Modulation-doped InAlAs/InGaAs heterostructures were grown on InP substrates by solid source molecular beam epitaxy. Lattice matching within +/-10(-3) was reproducibly obtained. The high quality of the ternary compounds is demonstrated by narrow photoluminescence linewidths of full width at half-maximum=2 and 13 meV for InGaAs and InAlAs, respectively. The transport properties are excellent, too, with a 4.2 K mobility of 84 000 cm2/Vs for two-dimensional electron gas concentrations of 1.3 X 10(12) cm-2 in conventional single heterostructures. Optimized single quantum-well structures with high current carrying capacity due to modulation doping in both barriers have sheet carrier concentrations of 4.0 X 10(12) cm-2 and 4.2 K mobilities of 28 000 cm2/Vs. Sub-mum-high electron mobility transistors processed from these structures show a maximum transconductance of 500 mS/mm at a drain current of 445 mA/mm. A very high maximum drain current of 11 20 mA/mm is obtained, while maintaining cutoff frequencies of f(T)=118 GHz and f(max)=191 GHz.