Graphene Schottky barrier diode acting as a semi-transparent contact to n-GaN

In this letter, we demonstrate the successful development of graphene Schottky barrier diodes (Gr SBDs), which act as an efficient semi-transparent contact to n-GaN. We show that Gr SBDs can be used for deep trap investigations in n-GaN by capacitance-based spectroscopic techniques. To demonstrate its functionality, Gr Schottky barrier diodes on an n-GaN sample grown by the metal organic vapor phase technique were fabricated and then used in the measurements of steady-state photo-capacitance (SSPC) and deep level optical spectroscopy (DLOS). It is shown that the SSPC and DLOS spectra obtained for Gr SBDs are in excellent agreement with Ni-based semi-transparent contacts to n-GaN used in this study for comparison. Deep trap levels located at Ec-3.3 eV, Ec-2.6 eV, and Ec-1.84 eV for Ni SBD and Ec-3.3 eV and Ec-2.6 eV for Gr SBD were found, respectively. The presence of a trap level with Ec-1.84 eV observed only in the Ni SBD samples suggests that this trap originates from different sample treatments prior to Schottky contact deposition. Additionally, the optical capture cross-section data (σ0) derived from DLOS were fitted using the Lucovsky model under the assumption of no lattice relaxation for all deep traps observed in this study. Discrepancies in trap concentration derived from SSPC measurements among different diodes for a trap with EC-3.3 eV were attributed to reduced light transmission through the Gr contact in the UV spectral range and the presence of some macroscopic defects related to Gr transfer to the n-GaN film.