For high-power applications such as amplifiers, GaN based transistors constantly set new output
power records, especially for frequencies at X-band to K-band [320,321]. A combination of
mediocre, but RF suitable transport properties together with excellent breakdown
properties [258], and extremely good charge control results in outstanding high-power
performance. The current record output power amounts to a saturated output power of
= 51 W
in pulsed operation mode in the C-band (4.6 GHz-7.0 GHz) at 6 GHz [320]. For a comparison of
power densities and overall output power, see Fig. 2.8 and Fig. 2.9. The
highest available power density at 20 GHz has been reported by [181] as 4 W/mm for
continuous wave (CW) operation on SiC substrate. The theoretical limit is taken from [145]
and shows the optimization potential remaining. High frequency operation has been reported up to
= 74 GHz for
= 150 nm [81] and the highest
product has
been reported with 101 GHz
at
= 120 nm with an astonishingly low transconductance
[166]. The highest overall value
= 110 GHz was reported for
= 50 nm by Micovic et
al. in [182]. These values suggest possible operation at least up to the Ka-band in this
stage of process development. So far InGaN/AlGaN based HEMTs have faced harsh material problems
due to the unsolved problem of high unintentionally doping concentrations. They are, however,
under development [246] for high-speed operation due to the suggested lower effective
carrier mass.
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