STRUCTURAL AND OPTICAL CHARACTERIZATION OF POLYCRYSTALLINE CUINSE2

In this study device quality CuInSe2 films were grown using a relative ly simple, tolerant and reproducible two-stage technique. This process involved the selenization of various CuIn precursors in a H2Se/Ar atm osphere. The variation in the microstructure (grain size and lattice d efects) and optical properties of the CuInSe2 thin films on gradually changing the stoichiometry from Cu rich to In rich was investigated. S canning electron microscopy (SEM) and transmission electron microscopy (TEM) studies revealed that Cu-rich and In-rich films were clearly di stinct in their defect structure. In general, In-rich material exhibit ed relatively small grains (0.2-0.8 mu m), which were highly defected. In contrast to In-rich films, Cu-rich films were characterized by the presence of large faceted grains (1-4 mu m) with relatively low defec t density. These material properties were clearly reflected in low tem perature photoluminescence (PL) studies, indicating sharp transitions for Cu-rich films compared to broad emission lines for In-rich materia ls. Cu-rich materials were characterized by four relatively sharp emis sion lines at 1.036 eV, 0.993 eV, 0.971 eV and 0.942 eV at 6 K. As the composition was gradually changed from Cu rich to stoichiometric comp ositions only one broad emission line could be observed at 0.964 eV, w hich corresponds to a donor-acceptor pair transition. In the case of I n-rich material (Cu/In atomic ratio = 0.3-0.6), three dominant transit ions were observed at 1.10 eV, 0.975 eV, and 0.89 eV. The observed spe ctra are explained by considering the formation energies of the defect s and the composition of the specific film.