A critical review of the growth and properties of a-(Si,Ge):H

The authors review the status of a-(Si,Ge):H technology for tandem solar cell applications. In particular, they show that the chemistry of growth and deposition conditions play a major role in determining the properties of a-(Si,Ge):H. They explain why dilution is necessary to make good films, and show that ion bombardment plays a major role in improving the properties of the material. Recent work on films deposited using ion bombardment in a controlled ECR reactor environment is discussed, and it is shown that fundamental material properties such as Urbach energies and mid-gap defects can be improved using controlled bombardment. It is also shown that high ion bombardment in glow-discharge deposited devices improves the fundamental material properties. They also discuss the unknown parameters in the a-(Si,Ge):H system, and suggest some research avenues that should be pursued