JPH02241064A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To obtain a photodetector having high sensitivity for detecting a light having a very-long wavelength band by providing a semiconductor substrate, a first contact layer provided thereon, a multiple quantum well layer provided further thereon, a second contact layer provided on the well layer, a signal light incident face, an exciting light incident face and external voltage applying means. CONSTITUTION:A semiconductor board 1, a first contact layer 2 provided on the board 1, a multiple quantum well layer 3 provided on the layer 2, a second contact layer 4 provided on the layer 3, a signal light incident face 5, an exciting light incident face 6, and external voltage applying means 7 are at least provided. The layer 3 is irradiated with an excitation light hnuP with short wavelength, electrons are excited to a quantum ground level 8 in the layer 3 from a valence band 21, and carrier electrons to be excited from the level 8 to high quantum levels are supplied at the time of incidence of a signal light hnuS with a long wavelength. for example, the excitation light hnuP is radiated as a pulse light synchronized with the signal light hnuS.

Description

[Detailed Description of the Invention] [Summary] Regarding a semiconductor light receiving element, a semiconductor substrate, a first contact layer provided on the semiconductor substrate, a multiple quantum well layer provided on the first contact layer, and the The method includes at least a second contact layer provided on the multiple quantum well layer, a signal light incident surface, an excitation light incident surface, and an external voltage applying means, and is configured to irradiate the multiple quantum well layer with short wavelength excitation light. The carrier electrons are excited from the valence band to the quantization base level in the multi-quantum well layer, and are excited from the quantization base level to a higher quantization level when a long wavelength signal light is incident. The semiconductor light-receiving element is configured so as to supply the following.

[Industrial application field]

The present invention relates to improvements in high-sensitivity semiconductor light-receiving elements for detecting light in an ultra-long wavelength band.

Infrared light in the wavelength band of 5 to 15 μm is used in fields such as non-contact measurement of object temperature and detection of pollutants (e.g. CO□ gas), and has become increasingly important in recent years. There is a need for a highly sensitive light-receiving element that can detect light in such long wavelength bands.

[Conventional technology]

A photodetector that detects long-wavelength light, that is, infrared light;
(In addition, InSb and HgC with a band gap of 0.5 eV or less are suitable for high-speed response photodetectors.
Photoconductive type using dTe etc. or pbl-
A photovoltaic type using X Sn x Te is known.

However, due to problems with S/N and light-receiving sensitivity, and the difficulty of making large single crystals, it was not possible to increase the number of elements (such as increasing the number of elements), making it unable to adequately support future more advanced application fields.

Recently, as a new semiconductor light-receiving element, a high-sensitivity light-receiving element in a long wavelength region that uses a quantum well structure and utilizes transitions between electronic levels within the quantum well has been proposed.

FIG. 5 is a diagram explaining an example of a conventional semiconductor light-receiving device having a quantum well layer.
(b) is an energy band diagram, and (c) is a time change diagram of the amount of carriers and output in the quantum well due to signal light irradiation.

In the figure, 1 is a substrate made of, for example, GaAs. 2 is the first contact layer, for example, n+4aAs
s3 is a multiple quantum well layer, for example, GaAs/^
l It is a multiple superlattice layer made of GaAs, and the well layer 31 and the barrier layer 32 are alternately formed by molecular beam epitaxial generation (MBE) or metal organic decomposition deposition (MO-CVD), respectively. It is made up of several 10 layers each. 4 is the second contact layer, for example n
-Constructed from GaAs.

5 is the incident plane of the signal light (hν3) to be detected, and 7 is a voltage applying means to pass the electric signal Fi7a, 7b to the signal light (hν,).
This is to take out the excited carriers (electrons) to the outside as a current and detect them as electrical output.

In a semiconductor superlattice, when the width of the well layer becomes as narrow as the quantum mechanical wavelength of electrons, such as 100 Å or less, the energy band of the quantum well becomes discretized (bandwifting) due to the so-called quantum size effect. A quantization level is generated in the well layer (edited by the Institute of Electronics, Information and Communication Engineers: Electronics, Information and Communication Handbook, p 430.198
8).

Figure (b) is an energy band diagram of such a semiconductor superlattice layer, in which the inside of the quantum well corresponds to the depth (band offset) of each well layer 31 (for example, a GaAs layer) in the conduction band 20. This shows the state in which the quantization level shown by the broken line occurs. In addition, Q.

is its ground state, which corresponds to the quantized base level 8.

On the other hand, in the valence band 21, as shown in the figure, it is known that a band offset that is too large in −m does not occur. Note that this energy band diagram shows a state where the energy band is tilted due to the application of an external electric field.

Normally, in the initial state, the ground state Q1 of the well layer 31
Since electrons (el) exist stochastically in , due to thermal excitation, etc., when signal light (hν, ) is irradiated on \, the electrons existing in the ground state Q, change to a higher level Q, The electrons (ex I e8.
) is taken out to the outside as a current by the electric field generated by the external voltage applying means 7 and detected.

That is, since light is detected by configuring a large number of quantum wells in a very thin photoconductive region, that is, a semiconductor superlattice layer, a highly sensitive semiconductor light-receiving device can be obtained.

In addition, by changing the material, thickness, and other configurations of the superlattice layer, we can set the band offset appropriately and detect the signal light (hν
3) wavelength band can be selected.

[Problem that the invention sought to solve]

However, in the conventional semiconductor light-receiving element described above, when continuous signal light or high-speed pulse signal light is irradiated, carrier replenishment due to thermal excitation or the like cannot keep up.

Figure (c) schematically shows the situation. That is, (
When a signal light (hνS) pulse as shown in a) enters the multi-quantum well layer 3, the average amount of carriers (electrons) in the quantum well decreases each time the signal light is irradiated, as shown in (b). As a result, as shown in (c), there is a problem that the output level gradually decreases and the detection sensitivity deteriorates, and it is necessary to solve this problem.

[Means to solve the problem]

FIG. 1 is a diagram for explaining the present invention in detail, and (A) in the same figure is a cross-sectional structural diagram of the element. The difference from the conventional example shown in FIG.
The multi-quantum well layer 3 is to be irradiated with the light.

As a result, the valence band and the quantized basis level 8 in the quantum well
The multi-quantum well layer 3 is irradiated with excitation light (HVP) having an energy difference greater than or equal to the energy difference between the two and the electrons are supplied to the quantization base level within the quantum well.

Further, by irradiating the excitation light (hvp) in synchronization with the signal light (hv3), the dark current of the light receiving element can be reduced.

On the other hand, the signal light (hν,) is incident on the multiple quantum well layer 3 not perpendicularly (, laterally or obliquely), and the signal light (hν,)
absorption is carried out effectively.

That is, the above problem is solved by the semiconductor substrate 1, the first contact layer 2 provided on the semiconductor substrate 1, the multiple quantum well layer 3 provided on the first contact layer 2, and the multiple quantum well layer 3. A second contact layer 4 provided on the layer 3, a signal light incident surface 5, an excitation light incident surface 6, and an external voltage applying means 7 are provided. The layer 3 is irradiated to excite electrons from the valence band to the quantized base level 8 in the multi-quantum well layer 3, and from the quantized base level to a higher level when a long wavelength signal light is incident. This problem can be solved by using a semiconductor light-receiving element configured to supply excited carrier electrons.

Further, the excitation light may be irradiated as pulsed light synchronized with the signal light, or the excitation light may be irradiated from above the surface of the multiple quantum well layer, and the signal light may be irradiated in a lateral or diagonal direction of the multiple quantum well layer. The S/N is better by inputting from
can be improved and stabilized to higher sensitivity.

[Effect]

FIG. 1(b) is an energy band diagram of the light receiving element of the present invention. The broken line is the quantization level caused by the quantum size effect, and when the signal light (hν, ) is irradiated, the electrons filled in the ground state Q1 are excited to the higher level Q7, and the barrier layer 32
The electrons (e3°ea) that have overcome the external voltage application means 7
Due to the electric field caused by this, the current is taken out to the outside and detected.

However, as mentioned above, when continuous signal light is irradiated,
The replenishment of carriers through thermal excitation cannot keep up, and the carriers (electrons) in the quantum well are depleted.

Therefore, in the present invention, excitation light (hν,) having sufficient energy to pump carriers (electrons) from the valence band 21 to the quantized base level 8 in the quantum well is applied to the quantum well layer 3. Since the quantization base level in the quantum well is always filled with electrons, it is possible to prevent deterioration of light reception sensitivity even when continuous signal light is received.

Furthermore, by irradiating the excitation light (hvp) in synchronization with the signal light (hν, ), when the incident signal light (hν3) is O, the excitation light (hν9) is also prevented from entering, thereby darkening the light receiving element. It is possible to prevent the current from increasing.

In other words, it is possible to improve the S/N ratio.

FIG. 2 is a time-varying diagram of the output according to the carrier excitation method of the present invention, which explains this in an easy-to-understand manner, and (a) shows the signal light (
(b) is an example of the pulse waveform of the excitation light (hν,) when the pulse waveform of the excitation light (hν,) is irradiated as continuous pulsed light synchronized with the signal light (hν,).

(c) shows a model of the average carrier amount in the quantum well in this case, and since electrons are constantly pumped by excitation light (HVP), can be considered to be V-constant.

As a result, as shown in (d), it can be seen that a constant and stable output can be obtained in response to the incidence of the signal light (hv, ) pulse.

As can be seen from the above, the responsivity of this photodetector is more important than the extinction time of the electrons in the quantum well.
) It is determined by the need to increase the interval between pulses, but normally the extinction time is several to several Lops, so
Sufficiently high responsiveness can be obtained.

In addition, the electrons at the quantization level in the quantum well have no degrees of freedom in the vertical direction of the quantum well layer and are discrete, and because the electrons in the ground state Q are excited to the higher quantization level Q7. In other words, in order to absorb the energy of the signal light (hν, ), the signal light (hν3
) must have an electric component. Therefore, it can be seen that it is effective to make the signal light (hv3) incident not from above the multi-quantum well layer 3 but from the side or oblique direction. On the other hand, the excitation light (HVP) is the excitation of electrons from the valence band, and there are no restrictions on the irradiation direction, so it is emitted from above the multiple quantum well layer 3, which has the highest irradiation efficiency and facilitates device configuration. , for example, it may be irradiated at an angle close to perpendicular.

〔Example〕

FIG. 3 is a diagram explaining the present invention in detail.

In the figure, 1 is a Cr-doped 5l-GaAs substrate (specific resistance ~
106 Ωcm semi-insulating substrate), 2 is the first contact layer, which is an n''-GaAs layer with a thickness of 0.5 μm, and 3 is a multiple quantum well layer, which is a well layer 31 made of n-GaAs with a thickness of 65 μm. 95 n 41 o, zs Gas, ?SA3
were used as the barrier layer 32, and 50 pairs were formed by the MBE method.

4 is a second contact layer made of n+-Ga with a thickness of 0.5 μm.
It is an As layer.

Reference numeral 5 denotes the incident surface of the signal light (hν,) to be detected, which is cut and polished at an angle θ on the surface of the substrate 1. Therefore, the signal light (hν,) is incident at an angle from the bottom of the multiple quantum well layer 3. It was made to be input to . Reference numeral 6 denotes a plane of incidence of excitation light (hv, ), and the excitation light (hlzP) is irradiated vertically from above the multi-quantum well layer 3. The excitation light (hν, ) is 0.
An 8 μm band semiconductor laser was used.

7 is the voltage application means, and is it an electrode? DCI through a, 7b
OV was applied, and carriers (electrons) excited by the signal light (hv, ) were taken out as a current to the outside and detected as an electrical output. Signal output detection is 11μm
The test was carried out in the same manner as in the case of a normal semiconductor light-receiving element, using the band light as the test signal light.

When the semiconductor light receiving element of this example was evaluated for detection using test signal light under the above conditions, it was confirmed that the expected stable high sensitivity characteristics could be obtained.

FIG. 4 is a diagram for explaining another embodiment of the present invention, in which a semiconductor laser 100 is provided closely to the excitation light (hν,) incident surface, making the entire light receiving element compact and robust. It has been constructed to improve credibility.

In the above embodiments, a single-element structure is shown, but it goes without saying that a multi-element type light-receiving device can be constructed by arranging a large number of light-receiving elements on a substrate.

Depending on the wavelength band of the detection signal light, the material composition of the multiple superlattice forming the multiple quantum well layer, the thickness and number of layers of the barrier layer and the well layer, etc. may be determined based on the spirit of the present invention.
It goes without saying that you can choose as appropriate.

Further, according to the present invention, the signal light is transmitted to the end face of the multiple quantum well layer.
That is, it can be applied to integrated optical circuits if it is made to enter from the lateral direction through an optical fiber or a light guide.

〔Effect of the invention〕

As described above, according to the present invention, excitation light can move the electrons from the valence band to the quantum well without affecting the transition between the quantization levels of electrons in the quantum well used for signal light detection. Since the electrons are pumped and supplied within the device, there is no deterioration in light-receiving sensitivity, which greatly contributes to improving the performance of semiconductor light-receiving elements.

It is a figure explaining the example of an element.

In the figure, 1 is the board, 2 is the first contact layer; 3 is a multiple quantum well layer, 4 is a second contact layer; 5 is a signal light incident surface; 6 is the excitation light incident surface, 7 is an external voltage applying means.

[Brief explanation of drawings]

FIG. 1 is a detailed explanation of the present invention, FIG. 2 is a time change diagram of the output by the carrier excitation method of the present invention, FIG. 3 is a detailed explanation of the present invention, and FIG. 4 is a diagram explaining the present invention in detail. FIG. 5 is a diagram illustrating an example of a conventional semiconductor light-receiving device (a) having a quantum well layer. !
T surface force Lm diagram 2nd P force and theory F3A of the present invention Figure 1

Claims (3)

[Claims] (1) A semiconductor substrate (1) and a first contact layer (
2), a multiple quantum well layer (3) provided on the first contact layer (2), a second contact layer (4) provided on the multiple quantum well layer (3), and a signal light. It comprises at least an entrance surface (5), an excitation light entrance surface (6), and an external voltage application means (7), and irradiates the multiple quantum well layer (3) with short wavelength excitation light to generate a valence band. from the quantized basis level in the multi-quantum well layer (3) (
8) A semiconductor light-receiving element, characterized in that carrier electrons are excited from the quantization base level to a higher quantization level upon incidence of long-wavelength signal light. (2) The semiconductor light-receiving device according to claim (1), wherein the excitation light is emitted as pulsed light synchronized with the signal light. (3) The excitation light is irradiated from above the surface of the multiple quantum well layer (3), and the signal light is incident on the multiple quantum well layer (3) from a side or an oblique direction. 1) or (2) the semiconductor light-receiving device.