Signature of Hot Phonons in Reliability of Nitride Transistors and Signal Delay

Abstract

Lifetime of non-equilibrium (hot) phonons in biased GaN heterostructures with two-dimensional electron gas channels was estimated from hot-electron fluctuations. Dependence of the lifetime on the electron density is not monotonous -the resonance-type fastest decay serves as a signature of hot phonons. The signature is resolved in nitride heterostructure field effect transistors when the gate voltage is used to change the channel electron density. The transistor cut-off frequency decreases on both sides of the resonance in agreement with the enhanced electron scattering caused by longer hot-phonon lifetimes. The signature is also noted in device reliability experiment: the enhanced temperature of hot phonons, possibly, triggers formation of new defects and accelerates device degradation.

Camelback channel for fast decay of LO phonons in GaN heterostructure field-effect transistor at high electron density

“…The thermal conductance helps to drain out the excess LA phonons, but a different approach is needed to treat the heat accumulated by non-equilibrium LO phonons (hot phonons) emitted by hot electrons. 9 Hot-phonon decay is often evaluated in terms of LOphonon lifetime. 10 It has been suggested, based on experimental data, 11 that the lifetime is shorter if the three-dimensional (3D) carrier density is closer to LO-phonon-plasmon resonance.…”

Current conduction mechanism and electrical break-down in InN grown on GaN

“…Accelerated self-heating can also be considered in this case, as increased n may modify the device thermal resistance by disturbing hot-phonon interactions. 33 Nevertheless, further investigations and physical modeling of InN resistors are needed to fully understand and assign particular mechanisms. We also tested a longer pulse width of 250 ns to enlighten the dynamics of the electron emission however; premature thermal breakdown appeared already before E knee was reached in this case.…”