JP2762004B2 - Light receiving element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer semiconductor light receiving device in a visible to infrared light region. More specifically, a layer having strong light absorption near a specific wavelength is defined as a photoconductive layer (A), and a wavelength region apart from the vicinity of the specific wavelength is composed of two layers that absorb and remove the other light absorption layer (B). Since the incident light is selectively absorbed in the light absorbing layer (B) except for a specific wavelength, and is transmitted and then absorbed in the photoconductive layer (A), the wavelength selectivity having strong light sensitivity only near the specific wavelength is excellent. It relates to a light receiving element.

[0002]

2. Description of the Related Art Conventionally, in order to realize wavelength selectivity, only light in a narrow wavelength band including a specific wavelength (λ1) is extracted from incident light using a band-pass filter or a monochromator (FIG. 1), and light is received in a wide band. By irradiating a normal light-receiving element having sensitivity (FIG. 2), the light-receiving sensitivity is obtained only in the transmission wavelength region shown in FIG.

[0003]

However, the size of the filter and the size of the monochromator are much larger than those of the light receiving element, and it is difficult to reduce the size. Therefore, it is difficult to make a multi-wavelength hybrid, and IC is hopeless. Further, the wavelength-selective light-receiving system is expensive, and among them, the ratio of the filter and the monochromator to the price is almost the same.

Further, light transmitted through a filter or a monochromator is subjected to intensity attenuation, and the effective light receiving sensitivity is reduced. Therefore, an inexpensive light-receiving element that can be miniaturized without lowering the light-receiving sensitivity even at a specific wavelength has not yet been obtained.

An object of the present invention is to provide a small and inexpensive light receiving element which has a light receiving sensitivity only in a narrow band including a specific wavelength without lowering the light receiving sensitivity at a specific wavelength.

[0006]

According to the present invention, there is provided a photoconductive layer (A) having a strong light absorption characteristic accompanied by carrier generation at a specific wavelength, and a light absorption layer having a strong light absorption characteristic except near a specific wavelength. This is a wavelength-selective light-receiving element made of a combination having a complementary relationship with the layer (B) and producing light-receiving sensitivity characteristics only at a specific wavelength.

That is, the light receiving element of the present invention has a low concentration photoconductive layer (A) laminated on a high concentration substrate,
A light-receiving element in which a high-concentration light-absorbing layer (B) is laminated on the low-concentration photoconductive layer, and receives light from the high-concentration light-absorbing layer side. The light absorption end wavelength is λ1, and the light absorption end wavelength of the high concentration photoconductive layer is λ1.
In the case of 2, both light absorption edge wavelengths λ1 and λ2 are set to satisfy the following conditions. λ1> λ2 0.006 <(λ1−λ2) / λ1 <0.072

That is, the light receiving element of the present invention comprises a combination of two types of semiconductor layers, a photoconductive layer (A) and a light absorbing layer (B). These two types of semiconductor layers each have a uniform composition,
Any of a super lattice structure and a multilayer structure may be used.

The photoconductive layer (A) as used herein means a light absorption at a light wavelength at which light-receiving sensitivity of the light-receiving element is desired to be exhibited, and a change in current between the electrode terminals of the element due to the generated carrier pair (electron / hole). Alternatively, it is a main layer of an element in which a large change in resistance or the like occurs, and usually indicates a high-purity layer having a low carrier concentration. Since the light absorption end wavelength is λ1, wavelengths equal to or shorter than λ1 are absorbed. In other words, for wavelengths longer than λ1, there is no light absorption and no sensitivity.

The light-absorbing layer (B) absorbs light at a light wavelength at which light-receiving sensitivity of the light-receiving element is not desired to be exhibited. This layer is added so as to be slightly smaller than the light wavelength to be obtained, and refers to a low resistance layer doped with p-type or n-type impurities at a high concentration or a layer that converts absorbed light energy into heat energy or the like. Then, since the light absorption end wavelength is λ2, wavelengths equal to or shorter than λ2 are absorbed. In other words, λ
For wavelengths greater than 2, there is no light absorption and no sensitivity.

The compounds constituting the two types of semiconductor layers (photoconductive layer and light absorbing layer) include GaAs, AlAs,
_{Al x Ga 1-x As,} In x Ga 1-x periodic table group III, such as As and compound semiconductor consisting of a combination of Group V are preferred. Also, ZnSe, ZnTe
Compound semiconductors composed of a combination of groups II and VI of the periodic table, such as GeSe, PbTe, etc., may also be used.

In the present invention, the light absorption edge wavelength (λ1) of the photoconductive layer (A) and the light absorption edge wavelength (λ) of the light absorption layer (B) are used.
2) is λ1> λ2 and 0.006 <(λ1
It is necessary to use two types of semiconductor layers such that -λ2) / λ1 <0.072. If the ratio deviates from this range, the light receiving sensitivity cannot be obtained only in a narrow band including the specific wavelength without lowering the light receiving sensitivity at the specific wavelength. For example, for In _x Ga _1-x As, the light absorption edge wavelength (λ) is 0.87 to 3.5 μm, for GaAs, the light absorption edge wavelength (λ) is 0.87 nm, and Al _x Ga _1-x A is used.
In s, the light absorption edge wavelength (λ) indicates 0.87 to 0.60 μm, respectively.

[0013]

The incident light first enters the light absorbing layer (B). Then, light having a wavelength of λ2 or less is absorbed by the light absorbing layer. Carriers are generated along with the light absorption, but due to the high-concentration layer, the change in conductivity is small, and the contribution to the electric signal is also negligible. Therefore, the sensitivity to wavelengths of λ2 or less decreases.

The light transmitted through the light absorbing layer without being absorbed (larger than the wavelength λ2) reaches the photoconductive layer (A).
Since the photoconductive layer absorbs light having a wavelength of λ1 or less, if the incident light is in that wavelength region, it is absorbed there and carriers are generated. At this time, since the concentration of the photoconductive layer is low, the change in conductivity accompanying the generation of carriers is large, and the photoconductive layer can be handled as an electric signal.

Light having a wavelength larger than λ1 is not absorbed by this photoconductive layer. And the light below λ2 is
Since it has already been absorbed by the light absorbing layer, it does not reach the photoconductive layer. Therefore, what is absorbed by the photoconductive layer is λ2
It is larger and in the wavelength range of λ1 or less. Therefore, light having a wavelength in the range of λ2 to λ1 can be selectively received.

That is, a layer having strong light absorption near a specific wavelength is defined as a photoconductive layer (A), and a wavelength region apart from the vicinity of the specific wavelength is separated from the two layers absorbed and removed by another light absorption layer (B). The incident light is selectively absorbed by the light absorbing layer (B) except for a specific wavelength, and after transmission, is absorbed by the photoconductive layer (A). Therefore, excellent wavelength selectivity having strong light sensitivity only in the vicinity of the specific wavelength. Light receiving element.

Next, In _x Ga is used as the photoconductive layer (A).
An example in which GaAs is used as the _1- xAs epitaxial single crystal and the light absorption layer (B) will be described.

FIG. 3 shows In _x Ga _1-x As (x <0.05) to be a photoconductive layer (A) formed on a GaAs substrate.
The photoconductivity of the single crystal layer is shown in FIG.
Peak wavelength increases.

FIG. 4 illustrates the light absorption characteristics of GaAs to be the light absorption layer (B). From the figure, the p-type carrier concentration is 1.2 ×
At 10 ¹⁸ cm ⁻³ , the photon energy is 1.42 e
3 × 10 ³ cm at V or more (wavelength 0.87 μm or less)
^It has a light absorption coefficient of ^-1 or more and an energy of 1.37 eV.
8 × 10 cm ⁻¹ below (wavelength 0.905 μm or more)
The following light absorption coefficient is obtained.

Since the light absorption edge wavelength (λ2) of GaAs as the light absorption layer (B) is constant at 0.87 μm, the above expression 0.006 <(λ1−λ2) / λ1 <0.072 is satisfied. in is a photoconductive layer _{(a) in x Ga 1-} x as
Is required to be 0.875 to 0.938. For this purpose, it is necessary to adjust x so that the ratio of In and Ga becomes appropriate. For example, when x is set to 0.01, the light absorption edge wavelength (λ1) of In0.01Ga0.99As is 0.905 μm. In this case, (λ1−λ2) /λ1=0.0387, which satisfies the above requirements.

FIG. 5 shows a structure in which an InGaAs photoconductive layer (A) is provided on a GaAs substrate via a buffer layer, and a GaAs light absorbing layer (B) is stacked thereon. Incident light is absorbed by the light absorbing layer (B) at a wavelength of 0.87 μm or less, and after transmission, is absorbed by the photoconductive layer (A) as light of a wavelength of 0.87 μm or more. Occurs. When a battery is connected between the light absorbing layer (B) and the n-GaAs substrate, a large current change is measured during light irradiation.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. * Example 1 FIGS. 6A to 6C are cross-sectional views illustrating a manufacturing process of a light receiving element device. As shown in FIG.
On a GaAs substrate (carrier concentration 1 × 10 ¹⁸ cm ⁻³ ), Si-doped (carrier concentration 1.5 × 10 ¹⁸ c)
m- ³ ) n-In _0.001 Ga _0.999 As (3
0 angstrom) / Al _0.2 Ga _0.8 As (3
Approximately 30 pairs of (1 angstrom) superlattices were stacked to form a buffer layer.

On top of that, high-purity undoped In _x Ga
_1-x As photoconductive layer (A) (x = 0.01, light absorption edge wavelength (λ1) = 0.905, carrier concentration 5 × 10 ¹⁶ c
m ^-3 or less) was laminated at 1.5 μm.

The uppermost layer is composed of two layers. First, Be-doped (carrier concentration: 1.2 × 10 ¹⁸ cm ⁻³ ) p-Ga
As (30 Å) / Al _0.2 Ga _0.8
A superlattice layer of As (31 Å) is
After stacking 0 pairs and obtaining surface smoothness, the p-GaAs light absorbing layer (B) having a carrier concentration of 1.2 × 10 ¹⁸ cm ⁻³ (light absorption edge wavelength (λ2) = 0.87) is 1 μm. Laminated.

Next, as shown in FIG. 6B, the epitaxial growth layer side was masked by a photoresist method and etched into a 0.8 mm square mesa. Furthermore, as shown in FIG. 6 (c), the SiO ₂ protective film on the mesa sloped portion, on the epitaxial surface, non-reflective SiO ₂ (A
R) A coat film is formed by sputtering, and finally, Au is formed on the n-GaAs substrate side and the p-GaAs layer side.
And electrodes such as Al are vapor-deposited at 420 ° C./min (N
_{(In two} gases).

FIG. 7 shows the relationship between the light receiving sensitivity and the wavelength of the obtained light receiving element device. It can be seen from the figure that the light receiving sensitivity is obtained only in a narrow band including a specific wavelength.

* Example 2 A buffer layer to a GaAs light absorbing layer are stacked on a semi-insulating Si-GaAs substrate in the same manner as in FIG. 6, and after forming a mesa, electrodes such as Au and Al are formed on the epitaxial surface. , FIG.
The light receiving device shown in FIG.

The light receiving sensitivity of this light receiving device was equal to or higher than that of FIG. The present embodiment is similar to the PIN type light receiving element, but is characterized in that both the vertical current type according to the first embodiment and the horizontal current type according to the second embodiment have high light receiving sensitivity.

[0029]

According to the present invention as described above, the following effects can be obtained. According to the present invention, a narrow band type (wavelength selective type) light receiving element using a combination of a band pass filter or a monochromator and a light receiving element is realized by a single semiconductor chip. The rise (fall) of the sensitivity and the wavelength characteristic is less than or equal to the order of the interference type multilayer glass filter (10 nm or less for half-value attenuation). Since the photoconductive layer (A) and the light absorbing layer (B) are made of a high-quality semiconductor crystal, a steep absorption coefficient change at an edge of a light absorption band inherent to the semiconductor can be used, and production with good reproducibility is possible. is there. It can be reduced in size, weight, and cost, and can be used for IC applications for multi-wavelength optical spectroscopy.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between light transmittance and wavelength in a conventional technique.

FIG. 2 is a graph showing a relationship between a light receiving sensitivity and a wavelength in a conventional technique.

FIG. 3 is a graph showing a relationship between a resistance change output of InGaAs and a wavelength.

FIG. 4 is a graph showing the relationship between the photon energy of GaAs and the absorption coefficient.

FIG. 5 is a sectional view showing an example of the structure of a light receiving element chip of the present invention.

FIG. 6 is a cross-sectional view illustrating a manufacturing process of the light receiving element device according to the first embodiment.

FIG. 7 is a graph showing the relationship between light receiving sensitivity and wavelength in Example 1.

FIG. 8 is a cross-sectional view illustrating a light receiving element device according to a second embodiment.

Claims (1)

(57) [Claims] 1. A low-concentration photoconductive layer is laminated on a high-concentration substrate, and a high-concentration light-absorbing layer is laminated on the low-concentration photoconductive layer. A light-receiving element adapted to receive light, wherein the light absorption edge wavelength of the low-concentration photoconductive layer is λ1 and the light absorption edge wavelength of the high-concentration photoconductive layer is λ2. λ1 and λ2 are such that λ1> λ2 and 0.006 <(λ1−λ2) / λ1 <0.072, and the wavelength λ is suppressed while suppressing the change in conductivity in the high concentration light absorbing layer.
2 is absorbed by the low-concentration photoconductive layer, and the light having a wavelength of λ1 or less is absorbed by the low-concentration photoconductive layer. A light receiving element characterized by being changed.