JPS63955B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a high-speed, high-sensitivity, low-dark current, and low-noise photodiode (hereinafter referred to as
This relates to avalanche photodiodes (hereinafter referred to as APDs) or avalanche photodiodes (hereinafter referred to as APDs).

PDs or APDs that use semiconductor materials as photodetectors are considered most important as high-speed and highly sensitive detectors for optical communication, and their development is being actively progressed along with semiconductor lasers as light sources. The oscillation wavelength of semiconductor lasers is from 0.8 μm to 1.5 μm, such as GaAS-AlGaAs or InGaAsP.
- InP-based semiconductor lasers are the mainstream and are being actively researched and developed. the current,
Main oscillation wavelength range of GaAs-AlGaAs laser: 0.8μ
PD or APD using Si single crystals is the most widely used photodetector for the range from m to 0.87 μm and is in practical use as it shows excellent characteristics. However, a photodetector using Si material has a wavelength of 1 μm.
It is difficult to detect light of this wavelength, and it cannot be used in the 1.1-1.6 μm wavelength range where optical fiber has low transmission loss. Ge-APDs are also available for wavelengths of 1.1 μm or more, but they are not optimal photodetectors for optical communications due to their large dark current and excessive noise, and the development of high-quality APDs made of - group compound semiconductor materials. is urgently needed. However, crystal growth technology and surface stabilization technology for compound semiconductor materials are still underdeveloped, and the current situation is that they cannot withstand the high reverse bias voltage required to perform avalanche operation. Currently, photodetectors in the 1.1 μm to 1.6 μm wavelength range include InGaAs, InGaAsP,
There are reports of - group multi-component mixed crystals such as GaAlSb and GaAlAsSb. For example, after growing InGaAs or InGaAsP on an InP substrate, zinc diffusion, etc.
An example in which a p-n junction is formed in the above InGaAs or InGaAsP layer and the device is formed by mesa etching, or a device is formed by mesa etching after growing an n-type InGaAs or InGaAsP layer on a p ⁺ -InP substrate without requiring a diffusion process. For example, there are reports of planar structures in which p-n junctions can be formed by selectively forming a p ⁺ layer by implanting ions such as beryllium into a wafer fabricated by a method similar to the above, but at present, the multiplication is low. The dark current is also large, and the results are extremely unsatisfactory as photodetectors for optical communications, which require high reliability.

An object of the present invention is to improve the reverse characteristics, especially the breakdown characteristics, under high reverse bias voltage, and to provide a Brenner type heterojunction photodetector (hereinafter referred to as photodetector) that has low current and excellent low noise characteristics. )
It gives The photodetector of the present invention includes a first semiconductor layer having at least a first conductivity type, and a first semiconductor layer having the same conductivity type as the first semiconductor layer and having a wider forbidden band width than the first semiconductor layer. a layered structure in which a second semiconductor having a first region and a second region exhibiting a second conductivity type and having a wider forbidden band width than the first semiconductor; The structure is such that a high resistance region is formed around the region to a depth extending from the surface of the second region to at least the first region.

Next, the advantages of the present invention will be explained based on one embodiment. FIG. 1 is a cross-sectional view of one embodiment of the photodetector of the present invention.
A case using InGaAsP will be explained. (100)
An n ⁺ type InP 22 with a thickness of several μm is formed by epitaxial growth on an n + type InP substrate 21 having a surface, and then an n ⁺ type InP 22 with a thickness of 2 μm and an impurity concentration of 2 × 10 ¹⁶ cm ^-3
An In _0.53 Ga _0.47 As layer 23 is epitaxially grown.

Next, an n-type In _0.88 Ga _0.12 As _0.26 P _0.74 layer (first semiconductor) 2 with a film thickness of 1 μm and an impurity concentration of 1 to 2 × 10 ¹⁶ cm ^-3
4, an n-type InP layer (second semiconductor) 25 having a thickness of 2 μm and an impurity concentration of 1 to 2×10 ¹⁶ cm ⁻³ is epitaxially grown. The wafer prepared as described above is placed in a closed tube that is evacuated using Cd ₃ P ₂ as a diffusion source, and Cd is selectively diffused by heat treatment at 566°C, thereby forming a Cd diffusion region (second region of the second semiconductor). )25a and pn junction surface 2
Get 5b. Here, the heat treatment time is about 25 minutes,
The pn junction surface 25b is connected to the In _0.86 Ga _0.12 As _0.26 P _0.74 layer 24.
Formed near the InP25 interface. Next, a Si ₃ N ₄ or SiO ₂ film 26 is formed by vapor phase growth, sputtering, or the like, and then the ring-shaped region 26' is removed for ohmic use.
Next, after forming the p-type electrode metal 27, the n-type electrode metal 29 is formed. Next, the p ⁺ type electrode 27
After forming about 1 μm of gold on the top, it is removed leaving circular regions 28 and 28' that block the p ⁺ type electrode 27, and using this gold film as a mask, the Si ₃ N ₄ or SiO ₂ film 2 is removed.
Remove 6. This wafer was processed using proton implantation technology at a dose of 5×10 ¹³ cm ^-2 and an acceleration voltage of 300 KV.
Using the gold film as a mask, protons are implanted into the high resistance region 25 of the p-type InP layer 25a.
a' and a high resistance region 25' of the n-type InP layer are formed.
Next, after forming a light introduction window 28', a photodetector is obtained by cutting into pellets.

Next, the excellent characteristics of this invention and the reason for the improved characteristics will be explained. In the structure shown in FIG. 1 described above, the outer diameter of the gold film 28 as a proton injection mask is 150μ.
In the mφ photodetector, it exhibited steep breakdown characteristics with a dark current of less than 100 pA, and exhibited excellent characteristics with an avalanche multiplication factor of more than 10 ³ times. These excellent characteristics of the present invention can be understood for the following reasons. In other words, the structure of the present invention has a guard ring effect by providing a high resistance region as shown in FIG. It is a well-known fact that a mesa structure is formed, and as a result, electric field concentration does not occur at the edge of the pn junction, resulting in uniform breakdown and high multiplication characteristics. In addition, in the structure of the present invention, light absorption is In _0.53 Ga _0.47
Since the As layer 23 or the In _0.88 Ga _0.12 As _0.26 P _0.74 layer 24 performs avalanche multiplication, and the InP layer 25 performs avalanche multiplication, the dark current is generated in the InP layer, which has a wider forbidden band width than the light absorption layer. The generated recombination current becomes dominant, and the dark current characteristics are significantly improved compared to the conventionally reported case in which a pn junction is formed for optical absorption with a narrow forbidden band width. Furthermore, since it is known that in InP, the ionization rate of holes is higher than that of electrons, the structure of the present invention in which the avalanche region is separated from the light absorption region by using an n-type InP layer greatly contributes to low noise. In addition, In _0.53 Ga _0.47 As is used to have sensitivity to long wavelengths up to about 1.7 μm.
In order to avoid as much as possible an increase in dark current due to the narrow band gap of the In _0.53 Ga _0.47 As layer, the In _0.88 Ga _0.12 As _0.26 P _0.74 layer 24, which has a relatively large band gap, is made of InP.
25 layers to reduce dark current.

The above materials are InP-InGaAsP-InGaAs.
Although the embodiment of the APD has been described, it is clear that the present invention has a guard ring effect and a low dark current effect on all semiconductor devices that operate in reverse bias.
-It is clear that it can be applied to GaAlAsSb systems, etc.

In addition, as a method for forming a high resistance region, the planar type of the present invention can also be achieved by removing a region that is not used for light reception using a technique such as etching, and then forming a high resistance layer using a growth technique such as epitaxial growth. It is clear that a telojunction photodetector is obtained.

[Brief explanation of the drawing]

FIG. 1 shows an embodiment of the present invention, where 21 is n ⁺
InP substrate having type (100) plane, 22 is n ⁺ type InP epitaxial layer, 23 is n type In _0.53 Ga _0.47 As epitaxial layer, 24 is n type In _0.88 Ga _0.12 As _0.26 P _0.74
Epitaxial layer 25 is an n-type InP epitaxial layer, 25a is an InP layer changed to p-type by Cd diffusion,
25' and 25a' are InP layers with high resistance, 26 is
The Si ₃ N ₄ film or SiO ₂ film 26' is the region from which the film 26 has been removed, 27 is the p-type electrode metal, 28 is the gold film, 28' is the region from which the gold film 28 has been removed, and 29 is the region from which the gold film 28 has been removed. It is a metal for n-type electrodes.

Claims (1)

[Claims] 1: a first semiconductor exhibiting a first conductivity type;
a first region exhibiting a conductivity type, and a second semiconductor having a second region exhibiting a second conductivity type on the first region; The second area is placed around the area for receiving light.
A high resistance region is provided from the surface of the region to a depth reaching at least the first region, and the first semiconductor has a two-layer structure of a semiconductor layer with a large forbidden band width and a semiconductor layer with a small forbidden band width; 2. A planar heterojunction photodetector characterized in that a layer with a large forbidden band width is provided on the semiconductor side.