Low-temperature growth of single-crystal Cu(In,Ga)Se2 films by pulsed electron deposition technique

High quality epitaxial crystalline Cu(In,Ga)Se2 (CIGS) films were grown on n-type (1 0 0)--Germanium (Ge) substrates using pulsed electron deposition (PED) technique at a remarkably low substrate temperature of 300 °C, thanks to the high-energy of adatoms arriving to the substrate. The crystalline quality was confirmed by X-ray diffraction techniques and from Transmission Electron Microscopy and the only defects found were twin boundaries along the (1 1 2) direction in these CIGS films; surprisingly neither misfit dislocations nor Kinkerdall voids were observed. A 100 meV optical band located below the band edge was observed by Photoluminescence technique. Current-voltage and capacitance-voltage measurements confirm an intrinsic p-type conductivity of CIGS films, with a free carrier concentration of ?3.5×1016 cm-3. These characteristics of crystalline CIGS films are crucial for a variety of potential applications, such as more efficient absorber layers in single-junction and as an integral component of multi-junction thin-film solar cells.