0.5-μm gate length self-aligned gate MODFET with reduced short-channel effects

Reduced short-channel effects were obtained by using a buried AlGaAs layer beneath the channel. A 0.5×10-μm² MODFET was fabricated that had a peak transconductance of 264 mS/mm with a K-factor of 425 mA/V²-mm. The measured output conductance was 2.37 mS/mm, a reduction from 18 mS/mm for a 0.5-μm device without the buried layer. This combination of high transconductance and low output conductance makes the device ideal for high-speed analog and digital applications. The reduced output conductance gives a maximum gain of 110, compared with a more typical gain of 25 for a standard 0.5-μm MODFET device. Threshold voltage dependence on gate length decreases from a 60-mV shift for 1.5- to 0.5-μm gate length to 20 mV over the same range. The structure of the device, which was grown by molecular-beam epitaxy, consists of a five-period AlGaAs/GaAs superlattice and AlGaAs cap and spacer layers. The GaAs conducting channel is located between this charge control layer and a buried AlGaAs channel confinement buffer layer. This double heterostructure forms a quantum well in the channel region to further confine the quasi-two-dimensional electron gas