Raman Scattering and Exciton Photoluminescence in Few-Layer GaSe: Thickness- and Temperature-Dependent Behaviors

The optical properties of few-layer (FL) GaSe are investigated using thickness- and temperature-dependent Raman scattering and photoluminescence (PL) spectroscopies. The vibrational modes exhibit linear softening with increasing temperature, with temperature coefficient values related to anharmonic phonon–phonon/electron coupling. Micro-PL is used to study the variation of exciton bands and structural features of FL GaSe. The temperature-dependent study from 100 to 380 K shows that the PL red-shifts due to a band gap narrowing, while the intensity decreases attributable to thermally stimulated nonradiative recombination caused by an increase in the electron–phonon interaction. The behavior of free and bound excitons and deep defect PL with temperature is studied by fitting the PL spectra with modeling equations. This enables the evaluation of their quenching activation energies and other significant aspects. The exciton binding energy of 0.3 eV has been calculated for the excitons in 10L GaSe. These novel findings extend the knowledge on the variety of exciton and deep defect levels in 2D GaSe and are important for its future applications in nano-optoelectronics involving external influence of optical properties.