THz generation mechanisms in the semiconductor alloy, GaAs1−xBix

Abstract

We present measurements of the THz emission from GaAs1−xBix epilayers excited with femtosecond laser pulses (λ ∼ 800 nm). We observed an increase in the peak-to-peak amplitude of the THz electric field with increasing Bi concentration. We also observed a polarity reversal of the THz transient in the epilayers with higher Bi concentration (x ≳ 1.4%). Taking into account the band gap reduction due to Bi incorporation and the excess energy of the carriers, our measurements suggest that there is a cross-over from a predominantly surface field emitter at low Bi concentrations (x ≲ 0.5%) to a predominantly photo-Dember field emitter at higher concentrations (x ≳ 1.4%).