Transport and related properties of InP based HBTs

InP/InGaAs heterojunction bipolar transistors (HBTs) have attracted considerable interest in recent years due to a series of advantages over the more traditional GaAs/GaAlAs based HBTs. These use nominally abrupt emitter-base junctions to take advantage of the conduction band discontinuity or `spike´ to launch ballistic electrons across the base. Whilst many of the reported HBTs in this materials system were single heterostructure devices there are advantages to be gained by having both emitter and collector made from the high bandgap material, such as for example symmetric operation and low offset voltage. It is important therefore to study the detailed electrical characteristics of both junctions in the HBT which will provide detail on the interfacial band structure. This work has investigated the I/V characteristics as a function of temperature in InP/InGaAs HBTs and points out the differences between the upper and lower junctions in MBE grown structures. Some comparisons are also made with device characteristics made from LPE and MOCVD grown material and also InGaP/GaAs devices grown in the same MBE kit