Nonequilibrium Electron Transport in InP Based Hybrid Heterojunction

InP based heterojunction bipolar transistors (HBTs) exhibit proven potential for use in high performance digital integrated circuits and discrete microwave components. For high speed applications, it is desirable to utilize structures that have been designed to promote high levels of nonequilibrium electron transport as this allows realization of higher electron velocities than possible for diffusive charge transport. Devices based on InP are especially well suited for effective nonequilibrium operation due to the high saturated electron velocities, small electron masses, and large G-L intervalley separations exhibited by these materials systems. Phase I will examine InP based HBT structures grown by MOCVD that exhibit varying degrees of nonequilibrium electron transport due to 1) hot electron injection over an abrupt emitter-base potential barrier, 2) built-in electric field acceleration of electrons in a compositionally graded base layer, or 3) a hybrid combination of hot electron launching and electric field acceleration. The effects of various structural parameters on overall hybrid device performance will be evaluated and the approach(es) suitable for future Phase II optimization and high speed characterization will be identified based on the perceived capability to effectively utilize nonequilibrium electron transport characteristics.