Interaction of E1 and E1 + Δ1 exciton recombination with LO phonons in III-V semiconductors

Abstract

The interaction of the E1 and E1 + Δ1 excitonic recombination with 1-LO and 2-LO phonon Raman scattering has been observed in GaSb and InSb at 90° and 300°K using Ar ion and tunable dye laser excitation (ħω1) in a backscattering collection geometry. The recombination radiation peaked at the E1 and E1 + Δ1 optical absorption gaps for all h̵ω1 > E1and E1 + Δ1, while the intensity varied with ħω1, temperature, and the surface preparation. The half-width (∼800 cm−1) of the recombination radiation became narrower as ħω1 approached the E1 + Δ1 gap from above.In addition to the broad recombination radiation, two narrow peaks were observed. These have been identified as 1-LO and 2-LO Raman scattering because of their constant wavenumber shift from ħω1. As these discrete peaks were tuned through the recombination bands, the intensity and lineshape of the peaks changed. The 1-LO and 2-LO intensity reached a maximum when the scattered photon was in resonance with the E1 and E1 + Δ1 excitons. The 2-LO lineshape remained unchanged as the scattered radiation was tuned through the recombination band, whereas the 1-LO peak developed a Fano-type lineshape: a dip on the low energy side of the peak followed by an extended high energy tail, an increased half-width, and a small shift in the peak position. The strength of the 1-LO Fano interference was greatest in the sample with the largest recombination radiation and is believed to be the result of a coupling between the 1-LO Raman phonon and the continuum of excitations produced by the excitonic recombination process. Two possible descriptions of the continuum radiation are presented which entail exciton relaxation by emission of acoustic phonons or by inelastic collisions with electrons at the surface of the semiconductor.