A pseudomorphic GaAs/GaInAs/AlGaAs SISFET

The authors report a pseudomorphic semiconductor-insulator-semiconductor field-effect transistor (PM-SISFET) that uses a thin layer of undoped GaInAs instead of GaAs as the channel-forming layer. The device consists of an undoped AlGaAs barrier layer, a heavily doped n-type GaAs gate, and an upper GaInAs contact layer. With this structure, the device has a naturally negative threshold voltage. The structures were grown by molecular beam epitaxy. The devices were fabricated using, as for conventional GaAs SISFETs, self-aligned ion implantation and rapid thermal annealing (RTA). High-resolution photoluminescence spectra at 4.2 K for both the as-grown layer and after RTA have a FWHM (full width at half-maximum) of 3.1 MeV for a 120-Å-thick GaInAs channel layer with an In content of about 12%. These measurements indicate that no structural degradation of the strained layer occurred during annealing. To compare performance, the authors also grew and processed conventional GaAs/AlGaAs/n⁺-GaAs SISFETs. At 300 K, the 1-μm-gate-length devices showed transconductances and drain currents in excess of 270 mS/mm and 250 mA/mm, respectively, for PM-SISFETs compared to 240 mS/mm and 200 mA/mm, respectively, for similar conventional SISFETs