CuGaS_2およびCuAlS_2結晶のフォトルミネッセンスとエネルギー準位

Photoluminescence and related studies have been made of CuGaS2 and CuAlS2 crystals grown by iodine transport method. In the case of CuGaS2, the luminescence which was not reported before have been found at 1.44 eV at room temperature. Heat-treatments of the crystals under sulfur atmosphere induced changes in photoconductivity excitation spectrum and the low temperature photoluminescence spectrum. These changes are considered to be related to the removal of a donor level having a binding energy of 0.12 eV. In the case of CuAlS2, the room temperature luminescence appears at 2.95 eV with half width of 0.15eV and at 1.8eV with broad half width of 0.5eV. The spectral width of these emissions are reduced at 77K. The higher energy emission at 77K showing shifts to higher energies with increasing excitation is considered to be due to donor-accept pair transitions. The higher energy emission at room temperature showing no spectral shift is assumed to be a bound-to-free transition involving the same donor. The relevant donor and accept binding energies are estimated to be 0.57eV and0.06eV, respectively. The broad lower energy band has its own characteristic excitation band roughly mirrored in energy, and considered to be strongly phonon coupled localized energy state in the band gap.departmental bulletin pape