Inversion
of the Internal Electric Field due to Inhomogeneous
Incorporation of Ge Dopants in GaN/AlN Heterostructures Studied by
Off-Axis Electron Holography
posted on 2023-02-15, 05:03authored byLou Denaix, Florian Castioni, Matthew Bryan, David Cooper, Eva Monroy
The engineering of the internal electric
field inside III-nitride
devices opens up interesting perspectives in terms of device design
to boost the radiative efficiency, which is a pressing need in the
ultraviolet and green-to-red spectral windows. In this context, it
is of paramount importance to have access to a tool like off-axis
electron holography which can accurately characterize the electrostatic
potentials in semiconductor heterostructures with nanometer-scale
resolution. Here, we investigate the distribution of the electrostatic
potential and chemical composition in two 10-period AlN/GaN (20 nm/20
nm) multilayer samples, one of these being non-intentionally doped
and the other with its GaN layers heavily doped with Ge at a nominal
concentration ([Ge] = 2.0 ± 0.2 × 1021 cm–3) which is close to the solubility limit. The electron
holography experiments demonstrate the effects of free carrier screening
in the case of Ge doping. Furthermore, in the doped sample, an inversion
of the internal electric field is observed in some of the AlN layers.
A correlated study involving holography, electron dispersive X-ray
spectroscopy, and theoretical calculations of the band diagram demonstrates
that the perturbation of the potential can be attributed to Ge accumulation
at the heterointerfaces, which paves the way to the use of Ge delta
doping as a design tool to tune the electric fields in polar heterostructures.