JPH0373576A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To prevent quantum efficiency from decreasing by forming a semiconductor substrate under a photodetecting region in a convex mirror shape, forming the specific region of an electrode at the substrate side under the formed part of the substrate to reflect the light passed through a light absorption layer of an incident light, thereby converging it to the absorption layer. CONSTITUTION:A photodetector p<+> type region 7 and a guard ring 8 are formed in a laminated structure formed by continuously growing an n<-> type InGaAs light absorption layer 3, an n-type InGaAsP layer 4 and n-type InP cap layers 5, 6 on an n<+> type InP substrate 1 through an n-type InP buffer layer 2 to grown an SiNx film as a surface protective film 9, the substrate is then etched to form a convex mirror shape. Thereafter, a p-type side electrode 10 and an n-type side electrode 11 are deposited to obtain an element structure. The electrode 11 is formed in a spherical shape having a radius of curvature in which its focus is disposed in the light absorption layer to perform a role of a mirror for reflecting again the light scattered without being absorbed by the layer 3 toward the layer 3, thereby contributing to improvement in quantum efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor light-receiving element used in optical communications, optical information processing, and the like.

[Conventional technology]

Figure 3 shows a conventional Ink/InGaAs-based heterostructure avalanche photodiode (hereinafter referred to as APD).
A cross-sectional view is shown. An n-InGaAs light absorption layer 3 is formed on the n''-InP substrate 1 via the n-InP buffer layer 2.
H-InGa As P layer 4. A light-receiving portion p1 region 7 and a guard ring 8 are formed on a laminated structure formed by continuously growing n-InP cap layers 5 and 6, thereby obtaining the device structure shown in FIG. 3. By separating it from the light absorption layer 3 having a narrow bandgap in the multiplication region and forming it in the rnP layer 5 having a wide bandgap, low dark current and high sensitivity characteristics are obtained.

The n-InGaAsP layer 4 is an intermediate layer inserted to alleviate the valence band discontinuity at the hetero interface and improve response characteristics, and the InP layer is an intermediate layer added to the n-layer 5. The reason why it has a double structure with the n layer 6 is to enhance the guard ring effect.

Current Ink/InGaAs APDs have a bandwidth of about IGb/s, but in order to further increase the bandwidth,
By thinning the light absorption layer, it is necessary to shorten the carrier transit time.

[Problem to be solved by the invention]

In general, when light is perpendicularly incident on a medium with absorption coefficient α2 layers thick, the number of photons absorbed is (1-e-“X
), the conventional Ink/InGaAs system A
In PD, when the light absorption layer is made thinner, the amount of transmitted light component increases. This transmitted light travels through the relatively thick n+-InP substrate of about 100 μm to 200 μm while being absorbed by some free carriers, and after being reflected by the back electrode 11, it goes through the same process again. 0 Normal light is a parallel beam Instead, the light is focused and then introduced into the light receiving element, so the probability that the reflected light is absorbed by the InGaAs 3 region below the light receiving area is low.

Therefore, a problem arises in that the quantum efficiency decreases significantly due to thinning of the light absorption layer 3.

[Means to solve the problem]

The light receiving element provided by the present invention has a semiconductor multilayer structure including a light absorption layer having a band gap E2 (El<El) on a semiconductor substrate having a band gap E1, and a light receiving region in the light absorption layer. The semiconductor substrate located under the specific area is processed into a curved surface with a certain curvature,
Further, the structure is characterized in that a part of the substrate-side electrode is formed on the lower surface of the processed portion.

In order to solve the above-mentioned conventional problems, in the present invention, the semiconductor substrate under the light receiving area is processed into a convex mirror shape, and a specific area of the substrate side electrode is formed under the processed part of the semiconductor substrate, so that part of the incident light is processed into a convex mirror shape. The light that has passed through the light absorption layer is reflected and focused on the light absorption layer. Therefore, it has the advantage of reabsorbing scattered light, which conventionally did not contribute to quantum efficiency, and providing the same effect as a thick absorption layer.

[Example specialist]

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, in which InP/I
1 is a cross-sectional view showing the structure of an nGaAs-based heterojunction APD. According to this embodiment, an n-InP buffer layer 2r is sequentially formed on an n''-InP substrate 1 by a vapor phase growth method.
n--InGaAs light absorption layer 3. n-InGaAs layer for relaxation of band discontinuity 4. Cap layer divided into two layers formed by crystal growth of n-InP5 and n''--InF3 A guard ring 8 is formed in the laminated structure by ion implantation of s''Be and activation annealing, and then zn.

After growing a SiNx film as the surface protective film 9 forming the p+ region of the light receiving part by sealed tube thermal diffusion using P as a source, n'' is grown using a bromide-based etching solution.
- The InP substrate is etched and processed into the shape shown in FIG. After that, the p-side electrode 10 and the n-side electrode 1
1 is vapor-deposited to obtain an element structure as shown in FIG.

The n-side electrode 11 formed by the above-mentioned etching and vapor deposition has a spherical surface with a radius of curvature such that the focal point is located in the light absorption layer, and is not absorbed by the n--InGaAs light absorption layer 3. The light scattered by the n--In
The transmitted light, which plays the role of a mirror that reflects toward the GaAs light absorption layer 3 and was therefore scattered and not absorbed again in the conventional element, contributes to improving the quantum efficiency. The degree of improvement in quantum efficiency was almost equivalent to that obtained by doubling the thickness of the light absorption layer 3. Also, there is a concern that the fall time will increase due to the time delay caused by the reflected light, but assuming that the total thickness of the n-InP buffer layer 2 and the n''-InP substrate is 100 μm, t = 100 x 10
-"m/ (3xlO'm/s) x 3x10-"s, which is a delay that is hardly a problem.

Next, FIG. 2 shows another embodiment of the present invention, InP/InG.
FIG. 2 is a cross-sectional view showing the structure of aAs pin-PD. p
Unlike an avalanche photodiode, the in-PD has a pn junction formed in n-''-InGaAs3 in order to achieve high-speed response at low bias. There is no InGaAsP layer and guard ring.

Further, the cap layer is a single layer consisting of only the n-InP layer 5. As in the case of APD, n”-I below the photosensitive area
The nP substrate 1 is processed to form a part of a sphere as shown in FIG. 2, and the back electrode 11 is formed thereunder. When achieving faster response by making the light absorption layer thinner, it is possible to obtain a quantum efficiency equivalent to having substantially twice the thickness of the light absorption layer.

〔Effect of the invention〕

As explained above, the present invention allows transmitted light from an absorption layer to be
By reflecting and reabsorbing the light with an n-side electrode having an appropriate shape, it is possible to provide a semiconductor light-receiving element that has both high response speed and high quantum efficiency.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor device showing an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a semiconductor light-receiving device showing another embodiment of the present invention, and FIG. 3 is a cross-sectional view of a semiconductor light-receiving device showing a conventional example. In the figure, 1... n''-InP substrate, 2...
...n-InP buffer layer, 3...n--
InGaAs light absorption layer, 4-n-'InGaAsP, 5
-- n -I n P s 8...n--I
nP, 7... Light receiving part p+ region 8...
Guard ring, 9...Surface protective film, 10...
. . . p-side electrode, 11 . . . n-side electrode, respectively.

Claims (1)

[Claims] It has a semiconductor multilayer structure including a light absorption layer having a band gap E_2 (E_2<E_1) on a semiconductor substrate having a band gap E_1, and the semiconductor is located under a specific region which is a light receiving region in the light absorption layer. The substrate is processed into a curved surface with curvature, and a part of the substrate side electrode is
A semiconductor light-receiving element, characterized in that it is formed on the lower surface of the processed portion.