586
21 Diodes
-V
+V
+V
+V
I
(b)
(e)
(d)
(c)
(a)
V
Fig. 21.75 I –V characteristics (upper row) and simplified band structure (lower row) of a tunneling diode at various
bias voltages as indicated with a dot in the I –V plot. a Reverse bias, b in thermodynamic equilibrium (V = 0), c in
the maximum of the tunneling current, d close to the valley and e forward bias with dominating thermal current. The
tunneling current is indicated with straight arrows. In (e) the thermionic emission current (curved arrow) and the excess
current with inelastic tunneling (dotted arrow) are shown
(a)
(b)
Fig. 21.76 a Current-voltage characteristic of silicon tunneling diode (model 1N4397 from American Microsemiconductor [1807]) at low temperature (T = 4.2 K). b d 2 I /dV 2 for small forward voltages, exhibiting characteristic phonon
energies. Adapted from [1805]
band states (filled with holes) on the p-doped side (Fig. 21.75c). We note that this tunneling process
is usually considered elastic. However, signatures at characteristic phonon and multi-phonon energies
are found (at low temperature) in the forward current [1802, 1803] and are best seen in a d
2 I /dV
2 -plot
[1804, 1805] (Fig. 21.76). Peaks appear at typical phonon energies of silicon.
27
A similar situation, now with electrons tunneling for the valence band on the p-side into the conduction band on the n-side, is present for small reverse bias (Fig. 21.75a). Thus the rectifying behavior
of the diode is lost. This property makes it suitable for the monolithic ohmic connection of two pn
diodes which is technologically used e.g. in multi-junction solar cells (cmp. Sect. 22.4.6).
For larger forward bias, the bands are separated so far that the electrons coming from the n-doped
side do not find final states on the p-doped side. Thus the tunneling current ceases (Fig. 21.75d). The
27 We note that for the 1N4396 silicon tunneling diode [1806] the phonon structure of germanium was found in [1805].
21 Diodes
-V
+V
+V
+V
I
(b)
(e)
(d)
(c)
(a)
V
Fig. 21.75 I –V characteristics (upper row) and simplified band structure (lower row) of a tunneling diode at various
bias voltages as indicated with a dot in the I –V plot. a Reverse bias, b in thermodynamic equilibrium (V = 0), c in
the maximum of the tunneling current, d close to the valley and e forward bias with dominating thermal current. The
tunneling current is indicated with straight arrows. In (e) the thermionic emission current (curved arrow) and the excess
current with inelastic tunneling (dotted arrow) are shown
(a)
(b)
Fig. 21.76 a Current-voltage characteristic of silicon tunneling diode (model 1N4397 from American Microsemiconductor [1807]) at low temperature (T = 4.2 K). b d 2 I /dV 2 for small forward voltages, exhibiting characteristic phonon
energies. Adapted from [1805]
band states (filled with holes) on the p-doped side (Fig. 21.75c). We note that this tunneling process
is usually considered elastic. However, signatures at characteristic phonon and multi-phonon energies
are found (at low temperature) in the forward current [1802, 1803] and are best seen in a d
2 I /dV
2 -plot
[1804, 1805] (Fig. 21.76). Peaks appear at typical phonon energies of silicon.
27
A similar situation, now with electrons tunneling for the valence band on the p-side into the conduction band on the n-side, is present for small reverse bias (Fig. 21.75a). Thus the rectifying behavior
of the diode is lost. This property makes it suitable for the monolithic ohmic connection of two pn
diodes which is technologically used e.g. in multi-junction solar cells (cmp. Sect. 22.4.6).
For larger forward bias, the bands are separated so far that the electrons coming from the n-doped
side do not find final states on the p-doped side. Thus the tunneling current ceases (Fig. 21.75d). The
27 We note that for the 1N4396 silicon tunneling diode [1806] the phonon structure of germanium was found in [1805].