Improvement of switching characteristics by substrate bias in AlGaN/AlN/GaN heterostructure field effect transistors

A simple and effective approach to improve the switching characteristics of AlGaN/AlN/GaN heterostructure field effect transistors （HFETs） by applying a voltage bias on the substrate is presented. With the increase of the substrate bias, the OFF-state drain current is much reduced and the ON-state current keeps constant. Both the ON/OFF current ratio and the subthreshold swing are demonstrated to be greatly improved. With the thinned substrate, the improvement of the switching characteristics with the substrate bias is found to be even greater. The above improvements of the switching characteristics are attributed to the interaction between the substrate bias induced electrical field and the bulk traps in the GaN buffer layer, which reduces the conductivity of the GaN buffer layer.

Si and Mg pair-doped interlayers for improving performance of AlGaN/GaN heterostructure field effect transistors grown on Si substrate

We report a novel structure of A1GaN/GaN heterostructure field effect transistors （HFETs） with a Si and Mg pair- doped interlayer grown on Si substrate. By optimizing the doping concentrations of the pair-doped interlayers, the mobility of 2DEG increases by twice for the conventional structure under 5 K due to the improved crystalline quality of the conduction channel. The proposed HFET shows a four orders lower off-state leakage current, resulting in a much higher on/off ratio （ - 10^9）. Further temperature-dependent performance of Schottky diodes revealed that the inhibition of shallow surface traps in proposed HFETs should be the main reason for the suppression of leakage current.

Effect of the side-Ohmic contact processing on the polarization Coulomb field scattering in AlN/GaN heterostructure field-effect transistors

Using the measured capacitance–voltage and current–voltage characteristics of the rectangular AlN/GaN heterostructure field-effect transistors（HFETs） with the side-Ohmic contacts, it was found that the polarization Coulomb field scattering in the AlN/GaN HFETs was greatly weakened after the side-Ohmic contact processing, however, it still could not be ignored. It was also found that, with side-Ohmic contacts, the polarization Coulomb field scattering was much stronger in AlN/GaN HFETs than in Al GaN/AlN/GaN and In0：17Al0：83N/AlN/GaN HFETs, which was attributed to the extremely thinner barrier layer and the stronger polarization of the AlN/GaN heterostructure.

A simulation-based proposed high-k heterostructure AlGaAs/Si junctionless n-type tunnel FET

We propose a heterostructure junctionless tunnel field effect transistor （HJL-TFET） using AIGaAs/Si. In the proposed HJL-TFET, low band gap silicon is used in the source side and higher band gap AlGaAs in the drain side. The whole AlGaAs/Si region is heavily doped n-type. The proposed HJL-TFET uses two isolated gates （named gate, gatel ） with two different work functions （gate = 4.2 eV, gatel = 5.2 eV respectively）. The 2-D nature of HJL-TFET current flow is studied. The proposed structure is simulated in Silvaco with different gate dielectric materials. This structure exhibits a high on current in the range of 1.4 × 10^-6 A/μm, the off current remains as low as 9.1 × 10^-14 A/μm. So /ON/OFF ratio of 10^8 is achieved. Point subthreshold swing has also been reduced to a value of 41 mV/decade for TiO2 gate material.