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The influence of emitter ledge length on the performance of InGaP/GaAs heterojunction bipolar transistors is comprehensively investigated. Due to the band-bending effect at the intersection of the emitter ledge edge with the exposed base surface, an undesired potential saddle point is formed. Moreover, emitter ledge passivations that are longer or shorter than an optimal length result in the deterioration of device performance. Based on the theoretical analysis and experimental results, the surface recombination effect of the device with an emitter ledge length of 0.8 μm is negligible compared with the unpassivated device. Also, the device with the emitter ledge length of 0.8 μm shows nearly the best dc characteristics and acceptable rf performance. Therefore, the optimum emitter ledge length in this study is near 0.8 μm. [ABSTRACT FROM AUTHOR]

The temperature-dependent dc characteristics of InGaP/GaAs heterojunction bipolar transistors with and without full sulfur passivation are systematically studied and demonstrated. The studied device with full sulfur passivation shows lower specific contact resistance ρC, lower sheet resistance Rsh, lower collector-emitter offset voltage ΔVCE, and higher dc gain βF than devices without sulfur passivation. The device with full sulfur passivation also exhibits better rf performance. In addition, the studied device with full sulfur treatment shows lower temperature variation coefficients of ρC, Rsh, ΔVCE, and βF. Thus, the device with sulfur treatment presents relatively temperature-independent characteristics that can extend the transistor action to higher temperature regimes. [ABSTRACT FROM AUTHOR]

The effect of (NH4)2Sx treatment on the device characteristics of an InGaP/InGaAs/GaAs heterostructure field-effect transistor are studied and demonstrated. Experimentally, it is found that the sulfur-passivated device shows significant dc characteristics including higher forward voltage, lower leakage current, lower output conductance, and higher voltage gain. The superior microwave performances with flat and wide operating region of drain saturation current are simultaneously obtained. Furthermore, the improved thermal stabilities over wide temperature range of sulfur-passivated devices are attained. Based on these advantages, the studied device with (NH4)2Sx treatment shows the promise for high-temperature and high-performance microwave applications. [ABSTRACT FROM AUTHOR]