310
10 Recombination
3.20
3.25
3.30
3.35
3.40
ZnO
1
PL Intensity (arb. units)
Energy (eV)
D ,X
0
X A
Fig. 10.5 Temperature-dependent luminescence spectra of a ZnO thin film (on sapphire). At low temperatures, the spectra
are dominated by donor-bound exciton transitions (Al 0 ,X)). The vertical dashed line indicates the low-temperature
position of the donor-bound exciton transition (D 0 ,X). The curved dashed line visualizes the energy position of the
free-exciton transition (X A ) that becomes dominant at room temperature
Fig. 10.6 Low temperature recombination spectra from silicon with low (solid lines) and sizeable (dashed line) phosphorus dopant concentration. Spectrum for N P = 2 × 10 14 cm −3 (N P = 8 × 10 16 cm −3 ) taken at 26 K (15 K). Transitions
in pure Si are label with ‘I’, transitions involving P donors are labeled with ‘P’. Q indicates the dissociation energy of
the bound exciton. Adapted from [950]
A low temperature recombination spectrum of silicon is shown in Fig. 10.6. In pure silicon, phononassisted exciton recombination (cmp. Sect. 10.4) is observed involving acoustic (I
TA ) and optical (I
TO )
phonons. The weakly observed no-phonon line (I
0 ) is forbidden in perfect Si.
10.3.2 Bound Excitons
Excitons can localize at impurities, defects or other potential fluctuations and subsequently recombine
[951, 952]. Excitons can be bound to neutral or ionized donors and acceptors impurities [953]. Also
10 Recombination
3.20
3.25
3.30
3.35
3.40
ZnO
1
PL Intensity (arb. units)
Energy (eV)
D ,X
0
X A
Fig. 10.5 Temperature-dependent luminescence spectra of a ZnO thin film (on sapphire). At low temperatures, the spectra
are dominated by donor-bound exciton transitions (Al 0 ,X)). The vertical dashed line indicates the low-temperature
position of the donor-bound exciton transition (D 0 ,X). The curved dashed line visualizes the energy position of the
free-exciton transition (X A ) that becomes dominant at room temperature
Fig. 10.6 Low temperature recombination spectra from silicon with low (solid lines) and sizeable (dashed line) phosphorus dopant concentration. Spectrum for N P = 2 × 10 14 cm −3 (N P = 8 × 10 16 cm −3 ) taken at 26 K (15 K). Transitions
in pure Si are label with ‘I’, transitions involving P donors are labeled with ‘P’. Q indicates the dissociation energy of
the bound exciton. Adapted from [950]
A low temperature recombination spectrum of silicon is shown in Fig. 10.6. In pure silicon, phononassisted exciton recombination (cmp. Sect. 10.4) is observed involving acoustic (I
TA ) and optical (I
TO )
phonons. The weakly observed no-phonon line (I
0 ) is forbidden in perfect Si.
10.3.2 Bound Excitons
Excitons can localize at impurities, defects or other potential fluctuations and subsequently recombine
[951, 952]. Excitons can be bound to neutral or ionized donors and acceptors impurities [953]. Also