Carrier relaxation dynamics in InN investigated by femtosecond pump‐probe technique

Abstract

We have investigated the relaxation processes of excess carriers in MBE‐grown InN layers by means of femtosecond pump‐probe technique. In contrast to other studies, photon energy of the probe was varied below and above the bandgap Eg of InN samples. We observed a change in the sign of optical nonlinearity from the induced bleaching to induced absorption. The nonlinearities observed in different spectral regions had different decay constants, thus we attributed them to different relaxation processes. Induced absorption originated from free carrier absorption (FCA) and its decay reflected a lifetime of excess carriers, while the bleaching transient followed the repopulation dynamics of the probed states in the conduction band. Dependence of the FCA decay rate on excess carrier density in N = 1018 ‐ 1020 cm‐3 range pointed out to a nonlinear recombination mechanism, which was attributed to trap‐assisted Auger recombination. Its decay rate 1/τ = B *N provided different B * values, equal to 4 ×10‐10 and 3×10‐9 cm3s‐1 for layers with lower and higher electron density. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)