Efficiency improvement of GaN-based ultraviolet light-emitting diodes with reactive plasma deposited AlN nucleation layer on patterned sapphire substrate.

Chia-Yu Lee,Gou-Chung Chi,Chun-Yen Chang,Chi-Hsiang Chen,Bing-Cheng Lin,Ray-Ming Lin,Ching-Hsueh Chiu,Hao-Chung Kuo,An-Jye Tzou,Yu-Pin Lan

doi:10.1186/1556-276x-9-505

Abstract

The flip chip ultraviolet light-emitting diodes (FC UV-LEDs) with a wavelength of 365 nm are developed with the ex situ reactive plasma deposited (RPD) AlN nucleation layer on patterned sapphire substrate (PSS) by an atmospheric pressure metal-organic chemical vapor deposition (AP MOCVD). The ex situ RPD AlN nucleation layer can significantly reduce dislocation density and thus improve the crystal quality of the GaN epitaxial layers. Utilizing high-resolution X-ray diffraction, the full width at half maximum of the rocking curve shows that the crystalline quality of the epitaxial layer with the (RPD) AlN nucleation layer is better than that with the low-temperature GaN (LT-GaN) nucleation layer. The threading dislocation density (TDD) is estimated by transmission electron microscopy (TEM), which shows the reduction from 6.8 × 107 cm−2 to 2.6 × 107 cm−2. Furthermore, the light output power (LOP) of the LEDs with the RPD AlN nucleation layer has been improved up to 30 % at a forward current of 350 mA compared to that of the LEDs grown on PSS with conventional LT-GaN nucleation layer.

Highlights

The emission wavelength of GaN-based semiconductor, a directly transitional wide bandgap material, is theoretically capable of covering the whole visible spectrum from UV to IR, and GaN-based semiconductors attract considerable attention due to their continuously expanding applications for optoelectronic devices, such as light emitting diodes (LEDs) and laser diodes (LDs) [1,2]
We demonstrated an UV-LEDs with an ex situ reactive plasma deposited (RPD) AlN nucleation layer on patterned sapphire substrate (PSS)
The better crystallinity of GaN with RPD AlN nucleation layer compared to that with low-temperature GaN (LT-GaN) nucleation layer is confirmed by the XRD spectra

Summary

Introduction

The emission wavelength of GaN-based semiconductor, a directly transitional wide bandgap material, is theoretically capable of covering the whole visible spectrum from UV to IR, and GaN-based semiconductors attract considerable attention due to their continuously expanding applications for optoelectronic devices, such as light emitting diodes (LEDs) and laser diodes (LDs) [1,2]. The applications of UV-LEDs with emission wavelengths of about 365 nm are widely expanding, such as in sterilization, medicine, biochemistry, water purification system, light sources for optical recording, fluorescence analyzer, biological sensor, and air purification systems. We demonstrated an UV-LEDs with an ex situ reactive plasma deposited (RPD) AlN nucleation layer on PSS. Comparing the RF sputtering system, the RPD system utilizes a lower bias voltage (15 ~ 20 V), and the distance between the target and the sample is longer. It is practical for avoiding the substrate from being damaged. Systematic experiments and investigations have been described in detail, which showed an up to 30 % output performance increase by using RPD AlN nucleation layer on PSS

Methods

Results

Conclusion