Download Growth, Optical Properties, and Optimization of Infrared

School of Electrical, Computer and Energy Engineering
PhD Final Oral Defense
Growth, Optical Properties, and Optimization of Infrared Optoelectronic Materials
by
Preston T. Webster
Thursday, May 5th, 2016 at 10:00 AM
Engineering Center G Wing, room 335
Committee:
Dr. Shane R. Johnson (chair)
Dr. Yong-Hang Zhang
Dr. José Menéndez
Dr. Dragica Vasileska
Abstract
High-performance III-V semiconductors based on ternary alloys and superlattice
systems are fabricated, studied, and compared for infrared optoelectronic applications.
InAsBi is a ternary alloy near the GaSb lattice constant that is not as thoroughly
investigated as other III-V alloys and that is challenging to produce as Bi has a tendency
to surface segregate and form droplets during growth rather than incorporate. A growth
window is identified within which high-quality droplet-free bulk InAsBi is produced and
Bi mole fractions up to 6.4% are obtained.
Photoluminescence with high internal
quantum efficiency is observed from InAs/InAsBi quantum wells. The high structural
and optical quality of the InAsBi materials examined demonstrates that bulk, quantum
well, and superlattice structures utilizing InAsBi are an important design option for
efficient infrared coverage.
Another important infrared material system is InAsSb and the strain-balanced
InAs/InAsSb superlattice on GaSb.
Detailed examination of X-ray diffraction,
photoluminescence, and spectroscopic ellipsometry data provides the temperature and
composition dependent bandgap of bulk InAsSb. The unintentional incorporation of
approximately 1% Sb into the InAs layers of the superlattice is measured and found to
significantly impact the analysis of the InAs/InAsSb band alignment. In the analysis of
the absorption spectra, the ground state absorption coefficient and transition strength of
the superlattice are proportional to the square of the electron-hole wavefunction overlap;
wavefunction overlap is therefore a major design parameter in terms of optimizing
absorption in these materials. Furthermore in addition to improvements through design
optimization, the optical quality of the materials studied is found to be positively
enhanced with the use of Bi as a surfactant during molecular beam epitaxy growth.
A software tool is developed that calculates and optimizes the miniband structure of
semiconductor superlattices, including bismide-based designs. The software has the
capability to limit results to designs that can be produced with high structural and optical
quality, and optimized designs in terms of maximizing absorption are identified for
several infrared superlattice systems at the GaSb lattice constant. The accuracy of the
software predictions are tested with the design and growth of an optimized mid-wave
infrared InAs/InAsSb superlattice which exhibits superior optical and absorption
properties.