Interdiffusion At a-Ge:H/Al and a-Si:H/Al Interfaces

Abstract

The degree of interdiffusion at the amorphous semiconductor/bulk Al interface was studied using Auger electron spectroscopy analysis. 300-500 Å thick a-Si:H and a-Ge:H films were deposited onto high-purity Al and 5052 Al alloy substrates and subsequently annealed to various temperatures up to 500 °C for 6 hrs. The high-purity Al is used as a substrate for our small-angle x-ray scattering studies of amorphous silicon-based alloys. For all the films deposited on the pure Al, little or no interdiffusion was noted at or below anneal temperatures of 400°C. This result is contrary to those commonly found for samples produced by evaporating Al onto the previously deposited amorphous semiconductor without breaking the vacuum where interdiffusion has been noted at temperatures at or below 200°C. We suggest interdiffusion in the amorphous semiconductor/bulk Al samples is hindered by the presence of a 150-300 Å Al oxide on the Al. A large amount of interdiffusion and partial crystallization is noted in the a-Ge:H sample after an anneal of 450°C while a temperature between 450 and 500°C is required for interdiffusion and crystallization to occur in the a-Si:H sample. In the case of the a-Ge:H films deposited on the 5052 Al alloy, interdiffusion occurs after 300°C anneals due possibly to the migration of Mg and other components of the alloy into the amorphous semiconductors or structural defects in the alloy which enhance interdiffusion.

Nanostructure of a-Si:H and Related Alloys by Small-Angle Scattering of Neutrons and X-Rays: Final Technical Progress Report, 22 May 1998 - 15 October 2001

“…This reaction may be of interest in other applications of Si-Ge alloys with Al contacts. The Al-induced crystallization of a-Si:H is a well-known phenomena [44] and has recently received interest for producing poly-Si at low temperature [45]. There have been no studies to our knowledge of Alinduced crystallization of a-SiGe:H, the phenomena we apparently have observed here.…”

Small-angle x-ray scattering studies of microvoids in amorphous-silicon-based semiconductors. Annual subcontract report, February 1, 1992--January 31, 1993

“…We conclude from this study that as long as substrate temperatures are kept below 450°C during deposition (or annealing experiments), there should be little or no interdiffusion or crystallization induced at the SAXS Al-foil/ amorphous semiconductor interface. More detailed results from this investigation will be published [29].…”

Comprehensive Research on Stability of Amorphous Silicon and Alloy Materials and Devices

“…5 Possible explanation for pressure results II. 6 Results on devices in a-(Si,Ge):H II. 7 Conclusions from a-(Si,Ge) research…”

“…Thus, it should come as no surprise that the standard a-Si:H is not homogeneous, and that its microstructure is full of voids, small and large. [6]. And this microstructure depends on how one grows the material.…”