JPH0831619B2 - Infrared detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an infrared detecting element, and more particularly to an improvement of a Schottky type infrared detecting element suitable for detecting long-wavelength infrared rays.

[Prior Art] In recent years, there is an increasing demand for a system for imaging a scene using infrared rays.

In view of such a demand, development of an infrared detecting element for a wavelength band of 3 to 5 μm and 8 to 14 μm, which is generally called an atmospheric window, is under development, and is particularly suitable for observing or imaging an object at room temperature. There is a strong need for an infrared detection element in the long wavelength region including the 8 to 14 μm band.

As such an infrared detection element, those having various structures are conceivable, but the Schottky type element has a simple structure and a simple manufacturing method, and further has excellent detection characteristic uniformity, Widely used as an infrared detection element.

As a conventional Schottky type infrared detection element, for example, there is one shown in FIGS. 2 (A) to (C).

As shown in FIG. 4A, this infrared detecting element has a structure in which a semiconductor 10 having a conductivity type of P and a predetermined conductor 12 are bonded to each other to form a bonding portion 14.

Then, in the case of the back surface type in which the infrared rays are incident on the joint portion 14 as indicated by the arrow FA, the conductor 12 may be thickened, but of the surface type in which the infrared rays are incident on the joint portion 14 as indicated by the arrow FB. In this case, the conductor 12 needs to be thin.

When infrared rays enter the vicinity of the junction 14 as indicated by arrows FA and FB, electron-hole pairs are formed and these are separated at the junction 14, as shown in FIG. That is, the holes H move to the semiconductor 10 side as shown by the arrow FC and are separated from the electrons E, and a voltage is generated across the element.
Then, due to this voltage, a current flows through the resistor 16 as shown by the arrow FE.

The above operation will be described below using an energy band model.

First, as shown in FIG.
The junction causes a junction interface or a junction portion 14 having a contact potential difference φ _ms called a Schottky barrier. In the figure, E _C , E _F ,
E _V denotes the conduction band edge level, the Fermi level, the filled band to the valence band edge levels, respectively.

When the frequency of infrared rays incident on the conductor 12 near the junction 14 is ν, it is possible to generate an excited hole having a kinetic energy exceeding the Schottky barrier when hν> qφ _ms. .

 Here, h represents Planck's constant and q represents unit charge.

The generated excitation hole H crosses the Schottky barrier and enters the semiconductor 10, as shown by the arrow FF, and the electron E remains in the conductor 12. Incident infrared rays are detected by detecting these accumulated charges.

Although the above description is for the case where the element is composed of the P-type semiconductor and the conductor, it can be similarly composed of the n-type semiconductor and the conductor. In this case, the carriers are reversed and electrons are injected into the semiconductor, leaving holes inside the conductor.

[Problems to be Solved by the Invention] By the way, the maximum detectable wavelength λ _C of the Schottky type infrared detection element as described above is represented by λ _C = hc / qφ _ms (c is the speed of light), To detect longer-wavelength infrared rays, a Schottky junction with a small φ _ms is required.

Further, even when detecting an infrared ray having a shorter wavelength than the wavelength λ _C , the quantum efficiency η is Since (C is a quantum efficiency coefficient), there is a relationship that η increases as φ _ms decreases (for example, H. Elabd an
d WFKosoncky, RCA Review vol.43 no.4 December 198
2 See P569-P589).

That is, reducing the contact potential difference φ _ms of the junction 14 in the Schottky type light receiving element enables not only detection of long-wavelength infrared light but also improvement of quantum efficiency.

However, if the contact potential difference φ _ms is made too small, thermal noise is generated, which requires cooling at a lower temperature.

That is, for the desired wavelength λ _C to be detected, an appropriate value of the contact potential difference φ _ms that satisfies the above conditions is determined.

However, since the value of the contact potential difference φ _ms is determined by the combination of the semiconductor and the conductor, it is impossible to arbitrarily change the value.

For the above reason, there is a problem that some semiconductors cannot satisfactorily detect long-wavelength infrared rays.

The present invention has been made in view of the above points,
(EN) Provided is a Schottky type photodetector capable of reducing the Schottky barrier even in a combination of a semiconductor and a conductor which cannot detect long-wavelength infrared rays, and varying its size, and capable of excellently detecting long-wavelength infrared rays. That is the purpose.

[Means for Solving the Problems] According to the present invention, a semiconductor that contacts an electric conductor to form an energy barrier for infrared detection has a first semiconductor layer and a second semiconductor layer having a band gap smaller than that of the first semiconductor layer. And a semiconductor layer having a superlattice structure in which the semiconductor layers are regularly arranged periodically.

[Operation] According to the present invention, since the semiconductor side has the superlattice structure, the subband is formed. Therefore, the contact potential difference of the Schottky junction is smaller than that in the case of the Schottky junction using only the first semiconductor layer and the conductor, and long-wave infrared rays can be detected.

Embodiment An embodiment of the present invention will be described in detail below with reference to FIG. The same reference numerals are used for the same components as those of the above-mentioned conventional technique.

FIG. 1 (A) shows the structure of an infrared detecting element according to an embodiment of the present invention. In this figure, the semiconductor 24 formed by the conductor 20 and the bonding portion 22 is formed by the first semiconductor layer 26 and the second semiconductor layer 28.

That is, the semiconductor 26 whose contact potential difference φ _ms is desired to be small
And the semiconductor layer 28 having a band gap smaller than that of the semiconductor layer 26 are regularly arranged periodically.
A superlattice structure is formed as a whole. By joining the semiconductor 24 of this superlattice structure and the conductor 20,
A Schottky type infrared detection element is configured.

Next, the action of the superlattice structure as described above will be described with reference to the energy band diagram of FIG.

First, when the semiconductor 24 has a superlattice structure and the region of the semiconductor layer 28 sandwiched between the semiconductor layers 26 has a thickness of de Broglie wavelength or less, or a thickness of the carrier mean free path or less. Becomes a quantum well layer, and an energy level is generated by the quantum effect.

Further, when the semiconductor layer 26 has a thickness equal to or less than the de Broglie wavelength, carriers can freely move between the quantum wells due to the tunnel effect, so that a subband is generated.

This subband becomes a conduction band subband in the conduction band and a valence band subband in the valence band. Of these, the valence band subband E _VS is formed in the energy band between the valence band edge of the semiconductor layer 26 and the valence band edge of the semiconductor layer 28.

By the way, the above valence band sub-band E _VS is
By changing the thickness of the semiconductor layer 28, which is a quantum well layer, the semiconductor layer can be brought close to the valence band edge of the semiconductor layer 26,
It is possible to get close to the valence band edge of 28. The same applies to the conduction band subband.

Therefore, the contact potential difference φ _{ms of} the conventional Schottky junction formed by the semiconductor 10 and the conductor 12 shown in FIG.
The contact potential difference φ _ms of the Schottky junction of this embodiment formed by the semiconductor 24 having the superlattice structure of the semiconductor layer 26 and the semiconductor layer 28 and the conductor 20 shown in FIG. 1 is smaller than that.

The contact potential difference φ _ms can be changed depending on the thickness of the semiconductor layer 28.

As described above, the contact potential difference φ _ms can be made smaller than that of the conventional one by changing the thickness of the semiconductor layer forming the superlattice structure, and the size can be varied within a certain range. You can

Therefore, infrared rays having a long wavelength can be favorably detected, and the quantum efficiency can be improved without being greatly affected by thermal noise.

Next, a specific application example of the above embodiment will be described.

The semiconductor 24 is, for example, a P-type Si semiconductor layer 26 and a P-type Ge.
The semiconductor layer 28 of _x Si _1-x (x is a composition ratio, 0 <x ≦ 1) is combined to form a superlattice structure. The semiconductor layer 26 has a thickness equal to or less than the de Broglie wavelength, for example, 100.
Å It is less than or equal to. Then, as the conductor 20, for example, PtSi
Is used.

The band gap of Si is 1.12 eV, the band gap of Ge is
It is 0.66 eV. On the other hand, the band gap of Ge _x Si _1-x changes in the range of 0.66 to 1.12 eV depending on the composition ratio x.

In the semiconductor 24 having a superlattice structure composed of Si and Ge _x Si _1-x , the Ge _x Si _1-x layer having a small band gap serves as a quantum well layer.

For example, when the x value is 0.3, the difference between the valence band edges of Si and Ge _0.3 Si _0.7 is about 0.22 eV (eg R. People, IEE
E J.Quant.Electron., Vol.QE-22, No.9 September 1986
See P1696-P1710).

Therefore, in the semiconductor 24 having the superlattice structure as described above, by changing the film pressure ratio of both semiconductor layers, the valence band subband E _{VS is set to} an energy level higher than the valence band edge of Si by 0 to 0.22 eV. Can be formed.

Therefore, according to the Schottky junction formed of PtSi and the superlattice structure of Si and Ge _0.3 Si _0.7 , the junction potential difference φ
It is possible to freely change and set _ms within the range of 0.03 to 0.25 eV.

On the other hand, the contact potential difference φ _ms of the conventional Schottky junction formed of P-type Si and PtSi is about 0.25 eV, which corresponds to λ _C = 5 μm when converted to the wavelength of detected infrared light.

Therefore, according to this example, it is possible to detect infrared rays in the 8 to 14 μm band (φ _ms = 0.09 eV) which could not be detected by the conventional Schottky junction, or in the longer wavelength band.

Further, even in the case of detecting infrared rays in the wavelength band of 3 to 5 μm, there is an advantage that the quantum efficiency can be increased.

As described above, according to this embodiment, the contact potential difference φ _ms of the Schottky junction, which was conventionally determined by the combination of the semiconductor and the conductor, can be reduced by using the semiconductor having the superlattice structure. In addition to enabling long-wavelength infrared detection with a Schottky type light receiving element,
It is also possible to improve quantum efficiency.

Further, not only the value of the contact potential difference φ _ms can be reduced but also it can be freely changed within a predetermined range, so that it is possible to obtain a Schottky type infrared detection element having an arbitrary detection wavelength. .

Incidentally, the present invention is not limited to any of the above embodiments, for example, in the above embodiments, the element was constituted by the superlattice structure of Si and Ge _x Si _1-x and the conductor of PtSi, single crystal, A superlattice structure made of various semiconductors such as polycrystal and amorphous may be combined with various conductors such as metal, metal silicide, and metallic amorphous.

Further, although the above-mentioned embodiment uses the P-type semiconductor, it is clear that the same effect can be obtained by using the n-type semiconductor.

Further, a large number of infrared detecting elements according to the present invention may be arranged one-dimensionally or two-dimensionally to form an imaging device.

[Effects of the Invention] As described above, according to the present invention, there is an effect that the Schottky barrier can be made small and the size thereof can be varied so that long-wavelength infrared detection can be favorably performed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment according to the present invention, and FIG. 2 is an explanatory view showing an example of a conventional device. [Description of symbols of main parts] 20 ... Conductor, 22 ... Junction, 24 ... Semiconductor (superlattice structure), 26 ... First semiconductor layer, 28 ... Second semiconductor layer, E _VS: Valence band subband, S: P ⁺ silicon substrate.

Claims (1)

[Claims] 1. An infrared detection element for detecting infrared rays by utilizing an energy barrier formed at a junction by bringing a semiconductor and a conductor into contact with each other, wherein the semiconductor is a first semiconductor layer, and A second semiconductor layer having a smaller band gap, the first and second semiconductor layers being regularly arranged periodically to form a superlattice structure. Infrared detector.