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A microscopic view of quasi-ballistic transport in HBTs

Publication Type:

Conference Paper

Source:

WOCSDICE 97. 21st Workshop on Compound Semiconductor Devices and Integrated Circuits, Scheveningen, Netherlands, p.126 - 7 (1997)

Keywords:

aluminium compounds;Boltzmann equation;carrier density;carrier mean free path;electric current;electron-phonon interactions;gallium arsenide;heterojunction bipolar transistors;high field effects;III-V semiconductors;impurity scattering;thermionic electron

Abstract:

Summary form only given. In the steady-state, field-free case, the Boltzmann transport equation reduces to an ordinary differential equation that can be solved exactly using an integrating factor. We have used such an approach to investigate transport in the short base region of an AlGaAs-GaAs HBT. The injection of electrons into the base by thermionic emission and tunneling at the emitter-base junction has been taken into account via an appropriate boundary condition. So far, scattering mechanisms due to ionized impurities and polar-optical phonons have been considered. The results are interesting because of the novel perspective of transport that is given by being able to view the evolution of the components of the distribution function at various positions in the base. Results at three positions in the base are shown for the case of screened ionized impurity scattering in a highly doped base (1019 cm-3) of width equal to one mean-free-path length (920 Å). The implications of these results with regard to the collector current and the base transit time for HBTs with very short bases are discussed. Results for polar-optical phonon scattering are also presented

Notes:

quasi-ballistic transport;HBTs;Boltzmann transport equation;steady-state field-free case;ordinary differential equation;integrating factor;AlGaAs-GaAs HBT;short base region transport;electron injection;thermionic emission;tunneling;emitter-base junction;boundary condition;scattering mechanisms;ionized impurity scattering;polar-optical phonon scattering;distribution function components;screened ionized impurity scattering;highly doped base;mean-free-path length;collector current;base transit time;HBT base length;920 angstrom;AlGaAs-GaAs;