Effects of substrate tilting in substantial improvement of DC performance of AlGaAs/GaAs n-p-n DHBTs grown by MBE

A marked improvement has been observed in the DC performance of Al _0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As double-heterojunction bipolar transistors (DHBTs) by tilting the (100) GaAs substrates 3° towards <111>A. On the tilted substrate, the surface, space charge, and bulk recombination currents are reduced, and the quality of AlGaAs/GaAs heterointerfaces is improved. As a result, both the emitter injection efficiency (η) and base transport factor are increased, leading to a substantial increase in current gain with a marked reduction of its current and junction geometry dependence. The device characteristics and current gain changed very little between 25 and 100°C on both substrates. The improved bulk and interfacial quality of AlGaAs/GaAs heterostructures on the misoriented substrates is confirmed by TEM cross sections and SIMS measurements and is due largely to the lower affinity of Ga-like surface steps for defects and impurity incorporation