Performances and limitations analyses of PHEMT and MHEMT for applications in high bit rate fiber-optic systems

These preliminary studies show that MHEMT technology (with more indium concentration in the active layer than in PHEMT), permits to obtain higher gain than PHEMT thanks to higher Ft and Fmax. It has been shown that a composite channel permits to improve the on-state breakdown voltage and to obtain suitable Ft (136 GHz) and Fmax (260 GHz) compared to a single channel process. However it remais necessary to further improve the on-state breakdown voltage needed for the required application (high voltage swing at 50 Gbits/s data rate) through a reduction of the impact ionisation phenomenon, without compromising Ft, Fmax and the gain.