JPH06260675A - Photosensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a photosensor in which a photoelectric current is not decreased and a dark current can be decreased and a method for manufacturing the same. CONSTITUTION:A photosensor of a heterostructure comprises two types of n-type Hg1-xCdxTe layer 2 and a Hg1-xCdxTe layer 3 containing different compositions and conductivity types and laminated on a Cd1-xZnxTe substrate 21, a composition variable part 11, and a p-n junction 12, wherein both layers 2 and 3 are laminated in a state that the position of the part 11 is deviated from that of the junction 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light detecting element, and more particularly to a light detecting element for detecting infrared rays in a long wavelength band of 10 μm band.

[0002]

2. Description of the Related Art Conventionally, a photo-sensing device has been provided with a MOCVD (Metal
 Organic Chemical Vapor Deposition; Organic Metal Vapor Deposition
Long method), for example, on a CdTe substrate
p-type Hg_1-xCd_xTe layer (x = 0.21) and n-type Hg_1-xCd_xTe
Layers (x = 0.21) formed by MOCVD method
P-type Hg_1-xCd_xTe layer (x = 0.21) and n-type Hg_1-xCd
_xTe layer (x = 0.21) is mesa-etched to form a pn junction
Both semiconductor layers have the same composition (x value).
Formed a junction-type photodetector with a cutoff wavelength of 10 μm.
ing.

By the way, the above-mentioned homojunction type photodetector with a cut-off wavelength of 10 μm has a large dark current, so that the resistance when a bias voltage for operating the detector is not applied, that is, the zero bias resistance R ₀ is low. In other words, a heterojunction photodetector has been proposed to overcome this drawback.

The structure is shown in FIG. This manufacturing method is, for example, an n-type Hg _1-x Cd _x Te layer (x = 0.21) on a CdTe substrate 1.
2 and the p-type Hg _1-x Cd _x Te layer (x = 0.24) 3 by MOCV
The n-type Hg _1-x Cd _x Te layer (x = 0.
21) Etch 2 and p-type Hg _1-x Cd _x Te layer (x = 0.24) 3 into a mesa.

Next, Zn is formed on the portion etched in the mesa shape.
A protective film 4 made of S is formed by vapor deposition, a predetermined position of the protective film 4 is opened, and an electrode 5 made of gold is vapor deposited by the lift-off method to form a photodetecting element. This photodetector is referred to as a heterojunction photodetector because the Hg _1-x Cd _x Te layers 2 and 3 have different compositions (x values).

Such a heterojunction type photodetector element
The energy band diagram is shown in Fig. 3 (b). As shown, p
Type Hg_1-xCd_xTe layer (x = 0.24) 3 is n-type Hg_1-xCd_xTe layer (x
= 0.21) Since the x value is larger than 2, p-type Hg_1-xCd_xTe
Energy gap E of layer 3 _gpIs n-type Hg_1-xCd_xTe layer
2 energy gap E_gnWill be greater. Dark current is heat
Hole 6 formed in the n layer by excitation, and by thermal excitation
It is generated by the movement of both carriers of the electron 7 generated in the p layer.
To live.

The dark current I _d is expressed by equation (1) and tends to increase as the carrier mobility μ increases.

[0008]

[Equation 1]

By the way, since the mobility of the electron 7 is about two orders of magnitude higher than the mobility of the hole 6, the dark current due to the electron 7 is dominant from the hole 6. That is, the thermal excitation of the electrons 7 may be suppressed to suppress the dark current. Therefore, p-type
Energy gap E _{gp of} Hg _1-x Cd _x Te layer (x = 0.24) 3
To make the electrons more difficult to be excited in the conduction band 9 than in the valence band 8. Thus, as a heterostructure, p-type Hg _1-x Cd _x
Increasing the energy gap E _gp of the Te layer (x = 0.24) 3 suppresses the generation of dark current.

Thus, the n-type Hg _1-x Cd _x Te layer 2 and the p-type Hg
By changing the x value of _1-x Cd _x Te layer 3 with each other,
An energy gap of the Hg _1-x Cd _x Te crystal changes, and by utilizing this, a dark current is reduced, and a zero-bias resistance R _{0 is} thereby increased to develop a photo-sensing element.

[0011]

By the way, as shown in the energy band diagram of FIG.
It is arranged so that the center position of the composition changing portion 11 where the value changes and the center position of the pn junction 12 where the conductivity type changes are the same position. The center position of the portion 11 is about 1 μm on the n-layer side and about 0.2 μm or less on the p-layer side.

Particularly, the allowable positional deviation toward the p-layer side is M
The yield is reduced because it is a narrow range that is difficult to control for a crystal growth method such as OCVD, MBE, or LPE or a P / N junction formation method such as ion implantation. When the center position of the composition variation portion 11 exceeds the allowable range and is deviated to the p-layer side, a spike 13 is formed in the valence band 8 of the n-layer as shown in FIG. An energy barrier 14 is formed. Hole 6 photoelectrically converted from this energy barrier 14
However, there is a problem in that the photocurrent is reduced and the optical signal amount is reduced.

Further, the conventional device has the following problems. Misfit dislocations are generated in the composition variation portion 11 due to lattice mismatch. If there is a pn junction at that position, a tunnel current is likely to occur via the trap order due to misfit dislocations, and the device characteristics deteriorate.

The present invention eliminates the above-mentioned problems and shifts the position of the pn junction and the position of compositional variation from each other, whereby photodetection of a hetero structure having different energy gaps in the p-type region and the n-type region is performed. It is an object of the present invention to provide a photo-detecting element in which a spike phenomenon (energy barrier) does not occur in a pn junction to prevent a decrease in photocurrent and a decrease in optical signal amount is prevented.

[0015]

According to a first aspect of the present invention, there is provided a photo-sensing device in which two kinds of semiconductor layers having different compositions and conductivity types are laminated on a substrate to form a composition variation part and a pn.
In the hetero-structured photodetector formed by providing the junction, the compositional variation portion and the pn junction portion are
It is characterized in that the two semiconductor layers are laminated and provided in a state of being displaced from each other.

In particular, as described in claim 2, the position of the composition variation portion according to claim 1 is provided in the p-type semiconductor layer. As described in claim 3, a semiconductor layer is formed on a substrate placed in a reaction vessel, a gas containing an element for controlling the composition of the semiconductor layer, and an impurity imparting p-type or n-type conductivity type. A method of manufacturing a photodetecting element by supplying a gas containing atoms, heating a substrate, and vapor-phase growing semiconductor layers having different compositions and conductivity types on the substrate, When the gas for controlling the composition of the semiconductor layer and the gas for imparting the conductivity type are supplied to the substrate by switching, the switching timings of the two gases are switched and supplied to the substrate, Characterized by vapor phase growth.

Further, it is characterized in that the gas for imparting the conductivity type is first switched and supplied to the substrate.

[0018]

In the photo-detecting element of the present invention, since the center position of the composition variation portion is provided on the p-layer side, the spike phenomenon disappears at the pn junction portion, and the movement of holes of photoelectrically converted minority carriers causes the spike energy. A photodetector having a heterostructure in which the barrier is not obstructed to prevent a decrease in photocurrent and a decrease in optical signal amount can be obtained with a high yield. Also, the tunnel current due to the misfit dislocations is reduced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 (a) is a cross-sectional view of the photodetector of the present invention.
(b) is an energy band diagram of the photodetector.

As shown in FIGS. 1 (a) and 1 (b), M is deposited on a cadmium-zinc-tellurium (Cd _1-x Zn _x Te, x = 0.03) substrate 21.
10 to 20 n-type Hg _1-x Cd _x Te layer (x = 0.21) 2 by OCVD method
A film with a thickness of μm is formed, and then p-type Hg _1-x Cd _x Te
Layer (x = 0.24) 3 is deposited to a thickness of 2 μm.

Next, the n-type Hg _1-x Cd _x Te layer 2 and the p-type Hg are formed.
_{The 1-x} Cd _x Te layer 3 was formed into a mesa shape by using a wet etching solution of a mixed solution of bromine (Br ₂ ) and methanol to form a mesa shape.

This n-type Hg _1-x Cd _x Te layer 2 and p-type Hg _1-x Cd
_x Te layer 3 is laminated to form a pn junction 12
Then, the film was formed so that the gap between the composition varying portions 11 was 0.2 to 0.4 μm. After that, n-type Hg _1-x Cd _x Te layer 2 and p-type Hg _1-x Cd
After the mesa etching of the _x Te layer 3 and the ZnS protective film 4, a protective film 4 of ZnS was formed by vapor deposition, and a predetermined position of the protective film 4 was opened.

In this way, the holes do not obstruct the movement of the holes due to spikes as in the conventional case, so that a photodetecting element in which the decrease in photocurrent is not observed and the amount of optical signals is difficult to decrease can be obtained.

In order to form this photo-sensing element, as shown in FIG. 2, in a reaction vessel 23 containing a cadmium-zinc-tellurium (Cd _1-x Zn _x Te) substrate 21 placed on a substrate setting table 22. Is replaced with hydrogen gas as a carrier gas.

Next, the valves 29, 31, 32 and 34 are opened in the reaction vessel 23, and Hg in the evaporator 24, dimethyl Cd in the evaporator 25, diisopropyl Te in the evaporator 26, and n in the evaporator 28. A carrier gas of hydrogen gas is introduced into isopropyl iodine as a mold dopant, and the carrier gas is supplied to the reaction vessel 23.
Introduce inside. Then, the high frequency induction coil 36 is energized to heat the substrate 21 to a temperature of 450 ° C.

Next, the total flow rate of hydrogen gas as a carrier gas was set to 6 l / min, and Hg, dimethyl Cd, diisopropyl
The gas partial pressures of Te and isopropyl iodine are 0.04 and 0.04, respectively.
The pressure is set to 5 × 10 ⁻⁵ , 1 × 10 ⁻⁴ , and 3 × 10 ⁻⁶ atmosphere, and the mixture is introduced into the reaction vessel 23 for 4 hours. As a result, the n-type Hg _1-x Cd _x Te (x = 0.21) layer 2 having a thickness of 10 μm is formed.

Next, the valve 34 is closed and the valve 33 is opened to introduce a carrier gas into the evaporator 27, and the partial pressure of the p-type dopant tert-butylarsine is set to 5 × 10 ⁻⁵ atm and the reaction is performed for 15 minutes. Introduced into the container 23, the n-type
Hg _1-x Cd _x Te (x = 0.21) Layer 2 (above) p-type Hg _1-x Cd _x
A Te (x = 0.21) layer 35 is formed to a thickness of 0.3 μm.

Next, the amount of carrier gas introduced into the evaporator 25 containing dimethyl Cd is increased to make the partial pressure of dimethyl Cd 6 × 10 ⁻⁵ atm and flow into the reaction vessel 23 for 1 hour.
A p-type Hg _1-x Cd _x Te (x = 0.24) layer 3 is formed to a thickness of 2 μm.

By doing so, the n-type Hg _{1- x} Cd _x Te layer 2 and the p-type in which the pn junction portion and the composition variation portion are displaced from each other are formed.
It can be formed by stacking the Hg _1-x Cd _x Te layer 3. When the characteristics of the photodetector thus formed were measured, a good photodetector with a cutoff wavelength of 12 μm, a quantum efficiency of 60% or more, and a zero bias resistance value R ₀ = 0.5 MΩ was obtained.

In this embodiment, the MOCVD method is used.
Although the Hg _1-x Cd _x Te layer was formed, the photodetector having the structure of the present invention can be formed by using not only the MOCVD method but also the molecular beam epitaxial growth method, the hot wall epitaxial growth method, and the liquid phase epitaxial method. is there.

[0031]

As described above, according to the photodetector of the present invention, it is possible to prevent a spike phenomenon that tends to occur at the upper end of the valence band, to prevent a decrease in photocurrent, and to prevent dark current from occurring. A photodetector whose generation was suppressed was obtained, and the tunnel current due to misfit dislocations was also suppressed.

[Brief description of drawings]

FIG. 1 is a photodetector of the present invention and its energy band diagram.

FIG. 2 is an explanatory diagram of an apparatus for manufacturing the photodetector of the present invention.

FIG. 3 is a conventional photo-sensing element and its energy band diagram, and an energy band diagram showing an inconvenient state of the conventional element.

[Explanation of symbols]

2 n-type Hg _1-x Cd _x Te layer (x = 0.21) 3 p-type Hg _1-x Cd _x Te layer (x = 0.24) 4 protective film 5 electrode 11 composition variation part 12 pn junction part 21 Cd _1-x Zn _x Te substrate 22 Substrate table 23 Reaction vessel 24,25,26,27,28 Evaporator 29,31,32,33,34 Valve 35 p-type Hg _1-x Cd _x Te layer (x = 0.21) 36 High frequency Induction coil

Claims (3)

[Claims] 1. A composition variation part (1) is obtained by laminating two kinds of semiconductor layers (2, 3) having different compositions and conductivity types on a substrate (21).
1) and a pn junction (12) are provided in a hetero-structured photodetector, the position of the composition variation part (11) and the position of the pn junction (12) are displaced from each other. In the state, both semiconductor layers (2,3)
A photo-detecting element, which is characterized by being provided by stacking. 2. A photo-detecting element, characterized in that the center position of the composition variation part (11) according to claim 1 is provided in the p-type semiconductor layer (3). 3. The substrate (21) installed in the reaction vessel (23),
Supplying a gas containing an element that constitutes the semiconductor layer (2,3) and controls the composition of the semiconductor layer (2,3) and a gas containing an impurity atom that imparts p-type or n-type conductivity At the same time, the substrate (21) is heated, on the substrate (21), a composition, and a semiconductor layer (2, 3) different in conductivity type from each other is vapor-deposited, in the method of manufacturing a photo-sensing element, When the semiconductor layer (2, 3) is formed and the gas for controlling the composition of the semiconductor layer (2, 3) and the gas for imparting the conductivity type are switched and supplied to the substrate (21), A method for manufacturing a photo-detecting element, characterized in that gas is supplied to the substrate (21) while being switched with gas switching timings shifted from each other, and vapor growth is performed.