Band edge and phonon-assisted deep level emissions in the ordered filled tetrahedral semiconductor LiMgP

Band edge and phonon-assisted deep level emissions in the ordered filled tetrahedral semiconductor LiMgP (space group: <F(4)over bar>3m, direct band gap: 2.43 eV at room temperature), viewed as a zincblende-like (MgP)- lattice partially filled with He-like Li+ interstitials, have been studied using a photoluminescence (PL) method. Two band edge emissions A and B, consisting of two PL peaks, were observed at around 489 nm at 15 K. Emissions A and B were associated with a free carrier recombination (2.535 eV) and a donor-to-valence band transition (2.532 eV), respectively. From the temperature dependence of the band edge emission and optical absorption data, the temperature variation of the band gap was approximated by the empirical formula E-g(eV) = 2.536-1.43 x 10(-3)T(2)/(T + 912) (T in K). A broad emission involving at least three phonon lines was observed at around 625 nm with full width at half maximum of similar to 150 meV, showing a large Franck-Condon shift. The main phonon lines in the broad PL emission were associated with two combinations of longitudinal-optical phonons relating to Li-P and Mg-P pairs. (C) 2000 American Institute of Physics. [S0021-8979(00)06604-4].