Optical characterization of bulk ZnSeTe solid solutions

Optical characterization was performed on wafers sliced from crystals of Zn Se, ZnTe, and ZnSe1-xTex(0 < x < 0.4) grown by physical vapor transport. En ergy band gaps at room temperature were determined from optical transmissio n measurements on 11 wafers. A best fit curve to the band gap versus compos ition x data gives a bowing parameter of 1.45. This number lies between the value of 1.23 determined previously on ZnSeTe bulk crystals and the value of 1.621 reported on ZnSeTe epilayers. Low-temperature photoluminescence (P L) spectra were measured on six samples. The spectra of ZnSe and ZnTe were dominated by near band edge emissions and no deep donor-acceptor pairs were observed. The PL spectrum exhibited a broad emission for each of the ZnSe1 -xTex samples, 0.09 < x < 0.39. For x=0.09, this emission energy is about 0 .2 eV lower than the band gap energy measured at low temperature. As x incr eases the energy discrepancy gradually decreases and reduces to almost zero at x=0.4. The single broad PL emission spectra and the spectra measured as a function of temperature were interpreted as being associated with the ex citon bound to Te clusters because of the high Te content in these samples. (C) 2000 American Institute of Physics. [S0021-8979(00)03222-9].