InN-Based Heterojunction Field Effect Transistor

Abstract

As a promising candidate for future high speed devices InN-based heterojunction held effect transistor (HFET) has gained a lot of attention in recent years. I lowever. InN-based devices are still a less studied compared with other Ill-nitride based devices. Ihis work describes a novel AlInN/lnN heterojiinction field effect transistor (HFET) without and with an oxide layer beneath the gate I'or high performance. A quantum mechanical charge control model based on the set f-consistent solution of one dimensional Schrodinger-Poisson equations is developed. The transport properties such as channel mobility and the velocity-field characteristics of the proposed device are calculated using Monte Carlo simulation. In order to investigate dc and high frequency perfbrrnances of the device an analytical drain current model is developed. The model takes into account the highly dominant spontaneous and piezoelectric polarization effects to predict the 21)FG sheet charge density more accurately at the heterointerfiice. The effect of parasitic source and drain resistances along with gate to source capacitance is incorporated in the high frequency analysis. The device transconductance is found from the channel current. The cut-off frequency is calculated using a simple equation relating transconductance and gate to source capacitance. The investigated parameters of the proposed device are maximum drain current (J/mtv). threshold voltage (V,,1 ), peak DC transconductance (gin) and unity gain cut oil frequency (I;). The typical DC characteristics for a gate length of 0.25 jim with 100 ,tm gate width are as Follows: = 715 mA/mm. g,,, = 280 mS/mm. f = 110 Gl Iz and Vth = -2.50 V br I IFLI. While using an oxide layer of thickness 13 nm these values are: = 786 mA/mm, gn, = 225 mS/mrn.f = 154 Gl lz and V,11 = - 2.52 V. The gate length dependence of transconductance and cuit-off fi'equency in AlInN/InN I-IFIF without and with an oxide layer has been theoretically investigated. In addition, the variation of these performance parameters with a gate to source voltage has also been studied. I he calculated values of g,1, is futind to be varied from 280 to 205 mS/mm and 225 to lOS v mS/mm (or HFET without and with oxide layer, respectively with the variation of L From 0.25 to 1.5 µm at 2 and V.= 1.5V. The cut off frequency varies from 110 to 12 GHz and 154 to 26 G}-Iz for HFET without and with oxide layer, respectively with the variation of L from 0.25 to 1.5 .tm at Vd = 2 V and Vg.c 1.5 V. The investigated results of the proposed device is compared with the GaN-based device and found to show excellent performance over the GaN-based devices. The above studies indicate that the proposed InN-based HFET is very promising for the fabrication of high performance high speed devices.