A.Carbone, R.Introzzi and H.C. Liu
Physics Department and INFM, Politecnico di TorinoC.so Duca degli Abruzzi, 24 – 10129 – Torino, (Italy)
Institute for Microstructural Sciences, National Research Council, Ottawa, Ontario, K1A 0R6 (Canada)
Photocurrent Noise in QWIPs:Theory and Experiment
Vb
Lb Lb
Lw
Ve
Vc
I e
EE
Fqw
1
EFe
0
Vw
Emitter
Collector
Redistribution of potential in the presence of radiation
M.Ershov, H.C.Liu, M.Buchanan, Z.R.Wasileski, V. Ryzhii, Appl.Phys.Lett. , 70, 414 (1997).
V. Ryzhii, J.Appl. Phys. 86, 6586, (1997)
V.Letov, M.Ershov, S.G.Matsik, A.G.U.Perera, H.C.Liu, Z.R.Wasilewski and M.Buchanan, Appl.Phys. Lett. 79, 2094, (2001)
Redistribution of potential at different applied bias
Noise gain Si/4eI
Samples
AlGaAs/GaAs QWIPs with the same design except the number of wells N
Well number: N = 4, 8,16, 32 Barrier width: Lb=241Å Well width: Lw =62Å Area=240x240 m2
Dark-current noise
1 10 100 1000 100001E-22
1E-21
1E-20
1E-19
1E-18
1E-17 (a)
16 wells
8 wells
4 wells
I=1.0mAdark
32 wells
SI(f
) [A
2 /Hz]
f[Hz]
Photo-current noise
1 10 100 1000 100001E-22
1E-21
1E-20
1E-19
1E-18
1E-17 (a)
16 wells
32 wells
8 wells
I=1.0mAirradiated
4 wells
SI(f
) [A
2 /Hz]
f [Hz]
A.Carbone, R.Introzzi and H.C.Liu, Appl.Phys.Lett., 82, (2003)
Dark-current noise
1 10 100 1000 100001E-23
1E-22
1E-21
1E-20
1E-19
32 wells
16 wells
8 wells
4 wells
SI(f
) [A
2 /Hz]
I=0.2mAdark
f [Hz]
Photo-current noise
1 10 100 1000 100001E-23
1E-22
1E-21
1E-20
1E-19
32 wells
16 wells
4 wells
8 wells
(b)
I=0.2mAIrradiated
S I(f) [
A2 /Hz]
f[Hz]
Power spectra over 4eI/N
21
p1
NeI40S
c
I )(
0.2 0.4 0.6 0.8 1.0 1.21
10
100
SI/4
eI/N
(f=2
0Hz)
I[mA]
32 wells 16 wells 8 wells 4 wells dark
f=20Hz
Contents
Noise measurements (in the dark and in the presence of IR radiation) in QWIPs with different number of wells.
Limits of the noise models, based on the continuity equation valid for standard semiconductors (models proposed so far).
Necessity of a noise model based on the QWIP continuity equation (proposed in this work).
c
nxnv
tn
To calculate the spectral intensity of the fluctuations in homogeneous semiconductors, a white noise excitation source (x,t) is applied to the right side of the first-order continuity equation :
Under the assumption that the transit time is much longer than the carrier recombination time the well-known expression:
dc
2c
2
2c
0n 14S
)(
If the carriers are photogenerated, the above relationship still holds provided that the thermal generation rate is replaced by the photo-generation rate . JS
The responsivity is obtained by the same differential equation:
)(
PnRn
c
cn i1R
)(
0
Since each photogenerated carrier induces a current pulse , the current noise power spectral density and the responsivity are obtained:
dpeg /
)(IS )(IR
2c
2pI 11eIg4S
)(
cpI i1
1gheR
)(
21
p1
NeI40S
cI )(
If , taking into account the expression of the photoconductivity gain gp for QWIPs
c
ppi p
1ege0R
)(
Np
cp Np
1g 0
Since for QWIPs having identical growth sequence but different N, the quantum efficiency:
N
1k
ks kLx
txnv
tn )(
The transport and the generation-recombination of carriers in QWIPs are described by the equation:
In order to calculate the spectral intensity of the fluctuations, a white noise excitation source k(x,t) is applied to the right side of the previous relationship
)(tjep
t k0
N
1k
ck
kLx
0.01 0.1 1 100.1
1
10
32 wells 16 wells
8 wells 4 wells
Cur
rent
Noi
se P
ower
Spe
ctru
m (a
.u.)
(a.u.)
0.1 1 100.1
1
10
32 wells
16 wells
8 wells
Cur
rent
Noi
se P
ower
Spe
ctru
m (a
.u.)
(a.u.)
4 wells
J-E zoomc
pdarki p
1eP
EJEJR
)()()(
10 15 20 25 30 350.0
1.0
2.0
3.0
4.0
5.0N=8N=32 N=4N=16
T=90K
Cur
rent
[10-4
A]
Electric Field [kV/cm]
0.2 0.4 0.6 0.8 1.0 1.21
10
N=32 N=16 N=4 N=8
1/p
c
I[mA]
Conclusion• The photocurrent noise, measured in QWIPs having
the same growth sequence but different number of wells, shows features related to the discrete structure of the device.
• A noise model based on the continuity equation developed for QWIPs instead of that valid for homogeneous semiconductors, seems to be able to account for the experimental results.
Top Related