Ultrafast time-resolved photoluminescence-a probe of radiative and non-radiative processes in amorphous tetrahedral and chalcogenide semiconductors

Picosecond time-resolved photoluminescence studies have determined that the initial decay in a-Si: H follows a power law dependence, proportional to t^−α, over the time range 50ps(t(3ns and at emission energies greater than 1·5eV. The temperature dependence of the exponent, a, takes the form α(T) = α₀+βT over the range 20 (T(180 K. The origin of this power-law decay (which is much faster than radiative recombination) is discussed in terms of non-radiative relaxation via electron band-tail thermalization. These results are compared with earlier picosecond studies in a-As₂S₃. Important similarities and differences are found and discussed in relation to the optical bandgap, band-tail state density and bonding environment in these two prototypical amorphous semiconductors.