The electron mobility in a heavily n-doped junctionless nanowire transistor is demonstrated by the experimental investigation of the transfer characteristics at low temperatures. It is found that the minimum electron mobility at a critical low temperature results from the interplay of the thermal activation and impurity scattering. The temperature-dependence tendency of the normalized electron mobility by theoretical calculation and experimental extraction reveals that the thermal activation is responsible for the impact of the donor ionization and thermal energy on the electron mobility.

The multi-step rapid thermal annealing process of Ti/Al/Ni/Au can make good ohmic contacts with both low contact resistance and smooth surface morphology for AlGaN/GaN HEMTs. In this work, the mechanism of the multi-step annealing process is analyzed in detail by specific experimental methods. The experimental results show that annealing temperature and time are very important parameters when optimizing the Ti/Al layer for lower resistance and the Ni/Au layer for smooth surface morphology. It is very important for good ohmic contacts to balance the rate of various reactions by adjusting the annealing temperature and time. We obtained a minimum specific contact resistance of 3.22 10 7 cm 2 on the un-doped AlGaN/GaN structure with an optimized multistep annealing process.

Femtosecond lasers have been found suitable for maskless photolithography with submicron resolution, which is very attractive for solving the problem of high photomask cost. Direct femtosecond laser writing of lithographic patterns is reported with submicron feature width on thin positive photoresist film. We use a scanning electron microscope to investigate the feature sizes of femtosecond laser lithography, which are determined by the incident laser power, the number of scan times and the substrate materials. Submicron T -shaped gates have been fabricated using a two-step process of femtosecond laser lithography where the gate foot and head can be separately defined on positive AZ4620 photoresist film. This work has led to the stable fabrication of sub-300 nm T -gates on the samples of GaN on sapphire substrate and AlGaN/GaN on Si substrate.