JPS6138871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an avalanche photodiode having a heterojunction, and particularly to an improvement in the structure of a guard ring provided for the purpose of preventing breakdown at the periphery of a photodetection region.

Among various semiconductor photodetectors, avalanche photodiodes (hereinafter abbreviated as "APD")
is a light-receiving element with high sensitivity and broadband characteristics, and is widely used as an optical communication component.

APD amplifies photocurrent by applying a reverse bias voltage to the pn junction and causing avalanche multiplication under a high electric field. Therefore, before avalanche multiplication of photocurrent occurs,
The disadvantage is that the electric field concentrates around the periphery of the photodetection area, causing breakdown there.

Traditionally, in order to solve the above-mentioned drawbacks, especially
APDs have been proposed in which an annular layer called a guard ring is provided around the photodetection region, as seen in the one-dimensional APDs made of Ge or Si. FIG. 1 is a diagram showing this conventional example, in which a is a perspective view including a cut section, and b is a cross-sectional view. In these figures, 1 is a high-concentration n-type semiconductor substrate, 2 is a low-concentration n-type semiconductor, and 3 is a photodetection region made of a high-concentration p-type semiconductor.
Configure a p-n junction. 4 is a guard ring made of a p-type semiconductor, 5 is an insulator, and 6 and 7 are electrode metals. In this conventional example, the carrier concentration of the guard ring 4 is made lower than that of the photodetection region 3, the electric field in the guard ring 4 is lowered, and breakdown occurs at the periphery of the photodetection region 3 during photocurrent multiplication. I'm trying not to wake up. Note that a diffusion means is used to manufacture the guard ring 4.

On the other hand, recently, 1 wavelength band has been recognized as effective for optical communication.
~1.7μm band is attracting attention, and APD used for this band
A quaternary or ternary APD expressed by the composition formula In _1-x Ga _x As _y P _1-y (0.42y≦x≦0.5y and 0<y≦1) has come to be manufactured. . this
Even in the In _1-x Ga _x As _y P _1-y system, there still remains the problem that breakdown tends to occur around the photodetection region, and one method to solve this problem is shown in Figure 1. It is conceivable to provide a guard ring as in the conventional example. however,
In the In _1-x Ga _x As _y P _1-y system, it is extremely difficult to form a low-concentration p-type region using the conventional diffusion method, and it is necessary to maintain a sufficient carrier concentration difference between the photodetection region and the guard ring. However, the electric field concentrates on the part of the guard ring that has a particularly large curvature, causing breakdown there.

The present invention has been made in view of the above-mentioned drawbacks.
By forming a large part of the guard ring's curvature in a semiconductor with a large forbidden band width, the breakdown voltage there can be increased and breakdown can be prevented by making it possible to prevent breakdown.
It provides diodes.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 2 is a cross-sectional view of an APD that is an embodiment of the present invention. 17 is n ⁺ −InP substrate, 18 is n
−1n _1-p Ga _p As _q P _1-q (0.42q≦p≦0.50q, and 0
≦q≦1) layer (second semiconductor layer), 19 is n-
In _1-x Ga _x As _y P _1-y (0.42y≦x≦0.50y, and 0≦
y≦1) layer (first semiconductor layer), 20 is p ⁺ −
In _1-x Ga _x As _y P _1-y layer forms a p-n junction with the layer 19; 21 and 22 are guard rings made of p-type semiconductor; 5 is an insulator; and 6 and 7 are electrode metals. . To further explain the guard rings 21 and 22, 21 is a p-type semiconductor having the same composition as the layer 19 and is represented by p-In _1-x Ga _x As _y P _1-y , and 22 is a p-type semiconductor having the same composition as the layer 18. It is a p-In _1-p Ga _p As _q P _1-q type semiconductor. Further, 25 indicated by an arrow line indicates a large portion of the curvature of the guard ring. The feature of this embodiment is that the forbidden band width of the layer 18 is made larger than the forbidden band width of the layer 19, and
The shaped region is formed to reach into the layer 18, and the large curvature portion 25 of the guard ring is located within the layer 18.

It is generally known that, other conditions being the same, a semiconductor with a larger forbidden band width has a larger breakdown voltage. Therefore, compared to the conventional example in which the guard ring is formed only in a semiconductor having the same composition as the photodetection region, it is better to extend the guard ring into the semiconductor with a large forbidden band width as in this example. The breakdown voltage of the portion 25 where the curvature is large becomes large, and breakdown can be effectively prevented.

Next, the manufacturing method of this example will be explained. n ⁺ −InP
n- is deposited on the substrate 17 by liquid phase epitaxial method.
In _1-p Ga _p As _q P _1-q (0.42q≦p≦0.50q, and 0≦
q≦1) layer 18, n-In _1-x Ga _x As _y P _1-y (0.42y≦
x≦0.50y and 0≦y≦1) layers 19 are sequentially grown. At this time, the forbidden band width of the In _1-p Ga _p As _q P _1-q layer 18 is made larger than that of the In _1-x Ga _x As _y P _1-y layer 19 . Next, a SiO ₂ film that will become the insulator 5 is deposited on this wafer by sputtering or a vapor phase chemical reaction method. Thereafter, the SiO ₂ film on the portion where the guard rings are to be formed is removed by photo-etching, and the guard rings 21 and 22 are formed by thermally diffusing Zn using the SiO ₂ film as a mask. Next, the SiO ₂ film above the photodetection area is also removed using photo-etching technology, and the Zn is thermally diffused using the SiO ₂ film as a mask to form the photodetection area. At the stage where the second thermal diffusion is completed, the tip of the guard ring portion where Zn has been diffused is in the In _1-p Ga _p As _q P _1-q layer 18, and the pn junction in the photodetection area is in the In _1-x Ga _x As _y P _1-y in the layer 19. After that, to form a non-reflective coating.
After depositing the SiO ₂ film again, the SiO ₂ film above the guard ring portion is removed to take out the upper electrode. Upper electrode 9 is formed using vacuum deposition and photo-etching techniques. Next, after polishing the back side of the InP substrate 17, the lower electrode 7 is formed by vacuum deposition. Finally, the electrodes are heat-treated to complete the APD.

Next, other embodiments will be described. In the example shown in FIG. 2, the guard rings 21 and 22 are constructed using semiconductors having different forbidden band widths, but the guard rings may be constructed using semiconductors having the same composition. In this case, the forbidden band width of the semiconductor forming the guard ring needs to be larger than the forbidden band width of the semiconductor in contact with the guard ring. FIG. 3 shows a sectional view of the APD according to this embodiment. As a method for manufacturing the APD of this example, an example in which a guard ring is formed by a crystal growth method will be described. n-In _1-p Ga _p As _q P _1-q on n ⁺ -InP substrate 17 by liquid phase epitaxial method
(0.42q≦p≦0.50q, and 0≦q≦1) layer 18;
The n-In _1-x Ga _x As _y P _1-y (0.42y≦x≦0.50y, and 0≦y≦1) layer 19 is sequentially grown. On this occasion
In _1-p Ga _p As _q P _1-q forbidden band width
In _1-x Ga _x As _y P Make it larger than the forbidden band width of _1-y . Next, a SiO ₂ film is deposited on this wafer by sputtering or a vapor phase chemical reaction method. After that, the SiO ₂ film that forms the guard ring is removed using photo-etching technology, and layer 1 is etched using the SiO ₂ film as a mask.
selectively removing layers 18 and 19 to the middle of layer 8;
Then p-In _1-l Ga _l As _n P _1-n (0.42m≦l≦
0.50m and 0≦m≦1) layer 27 is selectively grown to form a guard ring. guard ring part
The forbidden band width of In _1-l Ga _l As _n P _1-n is made larger than that of layers 18 and 19. Next, the SiO ₂ film above the photodetection area is removed using photo-etching technology, and Zn is thermally diffused using the SiO ₂ film as a mask to form the photodetection area. After that, an anti-reflective coating is formed, electrodes are formed, and heat treatment is performed to complete the APD.

FIG. 3 is another embodiment, which is shown in FIG.
In order to increase the quantum efficiency, an In _1-n Ga _n As _o P _1-o layer (0.42n≦m≦
0.50n and 0≦n≦1)26.

In the above examples, InGaAsP mixed crystal was used.
As mentioned above about APD, it is sufficient that the tip of the guard ring portion is formed in a semiconductor having a forbidden band width larger than that of the semiconductor constituting the photodetection region, and even a mixed crystal such as GaAlAsSb can be used. It is possible. Of course, it may be formed using semiconductor layers having different constituent elements. Moreover, a structure having the opposite conductivity type is also possible.

As explained above using the InGaAsP APD as an example, according to the present invention, the tip of the guard ring portion is formed in a semiconductor whose forbidden band width is larger than that of the semiconductor in the photodetection region, thereby improving the effect of the guard ring. It can be reliably demonstrated, and its industrial value is extremely large.

[Brief explanation of the drawing]

Figures 1a and 1b are perspective views including a cut section showing an example of a conventional avalanche photodiode;
3 and 4 are cross-sectional views showing embodiments of the present invention. 5... Insulator, 6,7... Electrode metal, 17...
n ⁺ -InP substrate, 18...n-In _1-p Ga _p As _q P _1-q layer (second semiconductor layer), 19... n-
In _1-x Ga _x As _y P _1-y layer (first semiconductor layer), 20...
p ⁺ −In _1-x Ga _x As _y P _1-y layer (photodetection area), 21,
22... Guard ring, 25... Part with large curvature, 26... In _1-n Ga _n As _o P _1-o layer, 27... p-
In _1-l Ga _l As _n P _1-n layer (guard ring).

Claims (1)

[Scope of Claims] 1. An avalanche photodiode comprising at least a photodetection region having a pn junction made of a compound semiconductor layer on a compound semiconductor substrate, and a guard ring around the photodetection region. A first compound semiconductor layer provided on the substrate side among the compound semiconductor layers forming the region;
A second compound semiconductor layer having the same conductivity type as the compound semiconductor layer and having a large forbidden band width is provided on the substrate side, and a tip portion of the guard ring having a large curvature extends to the second compound semiconductor layer. Avalanche Hot
diode. 2. The guard ring according to claim 1, wherein the guard ring is formed of a compound semiconductor layer having a band gap larger than the forbidden band width of the first compound semiconductor layer and the second compound semiconductor layer. Avalanche photo diode.