Enhanced Current Transport and Injection in Thin-Film Gallium-Nitride Light-Emitting Diodes by Laser-Based Doping

Abstract

This paper reports improvements in the electrical and optical properties of blue-emission gallium nitride (GaN)-based thin-film light-emitting diodes (TFLEDs) after laser-based Si doping (LBSD) of a nitrogen-face n-GaN (denoted as hereafter n-GaN) layer. Experimental results show that the light-output powers of the flat- and rough-surface TFLEDs after LBSD are 52.1 and 11.35% higher than those before LBSD, respectively, at a current of 350 mA, while the corresponding operating voltages are decreased by 0.22 and 0.28 V for the flat- and rough-surface TFLEDs after LBSD, respectively. The reduced operating voltage after LBSD of the top n-GaN layer may result from the remarkably decreased specific contact resistance at the metal/n-GaN interface and the low series resistance of the TFLED device. The LBSD of n-GaN increases the number of nitrogen vacancies, and Si substitutes for Ga (SiGa) at the metal/n-GaN interface to produce highly Si-doped regions in n-GaN, leading to a decrease in the Schottky barrier height and width. As a result, the specific contact resistances are significantly decreased to 1.56 × 10(-5) and 2.86 × 10(-5) Ω cm(2) for the flat- and rough-surface samples after LBSD, respectively. On the other hand, the increased light-output power after LBSD can be explained by the uniform current spreading, efficient current injection, and enhanced light scattering resulting from the low contact resistivity, low lateral current resistance, and additional textured surface, respectively. Furthermore, LBSD did not degrade the electrical properties of the TFLEDs owing to low reverse leakage currents. The results indicate that our approach could potentially enable high-efficiency and high-power capabilities for optoelectronic devices.

Dopant-Tunable Ultrathin Transparent Conductive Oxides for Efficient Energy Conversion Devices

“…One promising way to solve these problems is to dope the surfaces of electrodes with donors or acceptors, through co-sputtering [18], ion implantation [19], or optical excitation [20], during the fabrication process. However, with conventional doping methods, we cannot independently control the electrical and optical properties of TCOs.…”

“…For instance, the transmittance of TCOs decreases as the doping concentration increases, or vice versa [21]. Moreover, the doping process by co-sputtering is known to be quite sensitive to the material composition and applied power [18], whereas the other two methods require a costly external high-power source for dopant injection [19,20]. Therefore, it is important to find a way of tailoring the WF of ultrathin TCOs without compromising their innate electrical and optical properties.…”