Study of recombination and transport characteristics in strain-relaxed Si–SiGe layers

Abstract

A set of direct techniques were combined to resolve the carrier recombination, trapping and diffusion parameters in thin strain-relaxed SiGe buffer (SRB) layers in a contact-less way. The excess carrier density relaxation in a wide time scale from picoseconds to tens of microseconds was examined by the microwave absorption/reflection and light-induced reflection/grating transients. A decrease of recombination lifetime in nanosecond-time scale as a function of threading dislocations (TD) density was determined. The asymptotic hyperbolic-like carrier decay in the SRBs was ascribed to multi-trapping processes characterized by trapping coefficients Ktr > 10. Relaxation of multi-trapping in the disordered structure of the dislocation-rich SRBs was generalized by the stretched-exponent approach. The time-stretching index of 0.15 was found to be the same for dislocation-rich SRBs, containing different densities of TDs. Value of the lateral carrier ambipolar diffusion coefficient Da ⩽ 0.13 cm2 s−1 was estimated. Peculiarities of the J–V characteristics of diodes fabricated in the SRBs were examined and attributed to the space charge limitation effects. These features correlate with carrier trapping and slow diffusion unveiled by transient techniques.