MOLECULAR-BEAM EPITAXIAL-GROWTH AND CHARACTERIZATION OF PSEUDOMORPHIC MODULATION-DOPED FIELD-EFFECT TRANSISTORS

We have investigated the luminescent and device properties of pseudomorphic AlGaAs/InGaAs modulation-doped field effect transistors (MODFETs) with different InAs molar fractions in the InGaAs channel. Molecular beam epitaxy, which simultaneously deposits group III atoms and As4 molecules on the substrate surface, was used to grow the random alloy In(x)Ga(1-x)As channel layer for x less-than-or-equal-to 0.4, and migration-enhanced epitaxy (MEE), which alternatingly deposits group III atoms and As4 molecules on the surface, was used to grow sequential layers of InAs and GaAs in the channel region with large effective x (up to 0.5). For 1-mu-m gate length MODFETs with random alloy In(x)Ga(1-x)As channels the transconductance g(m) and saturation drain current I(dss) exhibit a maximum at x = 0.17 because of the superior electron transport properties of InGaAs compared with GaAs. g(m) and I(dss) decrease drastically for x higher than 0.32 as a result of misfit dislocation generation. The photoluminescence peaks of In(x)Ga(1-x)As channels of these MODFET samples show a similar trend, strong intensity for the In0.17Ga0.83As channel and very weak intensity for the In0.4Ga0.6As channel. However, MODFETs with a nominally (InAs)2(GaAs)2 channel grown by MEE exhibit higher g(m), I(dss) and photoluminescence intensity than those with an In0.4Ga0.6As channel.