Proceedings Article | 20 February 2009
KEYWORDS: Phonons, Magnetism, Field effect transistors, Gallium nitride, Reliability, Acoustics, Particles, Semiconductors, Resistance, Polarization
The QED quantum 1/f noise formulas have been recently refined for the case of AlGaN/GaN HFETs and FETs through a
better definition of the coherence parameter s, with much better agreement with the experiment. Indeed, for a FET/HFET
width w>>L>t, this yielded s≈πnrtLlog(w/2L) instead of the old s=2nrtw formula. Here we generalize this basic result
for the first time to a finite piezoelectric case. Here L= source to drain length, t is the thickness (depth) of the channel, n
is the concentration of carriers, π3.1416, and r=2.8•10-13 cm is the classical radius of the electron. In piezoelectric
materials, particularly those also showing ferroelectric spontaneous polarization, transversal phonons are the massless
quanta leading to large piezoelectric, or lattice-dynamic, quantum 1/f effects, conventional and coherent. As in the usual
QED case, the parameter s' yields the observed 1/f noise as a weighted sum of conventional and coherent quantum 1/f
effects. The HFET piezocoherence weighting parameter s', derived here is (gN'h/m*vs)(vs/u)3 F(u/vs)t/12w, with
N'=nLt, vs the piezophonon speed, u the drift velocity, and F(x) is a function defined earlier, equal to (2/3)x3 for x<<1.
This s' is increasing, ~t2, important for reliability and device optimization. For HFET stability, a slower decrease of
conductivity than of polarization is found to be needed for stability along the large device width, when the temperature
increases.
