Theoretical Performance Analysis of InN-Based Double Channel High Electron Mobility Transistors (DHEMTs)

Abstract

In recent years. it has been predicted that InN-based High Electron Mobility Transistors (HEMTs) may be record fast among 111-Nitride transistors due to their highly attracting inherent properties. Though the InN-based HEMTs possess superior performance in many aspects, they often suffer from low current densities due to the relatively small number of carriers in the channel. Moreover, carriers in the 2DEG can spill over into the buffer which increases low frequency noise and decreases transconductance. In addition; the spilled over carriers get trapped and thus give rise to slow transient processes and an RF-current collapse, which greatly limits the power performance. To overcome these limitations a Double Channel High Electron Mobility Transistor (DHEMT) made of lnGaN/InN/InGaN materials has been considered for better performance. The principal objective of this thesis is to establish a viable concept for the physical One Dimensional (ID) numerical modeling of InGaN/InN/lnGaN DHEMTs, to understand the operation mechanism with a focus on main issues improving device performance. At first, a quantum mechanical charge control model based on the self-consistent solution of ID Schrodinger-Poisson equations is developed. The mobility and velocity-field characteristics are then calculated using Monte Carlo simulation. In order to realize the device performance, a comprehensive quasi-21) model based on the solution of ID Schrodinger-Poisson-drift diffusion equations is developed. Finally, the dc characteristics i.e. current-voltage and transconductance are obtained from the quasi-2D model for the proposed DHEMTs. The transport properties provide an ideal platform for the in-depth investigation of InN-based DHEMTs. Among the transport properties electron density and mobility of 2DEGs are two most important concerns. The one dimensional internal electric field and distribution of charges in the channel are demonstrated with the proper material parameters at different bias conditions. The sheet charge density of the 2DEGs is linearly proportional to the number of channels, and reached 1.25x 10' cm 2 for a gate voltage (Vg) of 0.4 Vat an In composition (x) of 0.05 in the InGa1 N barrier layer. The highest mobility for the DHEMTs is found to be 11.5x10 cm2V 'sce at n = 5.2x 1012 crn 2 at 77K. The peak velocity of the carrier for the proposed device is found to be 4.95x 10 7 cm/sec at the field of 57.5 kV/crn. Finally, the maximum channel current is v found to be 1325 mA/mm at a gate voltage of 1.5 V for different values of drain to source voltage for 0.1 tm gate length. The calculated value of maximum transconductance is found to be 630 mS/mm. All the results are compared with the conventional InN-based HEMTs and GaN-based DHEMTs and are found excellent performance. The above analysis strongly suggests that the InGaN/InN/InGaN based DHEMTs have high potential in high frequency and high power applications.