Strain energy band engineering in AlGaInN/GaN heterostructure field effect transistors

We report on AlxInyGal-x-yN-GaN heterojunctions grown on sapphire and 6H/4H SiC substrates using a low pressure MOCVD. Based on a linear extrapolation of lattice constants as functions of molar fractions, we estimate that quaternary AlxInyGal-x-yN layers with Al/In mole fraction ratio of 5 should be nearly lattice-matched to GaN. The independent control of strain and of the band offset has been confirmed by X-ray and photoluminescence data. For AlxInyGal-x-yN-GaN junctions with barrier thickness less than 50 nm and varying alloy compositions (x from 0.1 to 0.2 and y from 0.00 to 0.02), room temperature sheet-carrier density and mobility values ranging from 0.5-1.5 x 1013cm ~2 and 1000-1500 cm2V-1sec-1 were measured. The mobility values increase by about a factor of 5 upon cooling to 77 K. This establishes the presence of the two-dimensional electron gas at the AlxInyGal-x-yN-GaN heterojunction interface and confirms a high quality of heterointerfaces. We also fabricated AlxInyGal-x-yN-GaN HFETs with the state-of-the art performance. The fabrication technology for these devices is substantially different from that for conventional AlGaN/GaN HEMTs. We will report on DC and microwave characteristics of these devices and compare these characteristics with those for conventional GaN-based HFETs