Solid state device uses sapphire windows and avoids coatings which absorb ultraviolet radiation and ultimately alter detector geometry. Ultimate solution for ultraviolet response is geometry with maximum peripheral area and horizontal field structure to draw out photon induced current carriers

Burrous, C. N.

Whiting, E. E.

English

NASA Technical Reports Server

1972	 B72-10053 
NASA TECH BRIEF 
Ames Research Center
	 -4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Offi ce, NASA, Code KT, Washington, D.C. 20546. 
Increasing the Response of PIN Photodiodes 
to the Ultraviolet 
The problem: 
Photomultipliers are not ideal for spacecraft experi-
ments designed to measure solar radiation because 
they are heavy and bulky and because they require 
high voltage for operation. Moreover, their sensitivi-
ties do not remain constant, and those which may 
be useful for measuring ultraviolet radiation show 
little response above 600 nanometers. On the other 
hand, silicon detectors such as PIN photodliodes 
are miniature low-voltage devices which have ade-
quate response in the near infrared, but they are of 
sharply limited applicability for measuring ultraviolet 
radiation in the region of 200 to 400 nanometers be-
cause of low quantum efficiency or high noise equiv-
alent power. In view of the advantages offered by 
solid state devices, improvement of the ultraviolet re-
sponse of commercially available diffused PIN diodes 
was considered an urgent problem. 
The solution: 
Use of sapphire windows and avoidance of coat-
ings which absorb ultraviolet radiation and ultimately 
alter detector geometry. 
How it's done: 
The glass protective window is removed from the 
housing of a commercial photodiode, and if the front 
surface of the diode is coated with a polymer or 
elastomer, this material is carefully scraped away. 
However, it is best to use photodiodes which have 
never been coated or packaged. 
The increased response of a typical commercial 
PIN photodiode is illustrated by the curves in the 
diagram. Measurement of the responsivity profile of
PIN photodiodes with a photometric microscope 
shows that the peripheral area outside the normal 
active area contributes to the overall response, es-
pecially at higher bias voltages. Moreover, the peri-
pheral area is the major contributor to ultraviolet 
I	 I I	 I	 I 
Without Window; 
- With Coating	 - 
'I 
Without Window; 
- Coating Removed - 
by Scraping
 
- 
-
With Window 
-
and Coating 
I	 I	 I 
200	 280 360	 440
Wavelength— nm 
response; thus, for sensitivity in this spectral region, 
the area adjacent to the normal active area must be 
illuminated. The peripheral response results from 
the fact that in this area the photons pass directly 
into an intrinsic, well-depleted area and the photo-
induced electron-hole pairs are immediately sep-
arated and drawn out. (In the active p-region, the 
absorption is so strong that UV photons are absorbed 
before they reach the depletion region.) 
The ultimate solution for ultraviolet response is a 
geometry with maximum peripheral area and hori-
zontal field structure to draw out the photon-induced 
current carriers. 
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(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately ownedrights. 
https://ntrs.nasa.gov/search.jsp?R=19720000053 2020-03-17T03:24:35+00:00Z
Reference: 
Whiting, E. E.; Burrous, C. N.; and Sorensen, H.: 
Improved Ultraviolet Response of a PIN Photodiode. 
Applied Optics, vol. 7, page 2141, October 1968. 
Notes: 
1. The stability of the response of windowless, 
scraped photodiodes was found to be quite con-
stant over several weeks. 
2. Recent Schottky barrier photodiodes have good 
ultraviolet response because the gold top surface 
is thin (15 nm).
3. No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B72-10053 
Patent status: 
No patent action is contemplated by NASA. 
Source: C. N. Burrous and

E. E. Whiting
Ames Research Center 
(ARC-10274) 
Category 03


Increasing the response of PIN photodiodes to the ultraviolet

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