JP2723069B2 - Semiconductor 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 semiconductor light receiving element.
In particular, PI used in optical communication, optical information processing, optical measurement, etc.
The present invention relates to a semiconductor light receiving element of an N-type photodiode.

[0002]

2. Description of the Related Art In recent years, GI plastic fibers (G
Research on a high-speed optical link using light having a wavelength of about 0.6 μm using I-POF) is being studied. When using this plastic fiber, transmission over a long distance is extremely difficult due to a large transmission loss. However, in a high-speed optical link system in a building or between computers, it is extremely inexpensive and easy to handle. Is expected from.

The light receiving element used in the optical communication is required to have a large diameter for low drive voltage and alignment free as well as low cost. At present, as one of the applicable light receiving elements, there is a PIN type light receiving element made of silicon (Si) which has been conventionally used as a semiconductor light receiving element of 1 μm band or less (for example, by Yonezu, "Optical Communication Device Optics", published by Kogyo Tosho Co., Ltd., 3
64, 1983). This PIN type light receiving element has the features that its structure is simple and that it is relatively inexpensive.

FIG. 8 shows a structural view of an example of a conventional semiconductor light receiving element. This conventional semiconductor light receiving element has a typical PI
It has an N-PD structure and is called a reach-through type. This conventional PIN type light receiving element comprises an i-Si light absorbing layer 22 and an n ⁺ type light receiving region 2 on a p ⁺ type substrate 21.
3 and p ⁺ -type channel stoppers 24 are formed, a passivation film 25 is further formed thereon, and an AR film 29 and a p-side electrode 30 are formed on the n ⁺ -type light receiving region 23. An n-side electrode 26 is formed on the other surface of the p ⁺ type substrate 21.

In this conventional PIN light receiving element, when a reverse bias voltage is applied between the n-side electrode 26 and the p-side electrode 30, the depletion layer extends from the n ⁺ / p ⁻ (i) interface to the substrate 21 side. . In this state, when the incident light 13 is incident on the AR film 29, photocarriers are generated in the depleted Si light absorption layer 22, and holes are generated by the electric field in the photocarriers.
In the direction of the side electrode 30, the electrons travel in the direction of the n-side electrode 26,
After that, the current reaches the electrodes 26 and 30 and becomes a current, whereby photoelectric conversion is performed.

[0006]

However, as described above, below the conventional 1 μm band light wavelength region, a Si PIN-PD (photodiode) having a homojunction structure as shown in FIG. 8 is used. However, Si has a low absorption coefficient due to indirect transition, and it is necessary to increase the thickness of the absorption layer to increase the quantum efficiency. Therefore, the band is limited to the carrier transit time, and the operating voltage increases (for example, 20 V) due to the thick film depletion. As an incidental problem, there is also a deterioration in external quantum efficiency due to surface recombination and photoexcitation-recombination in the surface high concentration layer.

Further, in the case of a large diameter for GI-POF, a CR limit accompanying a capacity increase is also added. Heretofore, a back lens incidence type has been known as a means for increasing the aperture. However, since the Si substrate itself absorbs the light, a Si PI
It is not applicable to N-PD.

[0008] The present invention has been made in view of the above points,
It is an object of the present invention to provide a semiconductor light receiving element having sensitivity to light near a wavelength of 0.6 μm, having a low voltage, a wide band, and an effective large light receiving area, and applicable to a high-speed optical link for GI-POF or the like. I do.

[0009]

The present invention SUMMARY OF] in order to achieve the above object, the structure in which the light-absorbing layer and the light-receiving region are sequentially stacked on a surface of the GaP made of a semiconductor substrate, a semiconductor group
In a semiconductor light receiving element that performs photoelectric conversion on incident light introduced from the back side of the plate , the light absorption layer is made of GaP and a lattice constant.
Formed of a nitrogen-based epitaxial layer whose number is almost the same
Is obtained by a structure in which there.

[0010]

[0011]

[0012]

FIG. 2 shows GaP for explaining the operation of the present invention.
The relationship between the lattice constant and the band gap of the light absorption layer of the substrate and the silicon (Si) epitaxy layer or the nitrogen (N) based epitaxial layer is shown. In FIG. 2, the lattice constant of GaP, which is a semiconductor substrate material in the present invention, is about 5.5 ° as shown by a, while the lattice constant of the N-based epitaxial layer is about 5.5 ° as shown by b, and Are almost the same, and it is expected that there is no concern about introduction of defects such as misfit transition during crystal growth.

The band gap of GaP at room temperature is 2.24 eV (the latest compound semiconductor handbook, supervised by Mr. Ikoma, published by Science Forum, p. 18). To
This corresponds to 0.55 μm. Therefore, the semiconductor substrate of the present invention made of GaP is transparent to light in a light wavelength region in the vicinity of the 0.6 μm band, and a back-illuminated structure having a microlens on the back surface of the semiconductor substrate is possible.

Next, the relationship between the light wavelength of Si and GaAs and the absorption coefficient will be described with reference to FIG. In FIG.
Curve I shows the characteristics of light wavelength and absorption coefficient of Si, and curve II shows the characteristics of light wavelength and absorption coefficient. Curve I in FIG.
As can be seen from the graph, the light absorption coefficient of Si for light having a wavelength of 0.65 μm in the light wavelength region is 3000 / cm.
The light absorption coefficient of s is 20000 / cm,
It can be seen that it has twice the absorption coefficient.

Therefore, in principle, it can be seen that in order to obtain the same quantum efficiency, in the case of GaAs, it is sufficient to use 1/7 of the Si layer thickness. However, as shown in FIG. 2, GaAs is not suitable as a light absorbing layer because its lattice constant is not substantially equal to that of GaP. When the composition is extremely small, it is considered to be equivalent to GaAs. Therefore, the thickness of the light absorbing layer can be reduced by using the N-type epitaxial layer as the light absorbing layer.

[0016] will be described in the following, in conjunction with FIG. 4 the operation of Ma microlenses. FIG. 1A is a schematic sectional view of the element structure, and FIG. 1B shows the effect on the band. FIG.
In (B), α indicates the absorption coefficient, Ct indicates the capacity, and N indicates the concentration. As shown in FIG. 4A, the semiconductor light receiving device of the present invention has a micro lens 8 on the back surface of a semiconductor substrate 1 having a PIN structure, and light introduced from the back surface of the semiconductor substrate 1 The light is focused on the light absorbing layer 2 by the lens 8.

FIG. 4B shows the relationship between the cut-off frequency (band) and the thickness of the light absorbing layer with the pn junction diameter as a variable.
In the case of a large light receiving element having a junction diameter (light receiving diameter) of 100 μm or more, the band is limited by the CR time constant limitation (mainly the element capacity limitation). The relationship between the device capacity and the band with respect to the light receiving diameter (pn junction diameter) is about 0.35 pF at a light receiving diameter of 100 μm when the light absorbing layer thickness is 3 μm, and FIG.
Although not shown, about 2.2 pF at a light receiving diameter of 300 μm
And the bands are about 7 GHz and 1.2 GHz, respectively.

On the other hand, as shown in FIG.
In the case of a back illuminated element having a micro lens, a small pn
The effective light receiving diameter can be enlarged while maintaining the junction diameter. Empirically, the effective light receiving diameter can be increased to 100 μm or more by providing the microlens 8 even if the pn junction diameter is 20 μm, which can provide the characteristics of the band of 15 GHz or more. GI-
Even in an element having an effective light receiving diameter of 500 μm required from the viewpoint of alignment-free POF, the microlens 8
Is applied, the pn junction diameter is 200 μm or less, and the band 2.
5 GHz or more can be obtained.

[0019]

[0020]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a structural sectional view of a first embodiment of the present invention. As the structure of this embodiment, first, p-type GaP (1
00) A high-density i-Si light-absorbing layer 2 having a thickness of 20 μm
Laminate. This i-Si light absorption layer 2 is an epitaxial layer. Next, an n ⁺ type light receiving region 3 and ap ⁺ type channel stopper 4 are formed by selective diffusion, and a SiNx film 5 is deposited on the surface as a passivation film by 800Å. The n-side electrode 6 penetrates through the SiNx film 5 and is connected to the n ⁺ -type light receiving region 3, and further forms a pad electrode 7 on the n-side electrode 6.

After polishing the back surface of the substrate obtained as described above to a desired thickness, a microlens 8 is formed on the back surface, and an AR film 9 and a p-side electrode 10 are further formed on the back surface. Complete.

Next, the operation of this embodiment will be described.
When a reverse bias voltage is applied between the n-side electrode 6 and the p-side electrode 10, the depletion layer forms p-type Ga from the n ⁺ / p ⁻ (i) interface.
It extends to the P substrate 1 side. In this state, when the incident light 13 in the light wavelength region of 0.6 μm enters the microlens 8 on the back surface of the substrate, it is condensed on the light absorbing layer 2 by the microlens 8 and the light carrier is depleted by the depleted light absorbing layer 2. Occurs,
Out of the photocarriers, holes move toward the p-side electrode 10 and electrons move toward the n-side electrode 6 due to the electric field.
The photoelectric conversion is performed when the current reaches each of 10 and becomes a current.

According to the present embodiment, as described in the operation section, the operation voltage 10
V, band width 1 MHz with light receiving diameter of 500 μm, external quantum efficiency 9
A 0% PIN type light receiving element can be realized.

Next, a second embodiment of the present invention will be described. FIG. 5 is a structural sectional view of a second embodiment of the present invention.
This example in the embodiment of flip chip type PIN-PD,
First, a p-type GaP (100) substrate 1 is used.
The high-density i-Si light absorbing layer 2 is laminated thereon by 20 μm. Next, an n ⁺ -type light receiving region 3 is formed by selective diffusion, a mesa is formed to the substrate depth by etching, and then a SiNx film 5 is deposited on the surface as a passivation film at 800 °.

An n-side electrode 6 penetrates through the SiNx film 5 and n ⁺
And the p-side electrode 10 is connected to the GaP substrate 1.
Formed on top. Then, the step wiring 11 is connected to the p-side electrode 10.
And a bump electrode 12 is formed on the n-side electrode 6 and the step wiring 11. After polishing the back surface of the substrate thus obtained to a desired thickness, a microlens 8 is formed on the back surface, and an AR film 9 is further deposited to complete the element structure.

Similar to the first embodiment, the present embodiment employs a PIN type having an operating voltage of 10 V, a light receiving diameter of 500 μm, a bandwidth of 1 MHz, and an external quantum efficiency of 90% by applying the microlens 8 as described in the section of the operation. A light receiving element can be realized. The device structure of the above embodiment can be specifically formed by a growth technique such as molecular beam epitaxy (MBE), gas source MBE, and vapor phase epitaxy (VPE). Note that the operation of this embodiment is the same as that of the first embodiment, and a description thereof will be omitted.

Next, a third embodiment of the present invention will be described. FIG. 6 shows a structural sectional view of a third embodiment of the present invention.
As the structure of this embodiment, first, p-type GaP (100)
I-GaN _0.08 As _0.92 light absorbing layer 1 on substrate 1
4 is laminated by 5 μm. This i-GaN _0.08 As
_{The 0.92} light absorbing layer 14 is an epitaxial layer. Next, an n.sup. ⁺ Type light receiving region 3 is formed by selective diffusion, an SiNx film 5 is deposited on the surface as a passivation film by 800.degree., And an n-side electrode 6 and a pad electrode 7 are respectively laminated. After polishing the back surface of the substrate obtained as described above to a desired thickness, a micro lens 8 is formed on the back surface, and A
The element structure is completed by forming the R film 9 and the p-side electrode 10 on the back surface.

Next, the operation of this embodiment will be described.
When a reverse bias voltage is applied between the n-side electrode 6 and the p-side electrode 10, the depletion layer forms p-type Ga from the n ⁺ / p ⁻ (i) interface.
It extends to the P substrate 1 side. In this state, when the incident light 13 is incident on the microlens 8 on the rear surface of the substrate, the incident light 13 is condensed on the light absorbing layer 14 by the microlens 8, and photocarriers are generated in the depleted light absorbing layer 2, Of these photocarriers, holes travel in the direction of the p-side electrode 10 and electrons travel in the direction of the n-side electrode 6 due to the electric field.

According to this embodiment, as described in the section of the operation, the operation voltage of 5 V
Hereinafter, a PIN light receiving element having a light receiving diameter of 500 μm, a band of 3 MHz, and an external quantum efficiency of 90% can be realized.

Next, a fourth embodiment of the present invention will be described. FIG. 7 shows a structural sectional view of a fourth embodiment of the present invention.
This embodiment is a flip-chip PIN-PD. In this embodiment, first, i-type is formed on the p-type GaP (100) substrate 1.
-The GaN _0.08 As _0.92 light absorption layer 14 is laminated by 5 μm. Next, an n ⁺ type light receiving region 3 is formed by selective diffusion, and a mesa is formed to a substrate depth by etching.
800N SiNx film 5 as passivation film
Å Deposit. Then, after forming the n-side electrode 6 and the p-side electrode 10 respectively, the step wiring 11 and the bump electrode 12 are formed. After polishing the back surface of the substrate thus obtained to a desired thickness, a microlens 8 is formed on the back surface, and an AR film 9 is further deposited to complete the element structure.

According to the present embodiment, as described in the operation section, the operation voltage is 5 V by applying the microlens 8.
Hereinafter, a PIN type light receiving element having a light receiving diameter of 500 μm, a band of 3 MHz, and an external quantum efficiency of 90% was realized. The device structure according to the above-described embodiment is specifically MBE, gas source MB.
It can be formed by a growth technique such as E or VPE.

[0032]

As described above, according to the present invention,
The semiconductor substrate supporting the layer that performs light absorption and photoelectric conversion is G
Since it is made of aP, it can be made transparent to light in the light wavelength region near the 0.6 μm band, and a semiconductor light receiving element of a high-speed optical link system in which light in the light wavelength region near the 0.6 μm band enters from the back of the semiconductor substrate. Can be used as Further, according to the present invention, by using the N-based epitaxial layer as the light absorbing layer, the thickness of the light absorbing layer can be made thinner than when using the silicon epitaxial layer, and when the silicon epitaxial layer is used as the light absorbing layer. Also, since the effect by electrode reflection is obtained, the thickness can be reduced to about 2/3 as compared with the conventional Si PIN-PD, so that the speed is increased by shortening the traveling time of the carrier and the operation is reduced by reducing the thickness of the depletion layer. It has advantages such as voltage.

Further, according to the present invention, since the semiconductor substrate 1 having the PIN structure has microlenses on the back surface, light introduced from the back surface of the semiconductor substrate can be efficiently transmitted to the light absorbing layer by the microlenses. Light can be collected at an effective light receiving diameter of 5
Even in the case of the 00 μm element, a band of 2.5 GHz or more can be obtained with a pn junction diameter of 200 μm or less by applying a micro lens. As described above, according to the present invention, a semiconductor photodetector having high-speed characteristics suitable for use in a high-speed optical link and having high quantum efficiency can be realized.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a lattice constant and a band gap for explaining the operation of the present invention.

FIG. 3 is a diagram illustrating the relationship between the light wavelength of Si and GaAs and the absorption coefficient for explaining the operation of the present invention.

4 is a semiconductors light receiving element illustration.

FIG. 5 is a structural sectional view of a second embodiment of the present invention.

FIG. 6 is a structural sectional view of a third embodiment of the present invention.

FIG. 7 is a structural sectional view of a fourth embodiment of the present invention.

FIG. 8 is a structural cross-sectional view of a conventional example.

[Explanation of symbols]

Reference Signs List 1 GaP substrate 2 i-Si light absorbing layer 3 n ⁺ type light receiving region 4 p ⁺ type channel stopper 5 SiNx film 6 n side electrode 7 pad electrode 8 micro lens 9 AR film 10 p side electrode 11 step wiring 12 bump electrode 13 incidence Light 14 i-GaN _0.08 As _0.92 Light absorbing layer

Claims (1)

(57) [Claims] 1. A semiconductor light receiving device that performs photoelectric conversion on incident light introduced from the back surface side of a semiconductor substrate by a structure in which a light absorbing layer and a light receiving region are sequentially laminated on at least a surface of a semiconductor substrate made of GaP. In the device, the light absorption layer is formed of nitrogen whose lattice constant substantially matches that of GaP.
A semiconductor light-receiving element characterized by being formed of a system epitaxial layer .