JPS597233B2 - Narrow wavelength band photodetector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light receiving sensitivity control method for a photovoltaic narrow wavelength band photodetector using ion implantation.

The practical application of optical information processing systems is progressing rapidly, supported by the recent development of various light sources represented by semiconductor lasers.
Semiconductor laser based on double heterostructure, GaAs
and GaP-based light-emitting diodes and He-Ne
Gas lasers and the like are used, but their emission spectra are relatively narrow.

On the other hand, photodetection for these is usually limited to Si photodetectors1, which respond to a wide band of light ranging from near infrared to visible regions, and the S/N ratio based on disturbance of external light is This is an important issue when discussing detection sensitivity. That is,
There is a need to develop a narrow wavelength band photodetector with spectral sensitivity characteristics that match the spectrum of the light emitting source in all wavelength regions from infrared light to visible light. Examples of photodetectors that have been attempted for this purpose in the past include photodetectors using 1-V and 2-group semiconductors.

These include a self-filtering narrow wavelength band photodetector (NBSF) that utilizes a Ge-GaAs heterojunction structure and has a spectral half-width of 250 A) and a peak sensitivity wavelength of 9090 A.
D■NarrowbandSelf-filterin
gDetectors) (A, Lope2 & R, L0
Anders0n, 501id-5, ateE1ec
tr0nics1V, 7, pp, 695-700, 19
64), spectral half-width o with GaAs homozygous structure.

200A) Peak sensitivity wavelength 8800A (■l) NBSF
D(D, B, Medved & G, P, P01ik, A
pp1iedPhysics Letters, V, 10
, n, 8, pp. 213-214, 1967), and a spectral half-width of 225 A and a peak sensitivity wavelength of 1.06 μm (R N
B5FD (M, D, Prince, 5emic0ndu
c to 0 sand5emimetals, V, 5, pp
, 101-105), etc.

However, although these devices have extremely excellent narrow band characteristics in terms of spectral half-width, they have a major drawback in terms of device structure, such as low photoelectric conversion efficiency, which is another important characteristic. Another method to achieve narrow wavelength band sensitivity is to create a narrow wavelength band photodetector with an interference filter, in which a multilayer thin film is formed by vapor deposition on a conventional wide wavelength band 51 photodetector; However, it is expensive, has poor characteristic reproducibility, and has serious practical disadvantages due to a decrease in absolute sensitivity due to light absorption in the filter.

In general, the optical absorption characteristics of direct transition semiconductors are that, as is well known, after showing weak absorption for photons with energy corresponding to the forbidden band width, the absorption coefficient decreases as the incident photon energy increases (shorter wavelength). Increase rapidly.

This means that the penetration depth of light incident on a direct transition type semiconductor substrate is very deep for light corresponding to forbidden band energy, and becomes rapidly shallower as the wavelength becomes shorter. When considering a p-n junction type (homostructure) photodetector as shown in Figure 1, if you change the layer thickness of the P layer on the light-receiving surface side and change the p-n junction depth (Xj), the light-receiving surface It is detected by the ammeter Ish that the sensitivity on the short wavelength side rapidly decreases as XJ increases with respect to the light (hv) irradiated by the human body. Accordingly, the spectral half-width also decreases. Figure 2 shows P/NGaAsO. 62 pO. FIG. 3 is a characteristic diagram showing spectral sensitivity characteristics experimentally obtained with a No. 38 photodetector, and shows dependence on p-n junction depth. The n-type GaASO. 62 pO. The carrier concentration of 38 substrates is 3X1016C! ! In the L-co, Zn+ ion implantation was used to form the P-type layer.

In Figure 2, t1 is Xj = 0.85 μM St2 is X
j=1.5μMlt3 is Xj=3.7μMSt4 is Xj
This is a spectral sensitivity characteristic curve when =4.8 μm. As is clear from the figure, the spectral half-width is 1 at Xj = 0.4 μm.
960A, whereas Xj=:-1.5μm is 8
60A,. When xj = 4.8 μm, it becomes 400~A and becomes sharply narrower as Xj increases.

By further increasing Xj, the spectral half-width becomes narrower, but the important thing to point out here is that
As the spectral half-width decreases, the peak wavelength sensitivity also rapidly decreases, resulting in a significant drop in the S/N ratio. The aforementioned GaAs homozygous NBSED and NAsl-X
This is exactly where the drawback of the Px junction type NBSFD lies.
It is an object of the present invention to provide a narrow wavelength band photodetector having excellent characteristics in both peak wavelength sensitivity and spectral half-width by improving the drawbacks of the above-mentioned conventional methods.

The principle of the present invention is to implant ions into the conductive layer on the light-receiving surface side of a p-n junction photodetector, and to effectively utilize the recombination center for a small amount of carriers formed at that time, to generate short wavelength light. By rapidly recombining electron-hole pairs formed by the excitation of
This narrows the spectral half-width.

Hereinafter, the present invention will be described in detail according to examples and with drawings.

FIG. 3 is a structural sectional view showing one embodiment of a narrow wavelength band photodetector having a conventional planar structure according to the present invention.

To explain the manufacturing process step by step, first, Sl
50μMf) Te doped n on doped n+ type GaAsl
Type GaASO. 62 pO. 38 (ND-3×1016c
A substrate on which Tn-3)2 is grown in vapor phase is prepared. After etching the surface of this substrate for 1 minute with a 3H204:H2O2:H2O (25°C) etching solution, a 1100A At2O3 film 3 and a 2000A (7) SiO2 film 4 were used as masks for Zn+ ion implantation (planar structure). C
Deposit sequentially with V@.

An ion implantation window was formed on this by photolithography, and 1 x 1016 (1-
After forming a Zn+ implanted P-type layer 5 on the surface region by pouring at room temperature in step 2, a 300% Zn+ implanted P-type layer 5 was formed on the entire surface of the device as a protective film during annealing.
A 0A SiO2 film is formed again by the CVD method, and annealed at 800° C. for 15 minutes in a N2 stream. After this,
Only the SiO2 protective film for annealing at 3000A is removed by etching. This forms a P-ha planar photodiode with a 1.5 μm (7) pn junction depth. The spectral sensitivity characteristic of this photodiode is shown by curve 4 in FIG. 4, and has a spectral half-width of 860A. Next, ion implantation for the purpose of controlling minority carrier (electron) diffusion length in the P-type layer according to the present invention↓
I do.

In a specific embodiment, proton (H) injection is adopted, and the diode substrate is 1×1 implanted with an acceleration energy of 200 KeV.
014 (177!-2 H1 beam 6 is implanted at room temperature.
This introduces the maximum density of reconsolidation centers due to defects during implantation into the P-type region with a defect of 1.4 μMf from the t-surface. At this time, along with the recombination center, a compensation center for the majority carrier also occurs, increasing the layer resistance of the Zn + cast P-type layer 5, which causes a delay in the response speed during light irradiation. In order to remove this carrier compensation center, annealing is performed at 600°C for 15 minutes in a N2 gas flow, but the recombination center for the minority carrier still remains effectively even after the annealing and causes minority carrier (electron) diffusion. It was confirmed that the length was significantly shortened. Next, P
The side electrode 7 is made of At, and the n-side electrode 8 is made of Au-GO/
Au is formed by vacuum evaporation. Through the above steps, a narrow wavelength band photodetector according to an embodiment of the present invention is obtained. Curve 4 in Figure 4
shows the spectral sensitivity characteristics of this device (when equal energy light is incident). As is clear from FIG. 4, in the device according to the present invention, P
In the mold layer, the diffusion length of electrons excited by short-wavelength light is shortened, so the electrons rarely reach the p-n junction, and as a result, the short-wavelength light sensitivity is large. The peak sensitivity wavelength is reduced to 28" as the 6600A1 spectral half-wavelength.
0A was detected.

What should be noted is that in the device according to the present invention, there is little decrease in peak wavelength sensitivity due to narrowing of the spectral half-width (see comparison with Fig. 2), which is an excellent feature of the present invention. . As detailed above, the minority carrier diffusion length control method based on the ion implantation method makes it possible to easily narrow the spectral half-width to a desired value, making it possible to easily narrow the spectral half-width to a desired value, making it possible to use a photodetector for a light source that emits relatively monochromatic light. The S/N ratio can be significantly improved.

The above explanation is based on GaASO. 62 pO. Although only the embodiment for GaASO.38 has been described, the present invention is applicable to GaASO. 62PO
．． Not limited to 38, but GaAsl ＼(
0? ≦0.45), Gal-XAtXAS (0≦x≦0
．． 37) It goes without saying that similar effects can be obtained for any semiconductor having a direct transition structure such as Inl-XGaxP (0≦x≦0.74).

[Brief explanation of drawings]

FIG. 1 is a cross-sectional structural diagram of a Lehe junction type homostructure photodetector. Figure 2 shows p/NGaASO. 62 pO. 38 light detection? FIG. 2 is an explanatory diagram showing the dependence of spectral sensitivity characteristics on pn junction depth (Xj) in FIG. FIG. 3 is a cross-sectional structural diagram of a photodetector showing one embodiment of the present invention. FIG. 4 is an explanatory diagram showing the spectral sensitivity characteristics of a normal ZN junction type photodetector (Xj-1.5 μm) before proton injection and a proton injection type narrow wavelength band photodetector of the present invention. 1...Si-doped revised type G
aAs substrate, 2...Te-doped n-type GaAsl
-XPx (X≦0.38) vapor phase growth layer,'
1,3...At2O3 film, 4...
... SlO2 film, 5 ... Zn-implanted P-type layer, 6 ... H+ beam, 7 ... P side At
Electrode, 8...NllAu-Ge/Au electrode.

Claims (1)

[Claims] 1. In a photovoltaic photodetector made of a direct transition semiconductor and equipped with a p-n junction, the detection limit on the long wavelength side is limited by the forbidden band of the material, and the detection sensitivity on the short wavelength side is increased. A narrow wavelength band photodetector characterized by narrowing the photodetection range by suppressing minority carrier diffusion length control based on ion implantation.