JP2630279B2 - Schottky photodetector and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photodetector using a Schottky diode.

[0002]

2. Description of the Related Art A conventional Schottky photodetector will be described with reference to FIG. FIG. 5A is a diagram showing a configuration of a Schottky-type photodetector.
vol.43 p569-587: H. Elabd and WF Kosonocky, “Theo
ry and Measurements of photoresponse for Thin Film
Pd ₂ Si and PtSi Infrared Schottky-Barrier Detector
s with Optical Cavity, RCAA Review Vol. 43, pp. 569-587: Erabud and Kosonoki, "Theory on the Photoresponse Characteristics of Schottky Barrier Infrared Detectors Using Palladium Silicide and Platinum Silicide Thin Films with Optical Resonance Structure" And in fact ", hereinafter referred to as" Reference Document 1 ").

Referring to FIG. 5A, a Schottky photodetector has a platinum silicide (Pt) as a metal electrode (1).
Si) film and p-type silicon (p) as a semiconductor substrate (2)
-Si) substrate. Semiconductor substrate (2)
The ohmic contact (3) to is shown schematically.

The p-type silicon substrate as the semiconductor substrate (2) has a specific resistance of 30 to 50 Ωcm.

[0005] As shown in FIG.
00) is incident from the back surface of the substrate.

A Schottky barrier height of platinum silicide (PtSi) with respect to a p-type silicon substrate is about 0.22 eV.
Therefore, the Schottky photodetector having this configuration can be used as an infrared detector having sensitivity to infrared rays of about 5.6 μm.

Conventionally, the incident light (infrared ray) is shown in FIG.
As shown in (B), platinum silicide (PtS
i) It was understood that hot holes absorbed in the film and generated in platinum silicide were selectively passed at the PtSi / p-Si interface.

In FIG. 5B, the hot holes passing therethrough are indicated by reference numeral 200, and the hot holes that are reflected are indicated by reference numeral 20.
This is indicated by 1. FIG. 5B shows the Fermi level (4) of the metal, the depletion layer (5), the potential (6) according to Reference 1, and the reverse bias voltage (7).

This process is described in detail in Reference 1. Hot hole 200 that has been selectively passed
Flows into the p-type silicon substrate and is detected as a signal.

With this understanding, Schottky type infrared image sensors have been actively developed, and, for example, a 1 million pixel infrared image sensor has been prototyped [Reference:
T.Seto, A.Mori, R.Ishigaki, S.Itoh, N.Yutani, MK
imata, N. Tubouchi, A. Akiyama, and T. Sasaki, "Perfo
rmance of IM-IRCCD imager with PtSi Schottky-barri
er detectors ", proceeding of SPIE 2020, p404 (199
3), Seto et al., "Performance of IM-IRCCD of PtSi Schottky Barrier Detector," Proc. Of SPII, 2020, 404 (1993)].

Unfortunately, the understanding based on FIG. 5B is not accurate.

That is, in an actual Schottky diode, the hot hole moves while feeling the potential (6 ') shown by the solid line in FIG.

The difference between FIG. 5 (B) and FIG. 5 (C) depends on whether or not the image force is considered. The potential actually felt by the hot hole is the potential indicated by the dotted line a (corresponding to the solid line in FIG. 5B) of FIG. 5C, and the potential due to the image force indicated by the broken line b in FIG. 5C. This is obtained by adding a char 1 / (16 * π * ε * x). Here, ε is the dielectric constant of the substance, and x is the distance from the platinum silicide (PtSi / p-Si) interface to the semiconductor side.

That is, the hot hole feels the potential (6 ') shown by the solid line in FIG. In FIG. 5C, the effective Schottky barrier height (also called “barrier height”) is Φb-effect, and its position (also called “barrier position”) is x-effect.

By absorbing light, platinum silicide (PtS
The hot hole generated in i) reaches the position of the effective Schottky barrier height, and a part of the hot hole selectively passes into the silicon substrate and is detected as a signal.

[0016]

As described above, actually,
The hot holes generated in platinum silicide (PtSi) move to the barrier position x-effect in addition to the moving distance in platinum silicide (PtSi). At that time, the number of hot holes decreases due to lattice scattering or the like during movement.

For this reason, in order to improve the sensitivity of the Schottky photodetector, it is necessary that the generated hot holes reach the barrier within a short moving distance and that the height of the barrier is reduced.

As a conventional example in which the sensitivity is improved by lowering the barrier height, for example, Japanese Patent Publication No. Sho 63-51546 discloses, as shown in FIG.
By implanting a p-type dopant (8) into the interface of the p-type silicon (PtSi / p-Si) Schottky diode, the structure shown in FIG.
A device having a potential as shown in FIG.

In this method, the width of the depletion layer is reduced by increasing the dopant concentration near the interface, and the effective barrier height is reduced by the tunnel effect.

However, in practice, as described with reference to FIG. 5C, it should be understood as a potential in consideration of the mirror image effect, and as in FIG. There is a distance to the barrier position.
In FIG. 6, a diagram showing potentials in consideration of the mirror image effect is omitted.

That is, in the conventional Schottky photodetector, no consideration is given to the fact that the effective barrier position is located on the semiconductor side from the metal / semiconductor interface due to the mirror image effect.

For this reason, no measure is taken against the effect that the number of hot carriers decreases during the movement from the metal / semiconductor interface to the effective barrier position. This can be said in common with the conventional example shown in FIGS.

Further, a conventional example shown in FIG.
In JP-A-51546, the effective barrier height is reduced by the tunnel effect. However, in this method, the detection of the thermally excited noise signal also increases. For this reason, as the S / N of the Schottky diode itself decreases and the charge amount increases, the load on a signal transfer element such as a CCD also increases.

Therefore, it is important to prevent the generated hot holes from decreasing.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a Schottky photodetector having improved sensitivity characteristics.

[0026]

In order to achieve the above object, the present invention provides a photodetector using a Schottky diode comprising a semiconductor substrate and a metal, wherein the photodetector is provided near an interface between the semiconductor substrate and the metal. Depletion layer in semiconductor substrate
Wherein a high dielectric constant layer having a higher dielectric constant than that of the semiconductor substrate is formed in a region where is spread .

In the Schottky photodetector according to the present invention, preferably, the high dielectric constant layer is formed in the Schottky diode depletion layer region in the semiconductor substrate.
Is formed.

Further, in the Schottky photodetector of the present invention, preferably, the high dielectric constant layer is formed of an extremely thin insulator as an insulator in a Schottky diode depletion layer region in the semiconductor substrate. It is characterized by.

The present invention relates to a method of driving a Schottky photodetector in which a high dielectric constant layer having a higher dielectric constant than the semiconductor is formed in a depletion layer region of a Schottky diode composed of a semiconductor substrate and a metal. The barrier position is
A method for driving a Schottky photodetector, characterized in that a bias voltage is applied so as to be located at the high dielectric layer portion.

The present invention also relates to a method for driving a Schottky photodetector in which a high dielectric constant layer having a higher dielectric constant than the semiconductor is formed in a depletion layer region of a Schottky diode comprising a semiconductor substrate and a metal. A method for driving a Schottky photodetector, characterized in that the Schottky photodetector is set in a floating state immediately after resetting to a predetermined bias voltage, and a potential is read out when resetting again after a predetermined time.

[0031]

In a Schottky diode composed of a metal and a semiconductor substrate, silicon (S) is used for a mirror image effect.
i) While the effective barrier is located at the back of the substrate, according to the present invention, the second semiconductor layer or the insulating layer having a higher dielectric constant than the semiconductor substrate is placed in the region where the depletion layer is spread. By forming, the effective barrier position is brought closer to the vicinity of the interface, and the decrease in the number of generated hot carriers is suppressed.

In the present invention, by forming the high dielectric constant layer, the tendency of the potential due to the mirror image effect becomes sharp, so that the barrier position of the effective potential, which is the sum of the mirror image effect and the potential of the Schottky diode depletion layer, is reduced. Utilizes approaching the interface.

[0033]

Embodiments of the present invention will be described below with reference to the drawings.

[0034]

Embodiment 1 FIG. 1 shows the structure of a Schottky photodetector according to an embodiment of the present invention. Referring to FIG. 1, a Schottky photodetector according to the present embodiment includes a platinum silicide (PtSi) film as a metal electrode (1) and a p-type silicon (p-Si) as a semiconductor substrate (2). Titanium nitride (TiN) is formed as a high dielectric constant material (9) in a p-type silicon substrate of a PtSi / p-Si Schottky diode.

Considering the multiple reflection effect of hot holes,
The platinum silicide (PtSi) film uses 3 nm, and the p-type Si substrate uses boron-doped 30 to 50 Ωcm.

Then, p is set so that light can be incident from the back side.
The mold silicon substrate is mirror-polished on both sides.

Titanium nitride (TiN), which is a high dielectric constant material, is formed to a thickness of 1 nm from a position approximately 2 nm to 3 nm from the PtSi / p-Si interface (high dielectric constant material (9 ) Is in the depletion region of the Schottky diode).

FIG. 2 shows the potential of the Schottky photodetector having the structure shown in FIG. FIG. 2A depicts the configuration of FIG. 1 as it is. The solid line in FIG.
The potential due to the structure of (A) is drawn.

The applied voltage of the Schottky diode is-
5 V (reverse bias). This solid line in FIG. 2B is the sum of the potential of the Schottky diode as a solution of the Poisson equation and the potential due to the mirror image effect.

In FIG. 2B, when deriving the two potentials, a one-dimensional profile model that takes into account the dielectric constant at each depth is used.

As a result, the effective barrier position x-effect
Is 3.0 nm from the PtSi / p-Si interface. Since the high dielectric layer (9) is a very thin film having a thickness of 1 nm, hot holes can pass through the high dielectric layer (9) by tunneling.

For comparison, the potential in the case where the high dielectric constant layer (9) is not formed (conventional example) is shown in FIG.
Are indicated by broken lines. In the conventional example, the effective barrier position is about 6.3 nm.

Next, an example of a method of driving a Schottky photodetector according to an embodiment of the present invention will be described with reference to FIG.

FIG. 3A is a diagram showing the potential of the Schottky photodetector having the structure shown in FIG. 1 under the condition of a reverse bias voltage of 5 V.

FIG. 3B is a diagram showing a potential under a condition of a reverse bias voltage of 6 V, and FIG. 3C is a diagram showing a potential under a condition of a reverse bias voltage of 7 V.

Referring to FIG. 3, it can be seen that the effective barrier height sharply decreases according to the value of the reverse bias voltage. The reverse bias voltage of 5 to 7 V is a condition for the reverse bias in a range where the effective barrier position is located in the high dielectric constant film.

As described above, the driving method of adjusting the reverse bias voltage so that the effective barrier position exists within the depth direction range of the high dielectric constant film greatly changes the effective Schottky barrier height with a small driving voltage difference. Can be done.

Further, since the effective barrier position is maintained in the vicinity of the interface, reduction of generated hot holes can be suppressed. Thereby, the sensitivity can be easily adjusted within the range while maintaining high sensitivity.

As the high dielectric constant layer (9), a compound semiconductor such as GaAs or InSb having a relative dielectric constant (electrostatic) higher than that of silicon (11.7) or Ge or the like may be used.

[0050]

Embodiment 2 A second embodiment of the method of driving a Schottky photodetector according to the present invention will be described.

In the driving method according to this embodiment, the Schottky photodetector having the structure shown in FIG. 1 is set to a floating state (floating state) immediately after resetting to a reverse bias voltage of 7 V, for example, 33 ms (millisecond; scanning). When resetting again after the period, the potential is read.

FIG. 4 shows the sensitivity characteristics of this driving method.
In FIG. 4, the horizontal axis is the amount of incident light, and the vertical axis is the read potential (signal potential).

As described with reference to FIG. 3, the sensitivity at a reverse bias voltage of 7 V is high, and the sensitivity is reduced strongly depending on the reverse bias voltage. Therefore, the sensitivity is high at low illuminance and the sensitivity is suppressed at high illuminance. Is done.

This tendency is similarly held in the conventional Schottky photodetector, but is slow as shown by the broken line in FIG.

In the present embodiment, as shown by the solid line in FIG. 4, the sensitivity characteristic is high at low illuminance (small irradiation light amount) (high readout potential) and does not saturate up to high illuminance. It can be said to be optimal for detecting physical phenomena whose relationship with infrared rays is close to logarithmic.

Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment but includes various embodiments according to the principle of the present invention.

[0057]

According to the Schottky photodetector of the present invention (claim 1), the decrease of the signal charge carriers in the movement from the metal / semiconductor interface to the effective barrier position is suppressed, and the photodetector has high sensitivity. Can be achieved.

The above-mentioned effects are similarly achieved by the preferred embodiments of the present invention.

According to the method of driving a Schottky photodetector of the present invention (claim 5), the disappearance of signal charges (carriers) during movement from the metal / semiconductor interface to the effective barrier position is suppressed. By applying a reverse bias voltage, high sensitivity of the photodetector can be achieved.

Further, according to the driving method of the present invention (claim 6), by using a driving method utilizing a sudden change in potential at the position of the high dielectric constant film, high sensitivity can be obtained at low illuminance, and A detector having a large dynamic range can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a Schottky photodetector of the present invention.

FIG. 2A is a diagram showing a configuration of an embodiment of the present invention. (B) is a diagram showing the potential of the Schottky photodetector of one embodiment of the present invention.

FIG. 3 is a diagram showing the potential of the first embodiment of the driving method of the Schottky photodetector of the present invention. (A) ~
(C) is a diagram showing the potential when the bias voltage is variable.

FIG. 4 is a diagram showing sensitivity characteristics of a second embodiment of the driving method of the Schottky photodetector of the present invention.

FIG. 5A is a diagram showing a configuration of a conventional Schottky photodetector. (B) is a diagram showing the potential of the configuration of FIG. 5 (A). (C) is a diagram showing a potential in consideration of the mirror image effect.

FIG. 6A is a diagram showing another configuration of a conventional Schottky photodetector. FIG. 7B is a diagram showing the potential of the configuration of FIG.

[Description of Signs] 1 Metal electrode 2 Semiconductor substrate 3 Ohmic contact 4 Metallic Fermi level 5, 5 ', 5 "Depletion layer 6, 6' Potential 7 Reverse bias voltage 8 P ⁺ dopant 9 High dielectric constant material (High dielectric constant Layer) 100 light 200-202 hot hole

Claims (6)

(57) [Claims] 1. A photodetector using a Schottky diode composed of a semiconductor substrate and a metal, wherein a depletion layer in the semiconductor substrate is provided near an interface between the semiconductor substrate and the metal.
A Schottky-type photodetector, wherein a high-permittivity layer having a higher permittivity than the semiconductor substrate is formed in a region where the width of the semiconductor substrate extends . 2. The Schottky photodetector according to claim 1, wherein a second semiconductor is formed as the high dielectric constant layer in a Schottky diode depletion layer region in the semiconductor substrate. . 3. The Schottky-type photodetector according to claim 1, wherein the high dielectric constant layer is formed of an extremely thin insulating material in a Schottky diode depletion layer region in the semiconductor substrate. vessel. 4. The high dielectric constant layer is made of titanium nitride (T
The Schottky photodetector according to claim 1, wherein the photodetector comprises iN). 5. A method for driving a Schottky photodetector, wherein a high dielectric constant layer having a higher dielectric constant than the semiconductor is formed in a depletion layer region of a Schottky diode made of a semiconductor substrate and a metal. Wherein a bias voltage is applied such that the bias voltage is applied to the high dielectric constant layer portion. 6. A method for driving a Schottky photodetector, wherein a high dielectric constant layer having a higher dielectric constant than the semiconductor is formed in a depletion layer region of a Schottky diode made of a semiconductor substrate and a metal. A method for driving a Schottky photodetector, characterized in that a floating state is set immediately after resetting a detector to a predetermined bias voltage, and a potential is read out when resetting after a predetermined time.