SELF-CONSISTENT CALCULATIONS OF (Ill)-ORIENTED GaAs AND InP BASED PSEUDOMORPHIC HEMT' s.

Band structure calculations, charge distribution and charge control properties in InGaAs-based pseudomorphic modulation doped [lllI-FET’s are presented. Compressive strain in AlGaAs/InGaAs/GaAs structures, and both tensile and compressive strains in AlInAs/InGaAs/InP devices are used to generate internal electric fields via the piezoelectric effect. Normal and inverted HEMT’s with maximum charge in the well and minimized parallel conduction have been designed using this piezoelectric internal field. Improvements in charge concentration (up to 50% more) and its distribution in the well (almost centered) are achieved in this new orientation. Transconductance and gate capacitance versus gate voltage are compared for the [lo01 and [llll orientations. We conclude that the device performance is improved when the ill11 substrate is used.