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

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Abstract
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 > 3 ns and at emission energies greater than 1·5 eV. The temperature dependence of the exponent, α, 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.