608
22 Light-to-Electricity Conversion
(a)
10
10
10
10
5
0
-10
-5
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
2
V RT V FB V B
p2 =0.2V
p2 =1.0V
n1 =0.85V
j p
j n
j
(b)
10
10
10
10
5
0
-5
-10
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
2
A=5 10 cm
-4
2
77K
193K
300K
T=350K
Fig. 22.23 Current-voltage characteristics of a Si MSM structure, N D = 4 × 10 14 cm −3 , L = 12 µ m (thin, polished,
111-oriented wafer), T = 300 K. a Theory for two different values of φ p2 , b experiment (for φ p2 = 0.2 V). Adapted
from [1840]
(b) +V
+V
V
+
(a)
InGaAs:Fe
(c)
(d)
Fig. 22.24 Scheme of MSM photodetector with interdigital contacts in a plan view and b cross section. In part (b),
the electric field lines are shown schematically together with an electron-hole pair ready to be separated. c Scheme of a
MSM mesa structure, d SEM image of an InGaAs/InP MSM mesa photodetector. Parts c and d adapted from [1841]
The time-dependent response of a MSM photodetector depends on the drift time of the carriers,
i.e. the time that a created electron and hole need to arrive at their respective contacts. In Fig. 22.26 a
simulation is shown for a MSM detector. The current has two components, a fast one due to the electrons
and a slow one due to the holes that have the lower mobility and smaller drift saturation velocity. A
similar dependence is found in experiment (Fig. 22.27a). For longer wavelengths the detector is slower
since they penetrate deeper into the material and thus the charge carriers have a longer path to the
contacts (cf. scheme in Fig. 22.24b). An important role is played by the finger separation; smaller finger
separation ensures a more rapid carrier collection (Fig. 22.27b). In [1842] a bandwidth of 300 GHz was
demonstrated for 100 nm/100 nm finger width and separation for LT-GaAs
8 and bulk GaAs, limited by
8 LT: grown at low temperature, i.e. containing many defects that reduce the carrier lifetime.
22 Light-to-Electricity Conversion
(a)
10
10
10
10
5
0
-10
-5
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
2
V RT V FB V B
p2 =0.2V
p2 =1.0V
n1 =0.85V
j p
j n
j
(b)
10
10
10
10
5
0
-5
-10
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
2
A=5 10 cm
-4
2
77K
193K
300K
T=350K
Fig. 22.23 Current-voltage characteristics of a Si MSM structure, N D = 4 × 10 14 cm −3 , L = 12 µ m (thin, polished,
111-oriented wafer), T = 300 K. a Theory for two different values of φ p2 , b experiment (for φ p2 = 0.2 V). Adapted
from [1840]
(b) +V
+V
V
+
(a)
InGaAs:Fe
(c)
(d)
Fig. 22.24 Scheme of MSM photodetector with interdigital contacts in a plan view and b cross section. In part (b),
the electric field lines are shown schematically together with an electron-hole pair ready to be separated. c Scheme of a
MSM mesa structure, d SEM image of an InGaAs/InP MSM mesa photodetector. Parts c and d adapted from [1841]
The time-dependent response of a MSM photodetector depends on the drift time of the carriers,
i.e. the time that a created electron and hole need to arrive at their respective contacts. In Fig. 22.26 a
simulation is shown for a MSM detector. The current has two components, a fast one due to the electrons
and a slow one due to the holes that have the lower mobility and smaller drift saturation velocity. A
similar dependence is found in experiment (Fig. 22.27a). For longer wavelengths the detector is slower
since they penetrate deeper into the material and thus the charge carriers have a longer path to the
contacts (cf. scheme in Fig. 22.24b). An important role is played by the finger separation; smaller finger
separation ensures a more rapid carrier collection (Fig. 22.27b). In [1842] a bandwidth of 300 GHz was
demonstrated for 100 nm/100 nm finger width and separation for LT-GaAs
8 and bulk GaAs, limited by
8 LT: grown at low temperature, i.e. containing many defects that reduce the carrier lifetime.