Epitaxial Ge/GaAs heterostructures by scanned cw laser annealing of a-Ge layers on GaAs

Abstract

Expitaxial Ge/GaAs heterostructures have been produced by scanned cw argon laser annealing of 440-nm-thick amorphous Ge films on (100) semi-insulating GaAs substrates. Depending on the incident laser power and scan rate, two modes of film regrowth were observed. At low powers (between ∼1.6 and 4.0 W for a beam diameter of ∼40μm) and scan rates between 1 and 400 cm/sec, polycrystalline Ge with a (100) preferred orientation was formed by an ’’explosive’’ crystallization mechanism. At higher powers, and over a scan rate range of 20–400 cm/sec, single-crystal films containing some dissolved GaAs in solution were obtained by liquid phase regrowth. Typical film resistivities ρ were as follows: as-deposited, ρ = 180 Ω cm; polycrystalline films, ρ = 3×10−2 cm; single-crystal films, ρ = 9×10−4Ω cm.

Epitaxial pulsed laser crystallization of amorphous germanium on GaAs

“…4,12 The laser beam profile was homogenized using a vacuum spatial filter, leading to a Gaussian-like intensity profile with a diameter 0 ϭ4 mm on the sample surface. The width of 7 ns of the Nd:YAG pulses is shorter than those of over 20 ns of conventional excimer lasers.…”

“…These results suggest the following scenario for the crystallization process in fluency regions C and D. When the a-Ge films melt upon laser irradiation, the GaAs material in contact with the film partially dissolves into the melt. 4 Further experiments are underway to clarify this point. Due to the dissolution process, the interface between the film and substrate remains relatively abrupt even when a large concentration of substrate species is incorporated into the melt ͓cf.…”

Cristalização epitaxial de ligas de SiGe sobre GaAs por laser pulsado

“…Greene 17 cristalizou epitaxialmente filmes de a-Ge/GaAs através do aquecimento gerado por um laser contínuo de Ar. A decisão de se estudar Ge/GaAs ao invés de GaAs/Ge está no fato de que o ponto de fusão do Ge (938 °C) é cerca de 300 ºC inferior ao do GaAs.…”