Interdiffusion At a-Ge:H/Al and a-Si:H/Al Interfaces
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INTERDIFFUSION AT a-Ge:H /Al AND a-Si:H/A! INTERFACES S.J. JONES*, A.B. SWARTZLANDER-FRANZ**, Y. CHEN* and D.L. WILLIAMSON* *Department of Physics, Colorado School of Mines, Golden, CO 80401 "**NationalRenewable Energy Laboratory, Golden, CO 80401
ABSTRACT The degree of interdiffusion at the amorphous semiconductor/bulk Al interface was studied using Auger electron spectroscopy analysis. 300-500 A 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 We suggest interdiffusion in the amorphous temperatures at or below 200'C. semiconductor/bulk Al samples is hindered by the presence of a 150-300 A 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. INTRODUCTION Several studies have shown a relationship between the structural and electronic properties of hydrogenated amorphous semiconductors[I-3]. It has been suggested that in order to improve the photoelectronic quality one must remove polyhydride regions[4], voids[5] and point defects[6] from these materials. Thus several techniques have been used to monitor the presence of such microstructure as the film deposition conditions are varied. To enable several of these structural measurements, substrates other than the Corning 7059 glass commonly used for opto-electronic characterizations are required. In particular, Al foil is often used as a substrate for magnetic resonance[l], gas evolution[l] and small-angle x-ray scattering[5,7,8] (SAXS) measurements. However, it is not obvious that the structure of the films deposited on Al is similar to that of films prepared on glass or that the films produced on the different substrates will behave similarly at the usual substrate temperatures of 200-400'C or with annealing. Some studies which have probed for substrate dependences have noted lower metastable defect densities[9] and less disorder[10] in thin a-Si:H films deposited on Al. We have recently completed SAXS measurements to probe for differences in the structure of films co-deposited on Al foils and crystalline silicon wafers and will re
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