Pulsed laser heating measurement of relaxation-induced melting point increase in amorphous Si

The difference in the melting temperature of unrelaxed and relaxed amorphous silicon has been determined by measuring the energy density threshold for surface melting during nanosecond laser irradiation (λ=347 nm). The melting onset was detected by time-resolved reflectivity technique. Using particular samples in which a surface unrelaxed layer was generated by reimplanting a 400-nm-thick relaxed amorphous Si (a-Si) the difference in the melting temperature has been determined independently of the thermal properties of the a-Si. The melting temperature of relaxed a-Si resulted to be only 3.9% higher than that of unrelaxed a-Si, while on the basis of calorimetric data an ∼14% difference was expected. The reasons for this discrepancy are discussed. In addition a 24% increase in the product of thermal conductivity and specific heat of a-Si upon relaxation has been found.