22.3 Photodiodes
611
The APD can used for single photon detection; then the variation in pulse height (with reasonable
limits) plays no role for the count rate. The number of dark counts can be reduced by cooling the APD.
Using constant fraction triggering, also the arrival time of the photon can be determined, allowing time
resolution typically in the 100 ps regime.
A particular APD structure is known as a solid-state multiplier. It has separate absorption and
amplification regions (SAM structure). In the low-field region the light is absorbed. One type of carrier
is transported with the drift field E d to the multiplication region in which a large field E m is present
and multiplication occurs. In Fig. 22.30a a homo-APD with SAM structure is shown. Regions with
different electric field are created by a special doping profile.
9 A π -p-π structure leads to regions with
homogeneous low and high field strengths.
The performance of a commercial silicon APD is depicted in Fig. 22.31. With increasing reverse
bias, both the dark current and the multiplication factor increase. Before breakdown at about 77 V, the
best ratio of M and I dark is found. This particular diode has a typical excess noise factor of F = 2 for
M = 100. Using (22.52), this shows that only one kind of carriers is multiplied.
(a)
n
p
0
w
x
E V
E C
j (0)
n
j (w)
p
h
h
n
(b)
p
n
n
h
n substrate
Fig. 22.28 Schematic band structure a and schematic device setup b of an avalanche photodiode (APD). From [1185]
(a)
10
3
10
2
10
1
10
0
10
0
10
2
10
1
10
3
(b)
10
3
10
2
10
1
10
0
10
0
10
2
10
1
10
3
theory
short
wavelength
E C
10
n
p
/
5
p
n
/
0.1
0.2
Fig. 22.29 a Excess noise factor for various values of the ratio of ionization coefficients k or k . Adapted from [1843].
b Experimental results for F for a Si APD with 0.1 µ A primary current. The empty (full) symbols are for short (long)
wavelengths [primary hole (electron) current]. The inset shows the schematic band diagram of the np-diode under reverse
bias. Adapted from [1844]
9 Employing spatially inhomogeneous Poisson’s equation ∂(( s (x)E(x))/∂ x = ρ(x).
611
The APD can used for single photon detection; then the variation in pulse height (with reasonable
limits) plays no role for the count rate. The number of dark counts can be reduced by cooling the APD.
Using constant fraction triggering, also the arrival time of the photon can be determined, allowing time
resolution typically in the 100 ps regime.
A particular APD structure is known as a solid-state multiplier. It has separate absorption and
amplification regions (SAM structure). In the low-field region the light is absorbed. One type of carrier
is transported with the drift field E d to the multiplication region in which a large field E m is present
and multiplication occurs. In Fig. 22.30a a homo-APD with SAM structure is shown. Regions with
different electric field are created by a special doping profile.
9 A π -p-π structure leads to regions with
homogeneous low and high field strengths.
The performance of a commercial silicon APD is depicted in Fig. 22.31. With increasing reverse
bias, both the dark current and the multiplication factor increase. Before breakdown at about 77 V, the
best ratio of M and I dark is found. This particular diode has a typical excess noise factor of F = 2 for
M = 100. Using (22.52), this shows that only one kind of carriers is multiplied.
(a)
n
p
0
w
x
E V
E C
j (0)
n
j (w)
p
h
h
n
(b)
p
n
n
h
n substrate
Fig. 22.28 Schematic band structure a and schematic device setup b of an avalanche photodiode (APD). From [1185]
(a)
10
3
10
2
10
1
10
0
10
0
10
2
10
1
10
3
(b)
10
3
10
2
10
1
10
0
10
0
10
2
10
1
10
3
theory
short
wavelength
E C
10
n
p
/
5
p
n
/
0.1
0.2
Fig. 22.29 a Excess noise factor for various values of the ratio of ionization coefficients k or k . Adapted from [1843].
b Experimental results for F for a Si APD with 0.1 µ A primary current. The empty (full) symbols are for short (long)
wavelengths [primary hole (electron) current]. The inset shows the schematic band diagram of the np-diode under reverse
bias. Adapted from [1844]
9 Employing spatially inhomogeneous Poisson’s equation ∂(( s (x)E(x))/∂ x = ρ(x).