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This paper proposes a double-heterostructure (DH) GaN/AlGaN epitaxial layer that contains an AlGaN interlayer. The electrical properties are characterized and compared with conventional single-heterostructure (SH) GaN/AlGaN epitaxial layers. The Hall effect measurement shows that the DH GaN/AlGaN epitaxial layer has a carrier mobility of 1815 cm2 V−1 s−1, which is approximately 20.37% higher than the SH GaN/AlGaN epitaxial layer. The weak-beam dark-field images taken by transmission electron microscopy show that the AlGaN interlayer in the DH GaN/AlGaN epitaxial layer can block dislocations. The full widths at half maximum results show that there is no significant difference in the screw dislocation density between the SH and DH GaN/AlGaN epitaxial layers. However, the edge dislocation density and the overall internal stress in the DH GaN/AlGaN epitaxial layer are less than those in the SH GaN/AlGaN epitaxial layer. Finally, the physical mechanism of how edge dislocations impact the electrical properties of a DH GaN/AlGaN epitaxial layer is discussed.

We propose a nonresonant terahertz (THz) detector based on double-channel (DC) GaN/AlGaN high-electron-mobility transistor (HEMT) utilizing a technology computer-aided design platform. The hydrodynamic model is simplified as the drift-diffusion model for nonresonant THz detection simulation. Dependence of THz photoresponse on various structure parameters of the detector is analyzed by simulation. The two typical metrics, responsivity and noise equivalent power (NEP), are theoretically calculated for the optimization of the structure parameters. The optimized responsivity and NEP reach 5.8 kV/W and 50 pW/Hz0.5 at the same gate voltage, respectively, and a minimum NEP of 20 pW/Hz0.5 is obtained. The comparison between our simulation results and the experiment data of single-channel HEMT detector proves that the DC HEMT detector shows an excellent THz detection performance.

Metal-sandwiched zinc oxide (ZnO)/titanium (Ti)/copper (Cu)/Ti/ZnO thin film systems were fabricated using magnetron sputtering technology and then annealed using a rapid thermal annealing system at temperatures from 100 to 400°C. The influence of the Ti film thicknesses and annealing temperatures on the surface morphologies, sheet resistance and optical properties were studied. The surface morphologies change a little with the annealing temperature rises. The sheet resistances reduce with the Ti film thickness or annealing temperature increasing. Both the max transmittance and figure of merit reduce with the increase of Ti film thickness. The max transmittance increases with the temperature increasing from 100 to 300°C and then reduces. However, the figure of merit increases with the temperature increasing which indicates that the metal-sandwiched ZnO/Ti/Cu/Ti/ZnO thin film system annealed at 400°C has the optimal performance.