Photoconductivity of Be-doped GaAs under intense terahertz radiation

Lyman transitions of the Be acceptor in GaAs have been investigated under intense radiation generated by a free electron laser. Photoconductivity was found to be a more sensitive method than transmission for detecting the transitions. Three regimes of photoconductive response were distinguished: at high intensity, the signal saturates; at intermediate intensity, it is proportional to intensity; at low intensity, it is background limited. Spectra were obtained by wavelength scanning and showed excellent reproducibility from run to run. With increasing radiation intensity, the D and C lines, being transitions from the 1s3/2(Γ8+) ground state to the 2p5/2(Γ8−) and 2p5/2(Γ7−) excited states, respectively, exhibit a pronounced splitting and broadening of components. This behavior is attributed to thermal stress induced by localized heating.