Aluminum nitride (AlN) exhibits large breakdown electric fields and high thermal conductivity which allows for excellent miniaturization and power density in high-power electronics.
In this talk, we investigate normally-off vertical n-channel trench MISFETs, with the channel consisting of nominally undoped graded AlGaN. The graded AlGaN layer creates immobile volume charges, and the lack of impurities reduces impurity scattering. The n-doped drift layer is composed of AlN for optimum electric field management. Contacts are placed on AlGaN for low ohmic resistance. Using TCAD simulations, the physics of device operation is studied. For comparison, a conventional impurity-doped FET without PID is taken as reference device. The simulations encompass calculation of local strain, solution of the Poisson-equation and electron and hole continuity equation on a 2-dimensional cross-section of the device. Transfer characteristics, threshold voltage, on-resistance and electric field are discussed. Surface states and interface charges at the nonpolar trench sidewall are included in the study. Finally, technological implementation and experimental results are discussed.
KEYWORDS: Gallium nitride, Temperature metrology, Luminescence, Diffusion, Visualization, Spatial resolution, Scanning electron microscopy, Line scan image sensors, Excitons, Electron microscopes
A lateral p+n GaN junction with a 10 µm drift layer has been characterized by combined Cathodoluminescence (CL) and Electron-Beam-Induced Current (EBIC) measurements performed at different temperatures. A vertical CL linescan across the pn-junction shows the evolution of luminescence in growth direction. The distinct changes of local emission in the space charge region are correlated with temperature dependent EBIC profiles. In particular in the drift zone, a mono-exponential behavior with a large characteristic length was observed. These profiles are correlated to the calculated band profiles for quantifying the evolution of electrical fields in the space charge region and drift zone.
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