when applying reactive ion etching on a znse polycrystalline substrate , reactive gas used therefor is only chlorine - based gas which does not include a hydrocarbon group . or the reactive gas is gas prepared by mixing chlorine - based gas which does not include a hydrocarbon group with other gas . the other gas is inert gas or gas which does not react to znse . bcl 3 gas is one kind of chlorine - based gas . ar gas is one kind of inert gas . rf power is one means for activating the gas .