Physical and optoelectronic properties of VxInySz intermediate band semiconductors deposited by atomic layer deposition

In this report, thin films of indium sulfide (In2S3) alloyed with vanadium have been deposited by atomic layer deposition. The physical and optoelectronic properties of these films have been studied to determine their potential for use in intermediate band solar cells. X-ray reflectivity measurements confirm control over stoichiometry by varying the ratio of In to V precursor pulses. As-deposited films on bare quartz and silicon substrates are amorphous and do not have absorption properties indicative of a mid-gap band. However, deposition of the VxInySz films on c-In2S3 appears to induce crystallization as seen by x-ray diffraction and scanning electron microscopy. A large, sub-band gap absorption peak is observed beginning near 1.0 eV, and increases with V concentration. Pronounced photoluminescence peaks occur at room temperature near 2.20 eV for both In2S3 and VxInySz films, while an additional 1.35 eV peak is observed for VxInySz. These results support the existence of a crystalline, thin-film, intermediate band semiconductor deposited by atomic layer deposition. Use of these heavily doped, thin film semiconductors could lead to cheap and simple fabrication of intermediate band solar cells.