• S H ZAHIRI

      Articles written in Pramana – Journal of Physics

    • Recessed insulator and barrier AlGaN/GaN HEMT: A novel structure for improving DC and RF characteristics

      S M RAZAVI S H ZAHIRI S E HOSSEINI

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      In this study, a gallium nitride (GaN) high electron mobility transistor (HEMT) with recessed insulator and barrier is reported. In the proposed structure, insulator is recessed into the barrier at the drain side and barrier is recessed into the buffer layer at the source side. We study important device characteristics such as electric field, breakdown voltage, drain current, maximum output power density, gate-drain capacitance, short channel effects and DC transconductance using two-dimensional and two-carrier device simulator. Recessed insulator in the drain side of the proposed structure reduces maximum electric field in the channel and therefore increases the breakdown voltage and maximum output power density compared to the conventional counterpart. Also, gate-drain capacitance value in the proposed structure is less than that of the conventional structure. Overall, the proposed structure reduces short channel effects. Because of the recessed regions at both the source and the drain sides, the average barrier thickness of the proposed structure is not changed. Thus, the drain current of the proposed structure is almost equivalent to that of the conventional transistor. In this work, length (Lr) and thickness (Tr) of the recessed region of the barrier at the source side are the same as those of the insulator at the drain side.

    • Electrical features in AlGaN/GaN high electron mobility transistors with recessed gate and undoped region in the barrier

      S M RAZAVI S H ZAHIRI S KARIMI

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      This study considers electrical parameters of AlGaN/GaN high electron mobility transistor (HEMT) with the recessed gate and un-doped region (URG-HEMT) in the barrier layer. We have investigated the main electrical factors such as the lateral electric field, breakdown voltage ($V_{B}$), drain current ($I_{D}$), threshold voltage ($V_{T}$), output conductance ($g_{o}$) and gate capacitance ($C_{g}$). Simulation findings compare these parameters in the single heterostructure (SH-HEMT), recessed gate (RG-HEMT) and the proposed (URG-HEMT) structures. Regarding the simulation outcomes, the maximum lateral field in the URG is less than those in the SH and RG-HEMTs. This improves the breakdown voltage of the suggested device up to 160 V, while the breakdown voltage in the SH and RG transistors is about 90 V. Therefore, breakdown voltage of the reported device is about 80% larger than that of the other transistors. Also, undoped region in the novel transistor reduces the output conductance and gate-to-drain capacitance. But, the recessed gate and undoped regions in the URG structure decrease in 2-DEG electron density and then reduce drain current.

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