JPH05129646A - Infrared detector and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide an infrared detector with good yield, which is less liable to produce false signals due to stray light. CONSTITUTION:A first layer 14 consisting of crystals of Hg, Cd and Te is formed by liquid-phase epitaxy. A second layer 16 consisting of crystals of Cd and Te is formed on the first layer by MOCVD. A third layer 4 consisting of crystals of Hg, Cd and Te is formed on the second layer by liquid-phase epitaxy, and the third layer serves as a photodetecting part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting element and a method for manufacturing the same. Mercury, Cadmium, Tellurium (Hg
_A single or a plurality of crystal blocks made of _1-x Cd _x Te) is provided on a supporting substrate, and a pair of contact electrodes are formed on both sides of the main surface of the crystal block, and an area between the electrodes serves as an infrared receiving section. Infrared detecting elements are known.

In this type of photoconductive type infrared detecting element, infrared rays to be received may enter the light receiving portion from the rear surface side through the supporting substrate to cause an undesired pseudo signal. In order to realize a high-performance infrared detecting element, it is required to deal with infrared rays incident on the light receiving portion from the back surface side.

[0003]

2. Description of the Related Art FIG. 4 is a diagram showing the structure of a conventional general infrared detecting element. Reference numeral 2 is a support substrate, 4 is a crystal block made of mercury, cadmium, and tellurium, 6 is contact electrodes provided on both sides of the main surface of the crystal block, and 8 is a lead wire for connecting the contact electrode 6 to an external circuit. ..

As the support substrate 2, a bulk crystal of cadmium tellurium or a crystal of cadmium tellurium grown on the surface of sapphire is used. The crystal block 4 is formed on the supporting substrate 2 by a liquid phase epitaxial growth method.

Infrared rays 1 are applied to the crystal block 4 as a light receiving portion.
When 0 is incident, the electric conductivity of the crystal block 4 changes according to the intensity of the infrared rays. Therefore, by applying an appropriate current between the electrodes 6 and 6, the intensity of the infrared rays received from the change in the resistance value of the light receiving portion. Can be detected.

[0006]

By the way, since the supporting substrate 2 is generally transparent to infrared rays to be received,
When infrared rays enter the support substrate 2 as stray light 12 from the side surface of the support substrate 2, the stray light is reflected by the upper surface and the lower surface of the support substrate 2 and enters the light receiving portion from the lower surface (back surface) side.

When stray light is incident on the light receiving portion, a pseudo signal is generated in addition to a signal based on infrared rays that should be originally received, and a ghost or the like occurs when an infrared image is obtained based on a detection signal of the element.

In order to prevent generation of a pseudo signal due to stray light, it is effective to form a shielding film that does not transmit infrared rays between the support substrate and the light receiving portion. Conventionally, as this type of shielding film, one in which a metal film such as Cr is interposed between the supporting substrate and the light receiving portion has been proposed.

However, in order to effectively prevent stray light from entering the light receiving portion, it is necessary to form a shielding film on almost the entire back surface side of the light receiving portion. At that time, there was a problem that the contact electrodes 6, 6 were easily short-circuited by the shielding film, and the manufacturing yield of the infrared detection element was low.

The present invention was created in view of the above circumstances, and an object thereof is to provide an infrared detecting element which is less likely to generate a pseudo signal due to stray light and has a good manufacturing yield, and a manufacturing method thereof.

[0011]

The infrared sensing element of the present invention comprises a first layer composed of mercury, cadmium and tellurium crystals,
A second layer made of a cadmium-tellurium crystal and a third layer made of a mercury-cadmium-tellurium crystal are laminated in this order from the back surface of the element, and the third layer is configured as a light receiving portion.

The method for manufacturing an infrared sensing element of the present invention is a method of liquid phase epitaxy on a cadmium-tellurium crystal surface of a supporting substrate made of a cadmium-tellurium crystal or a cadmium-tellurium crystal and sapphire by a liquid phase epitaxial growth method.
Forming a first layer made of cadmium tellurium crystals, forming a second layer made of cadmium tellurium crystals on the first layer by a metal organic chemical vapor deposition method, and forming a second layer on the second layers And a step of forming a third layer made of a mercury-cadmium-tellurium crystal by a liquid phase epitaxial growth method.

[0013]

According to the present invention, since the first layer made of mercury, cadmium and tellurium crystals is provided, the light receiving portion (third layer)
The stray light from the back side of the first layer is absorbed by the first layer, and there is no possibility of generating a pseudo signal due to the stray light.

Further, when the contact electrodes are formed on both sides of the main surface of the third layer which becomes the light receiving portion, there is no possibility of short-circuiting between the contact electrodes as in the case of forming the shielding film made of a conductor.

Further, since the second layer made of the cadmium tellurium crystal is interposed between the first layer made of the mercury cadmium tellurium crystal and the third layer, the composition of mercury and cadmium in the first layer made the third layer. When the ratio is made different, the composition ratio in the first layer and the third layer can be set to a desired value.

As described above, according to the present invention, it is possible to provide an infrared detecting element in which a pseudo signal due to stray light is unlikely to occur and which has a good manufacturing yield.

[0017]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is a configuration diagram of an infrared detection element showing an embodiment of the present invention. The same reference numeral represents the same object throughout the drawings.

Reference numeral 2 denotes a supporting substrate made of a cadmium-tellurium bulk crystal or a composite substrate of cadmium-tellurium and sapphire. On the supporting substrate 2, a first layer 14 made of mercury-cadmium-tellurium crystal is formed. There is.

A second layer 16 made of cadmium-tellurium crystal is formed on the first layer 14, and a third layer (light-receiving portion) 4 made of mercury-cadmium-tellurium crystal is formed on the second layer 16. Has been formed.

Reference numeral 6 denotes a contact electrode for passing a current through the third layer 4, and a pair of contact electrodes 6 are provided on the second layer 16 on both sides of the third layer 4. Reference numeral 8 is a lead wire for connecting the contact electrode 6 to an external circuit.

When the composition ratio of mercury to cadmium in the mercury-cadmium-tellurium crystal is (1-x): x, x in the first layer 14 is set to 0.1 or less. Further, x in the third layer 4 is set according to the wavelength of infrared rays to be received.

For example, the wavelength of infrared rays to be received is 3 to 5
In the case of the band of μm, x is set to about 0.3, and when the wavelength of infrared rays to be received is in the band of 10 μm, x is set to about 0.2.

FIG. 2 is a diagram schematically showing the relationship between the transmittance and the wavelength with the composition as a parameter. In the figure, the vertical axis represents the transmittance and the horizontal axis represents the wavelength. Reference numeral 18 is x = 0.1
The reference numeral 20 represents the characteristic when x = 0.2, and the reference numeral 22 represents the characteristic when x = 0.3. Reference numeral 24 represents the characteristics of the cadmium tellurium crystal (corresponding to the case of x = 1.0).

As is apparent from FIG. 2, the supporting substrate 2 made of, for example, cadmium tellurium crystal has a thickness of 3 to 10 μm.
Since the band is transparent to the infrared light to be received, the infrared light incident from the side surface of the element can become stray light.

In the present embodiment, since the first layer 14 made of mercury / cadmium / tellurium crystal having a composition ratio satisfying x≈0.1 is provided between the supporting substrate 2 and the light receiving portion 4,
Stray light having a wavelength corresponding to the wavelength of infrared rays to be received is rapidly attenuated when entering the first layer 14 side from the supporting substrate 2 side, and thus a pseudo signal due to stray light is hardly generated.

When a practical infrared detecting element is realized by setting x in the light receiving portion in the range of 0.2 to 0.3, x in the first layer is set to 0.1 or less, It is possible to effectively prevent generation of a pseudo signal due to stray light.

FIG. 3 is a diagram for explaining the manufacturing process of the infrared detecting element in this embodiment. First, FIG.
As shown in (A), at least on the supporting substrate 2 in which the cadmium-tellurium crystal is exposed on the crystal growth surface, mercury is used so as to satisfy a composition ratio such that x becomes 1 or smaller by the liquid phase epitaxial growth method. Forming a first layer 14 of cadmium tellurium crystals.

Here, the liquid phase epitaxial growth method is a method in which a solution in which a component element of a crystal is a solute is brought into contact with a supporting substrate at a high temperature, and then the temperature is gradually lowered to deposit a crystal having a required composition ratio on the supporting substrate. It is a method of growing.

Next, as shown in FIG. 3B, a metal organic chemical vapor deposition method (MOCVD method) is applied to the first layer 14.
Thus, the second layer 16 made of cadmium tellurium crystal is formed. Dimethylcadmium (DMCd) can be used as a source of cadmium in the MOCVD method, and diethyl tellurium (DET) can be used as a source of tellurium.
e) can be used.

If the second layer 16 is too thick, stray light may occur in this second layer, so it is desirable that the second layer 16 be sufficiently thinner than the first layer 14 and the like. After that, as shown in FIG. 3C, a third layer made of a mercury-cadmium-tellurium crystal in which x is set according to the wavelength of infrared rays to be received by the liquid phase epitaxial growth method on the second layer 16. 4 '
To form.

Then, as shown in FIG. 3D, the third layer 4'is formed by etching or the like to form the light receiving portion 4 having a predetermined shape, and then the contact electrode 6 and other apertures are formed as necessary. Form.

According to this embodiment, the liquid phase epitaxial growth method for forming the first layer 14 and the third layer 4'is generally carried out at a temperature of 500 ° C. or higher, while the second layer 16 is formed. Since the MOCVD method for achieving the above can be performed at a relatively low temperature of 300 ° C. or lower, there is no fear that the crystal composition ratio in the vicinity of the hetero interface becomes unstable,
The first layer 14 and the third layer 4'having a required composition ratio can be obtained. Further, when forming the contact electrode 6,
Since the short circuit need not be considered at all, the manufacturing yield is improved.

[0033]

As described above, according to the present invention,
The pseudo signal due to stray light is less likely to be generated, and the infrared detecting element having a good manufacturing yield can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an infrared detection element showing an embodiment of the present invention.

FIG. 2 is a diagram showing wavelength characteristics with a composition of a mercury-cadmium-tellurium crystal as a parameter.

FIG. 3 is a diagram showing a manufacturing process of the infrared detection element showing the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 2 Support substrate 4 3rd layer (light receiving part) 6 Contact electrode 14 1st layer 16 2nd layer

Claims (3)

[Claims] 1. A first layer (14) comprising a mercury-cadmium-tellurium crystal and a second layer comprising a cadmium-tellurium crystal.
Third layer consisting of (16) and mercury, cadmium and tellurium crystals
(4) is laminated in this order from the back side of the element, and the third layer (4) is used as a light-receiving portion, which is an infrared detecting element. 2. When the composition ratio of mercury and cadmium in the mercury-cadmium-tellurium crystal is (1-x): x, x in the first layer is 0.1 or less, and the third layer is the third layer. 2. In the infrared detection element according to claim 1, wherein x is in the range of 0.2 to 0.3. 3. A supporting substrate comprising a cadmium tellurium crystal or a cadmium tellurium crystal and sapphire.
(2) a step of forming a first layer (14) composed of a mercury-cadmium-tellurium crystal on the cadmium-tellurium crystal plane by a liquid phase epitaxial growth method, and a metal organic chemical vapor deposition method on the first layer A step of forming a second layer (16) made of a cadmium tellurium crystal, and a step of forming a third layer (4 ′) made of a mercury cadmium tellurium crystal on the second layer by a liquid phase epitaxial growth method. A method for manufacturing an infrared detecting element, comprising: