Download APD Gain Measure

APD Gain Measurement System
APD Gain Measure
Goal: measure the APD (Hamamatsu S8664-1010) intrinsic gain as a function of the bias voltage
and of the temperature.
Tecnique: the APD is lighted with a stable, continuous, light source (blue LED) and the current
flowing trough it is measures as a function of the bias voltage. The same measure is repeated
turning off the LED.
Experimental result:
Gain is given by:
For V “small” the APD avalanche
mechanism is off, and G=1: Ion and
Ioff @ G=1 are measured performing
a linear fit to these points and
taking the intercept of the result.
APD Gain Measure
I realized the following circuit to measure the gain of a single APD: note that the voltmeter is redundant,
since knowing the current trough the APD and the value of the resistances one can easily calculate the
“real” voltage drop across the APD.
Experimental results (@ room T) for the 9 APDs in the FT-Proto.
The system works fine, but it takes the operator ~
40 minutes to take a single measurement (at a
single temperature!).
Not useable to measure ~ 400 APDs
APD Gain Measure
We need an automatic system (“ACCOS-style”) to measure the gain of multiple APDs at the same time,
possibly at different temperatures, in a short time (~10 APDs/day).
Idea: use a “current de-multiplexer”, so I can measure more APDs contemporary, one at time.
After some R&D I decided to use commercial relays: other (simpler) solutions were not applicable because I
need to measure very low currents (~ 10 nA).
APDs holder (note the LED in the middle and the pipes to work
at controlled temperature using an external chiller)
PicoAmmeter: Keithley 6517A
HV Generator: Lambda Gen600
Current de-multiplexer (black-box are relays). Each APD is
connected to a relay using a coax cable.
APD Gain Measure
The software to control the whole system is written in LabView.
LIGHT CURRENT
I did a first measure with 2 APDs (@ room
temperature) to check the behavior of the system: it
works!
GAIN
DARK CURRENT