(a) Schematic cross section of the InGaN/GaN Schottky diode and (b) the Nomarski optical microscopy top view of a real diode with surface micromesas.
Nomarski optical microscopy images of (a) HP_InGaN/GaN, (b) LP_InGaN/GaN, (c) HP_GaN, and (d) LP_GaN. The inset in (b) is a zoom-in image of one surface micromesa.
Representative SEM and AFM (tapping mode) micrographs of the surface micromesas. (a) A SEM micrograph; (b) an AFM micrograph; (c) 3-D AFM micrograph of (b); and (d) surface profile along the line shown in (b). (b)-(d) are from the same micromesa and (a) is from a different one. Numbers in (b) indicate the resolvable spiral steps.
10 × 10 μm2 AFM images of (a) HP_InGaN/GaN, (b) surface profile along the line in (a), (c) LP_InGaN/GaN, and (d) surface profile along the line in (c) after H3PO4 etch.
Surface micromesa mapping by Nomarski optical microscopy. (a) Surface micromesas before etch and (b) etch pits in the same area of a LP_InGaN/GaN sample. (c) A schematic superposition of image (a) and (b). The inset in (b) is a representative SEM image of a large etch pit shown in (b). The circles and dots in (c) represent the surface micromesas and nanopipe-related etch pits, respectively.
An AFM (tapping mode) micrograph of surface micromesas with and without nanopipes at the center. The inset is a SEM image of a nanopipe without formation of a surface micromesa on the InGaN/GaN sample.
Leakage current at a reverse bias of 30 V versus diode diameter for LP_InGaN/GaN and HP_InGaN/GaN Schottky diodes. The black dashed lines have slope of two and the color dashed curves represent the trend of measured data points.
Leakage current at a reverse bias of 30 V versus micromesa number on the smallest (17-μm diameter) LP_InGaN/GaN and HP_InGaN/GaN Schottky diodes.
Representative forward IV curves for the smallest (17-μm diameter) Ni-InGaN/GaN Schottky barriers (a) without surface micromesas and (b) with surface micromesas. The red dots are measured data and the solid black curves are calculated thermionic emission (TE) currents. In (b), the green and pink dashed curves represent the calculated TE currents for micromesas and InGaN/GaN, respectively. The black solid curve is the summation of the two dashed curves. The inset is the equivalent circuit diagram of the InGaN/GaN Schottky diodes with surface micromesas.
Representative reverse-bias IV curves for the smallest (17-μm diameter) Ni-InGaN/GaN Schottky barriers (a) without surface micromesas and (b) with surface micromesas. The red dots are measurement data and the solid curves are calculated tunneling currents. In (b), the green curve is calculated tunneling current for micromesas and the pink curve is calculated tunneling current for InGaN/GaN.
RBS spectra of as-deposited, annealed at 200 °C for 60 min, 500 °C for 24 min, and 625 °C for 15 min Ni-InGaN/GaN samples. The inset on the left shows the zoom-in spectra and the inset on the right is a schematic diagram of the inter-diffusion at the Ni-InGaN interface.
Leakage current at a reverse bias of 30 V versus diode diameter for LP_InGaN/GaN and HP_InGaN/GaN Schottky diodes before and after annealing at different temperatures.
Sample labels and key growth details used in this work (the coalescence time for HP buffer and LP buffer is ∼50 min and ∼10 min, respectively; the growth rate for HP buffer an LP buffer is ∼0.52 nm/s and ∼0.46 nm/s, respectively; and the InGaN growth rate is ∼0.0326 nm/s).
FWHM of symmetric (0002) and asymmetric (10 2) XRCs, surface micromesa density estimated under Nomarski optical microscopy and nanopipe and TD densities estimated by EPD in all samples.
Values of the key parameters used for all calculations in this work (the other parameters used in the calculations but not listed here are all theoretical physical constants, e.g., q, k, etc.).
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