JPH0738142A - Infrared photodetector and photoreceiver - Google Patents

Abstract

PURPOSE:To prevent positive holes from being accumulated in a semiconductor substrate so as to enhance an infrared detector in output power by a method wherein light ray of wavelengths longer than those correspondent to the energy band gap of the semiconductor substrate are applied to the substrate to produce a photocurrent. CONSTITUTION:A P-type high concentration region 11 is formed on a part of a semiconductor substrate 1. A P-type ohmic contact metal alloy material is evaporated on the P-type region 11 for the formation of an electrode 21 which comes into ohmic contact with the P-type region 11. A metal thin film used for a Schottky junction electrode is evaporated on the same plate confronting the electrode 21 to form a Schottky junction electrode 2. Light ray 5 of wavelengths longer than those correspondent to the energy band gap of the semiconductor substrate 1 are made to incident on a gap between the ohmic contact electrode 21 and the Schottky junction electrode 2 to generate a photovoltaic current. A photovoltaic current accelerates carriers generated through an interband level with a high electrical field to efficiently collect holes into a P-type region. By this setup, an avalanche phenomenon being multiplied, an infrared detector of this constitution can be enhanced in output and response speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared light receiving element and device.

[0002]

2. Description of the Related Art As a semiconductor light receiving element for receiving near infrared light having a wavelength of about 1 μm or more, Si (up to 1.1 μm) is used.
m), InGaAs / InP (up to 1.7 μm), Ge
A photodiode having a substrate of (˜1.9 μm) or the like is used. Of these, InGaAs is used for long-wavelength (1.3, 1.55 μm) optical communication, which is in high demand.
/ InP and Ge photodiodes are widely used.

On the other hand, recently, as shown in FIG.
Even a light-receiving element made using a GaAs substrate can detect light in these long wavelength bands by utilizing an excitation mechanism different from optical carrier excitation based on band-to-band transitions. It has been found to have greater photosensitivity than diodes.
("Japanese Patent Application No. 3-194532", "Appl. Phy
s. Lett. , 61, 2575 (1992 ")

[0004]

Among the conventional techniques, 1.
InGaAs / InP and Ge photodiodes used for receiving light of 3 μm and 1.55 μm are very expensive because of high cost of semiconductor substrate material. In addition, the Ge photodiode has a large dark current and often needs to be cooled.

On the other hand, the light-receiving element made of semi-insulating GaAs has a characteristic that a large S / N ratio can be obtained because of the current multiplication function inside the element while suppressing the dark current to a low level. Moreover, the manufacturing cost is generally lower than that of the InGaAs / InP or Ge photodiode. However, in the light receiving element having the structure found in the conventional technique, both surface electrodes are Schottky junctions, and as shown in the energy band diagram of FIG. 6, holes of minority carriers excited by light are accumulated in this portion. As a result, the deterioration of the response speed has been a problem.

The present invention has been made in view of the above problems, and an object thereof is to provide a high-performance infrared light receiving element and an infrared light receiving device to which the infrared light receiving element is applied.

[0007]

In order to solve the above problems, the present invention has a structure in which a pair of electrodes are provided on a plane of a semi-insulating III-V semiconductor substrate with a gap for light incidence. In, a semiconductor light receiving element having an electrode structure in which one electrode is a p-type electrode and the other is a Schottky junction electrode,
In the state where a negative voltage was applied to the p-type electrode side, it was decided to obtain a photovoltaic current by irradiation light having a wavelength longer than the wavelength corresponding to the energy band gap of the semiconductor substrate.

[0008]

With this structure, the long-wavelength irradiation light accelerates the interband levels existing in the semi-insulating III-V semiconductor substrate and the carriers generated at the Schottky junction interface in a high electric field, and By making the speed higher than the saturation speed by an order of magnitude or more, avalanche multiplication occurs and a high output current is obtained, and holes that drifted toward the p-side electrode due to this high electric field are efficiently transferred to the p-type region. To be collected.

Further, in a structure in which a pair of electrodes are provided on a plane of a semi-insulating III-V semiconductor substrate with a gap for light incidence, one electrode is a p-type electrode and the other is an n-type electrode.
A semiconductor light receiving element having an electrode structure as a type electrode generates a photovoltaic current by irradiation light having a wavelength longer than a wavelength corresponding to the energy band gap of the semiconductor substrate in a state where a negative voltage is applied to the p-type electrode side. By accelerating the carriers generated in the inter-band level by a high electric field and increasing the speed to an order of magnitude higher than the normal saturation speed, avalanche multiplication occurs and a high output current is obtained. The influence of the surface level in the n-type region can be reduced.

Further, another electrode is provided on the surface of the substrate opposite to the side where the light-receiving portion electrode is provided so that another bias voltage can be added, so that a band-to-band level or a Schottky junction interface is formed. In addition to the photocurrent in the lateral direction of the surface due to the generated carriers, the photocurrent in the longitudinal direction of the substrate is also applied.

Further, since the electrodes of the light receiving portion are formed in a comb shape with each other, the light incident efficiency can be improved.

Further, by adding a window material for receiving long wavelength light to the infrared light receiving element, it is possible to detect light having a selective wavelength.

[0013]

FIG. 1 shows the basic structure of a semiconductor light receiving element according to the present invention. A high-concentration p-type region 11 is formed on a part of the semi-insulating semiconductor substrate 1 by the impurity selective thermal diffusion method or the like. A metal alloy material for p-type ohmic contact is vapor-deposited on this portion to form an ohmic contact electrode 21 with the p-type region 11. A metal thin film for a Schottky junction electrode is vapor-deposited on the same plane so as to face it, and is used as the other Schottky junction electrode 2. The distance between both electrodes is several to several tens of μm.

A bias voltage power supply 3 is connected between the electrodes 21 and 2 so that the p-type has a negative polarity, and a bias is applied so that the electric field strength becomes several kV / cm or more. In this state, light having a wavelength longer than the wavelength corresponding to the energy band gap of the semiconductor substrate (hereinafter, simply referred to as long-wavelength light 5) is incident on the gap portion between the electrodes 2 and 21, whereby the photocurrent is changed. Occurs,
Incident light can be detected. In the case of GaAs, the detection wavelength range at long wavelengths is approximately 1 to 1.6 μm. The output photocurrent is observed by the ammeter 4 connected to the outside. Instead of an ammeter to observe the light pulse,
Connect an oscilloscope or the like.

Next, the operating mechanism will be described. When long-wavelength light is incident, the interband transition of valence band electrons due to the energy band gap of the semiconductor substrate does not occur,
Excitation of carriers from the interband level existing in the semi-insulating semiconductor substrate 1 and excitation of carriers based on the energy difference of the conduction band that occurs at the metal-semiconductor interface represented by Schottky junction occur. Among the photocarriers generated by these, the electrons drift toward the Schottky junction electrode 2 side and the holes drift toward the p-type ohmic contact electrode 21 side by the electric field due to the bias voltage. However, the total number of optical carriers generated here is originally small. However, in the semi-insulating semiconductor substrate 1 to which an electric field of several kV / cm is applied by the external bias voltage power source 3,
It has been experimentally confirmed that when this is semi-insulating GaAs, scattering due to lattice phonons or the like with respect to drift motion of conduction band electrons is extremely small. "Ja
pan J. Appl. Phys. , 30, 3327,
(1991) ”Therefore, the traveling electrons have a normal saturation velocity (1 × 10 ⁷ cm / cm in the case of GaAs) within a short time.
It gains a large amount of kinetic energy by being accelerated to a speed higher than that of s) by an order of magnitude or more. With this, several kV / cm
Even with such a relatively low electric field strength, avalanche multiplication occurs and the number of carriers increases. This effect and the metal-
semiconductor-metal photo
A photoconductive multiplication effect of a horizontal type light receiving element represented by a detector (MSM-PD) “Japan J. Appl. Phys, 19, 459”.
(1980) "," IEEE J. Quatum E
electron, 22, 1073 (1986)].
It is possible to obtain an output current comparable to that of a photodiode of aAs / InP or Ge. Moreover, especially in GaAs, since the dark current can be suppressed to a low level, a high S / N ratio can be obtained.

Further, in the device structure of this example, since the Schottky junction electrode 2 on the positive bias side is a Schottky junction, the prior art "IEEE IEDM-91,421" is used.
(1991) ”, the holes are efficiently injected from the Schottky electrode 2 by the incidence of the long-wavelength light 5 as compared with the case of the horizontal pin. Therefore, greater photosensitivity can be obtained.

On the other hand, the holes drift toward the ohmic contact electrode 21 with the p-type region 11 and are collected in the p-type region 11. In the conventional technique, this portion also forms a Schottky junction, but in the Schottky junction portion that is normally formed, a thin semiconductor natural oxide film 100 exists at the metal-semiconductor interface, as shown in FIG. The band gap of this oxide film is wider than that of the semiconductor, and holes 102 having a large effective mass cannot pass through this thin gap. Therefore, the accumulation of holes here causes deterioration of the response speed. However, in the present invention, the holes 102 are efficiently collected in the p-type region 11 which is a majority carrier therein, and therefore are not accumulated in the semi-insulating semiconductor substrate 1. Therefore, the response speed is a value determined by the transit time between the carriers of the carrier and the CR constant, which is the product of the inter-electrode capacitance and the series load resistance, which is inherent in such a lateral element, and an extremely high-speed response is possible. .

Here, the Schottky junction electrode 2 for collecting the electrons 101 may be replaced by an ohmic contact electrode 22 having an n-type region 12 formed therein. An example of this structure is shown in FIG. The n-type region 12 is formed on the semi-insulating semiconductor substrate 1 by a method such as selective ion implantation of impurities. The ohmic contact electrode 22 is formed by depositing a metal alloy material for the n-type ohmic contact electrode on this portion. In this case, since the efficient injection of holes from the positive bias Schottky electrode 2 as described above does not occur, the photosensitivity to the long-wavelength light 5 is lowered, but the surface level of the surface level is lower than that of the Schottky electrode 2. It is characterized by being less affected and more stable in terms of manufacturing reproducibility.

In addition to the electrodes 2 and 21 formed on the same surface of the semi-insulating semiconductor substrate 1, an electrode 20 is provided on the semiconductor surface opposite to the electrodes 2 and 21, and another bias voltage power supply 30 is provided therein. Photosensitivity can be further increased by connecting and applying a bias and adding a vertical electric field. An example of this structure is shown in FIG. The polarity of the bias voltage 30 is selected and applied to the electrode 20 so as to increase the surface current on the side on which the long-wavelength light 5 is incident. Specifically, when a negative voltage is applied to the electrode 21 on the p-type region 11 side and the other electrode 2 is at the ground potential, a positive voltage is applied and the electrode 21 in the p-type region 11 is grounded. When a positive voltage is applied to one of the electrodes 2, a negative voltage is applied. As a result, the photocurrent in the vertical direction of the semi-insulating semiconductor substrate 1 is added in addition to the photocurrent in the lateral direction of the surface so far.
It can be higher than the photodiode of s / InP or Ge. On the other hand, this electrode 20 has a thickness of several tens to several hundreds of μm with the surface electrodes 2 and 21 on the light incident side.
Since the semi-insulating semiconductor substrate 1 having a high resistance (ρ> 10 ⁷ Ωcm) is formed between them, the dark current does not increase remarkably. Therefore, the structure of the electrode 20 may be Schottky junction or ohmic contact.

The intensity distribution of the incident light spreads in a plane, and the distance between the electrodes 2 and 21 in the light receiving portion (several to several tens of μm).
If it is difficult to focus the light on the surface, it is desirable that the electrodes 2 and 21 in the light receiving portion have a comb shape in order to increase the incidence efficiency of the long wavelength light 5. This embodiment is shown in FIG. In this case, since the light directly incident on the metal part of the electrodes 2 and 21 is reflected at this part and does not contribute to the photocurrent, there is a loss in the amount of light by that amount, but within a range where the series resistance does not increase significantly, By narrowing the width and increasing the numerical aperture of the light receiving portion, the amount of light loss can be minimized. Further, as described above, since this light receiving element has a current multiplication function, it is possible to sufficiently compensate for this loss.
As described above, according to the present invention, in the light receiving element made by using the semi-insulating semiconductor substrate 1, by removing the hole accumulation effect, a long wavelength band light receiving element excellent in high-speed response characteristics is realized. can do. This is InGaA
Unlike s / InP and Ge photodiodes, GaAs is low cost and high S / N, especially in the case of GaAs.
Is a ratio. Therefore, a semiconductor light receiving element that receives light with a wavelength of 1 to 1.6 μm is formed only by a wafer process such as thermal diffusion of impurities and ion implantation without performing complicated epitaxial growth using semi-insulating GaAs. be able to. In the light receiving element 301, the p-type region 1
Due to the formation of 1, a high speed response is possible, unlike the prior art.

An apparatus for receiving the infrared rays is shown in FIG.
As shown in, a window 303 for selectively passing infrared light can be combined, or the window can be used as a device combined with an intended infrared light emitter 304. Of course, when such selectivity is not used, the device receives light in a wavelength band wider than the conventional one at high speed.

[0022]

The holes drifting toward the p-side electrode due to the irradiation light of long wavelength are efficiently collected in the p-type region, so that these holes are accumulated in the semi-insulating semiconductor substrate. And an extremely high-speed response is possible.

By using one of the electrodes as a p-type electrode and the other as an n-type electrode, not only the same function and effect as above but also the effect of the surface level in the n-type region can be reduced. It is possible to further stabilize the reproducibility in production.

Further, another electrode is provided on the surface of the substrate on the side opposite to the side where the light receiving electrode is provided, and another bias voltage is added, so that in addition to the photocurrent in the lateral direction of the surface, the longitudinal direction of the substrate is increased. Photocurrent is also added, and the photosensitivity can be made higher than that of the InGaAs / InP or Ge photodiode. Further, since the electrodes of the light receiving portion are formed in a comb shape with each other, the light incident efficiency can be improved.

Further, by adding a window material for receiving long-wavelength light to the infrared light receiving element, it is possible to detect light having a selective wavelength.

As described above, in particular, by using the GaAs substrate, the light receiving element having sensitivity in the long wavelength band in the range of 1 to 1.6 μm is compared with the conventional light receiving element made of InGaAs / InP or Ge. , Can be created at low cost. Moreover, since complicated epitaxial growth is not required, the manufacturing cost can be kept low. Further, since it can respond at high speed, it is expected as an inexpensive light receiving element for optical communication using the 1.3 μm and 1.55 μm bands.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a basic structure of a semiconductor light receiving element according to the present invention.

FIG. 2 is a vertical sectional view showing a modified example of the semiconductor light receiving element according to the present invention.

FIG. 3 is a vertical sectional view showing a modified example of the semiconductor light receiving element according to the present invention.

FIG. 4 is a vertical sectional view and a plan view showing a modified example of the semiconductor light receiving element according to the present invention.

FIG. 5 is a diagram showing an example of a semiconductor light receiving element in a conventional technique.

6 is an energy band diagram of the semiconductor light receiving element shown in FIG.

FIG. 7 is an explanatory diagram showing a practical example of a light receiving element.

[Explanation of symbols]

1 ... Semi-insulating semiconductor substrate, 2, 20, 21, 22 ... Electrode, 3, 30 ... Voltage power supply, 4 ... Ammeter, 5 ... Long wavelength light,
11 ... P-type region, 12 ... N-type region, 100 ... Semiconductor native oxide film, 101 ... Electron, 102 ... Hole, 201 ... Valence band, 202 ... Conduction band, 203 ... Inter-band level, 301 ...
Light receiving element, 302 ... Case, 303 ... Window, 304 ... Infrared light emitter.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Iida 1 1126, Nomachi, Hamamatsu, Shizuoka Prefecture 1126 Hamamatsu Photonics Co., Ltd. (72) Inventor Sadahisa Warashi, 1126, 1126 Nomachi, Hamamatsu, Shizuoka Prefecture (72) Inventor Kenichi Sugimoto 1 1126, Nomachi, Hamamatsu, Shizuoka Prefecture 1126 Hamamatsu Photonics Co., Ltd. (72) Inventor Tomoko Suzuki 1 1126, Nomachi, Hamamatsu, Shizuoka Prefecture 1 Hamamatsu Photonics Co., Ltd. ( 72) Inventor Hirofumi Suga 1 Hamamatsu Photonics Co., Ltd. 1 No. 1126 Nomachi, Hamamatsu City, Shizuoka Prefecture

Claims (5)

[Claims] 1. In a structure in which a pair of electrodes are provided on a plane of a semi-insulating III-V semiconductor substrate with a gap for light incidence, one electrode is a p-type electrode and the other is a Schottky junction electrode. In the semiconductor light receiving element having the electrode structure described above, a photovoltaic current is obtained by irradiation light with a wavelength longer than the wavelength corresponding to the energy band gap of the semiconductor substrate in a state in which a negative voltage is applied to the p-type electrode side. An infrared light receiving element characterized by the above. 2. In a structure in which a pair of electrodes are provided on a plane of a semi-insulating III-V semiconductor substrate with a gap for light incidence, one electrode is a p-type electrode and the other is an n-type electrode. In the semiconductor light receiving element having the electrode structure described above, a photovoltaic current is obtained by irradiation light with a wavelength longer than the wavelength corresponding to the energy band gap of the semiconductor substrate in a state in which a negative voltage is applied to the p-type electrode side. An infrared light receiving element characterized by the above. 3. The method according to claim 1, wherein another electrode is provided on the surface of the substrate opposite to the side where the electrode of the light receiving portion is provided so that another bias voltage can be added. Infrared light receiving element. 4. The infrared light receiving element according to claim 1, wherein the electrodes of the light receiving portion have a comb shape with each other. 5. An infrared light receiving device in which the infrared light receiving element according to claim 1 or 2 is further added with a window material for receiving a long wavelength.