Low Resistance Indium-based Ohmic Contacts to N-face n-GaN for GaN-based Vertical Light Emitting Diodes

Abstract

We investigated the In-based ohmic contacts on Nitrogen-face (N-face) n-type GaN, as well as Ga-face n-type GaN, for InGaN-based vertical Light Emitting Diodes (LEDs). For this purpose, we fabricated Circular Transfer Length Method (CTLM) patterns on the N-face n-GaN that were prepared by using a laser-lift off method, as well as on the Ga-face n-GaN that were prepared by using a dry etching method. Then, In/transparent conducting oxide (TCO) and In/TiW schemes were deposited on the CTLM in order for low resistance ohmic contacts to form. The In/TCO scheme on the Ga-face n-GaN showed high specific contact resistance, while the minimum specific contact resistance was only 3 x 10(-2) Omega-cm(2) after annealing at 300 degrees C, which can be attributed to the high sheet resistance of the TCO layer. In contrast, the In/TiW scheme on the Ga-face n-GaN produced low specific contact resistance of 2.1x10(5) Omega-cm(2) after annealing at 500 degrees C for 1 min. In addition, the In/TiW scheme on the N-face n-GaN also resulted in a low specific contact resistance of 2.2x10(-4) Omega-cm(2) after annealing at 300 degrees C. These results suggest that both the Ga-face n-GaN and N-face n-GaN.