Effects of GaN/AlGaN/Sputtered AlN nucleation layers on performance of GaN-based ultraviolet light-emitting diodes

Hongpo Hu,Xingtong Liu,Chengqun Gui,Shengjun Zhou,Sheng Liu,Yilin Gao

doi:10.1038/srep44627

Hongpo Hu, Xingtong Liu + Show 4 more

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https://doi.org/10.1038/srep44627

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Journal: Scientific Reports	Publication Date: Mar 15, 2017
Citations: 96	License type: open-access

Affiliation: Wuhan University, Shanghai Jiao Tong University

Abstract

We report on the demonstration of GaN-based ultraviolet light-emitting diodes (UV LEDs) emitting at 375 nm grown on patterned sapphire substrate (PSS) with in-situ low temperature GaN/AlGaN nucleation layers (NLs) and ex-situ sputtered AlN NL. The threading dislocation (TD) densities in GaN-based UV LEDs with GaN/AlGaN/sputtered AlN NLs were determined by high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM), which revealed that the TD density in UV LED with AlGaN NL was the highest, whereas that in UV LED with sputtered AlN NL was the lowest. The light output power (LOP) of UV LED with AlGaN NL was 18.2% higher than that of UV LED with GaN NL owing to a decrease in the absorption of 375 nm UV light in the AlGaN NL with a larger bandgap. Using a sputtered AlN NL instead of the AlGaN NL, the LOP of UV LED was further enhanced by 11.3%, which is attributed to reduced TD density in InGaN/AlInGaN active region. In the sputtered AlN thickness range of 10–25 nm, the LOP of UV LED with 15-nm-thick sputtered AlN NL was the highest, revealing that optimum thickness of the sputtered AlN NL is around 15 nm.

Highlights

We report on the demonstration of GaN-based ultraviolet light-emitting diodes (UV LEDs) emitting at 375 nm grown on patterned sapphire substrate (PSS) with in-situ low temperature GaN/AlGaN nucleation layers (NLs) and ex-situ sputtered AlN NL
The threading dislocation (TD) densities in GaN-based UV LEDs with GaN/AlGaN/sputtered AlN NLs were determined by high-resolution X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM), which revealed that the TD density in UV LED with AlGaN NL was the highest, whereas that in UV LED with sputtered AlN NL was the lowest
We show that with AlGaN NL, the light output power (LOP) of UV LED is 18.2% higher compared to UV LED with GaN NL owing to a decrease in the absorption of 375 nm UV light in the AlGaN NL with a larger bandgap

Summary

Introduction

We report on the demonstration of GaN-based ultraviolet light-emitting diodes (UV LEDs) emitting at 375 nm grown on patterned sapphire substrate (PSS) with in-situ low temperature GaN/AlGaN nucleation layers (NLs) and ex-situ sputtered AlN NL. Light output power (LOP) of GaN-based UV LEDs has been greatly improved[7], the performance of GaN-based UV LEDs grown on sapphire substrate is still limited by the crystalline quality of GaN epilayers because of large mismatch in lattice constant and thermal expansion coefficient between GaN and sapphire substrate, leading to a high threading dislocations (TDs) density (107–1010 cm−2) in GaN epilayers[8,9] This high TD density would generate numerous non-radiative recombination centers, thereby deteriorating the optical and electrical properties of GaN-based devices[10,11]. We have further demonstrated that the thickness of sputtered AlN NL has a significant influence on crystalline quality, optical and electrical properties of UV LEDs

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