JPH01129476A - Infrared photodetector - Google Patents

Abstract

PURPOSE:To prevent the deterioration of element sensibility even when a photodetector is formed in film thickness exceeding the mean free path of electrons by discretely forming interlayer contact layers to quantum well layers held by two contact layers, electrically separating odd-numbered interlayer contact layers and even-numbered ones and respectively connecting the interlayer contact layers to several contact layer. CONSTITUTION:A first contact layer 13 composed of N-type GaAs is applied onto a semi-insulating GaAs substrate 11, and multiple quantum well layers 21 and interlayer contact layers 29 are deposited alternately. An N-type GaAs second contact layer 23 is deposited onto the multiple quantum well layer 21 as an uppermost section. An etching process is repeated, and stepped sections are shaped to the second contact layer 23 on one side of the substrate 11, the even-numbered interlayer contact layers at the time of viewing from the layer 23 and the odd-numbered layers on an end face on the side reverse to said interlayer contact layers and slant faces among the stepped sections. An insulating layer is deposited onto the whole surface, and grooves are formed to each stepped section and the second contact layer 23. A conductive material is applied onto the whole surface on the upper side, a groove (d) is shaped between the second contact layer 23 and the stepped section nearest to the layer 23, and first and second electrodes 43a, 43b are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light receiving element for detecting infrared rays and converting them into electric current, which is included in, for example, radiation thermometers, night vision monitoring equipment, and the like.

(Prior art) Conventionally, in order to detect infrared rays emitted from heat sources, etc.,
As an infrared receiving element that converts the infrared rays into electric current, for example, literature: "XV InternationalQ
uantum Electronics Conf
erence, mechanical Diquest” (X
V International Quantum Electronics Conference, Technical Digest) (pages 8-9, lecture number MCC2゜April 27, 1987)
The device disclosed in This infrared receiving element (hereinafter sometimes simply referred to as an element) is constructed using a gallium-arsenide (GaAs)-based semiconductor, which is a ■-■ group compound semiconductor, and is composed of n-type #jxGa+-xAs. A barrier layer and a well layer made of n-type GaAs are sequentially laminated to form a multiple quantum well, and light absorption occurs between two subbands in the conduction band of this multiple quantum well. There is.

Hereinafter, the structure of the light receiving element disclosed in the above-mentioned document will be explained with reference to the drawings.

FIG. 2 is an explanatory diagram schematically showing a conventional infrared light receiving element in cross section. In the figure, 11 is a substrate made of GaAsJ, 13 is a first contact layer made of n-type GaAs and has an ohmic 'l, and 15 is an n-type AQ x Ga l -X.
17 is a well layer made of n-type GaAs; 19 is the above-mentioned well layer 17; 2 is in contact with the layer 17;
21 is a multi-quantum well layer formed by laminating a plurality of quantum well layers 19, and 23 is a second cositact layer made of n-type GaAs and having ohmic properties. , 25 is an infrared light receiving element, and 27a and 27b are first electrodes or second electrodes disposed at the first point for extracting photocurrent from the element 25.

In the following explanation, if there are components that have the same function, some of them will be marked with a symbol, and the same components will be hatched uniformly. , some of the constituent components are shown as 1 with hatching omitted.

The device structure will be explained below according to the manufacturing process of this device.

According to the above-mentioned literature, molecular beam epitaxial (Mole
A first contact layer 13 is deposited on the substrate 11 by a cural beam epitaxy (MBE) method.

Subsequently, a barrier layer 15 and a well layer 17 are sequentially and repeatedly deposited on the above-described first contact layer 13 using a similar deposition method. Here, the barrier layer 15 and the well layer 17 (
A plurality of quantum well layers 19 composed of the above are repeatedly constructed to form a multiple quantum well layer 21. In constructing such a multi-quantum well layer (structure), each barrier layer 1
5 is made of n-type GaAs with a film thickness of 9.8 (nm) and an impurity concentration of about 1.4 x 10"(cm"3), and each well layer 17 has a film thickness of 6.5 (nm). )'s AQ,
It is composed of o24Gao76As.

In the above-mentioned document, the quantum well layer 19 is repeatedly deposited 50 times, and the barrier layer 15 is deposited roughly on top of the 50th well layer deposited as the top layer, for a total of about 821.
A multiple quantum well layer 21 is formed with a thickness of 5 (nm).

Subsequently, a second contact layer 23 is formed on the upper surface of the multiple quantum well layer 21 described above. After that, a first electrode 27a or a second electrode 27b is provided on each of the first contact layer 13 and the second contact layer 23, and the infrared light receiving element 25 is completed.

The operation of the element 25 made of Ly in this way will be briefly explained below.

First, a predetermined potential difference is provided between the first electrode 27a and the second electrode 27b provided in the above-described element 25, and an electric field is applied to the multiple quantum well layer 21. When creating a potential difference in the element shown in the figure, can the electrodes on the high potential side or the low potential side be arbitrarily selected depending on the design? First electrode 27a
A case will be described in which the second electrode 27b is set to the low potential side by being grounded, and the second electrode 27b is set to the high potential side by applying a positive potential.

When light (indicated by an arrow p in the figure) is incident from the substrate 11 side of the element 25 under such a potential difference (and electric field), each quantum well layer 19.5
The electrons bound in each well layer 17 (in particular, the well layer 17) are excited and pass through (tunnel) the barrier layer 15.

The excited electrons move from the first contact layer 13 side to the second contact layer 23 side due to the potential difference applied to the multiple quantum well layer 21, causing a photocurrent to flow. The intensity of this photocurrent is detected by the first electrode 27a and the second electrode 27b, and the intensity of the light incident on the element 25 can be determined.

(Problem to be Solved by the Invention) However, in the conventional infrared receiving element described above (as disclosed in the above-mentioned literature), the mean free path of electrons excited in the multi-quantum well layer is approximately This is about 250 (nm).For example, if the thickness of the multi-quantum well layer is made larger than the above-mentioned free path for the purpose of improving the sensitivity of the device, the excitation in the quantum well layer on the light incident side can be increased. The efficiency with which the ejected electrons reach the second contact layer on the other end side is reduced.

Therefore, in order to improve the light detection sensitivity, it is necessary to increase the area where the element is placed on the substrate surface, and it is difficult to improve the sensitivity without impairing the photocurrent gain of the element. There was a point.

In view of the above-mentioned conventional problems, an object of the present invention is to improve the detection sensitivity of an infrared receiving element, and to improve the detection sensitivity of an infrared receiving element, even if the film is constructed with a film thickness larger than the above-mentioned mean free path of electrons, it is possible to reduce the photocurrent. It is an object of the present invention to provide an excellent infrared receiving element that can be made smaller in area without impairing gain.

(Means for Solving the Problems) In order to achieve this object, the infrared light receiving device of the present invention has a plurality of quantum well layers each having a well layer sandwiched between barrier layers. In an infrared receiving element, the multiple quantum well layer is sandwiched between a first contact layer and a second contact layer, and electrodes are connected to the first contact layer and the second contact layer, respectively. Interlayer contact layers are individually provided between the quantum well layers constituting the above-mentioned multiple quantum well layer, and, for example, the odd-numbered interlayer contact layers and the even-numbered interlayer contact layers from the above-mentioned first contact layer side are electrically connected. It is characterized in that it is connected to the first contact layer or the second contact layer, respectively, while being separated from each other.

(Function) According to the infrared light-receiving device of the present invention, with the above-described configuration, light is transmitted from each of the multiple quantum well layers having a multilayer structure in the thickness direction by sandwiching the interlayer contact layer. It is possible to extract electric current. For this reason, even if the light-receiving element is formed with a film thickness exceeding the above-mentioned mean free path of electrons, the sensitivity of the element will not be reduced.

(Example) Examples of the infrared light receiving element of the present invention will be described below with reference to the drawings. In the following description, in order to facilitate understanding of the present invention, dimensions, shapes, numerical conditions, and other specific conditions will be used. However, it should be understood that the present invention is not limited only to these conditions. I want to be understood. In addition, in the drawings referred to in the following description, components having the same functions as the components already explained, except for components that are characteristic of the present invention, are shown with the same reference numerals, and detailed explanations are given. In some cases, the explanation may be omitted. In order to make it easier to understand the present invention, the manufacturing process of an element according to an embodiment will be briefly explained.

FIGS. 1A to 1G are explanatory diagrams showing schematic cross-sections of the infrared light-receiving element according to the present embodiment in the same way as in FIG. 2, according to each manufacturing process.

In the following explanation, in order to make the explanation easier to understand, the case where the component sandwiched between the interlayer contact layers in the structure of the element described above is a multiple quantum well layer is illustrated, and the multiple quantum well layer is The illustration of the quantum well layer constituting the quantum well layer and the well layer and barrier layer constituting the quantum well layer will be omitted. Further, the film thickness, shape, etc. in the drawings referred to below are merely shown schematically to the extent that the present invention can be understood, and the present invention is not limited to the illustrated examples.

First, on a semi-insulating GaAs substrate 11, the above-mentioned MBE method and metal organic vapor phase epitaxy (Metalorqan) are applied.
icChemical Vapor Deposit
A first contact layer 13 of n-type GaAs is deposited to a thickness of approximately 1 um by MOCVD or any other suitable deposition method. When configuring this first contact layer 13, approximately 2 to 3 x 10
It was formed with an n-type impurity concentration of 1.5 cm-3 to give ohmic properties.

After that, 15 quantum well layers were deposited in the order of the barrier layer and the well layer, and the barrier layer was roughly deposited on the well layer deposited on the top surface of the 15th quantum well layer. Multiple quantum well layer 21
form. When forming this multiple quantum well layer 21, the film thicknesses of the l barrier layer and the well layer are made to be about the same as conventional ones,
It is preferable that the thickness of the multiple quantum well layer 21 as a whole is approximately 250 (nm) or less, which is the mean free path of electrons mentioned above. In addition, the composition of the compound semiconductor constituting each layer is approximately 1.5 x
n-type GaAs with an impurity concentration of 10" (cm-3)
, and AQ, 0.2aGao, 711 for the III wall layer.
By using AS, the material composition was the same as the conventional one.

Next, an interlayer contact layer 29, which is a feature of the device of the present invention, is deposited on the upper surface of the multiple quantum well layer 21 described above. This interlayer contact layer 291, like the first contact layer 13 described above, has a thickness of approximately 2 to 4x to” (cm-
3) Provide ohmic properties with n-type impurity concentration,
The film was deposited to a thickness of about 1 (um).

Subsequently, on the first contact layer 13 by the above-mentioned process,
After forming the first multiple quantum well layer 21 and interlayer contact layer 29 as seen from the layer 13, the multiple quantum well layer 21 and interlayer contact layer 29 are formed above these layers.
The number of laminated layers is sequentially formed according to the design. However, when performing such a lamination process, the interlayer contact layer 2
9 are sandwiched between multiple quantum well layers 21.

After that, on the upper side of the multi-quantum well layer 21 deposited last,
A second contact layer 23 having a material composition similar to that of the first contact layer 13 described above and having a thickness of about 1.75 (um) is deposited.

In this way, in this embodiment, each of the six interlayer contact layers 29 is sandwiched between the multiple quantum well layers 21,
These are roughly sandwiched between the first contact layer 13 and the second contact layer 23 to obtain the state shown in FIG. 1(A).

Next, in order to form a step only on one end side of the second contact layer 23 described above, a resist pattern 31 is formed. After that, one side of the second contact layer 23 is etched using a conventionally well-known etching technique. Approximately 1.25 (
Step portion 33 with a height of um) and end surface a are formed (first
Figure (B)).

In this etching removal, the second contact layer 2 after being formed is
3, the film is left with a predetermined thickness (0.5 (um) in this example) so that it can function as an ohmic contact layer for extracting photocurrent.

Subsequently, after removing the resist pattern 31 described above,
A resist pattern 35 is formed. This resist pattern 35 is designed to completely cover at least the end face a of the step portion described above, and to leave the step portion 33 with a predetermined width (width necessary for arranging electrodes to be described later) according to the design. Form.

The resist pattern 35 thus formed is used as an "etching mask" to form an inclined surface on which a constraining film can be deposited in the process described later. Figure 1 (C)).

The stepped portion 37a formed in this way is similar to the stepped portion 33.
The interlayer contact layer is formed on an even-numbered interlayer contact layer when viewed from the second contact layer 23 formed above. That is, the step portion 33 mentioned above
The film thickness of the multiple quantum well layer 21 is approximately 0.5 (urn), the film thickness of the multiple quantum well layer 21 is approximately 0.25 (um), and the interlayer contact layer 2 is approximately 0.25 (um) thick.
Considering that the film thickness of 9 is 1 (um), if the total film thickness for the above-mentioned etching is about 2.5 (um), then the film thickness of the stepped portion 37a formed by this etching is It can be understood that is approximately 0.5 (um).

Further, the formation of the slope b1 and the stepped portion 37a can be achieved by various well-known etching techniques, or by etching the slope 37a and the stepped portion 1 by a directional etching technique such as reactive ion etching. )+'&
It is possible to form them at the same time.

Subsequently, by repeating the steps described above, the substrate 11
Step portions 37b to 37d and slopes b2 to b4 are formed on one side of the surface (FIG. 1(D)). However, when the interlayer contact layer 29 is deposited with an even number of laminated layers as in this embodiment, the finally formed step portion 37d has a thickness of 1 LIm as described above. As a result, the substrate 11 is formed by etching away approximately 0.75 (um). Furthermore, as is clear from the above description, the step portions 37a to 37d are all formed in odd-numbered interlayer contact layers counting from the first contact layer 13 (however, the step portions 37a to 37d are formed in the odd-numbered interlayer contact layers counting from the first contact layer 13). If you count from 23, all are even numbers).

Next, Fig. 1 (A) to (D) I? The process of forming the step portions and slopes described above is performed on the stacked end face on the side opposite to these, and the step portions 37e to 37h and the slope b5 are formed.
~b8 is formed to obtain the state shown in FIG. 1(E). Among the step portions formed by this step, step portions 37e to 3
79 are all formed in even-numbered interlayer contact layers counting from the first contact layer 13 (however, they are all odd-numbered when counting from the second contact layer 23).

An insulating layer made of silicon dioxide (S10□), for example, is deposited over the entire surface of the element substrate thus obtained in the state shown in FIG. 1(E). When depositing this insulating layer, a predetermined slope is provided on the series of slopes S, B8,
An insulating layer is applied in succession.

Next, stripe-shaped grooves 39a to 39c and 39e to 39 are formed corresponding to the stepped portions 37a to 37c and the stepped portions 37e to 37h, respectively, by a well-known photolithography technique.
In addition to forming grooves h, similar grooves c are also formed in predetermined portions of the upper surface of the second cositact layer 23. In this way, the slopes b1-b, husband)? Insulating pattern 41 covering
A to 411 are formed to obtain the state shown in FIG. 1(F).

Next, the entire upper surface of the substrate 11 on which the above-mentioned insulating patterns 41a to 411 have been formed (gold-germanium-nickel (Au-Ge-Ni) alloy or any other suitable conductive material is coated to the extent that no breakage occurs). The film is deposited to a sufficient thickness.Then, among the insulation patterns already described, a bond formed between the second contact layer 23 and the interlayer contact layer closest to the layer 23 is formed. pattern 41e
A stripe-shaped groove is formed in an arbitrary suitable portion (indicated by an arrow 1 in the figure) on the top, and a first electrode 43a and a second electrode 43b are formed to form an infrared ray according to an embodiment of the present invention. A light receiving element 45 is obtained (FIG. 1(G)).

As can be understood from FIG. 1(G), the first electrode 43a formed in this way electrically connects only the second contact layer 23 and the even-numbered interlayer contact layers counting from the layer 23. Connecting. On the other hand, the second electrode 43b connects only the first contact layer 13 and odd-numbered interlayer contact layers counted from the second contact layer 23. In other words, in the infrared receiving element 45 according to this embodiment,
When viewed from the first contact layer 13 which is the basis of lamination,
Even-numbered interlayer contact layers and first contact layers are separated by a first electrode 43a, and odd-numbered interlayer contact layers, second contact layers 23, and second electrodes are separated by a series of insulating patterns. In this state, they can be connected separately.

Hereinafter, the operation of the above-mentioned element 45 will be briefly explained.

In the same manner as already explained with reference to FIG. A case will be described in which the operation is performed by applying a positive potential to one electrode 43a. By providing a potential difference between the respective electrodes in this way, as can be seen from FIG. An electric field is applied to the multi-quantum well layer. Thereafter, an electric field is sequentially applied to each multiple quantum well layer by the first electrode 43a and the second electrode 43b, and each multiple quantum well layer functions as the minimum unit as an element, and light (indicated by arrow p) is applied to each multiple quantum well layer. ) can be extracted without attenuation.

Therefore, when the multi-quantum well layer 21 is used and the number of interlayer contact layers is set to 6 as in this embodiment, the conventional structure in which the film thickness of the multi-quantum well layer is set to the above-mentioned mean free path. A photocurrent equivalent to six elements can be expected.

In other words, even if the thickness of the device as a whole exceeds the mean free path of electrons, as long as the film thickness between each interlayer contact layer is less than that distance, photocurrent can be effectively generated without attenuation. The element sensitivity can be improved depending on the number of interlayer contact layers.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments.

For example, when constructing a multi-quantum well layer, if a flGaAs material having the above-mentioned composition is used, or if the valence X in the composition formula of AQxGa+-xAs is changed for the material constituting the barrier layer, Layer and 11M
This can be dealt with by changing the relationship between the film thickness and the wall layer.

In general, the same effect as described above can be obtained by using a conventionally well-known indium-phosphide (InP)-based material instead of a GaAs-based compound semiconductor.

In addition, when forming a multi-quantum well layer, the well layer and i
l! It is also possible to create a so-called strained superlattice by applying stress to the wall layer.

It is clear that any suitable design changes and modifications may be made to these materials, dimensions, shapes shown, number of laminated layers, distribution ratio and other conditions within the scope of this purpose.

(Effects of the Invention) As is clear from the above description (according to the infrared receiving element of the present invention, a plurality of multiple quantum well layers are formed into a multilayer structure in the thickness direction by interposing an interlayer contact layer). Therefore, even if the photodetector is formed with a film thickness that exceeds the mean free path of the electrons mentioned above, the sensitivity of the device will decrease. It's fleeting.

Therefore, in improving the detection sensitivity of the infrared light receiving element, it is possible to provide an excellent infrared light receiving element r8 that does not impair the photocurrent gain and can be made smaller in area.

[Brief explanation of the drawing]

1(A)-(G) are explanatory diagrams schematically showing cross-sections according to the manufacturing process of an infrared receiving element in order to explain the present invention in detail, and FIG. 2 is a schematic cross-sectional view of a conventional infrared receiving element. FIG. 11...Substrate, 13...First contact layer 15
...Barrier layer, 17..Well layer, Quantum well layer and...Multiple quantum well layer, 23..Second contact layer, Target...Infrared light. Light receiving elements 27a, 43a...first electrode, 27b, 43b...
...Second electrode 29...Interlayer contact layer 31, 35...Resist cover 33.37a to 37h---Step portion 39a to 39h
, c...Stripe-shaped grooves 41a to 411...
・Insulating Bakun p...Infrared rays incident direction a...Wall surface, b1 to b8...Slope. Patent applicant: Oki Electric Industry Co., Ltd. ``) 1,, honey ζ1℃ ≧yo 111 gooooooooooooooooooooooooooooooooooooooo

Claims (1)

[Claims] (1) A multiple quantum well layer is formed by configuring a plurality of quantum well layers each having a well layer sandwiched between barrier layers, and the multiple quantum well layer is sandwiched between a first contact layer and a second contact layer,
In an infrared receiving element in which electrodes are connected to the first contact layer and the second contact layer, respectively, between the quantum well layers constituting the multiple quantum well layer,
interlayer contact layers are individually provided, and the odd-numbered interlayer contact layers and the even-numbered interlayer contact layers are electrically separated from the first contact layer side, and the first contact layer or the second contact layer is electrically isolated from the first contact layer side. An infrared receiving element characterized in that it is formed by connecting each other.