Hailing Cheng

Magnetotransport properties of AlxGa1-xN/AlN/ GaN heterostructures grown on epitaxial lateral overgrown GaN templates

We studied the low-temperature magnetotransport properties of AlxGa1−xN∕AlN∕GaN heterostructures with a two-dimensional electron gas (2DEG). Structures with different Al compositions were grown by metal-organic vapor-phase epitaxy on three types of templates: conventional undoped GaN, in situ epitaxial lateral overgrown GaN using a SiNx nanomask layer, and ex situ epitaxial lateral overgrown GaN (ELO-GaN) using a stripe-patterned SiO2 mask. All of the samples display Shubnikov–de Haas (SdH) oscillations that confirm the existence of 2DEGs. Field-dependent magnetoresistance and Hall measurements further indicate that the overgrown heterostructures have a parallel conducting layer in addition to the 2DEG. To characterize the parallel channel, we repeated the measurements after the 2DEG was etched away. 2DEG carrier density values were then extracted from the SdH data, whereas the zero-field 2DEG conductivity was determined by subtracting the parallel channel conductivity from the total. The quantitative mob...

Energy relaxation probed by weak antilocalization measurements in GaN heterostructures

Energy relaxation and electron-phonon (e-p) interaction are investigated in wurtzite Al0.15Ga0.85N/AlN/GaN and Al0.83In0.17N/AlN/GaN heterostructures with polarization induced two-dimensional electron gases in the Bloch–Gruneisen regime. Weak antilocalization (WAL) and Shubnikov–de Haas measurements were performed on gated Hall bar structures at temperatures down to 0.3 K. We used WAL as a thermometer to measure the electron temperature Te as a function of the dc bias current. We found that the power dissipated per electron, Pe, was proportional to Te4 due to piezoelectric acoustic phonon emission by hot electrons. We calculated Pe as a function of Te without any adjustable parameters for both the static and the dynamic screening cases of piezoelectric e-p coupling. In the temperature range of this experiment, the static screening case was expected to be applicable; however, our data was in better agreement with the dynamic screening case.