32 research outputs found
First principles calculations of band offsets at heterovalent -Ge/InAlAs interfaces
First principles electronic structure calculations are carried out to
investigate the band alignments of tensile strained (001) Ge interfaced with
(001) InAlAs. The sensitivities of band offsets to interfacial
structure, interfacial stoichiometry, and substrate stoichiometry, are
investigated. Large qualitative variations of the valence and conduction band
offsets are observed, including changes of the band offset type, indicating the
importance of local structural variations of the interface for band offsets in
real samples. Our results explain recent measurements of band offsets derived
from XPS core level spectra in terms of As atoms penetrating through the first
few monolayers of the Ge film. Analogous studies are carried out for the
diffusion of other species across the interface, and in general the band
offsets vary approximately linearly with diffusion depth relative to the values
for pristine "sharp" interfaces, where the sign of the linear variation depends
on the diffusing species. This large sensitivity of the band alignments to
interface details indicates potential routes to chemically control the band
offset of this group IV/III-V interface by tuning the stoichiometry of the
substrate surface that the thin film is grown on.Comment: 12 pages, 10 figure
Direct and indirect band gaps in Ge under biaxial tensile strain investigated by photoluminescence and photoreflectance studies
Germanium is an indirect semiconductor which attracts particular interest as an electronics and photonics material due to low indirect-to-direct band separation. In this work we bend the bands of Ge by means of biaxial tensile strain in order to achieve a direct band gap. Strain is applied by growth of Ge on a lattice mismatched InGaAs buffer layer with variable In content. Band structure is studied by photoluminescence and photoreflectance, giving the indirect and direct bands of the material. Obtained experimental energy band values are compared with a k p simulation. Photoreflectance spectra are also simulated and compared with the experiment. The obtained results indicate direct band structure obtained for a Ge sample with 1.94 % strain applied, with preferable Γ valley to heavy hole transition