Nature of the band gap in Zn1-xBexSe alloys

We have investigated by low-temperature photoluminescence and reflectivity spectroscopies a series of Zn1-xBexSe alloys with x up to 0.70. This allows us to locate precisely the direct-to-indirect band-gap crossover at x = 0. 46+/-0.01. We demonstrate that above this composition the indirect band gap corresponds to a Gamma-->X transition. By extrapolation we determine the G amma-->X band gap of BeSe at 3.75+/-0.1 eV. Finally, we find a bowing param eter b = 0.97 eV for the Gamma-->Gamma direct band gap in the whole composi tion range. For x less than or equal to 0.60, this band gap increases linea rly with the Be content at a rate of 23 meV/% Be.