SEMICONDUCTOR HETEROJUNCTION STRUCTURE STUDIES.
CARNEGIE-MELLON UNIV PITTSBURGH PA DEPT OF ELECTRICAL ENGINEERING
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Feasibility studies have been made of semiconductor heterojunction structures and confirm that wide-gap emitter action is practical. Transistors of n-type ZnSe emitters on pGe-nGe base-collector structures have usable current gains even though the emitter doping levels are many orders of magnitude lower than the base doping levels. Effects on the current gain of parameters such as doping levels, base widths, current injection levels and temperature have been studied. Because of the low emitter doping levels, the emitter current flow is space-charge limited. The ZnSe was grown epitaxially on the Ge substrate by a close-spaced HCl transport process from doped source material. The optical properties of nZnSe-pGE junctions showed window-effect corresponding to the energy gap difference 2.6eV to 0.7eV. However, measurement of the photon quantum efficiency was not attempted with these specimens because of the high resistivity of the ZnSe. Analytical studies were made of the frequency response to be expected for heterojunction transistors, with doped or space-charge limited emitters, and for a homojunction high-frequency transistor of comparable geometry. The high base doping possible with heterojunction transistors should result in low base resistance and at least a factor of two increase in the frequency response relative to homojunction transistors. Author
- Electrical and Electronic Equipment
- Solid State Physics