DEVELOPMENT OF HIGH-QUALITY 1.36 EV AMORPHOUS SIGE-H ALLOY BY RF GLOW-DISCHARGE UNDER HELIUM DILUTION

The use of 1.35 in amorphous silicon-germanium (a-SiGe:H) alloy as the second/third intrinsic layer along with 1.85 eV front layer in double /triple tandem solar cells is believed to be the best combination for the maximum power output for multijunction cells. In this study high q uality low-band-gap (1.36 eV) a-SiGe:H alloy has been developed by RF glow discharge optimizing the deposition parameters and helium dilutio n of source gases. It has been observed that the structural, electroni c properties end defect densities oi alloy films developed under the d eposition condition which is the transition from low-discharge-power t o high-discharge-power regime, become optimum. In the present case thi s deposition condition is a combination of chamber pressure 0.8 Torr a nd RF power 60 mW/cm(2). The properties of the alloy films developed u nder helium dilution improve and defect density decreases with the inc rease of deposition rate up to 120 Angstrom/min. The 1.36 eV alloy fil m prepared under this condition has very low defect density (3.2 x 10( 16) cm(-3) eV(-1)). The analysis of spectral response of Pd/a-SiGe:H S chottky barrier solar cells reveals that the hole transport properties improve due to increase-of RF power from 15 to 60 mW/cm(2) and also d ue to increase of growth rate from 51 to 120 Angstrom/min.