Annealing effects on electrical, structural, and surface morphological properties of Ir/n-InGaN Schottky structures

The effects of thermal annealing on electrical and structural characteristics of iridium (Ir) Schottky contacts to n-type InGaN have been studied using current-voltage (I-V), capacitance-voltage (C-V), secondary ion mass spectrometer (SIMS), and X-ray diffraction (XRD) measurements. Measurements showed that the Schottky barrier height (SBH) of as-deposited sample is 0.79 eV (I-V) and 1.07 eV (C-V). It is observed that the barrier height increases to 0.85 eV (I-V) and 1.21 eV (C-V) after annealing at 300 °C for 1 min in N ₂ ambient. However, it is found that the SBH slightly decreases when the contacts are annealed at 400 and 500 °C and the corresponding values are 0.84 eV (I-V), 1.17 eV (C-V) for 400 °C and 0.80 eV (I-V), 1.11 eV (C-V) for 500 °C, respectively. Using Cheung's functions, the barrier height (ψ _b), ideality factor (n), and series resistance (R _s) are also calculated. From the above results, it is clear that the optimum annealing temperature for Ir Schottky contact is 300 °C. SIMS and XRD results shows that the formation of gallide phases at Ir/n-InGaN interfaces could be the reason for variation in the SBHs upon annealing at elevated temperatures. Atomic force microscopy (AFM) results show that the overall surface morphology of Ir Schottky contacts on n-InGaN stays reasonably smooth. These results make Ir Schottky contacts attractive for high-temperature device applications.