Excitonic Photoluminescence from CuGaSe₂ Single Crystals and Epitaxial Layers: Temperature Dependence of the Band Gap Energy

Abstract

Excitonic line spectra from CuGaSe2 single crystals and epitaxial layers are investigated as a function of temperature. Near band edge luminescence from free and bound excitons is observed at 10 K. The identification of both, free exciton ground and first excited state allows to determine the free exciton binding energy, which is found to be (13±2) meV. The bound exciton line is attributed to the recombination of an exciton bound to a neutral acceptor (A0, X). The widely discussed phenomenon of an anomalous temperature dependence of the band gap energies in different chalcopyrite-type I-III-VI2 compounds is reconsidered for CuGaSe2 on the basis of temperature dependent photoluminescence studies. No anomalous behaviour of the band gap energy as a function of temperature is found in CuGaSe2.

Diamagnetic shift of the A free exciton in CuGaSe2 single crystals

“…͑3͒ using the determined = 0.115m 0 and =11 is Ry ‫ء‬ = 12.9 meV. This is in excellent agreement with the value E b =13Ϯ 2 meV, determined from the experimentally measured energy of the A exciton first excited state, 14 Ry ‫ء‬ = 13.6eV ϫ m 0 ϫ 1 2 . ͑3͒…”

“…This BE peak has been reported in the literature and attributed to the radiative recombination of an exciton bound to a neutral acceptor. 14 This letter focuses on the properties of the A free exciton under magnetic fields.…”

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

“…No intensity-dependent peak shift can be observed and the intensity increases nearly quadratic with the laser power. By adding the exciton binding energy of 13 meV, 16 the band gap is estimated to be E g ¼ 1.722 eV. The value is slightly lower than expected for a single crystal due to strain from the GaAs-substrate lattice mismatch.…”

“…The value is slightly lower than expected for a single crystal due to strain from the GaAs-substrate lattice mismatch. 16,17 Thicker samples were grown under the same preparation conditions and a shift of the exciton-peak and the XRD-008-peak towards the single crystal value was observed. But for higher thicknesses, the spectrum was disturbed by interference effects.…”

Pressure‐dependent photoluminescence study of CuGaSe2

“…The rapid thermal quenching implies that the exciton is bound very weakly with the localization energy of ~4 meV (the energy separation between FX and BX peaks); hence it is most likely bound to a neutral acceptor [14].…”