The effects of silicon substrate thickness and annealing temperature on surface coverage for aluminum-induced crystallization of germanium films

摘要

This work investigates polycrystalline germanium films for photovoltaic applications that were developed using aluminum-induced crystallization on silicon substrates coated with 500 nm of thermally grown silicon dioxide. Five silicon substrate thicknesses were investigated between 200 and 525 mu m and the samples were annealed for 50 hours at either 365 degrees C, 375 degrees C, or 385 degrees C. When annealed, the amorphous germanium films deposited on the 200 mu m silicon substrate developed into discrete monocrystalline germanium islands with an average grain size of 10.76 mu m, but poor overall surface coverage between 50% and 59%. The germanium films deposited on silicon substrates with thickness between 250 and 375 mu m and annealed below 385 degrees C revealed the highest and most uniform polycrystalline germanium surface coverage between 80% and 97% and demonstrated similar to 300 nm grain size. The 525 mu m silicon substrate exhibited dense island formation at 385 degrees C as well as high residual aluminum content, and cracks in the film at lower temperatures.