JPH0330479A - Infrared detector - Google Patents

Abstract

PURPOSE:To obtain an infrared detector high in sensitivity to infrared rays of long wavelength and small in dark current by a method wherein the infrared detector is provided with a photodiode whose P-N junction region with a prescribed pattern is formed on a semiconductor substrate, where the substrate is continuously decreased in minority carrier density starting from the P-N junction along the depthwise direction of the substrate. CONSTITUTION:An infrared detector is provided with a photodiode whose P-N junction region 11A with a prescribed pattern is formed on a semiconductor substrate 11 by introducing impurity atoms whose conductivity type is opposite to that of the substrate 11 into the semiconductor substrate 11, where the substrate 11 is continuously decreased in minority carrier density starting from the P-N junction 11A along the depthwise direction of the substrate. For instance, the P-type Hg1-XCdXTe substrate 11 so structured as to increase in carrier density 11A along the depthwise direction is employed, where the minority carrier concentration of the substrate 11 decreases continuously starting from the P-N junction 11A along the depthwise direction form 10<10>/cm<2> through 10<8>/cm<2>. By this setup, the electron density decreases in rate of change at the end of a P-N junction when a reverse bias is applied, and a detector small in dark current can be obtained.

Description

[Detailed Description of the Invention] [Summary] Infrared with a photodiode having a P-N junction! la
Regarding the detection device, with the aim of constructing an infrared detection device that has high sensitivity to long-wavelength infrared rays and low dark current, impurity atoms of the opposite conductivity type of the substrate are introduced into a semiconductor substrate to form a predetermined pattern. l
In an apparatus including a photodiode having a -N junction region formed therein, the minority carrier concentration of the substrate is configured to decrease continuously from the P-N junction along the depth direction of the substrate.

[Industrial application field]

The present invention relates to a photovoltaic infrared detection device.

Infrared detection devices are required to be small, have a large number of pixels, and have high sensitivity in long wavelength bands.

When forming a detection device with high sensitivity in a long wavelength band, it is necessary to form a photoelectric conversion section using a P-N junction on a semiconductor substrate with a narrow energy bandgap. When a PN junction is formed in a narrow semiconductor substrate, the dark current (1) leakage current when no signal light is incident on the N junction at the PN junction tends to increase.

If this dark current is large, the signal-to-noise ratio will be small when signal light is photoelectrically converted by a diode, so it is necessary to reduce the generation of this dark current.

[Conventional technology]

In a conventional infrared detection device using a P-N junction such as a photodiode, impurity atoms of the opposite conductivity type are introduced onto a compound semiconductor substrate having an energy hand gear corresponding to a desired photosensitive wavelength. A photodiode was formed by forming a P-N junction on the substrate.

Therefore, for example, mercury, cadmium, tellurium (Hgl-
When a photodiode is formed on a compound semiconductor substrate such as 8CdXTe), the composition ratio of atoms constituting the substrate, that is, the X value, is changed so that the substrate has a desired energy band gap. .

FIG. 4 shows an explanatory diagram of energy bands of a conventional infrared detection device made of a photodiode.

In the figure, 1 is a P-type tlgl-, Cd, Te substrate crystal;
2 is the depletion layer of the P-N junction of the photodiode formed in the substrate crystal, 3 is the N-type region 4 in which N-type impurities are introduced into the substrate crystal, is the Fermi level, and 5 is the energy at the bottom of the conduction band. Level 6 is the energy level of the −L portion of the valence band.

As shown in the figure, in the conventional device, the P-
The carrier concentration of the substrate at the N junction 7 and the P of the substrate
The carrier concentration of the substrate in a region with a predetermined depth (1) from the -N junction 7 was formed to be equal.

Here, in general, if the energy band gap of the semiconductor substrate is F and the speed of light of infrared rays is C311 as a blank constant, then the maximum window light wavelength λ of this diode is given by equation (1).

λ=hc/E, (1) As shown in equation (1), the above 1.
By changing the values of 1g and □CdXTe0X and determining the value of □ to a predetermined value, an infrared sensing element sensitive to a desired wavelength λ was formed.

[Problem to be solved by the invention] The dark current of a photodiode is dominated by the characteristics of the crystal itself, such as the size of the energy band gap, which is based on the composition of atoms constituting the semiconductor substrate for forming the photodiode. It is actually difficult to obtain a photodiode with a dark current that is lower than the dark current value determined by the characteristics of the crystal itself.

Therefore, in order to minimize the dark current value within the range of values determined by the characteristics of the crystal itself, for example, the number of impurity atoms introduced into the crystal, or the treatment method of the P-N junction surface, etc. By improving the various conditions in the diode manufacturing process, the dark current value of the formed detection device can be formed to be the smallest value among the dark current values naturally determined by the characteristics of the crystal itself. Ta.

An object of the present invention is to provide an infrared detection device that is sensitive to long wavelengths and has a small dark current value.

(Means for Solving the Problems) As shown in the principle diagram of FIG. 1, the infrared detecting device of the present invention has a predetermined pattern of P-N by introducing impurity atoms of the opposite conductivity type into a semiconductor substrate 11. In a device equipped with a photodiode forming the junction 11A, the minority carrier concentration ratio in the thermal equilibrium state of the substrate is continuously smaller along the depth direction of the substrate 11 than the P-N junction 11A. Configure it so that it becomes

[For production]

FIG. 2 shows a carrier concentration distribution diagram when a reverse voltage is applied to the infrared detecting device of the present invention.

In FIG. 2, 11 is a P-type IIg+-x CdXTe substrate, 12 is a depletion layer at the P-N junction, and 13 is an N' region 14 into which N-type impurities are introduced, which are in a schematic thermal equilibrium state (imaginary). 15 is a schematic electron concentration curve in a thermal equilibrium state, and 14A is a schematic electron concentration curve in a thermal equilibrium state in a conventional device.

As shown in the figure, in the apparatus of the present invention, the electron concentration of minority carriers decreases along the depth direction of the substrate 11 as shown by the arrow, as shown in the electron concentration curve "KIA 14" in the thermal equilibrium state. The electron concentration vA16 when a voltage is applied in the reverse direction to the diode of the present invention moves along the electron density curve 14 when no voltage is applied to the diode of the present invention, so the electron concentration vA16 is The state approaches the concentration curve 14.

On the other hand, when a reverse voltage is applied to a diode having a conventional electronic 4th curve 4i14A in a constant thermal equilibrium state in the depth direction of the substrate, the conventional electronic 4th curve 17 is different from that when no voltage is applied. The state approaches the conventional electron concentration curve 14A. Comparing the electron concentration curve 16 of the present invention with the electron concentration curve 17 of the conventional device when a reverse bias is applied, it is found that at the PN junction 11A at the interface between the depletion layer 12 and the substrate 11. The rate of change of electron 4 degrees when a reverse bias is applied is lower in the present invention.

At the interface between the depletion layer and the substrate, the smaller the rate of change in electron concentration when a voltage is applied in the opposite direction, the less dark current will be generated due to the so-called diffusion current that flows according to the concentration gradient. By lowering the minority carrier (minority carrier) 1 degree in the thermal equilibrium state of the substrate along the depth direction of the substrate as in the present invention, the rate of change in the electron concentration when a reverse bias is applied is reduced and dark An infrared sensing element with low current consumption can be obtained.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 3 shows the carrier concentration distribution (B) of the infrared detection device according to the present invention.
It is a diagram schematically shown along with an energy band diagram (^) of the device in the depth direction of the xTe substrate.

As shown in the figure, in the device of the present invention, the minority carrier concentration is from 101 G/cm3 to 108 G/cff along the depth direction of the substrate from the P-N junction 11A of the detection device.
It has become smaller continuously since i3. In order to reduce the minority carrier concentration along the depth direction of the substrate, it is preferable to form a substrate of Hg1-x caXTe in which the carrier concentration increases along the depth direction of the substrate. To form such a substrate, for example MOCVD
(Metal Organic Chemical V
In vapor phase growth methods such as apor deposition method and molecular beam epitaxial growth method, CdTe1
While forming an epitaxial layer on the plate, the supply amount of impurity atoms such as gold (ΔU), arsenic (^S), etc., which become dopants is increased at the initial stage of growth, and gradually decreased as the growth time progresses. In this embodiment, the P-N junction 1
101b/am” at 1A, the specified depth,
For example, it is set to 1018/cna' at 20 μm.

After forming an epitaxial layer of lIg+-x Cdx Te in which the hole carrier concentration gradually decreases on the substrate in this way, boron atoms are ion-implanted from the Hg+-x Cdx Te crystal in the top layer to form a P-type layer. to form a photodiode.

In this way, a photodiode is formed on a substrate where the majority carrier concentration is higher in the depth direction than at the PN junction of the substrate.

In a semiconductor substrate, there is generally a (2)-2 relationship between the intrinsic carrier concentration N1, the electron concentration N, and the hole 4 degree P.

(Nil=N-P (2) Therefore, P
In a Hg+-x CdXTe substrate, when the minority carrier concentration N decreases along the depth direction of the substrate, the majority carrier concentration increases along the depth direction of the substrate.

In this way, the minority carrier concentration decreases from the P-N junction along the depth direction of the substrate, so that when a reverse bias is applied at the P-N junction end, the rate of change in electron concentration decreases, A detection device with less dark current generation can be obtained.

In the above embodiment, Hgl□Cd, Te
II-Vl group compound semiconductor crystal was used, but other
Compound semiconductors such as CdTe of the n-vr group, compound semiconductors such as GaAs of the m-v group, P of the IV-Vl group
A compound semiconductor such as b5nTe or a ternary compound semiconductor crystal such as A I GaAs may also be used.

In addition, a P-N junction is formed two-dimensionally on a compound semiconductor substrate,
An infrared sensing device may be formed with a two-dimensional photodiode.

[Effects of the Invention] As is clear from the above description, the present invention has the effect of providing a high-quality infrared detection device with reduced dark current and a high S/N ratio.

Electron concentration curve of the previous device, Show the line.

18 is the intrinsic carrier concentration

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the infrared detection device of the present invention, Fig. 2 is a carrier concentration distribution diagram of the detection device when reverse bias is applied, and Fig. 3 (A) and (B) are implementations of the detection device of the present invention. An example energy band diagram and carrier concentration distribution diagram, FIG. 4 is an explanatory diagram of the energy band of a conventional infrared detection device. In the figure, 11 is a semiconductor substrate (P type 11g+-++ Cd, Te
1 plate), 11^ is the P-N junction surface, 12 is the depletion ", 13 is the N" region 14 is the electron concentration curve, 14A is the electron concentration curve in the conventional device, 15 is the hole concentration curve, 16 is the voltage The electron concentration curve of the device of the present invention when voltage is applied, 17 is the cousin diagram when voltage is applied.
'yg degree power, zutoo' Fm 2nd figure misfire day kamichizaki 1 nazubodai da jha τ narrowing! Muki "- Bashi F diagram < A) v: 7th completion; t7t, l 粁gJ (B) Figure 3

Claims (1)

[Scope of Claims] In an apparatus in which a photodiode is provided in which a semiconductor substrate (11) is doped with impurity atoms of the opposite conductivity type of the substrate to form a P-N junction (11A) in a predetermined pattern, An infrared detection device characterized in that the minority carrier concentration of the substrate decreases continuously from the P-N junction along the depth direction of the substrate.