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AlGaN/GaN single heterojunction bipolar transistors (SHBTs) without using regrown emitter junction are demonstrated. Secondary ion mass spectroscopy analysis shows that a severe codiffusion of Al and Si exists in AlGaN/GaN heterostructures grown at 780 °C. The altered composition and doping profiles greatly degrade the common-emitter current gain of AlGaN/GaN HBTs to ≤0.8. A GaN spacer layer is inserted at the emitter-base junction to alleviate this problem. In an AlGaN/GaN HBT structure inserted with a 20 nm unintentionally doped GaN spacer layer, a current gain $\beta $ about 2 is achieved. [ABSTRACT FROM AUTHOR]

A series of lateral junctions consisting of NiFe/Al2O3/p-Si/Al2O3/NiFe have been investigated for the understanding of manipulating the electronic spin in semiconducting channel. Devices with various conducting channel lengths between two electrodes were fabricated using a top–down technique. An ion beam sputtering was used for the required film stack and an electron beam lithography in combination with ion beam etching technique were adopted for patterning. The current-voltage measurements reveal a remarkable phenomenon of current enhancement, indicating a formation of the interface state in such devices. This transport behavior associated with trapping assistance has also been demonstrated with a fitting based on Poole–Frenkel effect. The results also show that a transition from trapping assisted process to direct tunneling process occurs when the semiconducting channel length is below 1 \mum. In addition, the current enhancement may be suppressed with increasing the thickness of the oxide layer. [ABSTRACT FROM AUTHOR]