Introduction/Glossary of Terms
CC
Introduction
GPD manufactures a broad range of Ge and
InGaAs photodetectors, as well as Si/Ge dual
detectors to meet the most demanding military
and commercial applications. This brochure
contains technical specifications for Ge pn, pin
and dual (Si/Ge) detectors; other brochures
describe InGaAs detectors (including extended-
wavelength) and APDs.
Custom devices and packages are also available.
Glossary of Terms
DARK CURRENT (I
D
)
The current through a photodetector when a
specified reverse bias is applied under conditions
of no incident radiation.
SHUNT RESISTANCE (R
SH
)
The resistance of a photodetector at or near zero
bias; shunt resistance values in this catalog are
calculated at 10mV reverse bias.
MAXIMUM REVERSE VOLTAGE (V
RM
)
The maximum reverse voltage that may be
applied without damaging the detector.
RESPONSIVITY (R)
Responsivity vs. Wavelength Comparison
1
Silicon
Germanium
Responsivity
(A/W)
0.1
InGaAs
The photocurrent output per unit incident radiant
power, usually at a specified wavelength.
NOISE EQUIVALENT POWER (NEP)
0.01
400
600
800
1000
1200
1400
1600
1800
The incident radiant power that creates a signal-
to-noise ratio of one at the photodetector output.
JUNCTION CAPACITANCE (C
J
)
The total device capacitance, usually measured
at a specified reverse bias and frequency.
Wavelength
(nanometers)
Both Germanium and InGaAs are sensitive to
light in the near-infrared region of the spec-
trum. While InGaAs detectors offer better
noise performance, Ge detectors offer signifi-
cant cost advantages, particularly where a
large detection area is required. In addition,
Ge detectors have linear response at higher
optical input power levels.
Table of Contents
Glossary of Terms
Operating Circuits
Ge pn Detectors
Ge pin Detectors
Two-color Detectors
Package Outline Drawings
2
3
4-5
6
6
7-12
CUTOFF FREQUENCY (f
c
)
The frequency at which the responsivity de-
creases by 3 dB from the DC responsivity value.
It can be calculated from the load resistance and
the junction capacitance. f
c
= 1/(2πR
L
C
J
)
GPD Optoelectronics Corp.
2
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