Indium phosphide-based quantum tunneling transistors grown by chemical beam epitaxy.

Abstract

InP-based quantum tunneling transistors were studied systematically using Chemical Beam Epitaxy (CBE) for the first time. Four transistors were studied, including Hot Electron Transistors (HET's), Resonant Tunneling Hot Electron Transistors (RHET's), Bound State Resonant Tunneling Transistors (BSRTT's) and Resonant Tunneling Bipolar Transistors (RTBT's). Using the negative differential resistance (NDR) or transconductance (NDT) characteristics, these transistors can be applied to high speed digital circuits and reducing the complexity of conventional transistor technology. After investigating the fundamental device physics and ballistic transport, CBE growth studies were performed to satisfy the stringent growth requirements for the transistor structures. Fabrication technologies were also developed for the InP-based material system, including shallow ohmic contacts, selective and non-selective etching, and a self-aligned process. In addition, numerical techniques were developed to simulate resonant tunneling structures. Combining all the techniques, quantum tunneling transistors were realized with reasonable DC and microwave performance. For the HET's fabricated, the highest observed differential transport ratio (d$\alpha$) at 80 K was over 0.99, corresponding to a common emitter differential current gain (d$\beta$) over 100. Using an energy spectrometer technique, ballistic transport was realized both from the HET's and RHET's. The highest $\alpha$ observed for the RHET's averaged around 0.98, with peak-to-valley current ratios (PVR's) of 20 and 200 in I$\sb{\rm C}$ and I$\sb{\rm B}$ at 80 K. Additionally, the RHET's also showed a DC $\beta$ of 4 and a cutoff frequency of 31 GHz at 300 K. Some RHET digital functions were also demonstrated, such as a flip-flop gate and an exclusive NOR function. BSRTT's with direct contact to the ultra thin base layers ($\sim$60 A) were also experimentally realized for the first time. The d$\beta$ and DC $\beta$ were 9 and 3.1 respectively at 77 K. The RTBT's showed 1 to 4 NDT peaks with PVR's of 1.5 to 5.28 and DC $\beta$ of 10 (20) at 300 K (77 K). The highest f$\sb{\rm T}$ and f$\sb{\rm max}$ measured were 15 and 10 GHz at 300 K. Finally, several RTBT digital functions were demonstrated at 300 K, including a frequency multiplier and an exclusive NOR function.