Novel heterojunction devices

In this paper, recent progress in the fabrication and realization of novel heterojunction devices based on band structure engineering will be described. The fact that strained layer epitaxy can be used to create entirely new structures will be illustrated through such diverse examples as ordered growth of Ge/Si on Si, strained p-type quantum well FETs with light-hole dominated transconductance on GaAs, and high speed strained InGaAs/GaAs MODFETs. Recent calculations involving molecular dynamic simulations of strained layer growth, with mismatches of up to 4%, will be described and the outstanding puzzle of crystal thicknesses much larger than allowed by equilibrium theories for coherent crystal growth will be resolved. Some recent examples of the perfection of quantum well structures will be illustrated through the fabrication of devices based on perpendicular transport such as the resonant tunneling bipolar transistor and 10 µm superlattice IR detectors.