RECRYSTALLIZATION METHOD TO SELENIZATION OF THIN-FILM Cu(In,Ga)Se2 FOR SEMICONDUCTOR DEVICE APPLICATIONS

摘要

A process for fabricating slightly Cu-poor thin-films of Cu(In,Ga)Se2 on a substrate for semiconductor device applications includes the steps of forming initially a slightly Cu-rich, phase separated, mixture of Cu(In,Ga)Se2:CuxSe on the substrate in solid form followed by exposure of the Cu(In,Ga)Se2:CuxSe solid mixture to an overpressure of Se vapor and (In,Ga) vapor for deposition on the Cu(In,Ga)Se2:CuxSe solid mixture while simultaneously increasing the temperature of the solid mixture toward a recrystallization temperature (about 550 DEG C.) at which Cu(In,Ga)Se2 is solid and CuxSe is liquid. The (In,Ga) flux is terminated while the Se overpressure flux and the recrystallization temperature are maintained to recrystallize the CuxSe with the (In, Ga) that was deposited during the temperature transition and with the Se vapor to form the thin-film of slightly Cu-poor Cux(In,Ga)ySez. The initial Cu-rich, phase separated large grain mixture of Cu(In,Ga)Se2:CuxSe can be made by sequentially depositing or co-depositing the metal precursors, Cu and (In, Ga), on the substrate at room temperature, ramping up the thin-film temperature in the presence of Se overpressure to a moderate anneal temperature (about 450 DEG C.) and holding that temperature and the Se overpressure for an annealing period. A nonselenizing, low temperature anneal at about 100 DEG C. can also be used to homogenize the precursors on the substrates before the selenizing, moderate temperature anneal.