Equivalent Circuit Modeling of a Dual-Gate Graphene FET

This paper presents a simple and comprehensive model of a dual-gate graphene field effect transistor (FET). The quantum capacitance and surface potential dependence on the top-gate-to-source voltage were studied for monolayer and bilayer graphene channel by using equivalent circuit modeling. Additionally, the closed-form analytical equations for the drain current and drain-to-source voltage dependence on the drain current were investigated. The distribution of drain current with voltages in three regions (triode, unipolar saturation, and ambipolar) was plotted. The modeling results exhibited better output characteristics, transfer function, and transconductance behavior for GFET compared to FETs. The transconductance estimation as a function of gate voltage for different drain-to-source voltages depicted a proportional relationship; however, with the increase of gate voltage this value tended to decline. In the case of transit frequency response, a decrease in channel length resulted in an increase in transit frequency. The threshold voltage dependence on back-gate-source voltage for different dielectrics demonstrated an inverse relationship between the two. The analytical expressions and their implementation through graphical representation for a bilayer graphene channel will be extended to a multilayer channel in the future to improve the device performance.

High-Frequency InP-InGaAsP Heterojunction Phototransistor Employing a UTC Structure

In this paper, the working mechanism and high characteristics of an InP/InGaAsP uni-traveling-carrier (UTC) double hetero-junction phototransistor (DHPT) has been analyzed. The UTC-DHPT employs a heavy doping base and two hetero-junctions to realize UTC structure to ease the contract between HPT responsivity and HPT working speed. Optical responsivity and optical transit frequency are analyzed physically through illustrated several kinds of paramistic capacitors in BE junction and BC junction under different electrical bias, optical bias and combined electrical and optical bias in this work. The results show that three-terminal (3T) working mode with combined electrical bias and optical bias in base achieves a highest maxim fT of 120GHz at collector current of 30mA and keeps the same optical responsivity (37.5A/W) compared with two-terminal (2T) working mode.