Photo-acoustic response and optical features of 2D-TlGaSe₂ and GaAs semiconductors

Abstract

The paper focuses on investigation of the acoustic-optical properties of 2D-TlGaSe2 and GaAs semiconductors using laser pulses. We present the photo-darkening experiments performed by using CW light in spectral ranges below the band gap of TlGaSe2. The data provides evidence that photo-acoustic signals (PAS) for the above band gap are significantly stronger and linear in 2D-TlGaSe2 while they are distorted by nonlinear processes in isotropic GaAs. The comparison discloses characteristic parameters of TlGaSe2, namely a high factor and a negative sign in the refraction coefficient with pressure, a low absorption coefficient and absence of band filling; all guarantee stabile energy conversion by thermoelastic deformation mechanism. Below the band gap range, we found a new kind of PAS in TlGaSe2 on near surfaces. Likewise, we demonstrate that in such spectral range the giant Stark effect in TlGaSe2 is created by focused CW beams. The Stark effect produces local optical darkening which can provide explosion at extreme light power. Likely, both effects could be related to the planar stacking faults in 2D-TlGaSe2, which produce a spontaneous charge separation on layers.