Transcript Lecture Notes 13a - Noise Sources in Semiconductor Detectors

Noise Sources in
Semiconductor Detectors
S W McKnight and
C A DiMarzio
Sources of Noise
• Johnson Noise (Nyquist noise)
– Random thermal fluctuations of electrons in resistive
elements
• Shot Noise
– Statistical fluctuations in photo-electron generation
• Generation-Recombination Noise
– Statistical fluctuations in current carrier generation
due to photons and thermal excitation and
recombinations
• 1/f Noise
– Low-frequency noise related to interfaces and
contacts
Johnson (Nyquist) Noise
Connection between fluctuations and dissipation in system:
Brownian motion:
= slowly varying external force
F(t) = random thermal force
drives system back towards equilibrium
(v=0 for
=0)
F’(t) = fluctuation force
“Frictional” force
Ensemble average:
For time scales slow
compared to thermal
fluctuations:
Electrical Analogy
Circuit with self-inductance L:
Current flows under influence of external emf + fluctuating
thermal emf: V + V(t)
Average thermal force
opposes current, drives
system toward thermal
equilibrium (I=0)
Fluctuating
thermal force
creates thermal
noise
Circuit Equation
V
R
V
Fluctuation-Dissipation Theorem
“Frictional” force is related to the time
correlation of the rapidly varying
random fluctuation force
Resistance and Noise
Time-correlation of random thermal
voltage fluctuations:
Spectral Density of Autocorrelation
Function
Voltage and Current Thermal
Fluctuations
“Johnson” or “Nyquist” noise
Shot Noise or G-R Noise
From Poisson statistics:
Noise in Photoconductors