Piezoreflectance of the First Exciton Band of TlBr

Abstract

The piezo-modulated reflection spectra of the first peak of TlBr have been measured at LNT using bending mode resonance to investigate the stress response and to locate the critical point in the Brillouin zone where the transition occurs. They have been analysed with the aid of the wavelength modulation spectra measured simultaneously with the piezo-spectra. The piezo-optical responses for [001], [111] and [110] stresses are well described in terms of three symmetry-adapted response functions: W₁(E) and W₃(E), with W₅(E) being zero. The first peak is attributed to the transition at the X point in agreement with the band calculations. The tetragonal deformation potential is estimated to be about 0.9 eV. The behavior of the W₃ spectrum is interpreted well by taking into account the intra- and intervalley interactions of direct exciton states at different X points.