Fabrication of p-channel heterostructure field effect transistors with polarization-induced two-dimensional hole gases at metal-polar GaN/AlInGaN interfaces

Novel nitride-based heterostructures have been fabricated demonstrating two-dimensional hole gases as the basis for p-channel transistors. The carrier density in the 2DHG is adjusted between very high values of 2 x 10(13) cm(-2) and low values of 6 x 10(11) cm(-2) by the polarization difference, Delta P, between quaternary AlInGaN backbarriers and a GaN channel on top. Record mobilities for holes in GaN of 43 cm(2) V-1 s(-1) (median 30 cm(2) V-1 s(-1)) are observed for a moderate 2DHG density of 1.3 x 10(12) cm(-2) (median 2.2 x 10(12) cm(-2)). Heterostructures with different backbarrier compositions are processed to field effect transistors and show a systematic threshold voltage shift from positive to negative values according to the corresponding 2DHG density. It is shown for the first time that by appropriate polarization-engineering through changing the AlInGaN composition, both depletion and enhancement mode behaviour can be achieved for p-channel devices. Drain current densities |I-d| above 40 mA mm(-1) at a drain source voltage V-ds of -10V are achieved for heterostructures with high polarization differences, Delta P, between AlInGaN backbarrier and GaN channel. Reducing Delta P leads to decreasing on-state drain currents |I-d| with a simultaneous reduction in off-state current. This results in very large on/off ratios of up to 10(8) for enhancement mode devices, demonstrating record performances and great potential for future applications.