Electrical parameters of Au/n-GaN and Pt/n-GaN Schottky diodes

Abstract Electrical properties of Si-doped GaN epitaxial layers, grown on a c-plane sapphire substrate by MOCVD to form Schottky diodes with Gold (Au) and platinum (Pt) and using Ti/Al/Au as Ohmic contact, are investigated. Characterization was performed through I-V and C-V-f measurements at room temperature. Schottky barrier height (Φ_b), ideality factor (n), and series resistance (R_s) were extracted from forward I-V characteriztics using Cheung and Lien methods. Φ_b, doping concentration (N_d) and R_s frequency dependence were extracted from C-V-f characteriztics. Pt/n-GaN shows a non-linear behavior with a barrier height of 0.63 eV, an ideality factor of 2.3, and series resistance of 63 Ω. Au/n-GaN behaves like two diodes in parallel with two barrier heights of (0.83 and 0.9 eV), two ideality factors of (5.8 and 3.18) and two series resistance of (10.6 and 68 Ω). Interface state properties in both samples have been investigated taking into account the bias dependence of the effective barrier height. The amount of stimulated traps along the energy-gap at the interface increases with voltage bias, which increases N_SS exponentially from 4.24 × 10¹³ to 3.67 × 10¹⁴ eV^-1 cm^-2 in the range (E_c - 0.17) to (E_c - 0.61) eV for Pt/n-GaN, and from 2.3 × 10¹³ to 1.14 × 10¹⁴ eV^-1 cm^-2, in the range (E_c - 0.31) to (E_c - 0.82) eV for Au/n-GaN. The values of interface states density and series resistance for both samples are found to decrease with increasing frequency. Peak intensity was a measure of active interface states. C-V-f results confirm the model of the Schottky diode with a native interfacial insulator layer along the space charge region.