III-Nitride Tunneling Hot Electron Transfer Amplifier (THETA)

  • Zhichao Yang
  • Digbijoy N. Nath
  • Yuewei Zhang
  • Sriram Krishnamoorthy
  • Jacob Khurgin
  • Siddharth RajanEmail author


In this chapter, we investigate vertical transistors based on hot electron transport—tunneling hot electron transfer amplifier (THETA). As compared to lateral transport devices such as HEMTs, electron transport can be defined by heterojunction growth at a scale shorter than 10 nm, and output conductance can be controlled through doping and epitaxial engineering. Furthermore, the power dissipation in a vertical device occurs over a volume rather than in a 2D sheet; the local temperature rise is not as significant as in the lateral case. THETA had been previously demonstrated in GaAs systems, and current gain in excess of 10 had been achieved with wide bandgap AlSbAs emitter at room temperature. GaN THETA has been reported in recent years, but the current gain in these devices has remained relatively low.

We demonstrate GaN THETA operating with common-emitter current gain above 10 for the first time by implementing polarization-engineered barriers in the emitter-base and base-collector junctions. Hot electron spectrometry and ballistic electron reflection in THETA were observed with the evidence of electron energy distribution and room temperature negative differential resistance (NDR). The electron-electron and coupled plasmon-phonon scatterings are key factors for the hot electron energy relaxation and broadening in base, in accordance with Monte Carlo simulation. Shrinking base thickness will reduce scattering rates and thereby increase current gain. Small signal model suggests above 200 GHz ft can be expected with a current density above 500 kA/cm2, base thickness of 5 nm and base doping of 2E20 cm2 for device mesa area less than 5 μm2.

For future work, optimizing of design to suppress output conductance and advanced processing technology to reduce parasitic components will enable highly scaled THETA for high-frequency operation.


Tunneling hot electron transistor THETA Phonon scattering Device fabrication Hot electron transport Hot electron transistor Monte Carlo simulation Polarization engineering Negative differential resistance Common-emitter current gain Gallium nitride Small signal models Vertical transistors Alloy fluctuation leakage Digital alloys Heterojunction bipolar transistor 


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Copyright information

© Springer Nature Switzerland AG 2020

Authors and Affiliations

  • Zhichao Yang
    • 1
  • Digbijoy N. Nath
    • 2
  • Yuewei Zhang
    • 1
  • Sriram Krishnamoorthy
    • 3
  • Jacob Khurgin
    • 4
  • Siddharth Rajan
    • 1
    Email author
  1. 1.Ohio State UniversityColumbusUSA
  2. 2.Indian Institute of ScienceBengaluruIndia
  3. 3.University of UtahSalt Lake CityUSA
  4. 4.Electrical and Computer Engineering, Johns Hopkins UniversityBaltimoreUSA

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