JP2854634B2 - Light receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a structure and a manufacturing method of an avalanche photodiode (APD) used for an optical communication system or the like.

[Conventional technology]

At present, the basic structure of APD used for optical communication is noise,
In order to reduce dark current, a structure in which a light absorption layer and a multiplication layer are spatially separated as shown in FIG. 2 is mainly used. At that time, what is important in terms of increasing the speed of the element and reducing noise is the type of carrier injected into the multiplication layer. That is, the ionization rate α for electrons and the ionization rate β for holes
When the ionization rate ratio k (= α / β), which is the ratio, is larger than 1, electron injection is desirable, and when it is smaller than 1, hole injection is desirable.

FIG. 2 (a) shows a hole injection type device, and FIG. 2 (c)
FIG. 2 is a schematic view of a conventional structure of an electron injection element. (A),
Specific examples of (b) include InP / InGaAs-based APD and Ga, respectively.
As / GaAlAs Superlattice APD [Semiconductors and Semimetals Vol.22
p117 (1985) Academic Press Inc. (Academic Press Inc.). In the same figure, black circles (●) and white circles (）) indicate electrons and holes generated in the light absorption layer by light indicated by wavy lines, and arrows indicate the drift directions of the respective carriers in APD operation. .

[Problems to be solved by the invention]

In order to increase the speed of the device and reduce the dark current, in a normal APD using a pn junction, the junction area needs to be limited and reduced. From such a viewpoint, comparing the structures of FIGS. 2 (a) and 2 (c), FIG. 2 (a) shows a planar type having a limited p-type region, and FIG. 2 (c) shows a mesa type. Element reliability,
In consideration of the influence of the surface state, a planar type having few PN junction exposed portions is desirable.

However, in the conventional structure, it is difficult to easily fabricate a planar structure with the electron injection type (c).

FIG. 2 (b) shows a typical electron injection type APD, Si.
FIG. 3 is a diagram showing a principle configuration of an APD structure. In this case, planarization can be achieved by implanting n-type impurities. However, in III-V compound semiconductors that are APD materials for optical communication, it is difficult to form an n-type region having a depth of 1 to 2 μm by selective diffusion of n-type impurities or ion implantation. Is difficult. Also,
As another manufacturing method, a method of manufacturing a structure corresponding to (b) by multiple crystal growths can be considered, but it is difficult to apply the structure to a practical device due to a decrease in crystallinity at a regrowth interface.

An object of the present invention is to propose a structure that can be made planar in an electron injection type APD and a method for manufacturing a practicable element.

[Means for solving the problem]

FIG. 2 (d) shows a schematic diagram of the APD of the present invention. The structure of the present invention is the same as the structure shown in FIG.
Is a structure in which the conductivity type is reversed. It is clear that this structure satisfies the electron injection condition. In addition, the structure of this multiplication layer is InGaAs / InA, which is known to have k> 1.
An lAs superlattice multiplication layer is used.

As a method of manufacturing this structure, a multilayer structure including a pn junction of the central light receiving function portion is manufactured by crystal growth, and then Zn is formed.
The p-type junction limiting region may be formed by diffusion, Be ion implantation, or the like.

In the present invention, FIG. 2 (d) is a basic principle diagram, and as shown in an embodiment described later, adding another layer,
Deformation is possible by changing the conductivity type of the multiplication layer and the like.

[Action]

A feature of the present invention is that it is possible to prevent the main pn junction involved in the light receiving function from being exposed to the crystal surface. This is clear from comparison with the conventional example of the electron injection type (FIG. 1 (c). As a result, a reduction in surface leakage current,
The stable operation of the element and the improvement of the reliability can be achieved.

〔Example〕

Embodiment 1 FIG. 1A shows a light receiving device according to an embodiment of the present invention.
In this embodiment, InGaAs / InAlA satisfying the ionization rate ratio k> 1
This is a planar APD having the s superlattice 26 as a multiplication layer. p-In
A p-InAlAs buffer layer (p = 2 × 10 ¹⁸ cm ⁻³ , film thickness d = 1 μm) 29 on a P substrate (p = 2 × 10 ¹⁸ cm ⁻³ ) 30, p-InGa
As light absorbing layer (p = 5 × 10 ¹⁵ cm ⁻³ , d = 1.5 μm) 28, p-I
nAlAs electric field relaxation layer (p = 5 × 10 ¹⁶ cm ⁻³ , d = 0.2 μm) 27,
p-InGaAs / InAlAs superlattice multiplication layer (p = 1 × 10 ¹⁵ cm ⁻³ , In
GaAs wale layer, width 15nm, InAlAs barrier layer width 15nm, cycle number
15) 26, n-InAlAs layer (n = 2 × 10 ¹⁸ cm ⁻³ , d = 1 μm)
25, and n-InGaAs contact layer (n = 1 × 10 ¹⁹ c
m ⁻³ , d = 0.2 μm) 24 are laminated. Reference numeral 22 denotes a SiN passivation film, and reference numerals 21 and 31 denote electrodes. The p-type region for limiting the junction region according to the present invention is indicated by 23 shaded portions.

The device is fabricated by crystal growth by molecular beam epitaxy (growth temperature 500 ° C), selective diffusion using zinc calcined, formation of SiN passivation film by plasma CVD, formation of n-electrode by vacuum deposition, and patterning of n-electrode by lift-off. Then, Cr-Aup side electrodes were formed sequentially by electron beam evaporation. The depth of the p region 23 was set to about 3 μm, and was made deeper than the pn junction (the interface between 25 and 26) of the light receiving portion.

FIG. 1B shows an APD manufactured by the same structure and the same process as that of FIG. 1A, except that the depth of the p region is 1.2 μm.
This is the same as the light receiving unit joining position.

The electrical and optical characteristics of the devices shown in FIGS. 1A and 1B were evaluated. As a result, the maximum multiplication factor is (a),
(B) Good results were obtained at dark currents of 100 and 40 nA, respectively, with gains and band products of 95 GHz and 90 GHz, respectively, at 30, 25 and a gain of 1. Note that the in-plane sensitivity distribution is slightly (a)
Was better.

Next, a mesa element corresponding to the structure in which the p region 23 in FIG. 1A was removed was prototyped, and the above characteristics were compared. The mesa-type device has a large dark current of 800 nA, which is considered to be one of the improvement effects of the present invention. It should be noted that there was no remarkable difference in the characteristics regarding the multiplication factor and the band.

Next, in order to examine the effects of improving the reliability and life expectancy of the device expected according to the present invention, the above three devices (a), (b) and the mesa type were subjected to a reverse current of 100 μA and an ambient temperature of 20 ° C. A life test was conducted. In each of the elements shown in FIGS. 1A and 1B according to the embodiment of the present invention, no characteristic deterioration was observed until a time corresponding to 10 ⁶ kr. On the other hand, 10
^At a time corresponding to ⁴ kr, a remarkable increase in dark current was observed, confirming the effect of the present invention.

Subsequently, another embodiment is shown in FIG. This element is
This is a planar APD having a light absorption layer 48 of p-InGaAs and a multiplication layer 46 of n-InAlAs. The difference from the embodiment of FIG. 1 (a) is that the InGaAs contact layer 44 of the light receiving section is removed and the multiplication layer 46 is replaced with n-type InAlAs (n = 1 ×
10 ¹⁵ cm ⁻³ , d = 1 μm).
It is formed by Be ion implantation and subsequent annealing. Reliability present element corresponding to 10 ⁶ hours at life test described above, exhibited the characteristic stability.

[Effects of the Invention] According to the present invention, a planar structure can be easily manufactured using an electron injection type APD. At this time, since a step of exposing the main junction to the air is not included, deterioration of device characteristics due to a process, particularly an increase in dark current can be prevented. Further, by using a planar structure, stability and reproducibility of operating characteristics can be realized, and reliability and life of the element can be improved.

[Brief description of the drawings]

1 (a), 1 (b) and 1 (c) show an embodiment of the present invention.
Sectional views showing the structure of the APD, FIGS.
FIG. 2C is a cross-sectional view of an APD having a conventional structure, and FIG. 2D is a cross-sectional view of the APD showing a basic configuration of the present invention. 21,31,41,51 ... electrode, 23,43 ... p-type region, 25,45 ...
n-InAlAs, 26 ... n-InAlAs / InGaAs multiple quantum well multiplication layer, 27,47 ... p-InAlAs electric field relaxation layer, 28,48 ... p-
InGaAs light absorption layer, 46... P-InAlAs multiplication layer.

Continued on the front page (72) Inventor Chiaki Notsu 3681 Hayano, Mobara-shi, Chiba Hitachi Device Engineering Co., Ltd. 72) Inventor Koji Ishida 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-1-205477 (JP, A) JP-A-63-128679 (JP, A) JP-A-60-58684 (JP, A) JP-A-60-49681 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/10

Claims (1)

(57) [Claims] 1. A predetermined compound semiconductor substrate, a light absorbing layer provided on the compound semiconductor substrate and receiving incident light to generate carriers, and an electron injection type for multiplying the generated carriers. A light receiving device having at least a multiplication region and a pn junction, wherein the light absorption region is a p-type III
The multiplication region is formed of a superlattice structure, exhibits p-type characteristics, and has a ratio (k) between the ionization rates α and β for electrons and holes in the superlattice structure. = Α / β) is greater than 1 and the pn junction is introduced into the n-type group III-V compound semiconductor layer by impurity diffusion in a direction parallel to the substrate surface of the compound semiconductor substrate to form a p-type junction. Exists between the impurity regions,
In the direction crossing the substrate surface of the compound semiconductor substrate of the pn junction, the light absorption region and the multiplication region do not reach the light absorption region and the multiplication region, and at least the light absorption layer and the multiplication region are formed between the pn junction and the compound semiconductor substrate. A light receiving device, which is located between the two and has an n-electrode on the compound semiconductor substrate side and a p-electrode on the n-type III-V compound semiconductor layer side.