Full band ensemble monte carlo simulations for reliability investigation of highvoltage single & double heterojunction bipolar transistors for military and base station applications including a proposed high breakdown composite collector design

Abstract

High-voltage HBTsaregaining considerable interest foremerging military andcommercial CATV and microwave base station applications. Understanding ofcarrier transport anddynamics assumes vital importance to establish safe operating areas (SOAs) forthese devices inorder toavoid detrimental effects suchasimpact ionization leading todevice breakdown. Contemporary formalisms based on'drift-diffusion ' theories suffer from several shortcomings inaccurate modeling ofchare transport under such high-field regimes through sub-micron device geometries. Ourcomprehensive 'full-band' ensemble MonteCarlo simulations modelcharge transport through n-GalnP/p+GaAs/n-GaAs single heterojunction bipolar transistors (SHBTs), while establishing the ionization coefficients andv-Fcharacteristics forthecollector region. Double heterojunction bipolar transistors (DHBTs)involving acomposite collector design (CCD)withwidebandgap materials holdgreater promise in pushing theJohnson figure-of-merit forhighvoltage applications. However, CCD implementation involves numerous challenges, including butnotlimited tothefollowing: lattice matching toGaAs, negligible conduction bandoffset atallheterojunctions toavoid current blocking duetopotential 'spike', loweffective massandhigh electron velocity, acceptable dielectric permittivity, wideseparation between valence andconduction bandto avoid high-field tunneling, high breakdown strength andimpact ionization threshold energies. Wediscuss ahighbreakdown composite collector DHBTwhich incorporates all these desirable aspects.