| PhD Seminar

Name of the Speaker: Mr. Soumen Deb (EE14D036)
Guide: Dr. NanditaDasGupta
Venue: ESB-244 (Seminar Hall)
Date/Time: 20th Aug 2025(Wednesday), 3 PM
Title: Analytical Modelling of Off-state Breakdown Voltage of GaN-Based HEMTs.

Abstract :

Over the past two decades AlGaN/GaN High Electron Mobility Transistors (HEMTs) have emerged as efficient power electronic switches, because of the high breakdown field strength of GaN and high concentration of 2-DEG at the hetero interface. Being a power transistor, its off-state breakdown voltage (VBR), is a parameter of keen interest which depicts the Power Aided Efficiency (PAE) of the transistor. While a significant volume of work (both experimental and/or simulation based) has been reported in literature in order to enhance VBR, a systematic and quantitative evaluation technique of VBR is still not available. It is important to note that, estimation of VBR requires an elaborate knowledge of off-state electric field distribution at AlGaN/GaN interface. For the first time we have developed a simple physics based analytical model for the lateral electric field in the channel. The maximum lateral electric field (Emax) and length of depletion region in drain access region (lZ3) are expressed as explicit function of drain voltage (VDS) by solving 2-D Poisson’s equation for intrinsic HEMT and considering a piecewise linear distribution lateral electric field in depletion region, near the drain edge of the channel. A new extraction method of breakdown voltage has been adopted considering the impact ionization integral in the depletion region as unity and a rigorous analytical expression for VBR is derived. The analytical model has been validated with simulation results obtained from Sentaurus TCAD for different gate voltages (VGS < VTh) and various design parameters of AlGaN barrier layer (aluminium mole fraction m and thickness dAlGaN) as well as experimental results from literature.

VBR can be enhanced manifolds by incorporating a field plated structure. The simplest structure of field plate is a gate field plate, which is a typical extension of the gate metal deposited over the Si3N4 passivation layer in the drain access region. It is reported in literature that VBR increases as the field plate length is increased up to a certain limit for a given length of drain access region (LGD). Similar to a conventional HEMT, estimation of VBR for a gate field plated HEMT also requires proper quantification of channel lateral electric field. For the first time, a physics based analytical model for lateral electric field is developed by solving 2-D Poisson’s equation in both gated and field plated regions, combined with piecewise linear approximation of the lateral electric field in drain access region. The model provides analytical expressions for peak electric field at gate edge (Eg,peak) and the field plate edge (Efp,peak) as explicit functions of VDS as well as expressions for VBR following the previous approach. The model is verified by comparing with TCAD simulation results for different VGS (< VTh), VDS as well as various design parameters of the field plate (length of the field plate LFP and thickness of the Si3N4 passivation layer dpas) and will be presented in seminar.