Influence of quantum well width on DC and RF device performance in pseudomorphic Al/sub 0.30/Ga/sub 0.70/As/In/sub 0.25/Ga/sub 0.75/As MODFETs

An experimental study of the influence of quantum well width on DC and RF device performance in nominally 0.2- mu m gate-length atomic-planar doped pseudomorphic Al/sub 0.30/Ga/sub 0.70/As/In/sub 0.25/Ga/sub 0.75/As MODFETs is reported. Three important results have been obtained: (1) a well width of approximately 120 AA appears to be optimum for overall device performance and gives a current gain cutoff frequency (f/sub T/) of 122 GHz; (2) thinner quantum wells ( approximately 45 AA) result in a significant reduction ( approximately 40%) in maximum channel current density; and (3) thicker quantum wells (150-200 AA), which exceed the critical thickness (90-100 AA) predicted by the Matthews and Blakeslee model, still give excellent device performance (f/sub T/=107 GHz). As a result of the latter, it might be possible to realize much higher-indium-percentage (30-40%) quantum wells without having to reduce the well width to an unacceptable value. >