Polar and Nonpolar III-Nitride Heterostructures for Near-Infrared Intersubband Materials and Devices
III-nitride semiconductors are currently intensively studied for applications in infrared optoelectronics, such as detectors and emitters for spectral regions not easily accessible with other semiconductors. Owing to the large conduction band offset (>1 eV) and sub-picosecond intersubband relaxation times, III-Nitride materials are promising for intersubband devices. These intersubband devices rely on transitions between quantum-confined electronic states within the conduction band of multiple quantum wells or quantum dots. We investigate near-infrared intersubband transitions using near-lattice-matched polar (c-plane) InAlN/GaN superlattices. In0.17Al0.83N is exactly lattice-matched to GaN on the c-plane, and therefore thick InAlN/GaN structures can be grown along the c-direction without generating macroscopic defects such as cracks on the surface. We report substantial improvement of near-infrared (2–2.6 μm) intersubband absorption in c-plane InAlN/GaN superlattices grown by molecular beam epitaxy (MBE). Progress was obtained through optimization of InAlN growth conditions as well as by judiciously placing the charge into two delta-doping sheets. The role of Si as an anti-surfactant in highly doped InAlN/GaN structures is discussed. We also investigate near-infrared intersubband transitions in high-Al content AlGaN/GaN superlattices using the nonpolar m-plane orientation. The nonpolar orientation lacks the polarization-induced internal electric field along c-axis that is not desirable in optoelectronics. However, development of nonpolar m-plane infrared devices in a broad spectral range has been hampered, so far, by challenges to grow homogeneous high Al-composition AlGaN on mplane GaN. AlxGa1–xN layers with 0.6
Manfra, Purdue University.
Electrical engineering|Materials science
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