In this work, the impact of nitrogen doping (N-doping) on the distribution of sub-gap states in amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) is qualitatively analyzed by technology computer-aided design (TCAD) simulation. According to the experimental characteristics, the numerical simulation results reveal that the interface trap states, bulk tail states, and deep-level sub-gap defect states originating from oxygen-vacancy- (V_o) related defects can be suppressed by an appropriate amount of N dopant. Correspondingly, the electrical properties and reliability of the a-IGZO TFTs are dramatically enhanced. In contrast, it is observed that the interfacial and deep-level sub-gap defects are increased when the a-IGZO TFT is doped with excess nitrogen, which results in the degeneration of the device’s performance and reliability. Moreover, it is found that tail-distributed acceptor-like N-related defects have been induced by excess N-doping, which is supported by the additional subthreshold slope degradation in the a-IGZO TFT.

In this study, the electrical performance and bias stability of InSnO/a-InGaZnO (ITO/a-IGZO) heterojunction thin-film transistors (TFTs) are investigated. Compared to a-IGZO TFTs, the mobility (µ_FE) and bias stability of ITO/a-IGZO heterojunction TFTs are enhanced. The band alignment of the ITO/a-IGZO heterojunction is analyzed by using X-ray photoelectron spectroscopy (XPS). A conduction band offset (∆E_C) of 0.5 eV is observed in the ITO/a-IGZO heterojunction, resulting in electron accumulation in the formed potential well. Meanwhile, the ∆E_C of the ITO/a-IGZO heterojunction can be modulated by nitrogen doping ITO (ITON), which can affect the carrier confinement and transport properties at the ITO/a-IGZO heterojunction interface. Moreover, the carrier concentration distribution at the ITO/a-IGZO heterointerface is extracted by means of TCAD silvaco 2018 simulation, which is beneficial for enhancing the electrical performance of ITO/a-IGZO heterojunction TFTs.

In this work, we fabricated high-voltage (HV) amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) consisting of an ultra-thin buried layer of amorphous InZnO (a-IZO) and a drain offset region. With a drain offset length ( L _offset ) of 2 μm, a breakdown voltage ( V _BD ) of 457 V is achieved. The output current is four times higher than the conventional device, thanks to the a-IZO buried layer. TCAD simulation is performed to reveal the operating mechanism of the fabricated device. A sub-channel is formed at the a-IZO/a-IGZO interface to improve the current capability of the HV device, achieving an excellent specific on-resistance ( R _{on, sp} ) of 6.25×10 ³ mΩ∙cm ² and a Baliga’s Figure of Merit (BFOM) of 33.4 KW/cm ² .

The electrical characteristics of amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) deposited with different N₂/O₂ partial pressure ratios (P_N/O) are investigated. It is found that the device with 20% P_N/O exhibits enhanced electrical stability after positive-bias-stress temperature (PBST) and negative-bias-stress illumination (NBSI), presenting decreased threshold voltage drift (ΔV_th). Compared to the N-free TFT, the average effective interface barrier energy (E_τ) of the TFT with 20% P_N/O is increased from 0.37 eV to 0.57 eV during the bias-stress process, which agrees with the suppressed ΔV_th from 3.0 V to 1.12 V after the PBS at T = 70 °C. X-ray photoelectron spectroscopy analysis revealed that the enhanced stability of the a-IGZO TFT with 20% P_N/O should be ascribed to the control of oxygen vacancy defects at the interfacial region.

The AlGaN/GaN high electron mobility transistor with a step–doped channel (SDC–HEMT) is first proposed in this paper. The potential distribution and the electric field (E–field) distribution of the device are explored by the numerical approach and analytical approach simultaneously. By introducing extra dopants to the channel layer, the E–field distribution along the AlGaN/GaN heterojunction interface is reshaped, resulting in an improved breakdown characteristic. An optimized doping concentration gradient of channel layer of 2 × 10¹⁶ cm⁻³/step is proposed and verified by simulations. The breakdown voltage (BV) of the optimized SDC–HEMT reaches 1486 V with a 59.8% improvement compared with conventional AlGaN/GaN HEMT. In addition, the average E–field in the region between gate and drain improves from 1.5 to 2.5 MV/cm. Based on the equivalent potential method (EPM), an analytical model of the E–field and potential distribution is presented. The veracity and effectiveness of the proposed methodology is verified by the good agreement between the simulated and modeled results.