MOVPE Growth of High Electron Mobility AlGaN/GaN Heterostructures

ABSTRACTWe have fabricated AlxGa1−xN/GaN heterostructures with high two-dimensional electron gas (2DEG) mobilities and high sheet carrier densities by metalorganic vapor phase epitaxy (MOVPE). The 2DEG sheet density and mobility exhibit a compositional dependence on the Al fraction of the electron donor layer. The highest mobility (5750 cm2/Vs at 16K) was measured in a sample with x=0.15 that had a sheet carrier density of 8.5×1012 cm−2. The undoped AlxGa1−xN layers have low background carrier concentrations and can be intentionally doped n-type using SiH4. The effect of intentional n-type doping of the AlxGa1−xN donor layer on the electrical properties of the 2DEG was studied in structures that included an undoped AlxGa1−xN spacer layer of varying thickness. Higher 2DEG mobilities were obtained when a 100Å thick undoped layer was included in the structure due to spatial separation of the 2DEG from ionized impurities in the doped AlxGa1−xN. These initial results demonstrate that the electrical properties of AlxGa1−xN/GaN heterostructures can be controlled by intentional doping and appropriate layer design.