Inversion domains (IDs) are common defects in N-polar
III-nitride
thin films grown on sapphire substrates. In this work, the atomic
structure and lateral migration of the randomly distributed Al-polar
nanoscale IDs in N-polar AlN films subjected to high-temperature thermal
annealing are investigated. With the increasing annealing temperature
and time, Al-polar AlN IDs gradually shrunk in sizes. The vertical
stripes transformed into cone-shaped caps on top of the AlN columns
and were completely removed at last. The annihilation of the IDs was
explained in terms of the lateral migration of the inversion domain
boundary (IDB) induced by the imbalance of the strain state on two
sides of the IDB. This work clarifies the evolution mechanism of AlN
IDs during high-temperature annealing, providing a promising approach
in the realization of uniform-polar AlN template for the development
of high-efficiency optoelectronic and electronic devices.
In this work, the insertion of AlScN ferroelectric gate dielectric on the performance of AlGaN/GaN HEMT device is investigated. With negative pre-poling on AlScN, the threshold voltage (Vth) of the device shifts positively with a swing range of 3.26 V. The influence of polarization modulation is also reflected by the suppression of gate leakage and the reduction of subthreshold swing of the device. The AlScN-integrated GaN HEMT exhibits on/off ratio of 106 and a subthreshold swing of 80 mV/dec. The depletion mechanism of 2DEG at the AlGaN/GaN interface was well described by a TCAD model.
Semipolar AlGaN multiple quantum wells (MQWs) have unique advantages in deep ultraviolet light emitters due to the weak Quantum-Confined Stark Effect. However, their applications are hampered by the poor crystalline quality of semipolar AlGaN thin films. Different treatments were developed to improve the crystal quality of semipolar AlGaN, including a multistep in situ thermal annealing technique proposed by our group. In this work, temperature-dependent and time-resolved photoluminescence characterizations were performed to reveal the carrier localization in the MQW region. The degree of carrier localization in semipolar AlGaN MQWs grown on top of the in situ-annealed AlN is similar to that of conventional ex situ face-to-face annealing, both of which are significantly stronger than that of the c-plane counterpart. Moreover, MQWs on in situ-annealed AlN show drastically reduced dislocation densities, demonstrating its great potential for the future development of high-efficiency optoelectronic devices.
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