Initial photoluminescence decay rates in amorphous phosphorus

Previous measurements of the photoluminescence of amorphous phosphorus have not been able to distinguish between two models of the time-dependent shift of the emission energy of the early radiative recombination. This may arise from recombination of carriers trapped at charged defects or from thermalisation of a carrier in a tail of localised states. The present work extends the time resolution of the luminescence measurement to ≈50 ps which enables a distinction to be made between the two models. The initial decay rates for luminescence in the photon energy ranges 1.45 – 1.6 and 1.45 – 1.85 eV are the same to within ≈1% at 4 K, which supports the assignment of the recombination to carriers trapped at oppositely charged intrinsic defects. The temperature dependence of the initial decay follows the empirical law ν( T ) = ν 1 + ν 0 exp( T T 0 ) with ν 1 = 8.6 × 10 8 s -1 , ν 0 = 3.7 × 10 8 s -1 and T 0 = 104 K. A temperature-dependent branching between two radiative channels is proposed in order to reconcile these observations with earlier work.