JP2004327886A - Semiconductor photo-receiving element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor photo-receiving element which allows improvement of photo-sensitivity and increase of photo-response rate which are contradictory each other. <P>SOLUTION: An n-type InP buffer layer 22, a reflector layer 23, an i-type InGaAs photo-absorption layer 24, and an n-type InP cap layer 28 are laminated on an n-type InP substrate, and zinc(Zn) is diffused in the n-type InP cap layer 28 to form a p-type diffusion region 32 as a photo-receiving portion. The reflector layer 23 is formed of a laminated structure where 16 to 22 pairs of InP and AlGaInAs are laminated. The light passing through the i-type InGaAs photo-absorption layer 24, in light incident from the p-type diffusion region 32, is reflected to the i-type InGaAs photo-absorption 24 by the reflector layer 23, and a film thickness of the i-type InGaAs photo-absorption layer 24 may increase in appearance. Since carriers, produced in the i-type InGaAs photo-absorption layer 24, pass through the reflector layer 23 as it is, an effect on a photo-response rate does not occur. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a semiconductor light receiving element that is used for a photodetector module and converts an input optical signal into an electric signal.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a semiconductor light receiving element, for example, one disclosed in Patent Document 1 is known. The conventional semiconductor light receiving element disclosed in this publication is a photodiode having a pin structure in which a pn junction serving as a light receiving portion is formed by diffusion. FIG. 1 shows a sectional view of a wafer structure on which a conventional light receiving element is formed. An n-InP buffer layer 22, an i- (undoped) -InGaAs light absorbing layer 24, and an n-InP cap layer 28 are stacked on an n-InP substrate 20, and zinc (Zn) diffuses into the n-InP cap layer 28. Thus, a p-type diffusion region 32 is formed, and a pin photodiode is manufactured.
[0003]
A p-type electrode 34 is formed in the p-type diffusion region 32, an n-type electrode 36 is formed on the back surface of the substrate, and an antireflection film 30 of a single silicon nitride film is formed on the surface.
[0004]
Light is absorbed by the i-InGaAs light absorbing layer 24 to generate carriers, and photovoltaic power is generated between the p-type electrode 34 and the n-type electrode 36 due to the drift of the carriers. When the p-type electrode 34 and the n-type electrode 36 are closed by an external circuit, a photocurrent (a current proportional to the amount of incident light) flows through the circuit.
[0005]
[Patent Document 1]
JP-A-5-37002
[Problems to be solved by the invention]
However, in a conventional semiconductor light receiving element using InGaAs for the light absorbing layer, there are the following problems when trying to improve the light receiving sensitivity.
[0007]
That is, in order to improve the light receiving sensitivity, it is necessary to increase the light absorption in the InGaAs layer. The light absorption amount I ₀ -I in the InGaAs layer is
I ₀ −I = I ₀ −I ₀ exp (−αd) = I ₀ {1-exp (−αd)}
I ₀ : incident light amount I: transmitted light amount α: absorption coefficient d: determined by the film thickness, it is necessary to increase the film thickness of the InGaAs layer in order to increase light absorption in the InGaAs layer.
[0008]
FIG. 2 is a diagram showing the relationship between the thickness of the InGaAs layer and the amount of light absorption for light of λ = 1.55 μm when the absorption coefficient of the InGaAs layer is 1.23 × 10 ⁻⁴ / cm. . The light absorption amount is shown as 1.0 when all the incident light amounts are absorbed. As shown in FIG. 2, the light absorption increases as the film thickness increases.
[0009]
On the other hand, carriers generated in the InGaAs layer move in the direction of the electric field, that is, in the direction of the film thickness. Therefore, increasing the film thickness increases the drift time of the carriers to the electrode, and lowers the optical response speed. is there. FIG. 3 is a diagram showing the relationship between the thickness of the InGaAs layer and the response time. The size of the light receiving portion was 50 μmφ, the carrier concentration was 1 × 10 ¹⁵ cm ⁻³ , the external resistance was 50Ω, and the drift speed was 10 ⁷ cm / s. The thin solid line shows the carrier drift time, the dotted line shows the response time due to the RC time constant, and the thick solid line shows the total time. From FIG. 3, it can be seen that the light response speed decreases as the film thickness increases in a portion where the film thickness is about 1 μm or more.
[0010]
As described above, the carriers generated in the light receiving region drift in the direction of the electric field, that is, in the thickness direction. Therefore, the longer the film thickness, the longer the time and the slower the optical response speed. The absorption is reduced, leading to a reduction in sensitivity.
[0011]
The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a semiconductor light receiving element capable of improving contradictory light receiving sensitivity and light response speed.
[0012]
[Means for Solving the Problems]
The present invention includes a first semiconductor layer of a first conductivity type, a light absorption layer, and a second semiconductor layer of a first conductivity type stacked on a semiconductor substrate, wherein the second semiconductor layer is provided in the second semiconductor layer. In a semiconductor light receiving element having a diffusion region of the second conductivity type reaching the light absorption layer, a reflection mirror layer for reflecting light incident from the surface is provided between the light absorption layer and the first semiconductor layer. It is characterized by.
[0013]
The reflecting mirror layer preferably has a laminated structure in which a plurality of pairs of a first reflecting mirror layer and a second reflecting mirror layer satisfying the Bragg reflection condition are stacked as one pair. It is preferable to have a structure in which 16 to 22 pairs are stacked as one pair in which a layer and a second reflecting mirror layer are stacked.
[0014]
Preferably, the first reflector layer is made of InP, the second reflector layer is made of AlGaInAs, the light absorbing layer is made of undoped InGaAs, and the first and second semiconductor layers are n-type. Of InP.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0016]
FIG. 4 is a sectional view showing a wafer structure on which the semiconductor light receiving element according to the present invention is formed. In the semiconductor light receiving device according to the present invention, two layers satisfying the Bragg reflection condition are stacked below the light absorption layer of the conventional diffusion type light reception device shown in FIG. 1, that is, between the InP buffer layer and the InGaAs light absorption layer. In this example, a plurality of layers are stacked as a pair, and layers of a reflecting mirror structure in which a plurality of pairs are stacked are inserted. Of the light incident from the surface, light that has passed through the light absorbing layer is reflected by the light absorbing layer by the reflecting mirror structure. 4, the same components as those in FIG. 1 are denoted by the same reference numerals.
[0017]
On an n-InP substrate 20, an n-InP buffer layer 22, a reflector layer 23, an i (undoped) -InGaAs light absorbing layer 24, and an n-InP cap layer 28 are stacked. (Zn) is diffused to form a p-type diffusion region 32 serving as a light receiving portion.
[0018]
A p-type electrode 34 is formed in the p-type diffusion region 32, an n-type electrode 36 is formed on the back surface of the substrate, and an antireflection film 30 made of a single silicon nitride (SiN) film is formed on the front surface. . That is, the semiconductor light receiving element according to the present invention is a photodiode having a pin structure.
[0019]
Such a light receiving element is manufactured as follows. On the n-InP substrate 20, an n-InP buffer layer 22, a reflecting mirror layer 23, an i-InGaAs light absorbing layer 24, and an n-InP cap layer 28 are successively epitaxially grown by MOCVD. Next, Zn is diffused into a part of the n-InP cap layer 28 to form a light receiving portion including the p-type diffusion region 32 reaching the i-InGaAs light absorption layer 24. Then, an anti-reflection film 30 is formed on the n-InP cap layer 28, a p-type electrode is formed on a part of the p-type diffusion region 32 on the surface of the substrate, and an n-type electrode 36 is formed on the back surface of the substrate. .
[0020]
When the reflecting mirror layer 23 having a reflecting mirror structure was inserted between the i-InGaAs light absorbing layer 24 and the InP buffer layer 22, of the light incident from the p-type diffusion region 32, the light passed through the i-InGaAs light absorbing layer 24. The light is reflected by the reflecting mirror layer 23 to the i-InGaAs light absorbing layer 24. For example, when the light absorption in the reflecting mirror layer 23 is set to zero, the thickness of the i-InGaAs light absorbing layer 24 is substantially doubled. However, the generated carriers pass through the reflecting mirror layer 23 as they are, so that there is no influence on the optical response speed.
[0021]
FIG. 5 is a diagram illustrating an example of the structure of the reflecting mirror layer. As shown in FIG. 5, 16 to 22 pairs of reflective mirror layers are stacked, with InP and Al _0.05 Ga _0.42 In _0.53 As (hereinafter abbreviated as AlGaInAs) as one pair. It has a structure. Since this material is a material system that is lattice-matched to InP, no special growth technique is required.
[0022]
The refractive index of each layer at a wavelength of 1.55 μm is 3.17 for the InP layer and 3.80 for the AlGaInAs layer.
[0023]
The thickness of each layer is set based on the condition of Bragg reflection (λ / 4n, where λ is a wavelength and n is a refractive index). When the wavelength λ is 1.55 μm, the thickness of the InP layer is 1550 / (4 × 3.17) = 122.2 nm, and the thickness of the AlGaInAs layer is 1550 / (4 × 3.80) = 102.0 nm.
[0024]
Therefore, the film thickness of one pair of the InP layer and the AlGaInAs layer is 224.2 nm, and the film thickness of the reflecting mirror layer having a structure of 22 pairs is 224.2 × 22 = 4932.4 nm = 4.93 μm. The thickness of the reflecting mirror layer having a structure in which 16 pairs are stacked is 224.2 × 16 = 3587.2 nm = 3.59 μm.
[0025]
When 22 pairs of such an InP layer and an AlGaInAs layer were stacked, the reflectance reached 99.9%, almost reaching 100%. In addition, the reflectivity when 16 pairs were stacked was 96%.
[0026]
Light receiving elements were manufactured using the conventional wafer structure shown in FIG. 1 and the wafer structure in which the reflecting mirror layer was inserted as shown in FIG. 4, and the light sensitivity was measured. The thickness of the InGaAs light absorbing layer was 1.4 μm for both the conventional wafer structure and the wafer structure in which the reflecting mirror layer was inserted. The reflecting mirror layer was formed by laminating 22 pairs of an InP layer and an AlGaInAs layer.
[0027]
The light sensitivity in the case of the light receiving element without the reflecting mirror layer was 1.0 A / W, but in the case of the light receiving element with the reflecting mirror layer, the light sensitivity increased to 1.14 A / W, and the light sensitivity was increased. Improvement was confirmed.
[0028]
This is because the incident light is reflected by the light absorbing layer again without being transmitted by the reflecting mirror and contributes to the absorption, so that the film thickness of the light absorbing layer is substantially doubled, and the amount of light absorption increases. is there.
[0029]
【The invention's effect】
As described above, according to the present invention, compared with the conventional semiconductor light receiving element structure, the same light sensitivity can be obtained with a thinner light absorbing layer thickness, and the carrier absorption time can be reduced because the light absorbing layer thickness is thinner. Is reduced, and the light response speed is improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a wafer structure on which a conventional light receiving element is formed.
FIG. 2 is a diagram showing the relationship between the thickness of an InGaAs layer and the amount of light absorbed.
FIG. 3 is a diagram showing a relationship between the thickness of an InGaAs layer and a response time.
FIG. 4 is a sectional view showing a wafer structure on which a semiconductor light receiving element according to the present invention is formed.
FIG. 5 is a diagram showing an example of the structure of a reflecting mirror layer.
[Explanation of symbols]
Reference Signs List 20 n-InP substrate 22 n-InP buffer layer 23 reflecting mirror layer 24 i-InGaAs light absorbing layer 28 n-InP cap layer 30 antireflection film 32 p-type diffusion region 34 p-type electrode 36 n-type electrode

Claims (5)

A first conductivity type first semiconductor layer, a light absorption layer, and a first conductivity type second semiconductor layer laminated on a semiconductor substrate, wherein the light absorption layer is provided in the second semiconductor layer; In a semiconductor light receiving element in which a diffusion region of the second conductivity type reaching
A semiconductor light receiving element comprising a reflector layer between the light absorbing layer and the first semiconductor layer for reflecting light incident from a surface. 2. The reflection mirror layer according to claim 1, wherein a plurality of pairs of a first reflection mirror layer and a second reflection mirror layer satisfying a Bragg reflection condition are stacked. 3. The semiconductor light receiving element according to item 1. The said reflecting mirror layer has the structure which laminated | stacked 16-22 pairs as what laminated | stacked the 1st reflecting mirror layer and the 2nd reflecting mirror layer as one pair, The Claim 1 or 2 characterized by the above-mentioned. Semiconductor light receiving element. 4. The semiconductor light receiving device according to claim 1, wherein said first reflecting mirror layer is made of InP, and said second reflecting mirror layer is made of AlGaInAs. 5. The semiconductor light receiving device according to claim 1, wherein said light absorbing layer is made of undoped InGaAs, and said first and second semiconductor layers are made of n-type InP.

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