Application specific devices: transport and performance of the Quasi-MODFET and the graded base heterojunction bipolar transistor

Two application-specific devices, a novel doped-channel Quasi-MODFET on AlInAs/InGaAs/InP, and an AlGaAs/GaAs graded-base heterojunction bipolar transistor, suitable for high current/gain applications in energy efficient mobile communication and optical communication and computer networks, have been developed. The study of transport and performance of the doped-channel MODFETs included the quantum well, channel width, doping profile, and composition, and revealed that the position of the electron wavefunction peak can be engineered to shift in areas of minimum scattering, which resulted in the development of the 0.5 μm Q-MODFET with a g_m=703 mS/mm and I_dent=800 to 940 mA/mm at V_g=0 to 0.4 V, the highest g_m recorded for a doped-channel device. In the HBT, the development of a rigorous two-dimensional model providing the optimum compositional grading of the base, the improvement of the collector using thinner layers and higher doping, and the emitter using compositional grading, resulted in the development of a high current heterojunction bipolar transistor appropriate for laser drivers