changing the amount of doping, and if the device is to be used in a longer wavelength band, it can be handled by increasing the amount of doping.

This also applies to fabrication using other material systems.

Moreover, any dopant may be used as long as it can form P-type or N-type.

[Effect of the invention] The photodetecting element of the present invention has the following effects.

(1) Since a highly doped semiconductor is used, it is unaffected by small amounts of impurities, so even low-quality crystal materials can be used, and the characteristics will hardly change even if a small amount of distortion occurs during the manufacturing process. Therefore, stable characteristics can be obtained.

(11) Since the device generates photovoltaic force, the dark current is 0 during zero-bias operation, and unlike photoconductive devices, the dark current does not fluctuate due to temperature changes, and the device does not change over time. Since no dark current is generated even when the light is on, it is possible to detect very small amounts of light.

(Compared to a calorimeter-type thermocouple light meter,
Since the sensitivity is about 1000 times higher, electrical processing of signal output becomes easier.

It is also mechanically extremely strong and will not be damaged by vibrations.

Moreover, it can be extremely miniaturized, and light in a minute area can be detected with high precision.

(1v) The electrical response speed to optical input is extremely fast, about 10 μs, and can be applied to fields that require high speed (such as optical output control of laser light).

By changing the amount of M doping, the spectral sensitivity characteristics can be greatly changed, making it possible to control semiconductor materials.

It is possible to utilize an operating region beyond the long wavelength limit that comes from approximately
This is effective for designing light weight C, etc.

In addition, it is easy to make an optical detector that can be used in a wavelength range of about 5 μm using Sl, and if a slight decrease in sensitivity is acceptable, a photodetector that can be used in a wavelength range of several tens of μm can be obtained, so special A long-wavelength detector can be constructed from inexpensive silicon without using other materials.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a photodetecting element for explaining the present invention in detail. FIG. 2 is a spectral sensitivity characteristic diagram for explaining the present invention in detail. FIG. 5 is a bar diagram for explaining the present invention in detail. 1...Extractor electrode 2...5102 Protective film 6...:...P Region 4...N+Si substrate 5...Extractor electrode 1... ... Spectral sensitivity characteristics 2 of conventional 31 photodiode ... Spectral sensitivity characteristics 1 of the photodetecting element of the present invention
...N+ layer 2...PN junction 6...P+ layer 4...Fermi level or higher

Claims (1)

[Claims] In a photodetecting element having a junction of a P-type semiconductor and an N-type semiconductor, the Fermi level of the P-type semiconductor is in a valence band, and the Fermi level of the N-type semiconductor is in a conductor. A photodetecting element characterized by: