| Summary: | 博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 95 === In this dissertation, the influences of various emitter-ledge thickness and length on the InGaP/GaAs heterojunction bipolar transistors performance are investigated based on the simulation and experimental data. The undesired surface channel phenomenon at the exposed base surface between the base contact and the emitter ledge is comprehensively analyzed. Moreover, improper thickness of emitter-ledge passivations would cause serious surface recombination at the edge of emitter ledge. In addition, the electron density and recombination rate are decreased with increasing the emitter-ledge length at the surface channel. However, the longer emitter-ledge length increases the base-collector junction area which in turn deteriorates the high frequency performance. Therefore, the thickness and length of emitter ledge are a critical issue and should be carefully considered. From simulated and experimental results, the optimum emitter-ledge thickness of InGaP/GaAs HBT is between 100 and 200 A and the corresponding optimum emitter-ledge length is near 0.8 μm.
The temperature-dependent DC characteristics and RF performance of an InGaP/GaAs HBT with the conformal passivation on base surface are studied and demonstrated. For the conformal passivation, an additional sulfur passivation layer is passivated on (1) the emitter sidewall; (2) the exposed emitter-ledge surface; (3) the exposed base surface between the base contact and the emitter ledge; and (4) the interface between the base contact and the base layer. Therefore, the related problems of emitter-ledge thickness, undesired surface-channel phenomenon of unpassivated base surface, and poor base contact are shown to have improved by using a conformal passivation method successfully.
Finally, the temperature-dependent DC characteristics and microwave performance of InGaP/GaAs HBTs with and without full sulfur treatment are systematically studied and demonstrated. Not only the top surfaces of emitter, base and collector but also the sidewalls of emitter and base are completely passivated by the proposed full sulfur treatment. This technique is significantly different from previous reports since those methods passivated only the exposed base surface.
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