Numerical modelling of AlGaAs/GaAs and InGaP/GaAs single and double HBTs

Abstract

The dc characteristics of a graded AlGaAs/GaAs single HBT (SHBT) and an abrupt InGaP/GaAs double HBT (DHBT) are studied using a thermionic-field emission boundary condition model. The model incorporates tunnelling and thermionic emission into a one-dimensional drift-diffusion numerical scheme and accounts for carrier degeneracy and bandgap narrowing. To our best knowledge, this is the first ever reported numerical analysis of InGaP/GaAs HBTs. A variety of existing data from different sources is analysed to find the best theoretical/empirical relations for the bandgap and transport related parameters of In1-xGaxP. The room temperature calculated Gummel plots and common-emitter output characteristics are compared to the experimentally measured ones and a good fit is observed between the two results. Finally, the simulated variation of current gain with temperature in various devices will be demonstrated.