Measurements of the Fermi level mobility of the GaInP/InGaAs/GaAs wide and narrow channel MODFETs

We have introduced a new technique to measure electron mobility at the highest energy levels (/spl mu//sub max/) of the two-dimensional electron gas. This quantity is easy to measure and is sensitive to the occupation of the excited energy levels. This technique was applied to the investigation of the population of the excited energy levels in the wide and narrow channel GaInP/InGaAs/GaAs MODFETs. It is shown that electrons on excited energy levels in the wide channel device actually deteriorate the device performance. In the narrow channel MODFET only the ground state is populated. Thus the energy of the electrons is higher than in the wide channel device. Consequently, the narrow channel device has a higher mobility. With the help of these measurements we optimized the MODFET structure for low voltage operation. For the first time 136 mW/mm output power with 46% power added efficiency at 2 V drain bias has been achieved with GaInP/InGaAs/GaAs MODFET.