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

Abstract

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 µm and the samples were annealed for 50 hours at either 365 °C, 375 °C, or 385 °C. When annealed, the amorphous germanium films deposited on the 200 µm silicon substrate developed into discrete monocrystalline germanium islands with an average grain size of 10.76 µm, but poor overall surface coverage between 50% and 59%. The germanium films deposited on silicon substrates with thickness between 250 and 375 µm and annealed below 385 °C revealed the highest and most uniform polycrystalline germanium surface coverage between 80% and 97% and demonstrated ~300 nm grain size. The 525 µm silicon substrate exhibited dense island formation at 385 °C as well as high residual aluminum content, and cracks in the film at lower temperatures.