High electron mobility in heavily doped bases of InP/GaInAs HBTs

The minority carrier electron mobility in the base of InP/GaInAs HBTs was measured as a function of temperature using a new magneto transport method. At room temperature the mobility was found to be as high as 3400 cm² V^-1 sec^-1 at a base doping level of 3.4×10¹⁹ cm^-3. The measured mobility was compared with calculations carried out using the dielectric function formalism. The dominant scattering mechanisms are ionized impurity scattering and coupled LO phonon-plasmon scattering. The calculations correctly predict the high temperature mobility. At low temperatures a Monte Carlo analysis must be performed to model the experimental results because the electron distribution is nonthermal. The momentum relaxation rate strongly depends on the electron energy due to the elastic nature of the coupled LO phonon-plasmon scattering at low electron energy