posted on 2017-03-03, 00:00authored byMatthew
M. Willmering, Zayd L. Ma, Melanie A. Jenkins, John F. Conley, Sophia E. Hayes
We have measured
the 75As signals arising from the interface
region of single-crystal semi-insulating GaAs that has been coated
and passivated with an aluminum oxide film deposited by atomic layer
deposition (ALD) with optically pumped NMR (OPNMR). Using wavelength-selective
optical pumping, the laser restricts the volume from which OPNMR signals
are collected. Here, OPNMR signals were obtained from the interface
region and distinguished from signals arising from the bulk. The interface
region is highlighted by interactions that disrupt the cubic symmetry
of the GaAs lattice, resulting in quadrupolar satellites for nuclear I=32 isotopes, whereas NMR
of the “bulk”
lattice is nominally unsplit. Quadrupolar splitting at the interface
arises from strain based on lattice mismatch between the GaAs and
ALD-deposited aluminum oxide due to their different coefficients of
thermal expansion. Such spectroscopic evidence of strain can be useful
for measuring lattice distortions at heterojunction boundaries and
interfaces.