Arsenic diffusion in MOVPE-Grown GaAs/Ge epitaxial structures
arxiv(2024)
摘要
Germanium is reemerging as a prominent material in the semiconductor field,
particularly for electronic applications, photonics, photovoltaics and
thermophotovoltaics. Its combination with III-V compound semiconductors through
epitaxial growth by metal organic vapor phase epitaxy (MOVPE) is instrumental
and thus, the comprehension of the sequential stages in such epitaxial
processes is of great importance. During the deposition of GaAs on p-type Ge,
the formation of n/p junctions occurs when As diffuses into Ge. It is found
that this formation begins in the so-called AsH3 preexposure where Ge substrate
is firstly exposed to AsH3. Also important is the fact that both free carrier
profiles and As profiles indicate that prolonged AsH3 preexposure times lead to
deeper diffusion depths for the same process time. This effect is concomitant
with the degradation of the Ge surface morphology, characterized by higher
roughness as the AsH3 preexposure duration is extended. Contrary to
ion-implanted As in germanium, which shows quadratic dependent diffusivity, our
MOVPE investigation using AsH3 indicates a linear relationship, consistent with
Takenaka et al.'s MOVPE study using TBAs. Analyzing As profiles alongside
simulations, with and without subsequent GaAs epitaxy, suggests the generation
of Ge vacancies during the process, contributing to deeper As diffusion.
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