Kavli Affiliate: Grace Xing
| First 5 Authors: Chuan F. C. Chang, Joseph E. Dill, Zexuan Zhang, Jie-Cheng Chen, Naomi Pieczulewski
| Summary:
GaN has emerged to be a major semiconductor akin to silicon due to its
revolutionary impacts in solid state lighting, critically enabled by p-type
doping, and high-performance radio-frequency and power electronics. Suffering
from inefficient hole doping and low hole mobility, quantum oscillations in
p-type GaN have not been observed, hindering fundamental studies of valence
bands and hole transport in GaN. Here, we present the first observation of
quantum oscillations of holes in GaN. Shubnikov-de Haas (SdH) oscillations in
hole resistivity are observed in a quantum-confined two-dimensional hole gas at
a GaN/AlN interface, where polarization-induced doping overcomes thermal
freeze-out, and a sharp and clean interface boosts the hole mobility enough to
unmask the quantum oscillations. These holes degenerately occupy the light and
heavy hole bands of GaN and have record-high mobilities of ~1900 cm2/Vs and
~400 cm2/Vs at 3K, respectively. We use magnetic fields up to 72 T to resolve
SdH oscillations of holes from both valence bands to extract their respective
sheet densities, quantum scattering times, and the effective masses of light
holes (0.5-0.7 m0) and heavy holes (1.9 m0). SdH oscillations of heavy and
light holes in GaN constitute a direct metrology of valence bands and open new
venues for quantum engineering in this technologically important semiconductor.
Like strained silicon transistors, strain-engineering of the valence bands of
GaN is predicted to dramatically improve hole mobilities by reducing the hole
effective mass, a proposal that can now be explored experimentally,
particularly in a fully fabricated transistor, using quantum oscillations.
Furthermore, the findings of this work suggest a blueprint to create 2D hole
gases and observe quantum oscillations of holes in related wide bandgap
semiconductors such as SiC and ZnO in which such techniques are not yet
possible.
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