TABLE OF CONTENTS Although much of the initial MBE research was directed toward the study of surface film growth kinetics, the driving force today is the fabrication of advanced electronic and optoelectronic devices. As the film growth capabilities of MBE became clear, researchers began producing a wide variety of heretofore impossible and unimagined devices. Some of these devices have subsequently been fabricated using other epitaxial techniques, but many were initially conceived in MBE systems. The advantages of generally lower growth temperature and growth rate allow MBE to produce atomically abrupt heterojunctions and doping profiles. The ability to produce these composition variations with material systems of inherently high electron mobility (i.e., GaAs, InP, InGaAs) has permitted the fabrication of very fast devices. Microwave devices with operating frequencies near 100 GHz[23] and high speed digital switching near 5 picoseconds[24] have been achieved. Also, the control of contact layers has reduced parasitic resistances, significantly improving FET performance (e.g., MAG and NF). The ability of MBE to deposit epitaxial metal layers in situ promises to permit the construction of a metal base transistor.[25] The fact that several material systems (e.g., GaAs/AlGaAs) are also optically active allows for the possibility of integrating high speed digital and optical circuits. Recent progress in the growth of GaAs on silicon further increases the options by promising to combine the virtues of these two semiconductor technologies in a monolithic device. MBE silicon devices are discussed in an article by K. L. Wang.[26]
Since it is not the intent of...
