Growth and characterizations of GaN micro-rods on graphene films for flexible light emitting diodes

Kunook Chung,Gyu-Chul Yi,Hyeonjun Beak,Youngbin Tchoe,Hyobin Yoo,Miyoung Kim,Hongseok Oh

doi:10.1063/1.4894780

Abstract

We report the growth of GaN micro-rods and coaxial quantum-well heterostructures on graphene films, together with structural and optical characterization, for applications in flexible optical devices. Graphene films were grown on Cu foil by means of chemical vapor deposition, and used as the substrates for the growth of the GaN micro-rods, which were subsequently transferred onto SiO2/Si substrates. Highly Si-doped, n-type GaN micro-rods were grown on the graphene films using metal–organic chemical vapor deposition. The growth and vertical alignment of the GaN micro-rods, which is a critical factor for the fabrication of high-performance light-emitting diodes (LEDs), were characterized using electron microscopy and X-ray diffraction. The GaN micro-rods exhibited promising photoluminescence characteristics for optoelectronic device applications, including room-temperature stimulated emission. To fabricate flexible LEDs, InxGa1–xN/GaN multiple quantum wells and a p-type GaN layer were deposited coaxially on the GaN micro-rods, and transferred onto Ag-coated polymer substrates using lift-off. Ti/Au and Ni/Au metal layers were formed to provide electrical contacts to the n-type and p-type GaN regions, respectively. The micro-rod LEDs exhibited intense emission of visible light, even after transfer onto the flexible polymer substrate, and reliable operation was achieved following numerous cycles of mechanical deformation.

Highlights

The preparation of high-quality inorganic compound semiconductors on polymer substrates represents a significant breakthrough in fabrication technology, which may enable next-generation optoelectronic devices that are flexible and can be manufactured using large-scale and low-cost processes.[1,2,3] A number of difficulties remain in the fabrication of high-quality compound semiconductors on polymer substrates
To prepare the graphene substrates, graphene films were synthesized on copper foil using chemical vapor deposition (CVD), and transferred onto supporting substrates of amorphous SiO2-coated Si (SiO2/Si) substrates
According to other previous research, vertical growth of nanostructures on CVD-grown graphene depends on the surface roughness of the graphene, and ledges or kinks in the graphene film act as nucleation sites and result in random growth directions.[14]

Summary

Introduction

The preparation of high-quality inorganic compound semiconductors on polymer substrates represents a significant breakthrough in fabrication technology, which may enable next-generation optoelectronic devices that are flexible and can be manufactured using large-scale and low-cost processes.[1,2,3] A number of difficulties remain in the fabrication of high-quality compound semiconductors on polymer substrates, . We demonstrate flexible LEDs by growing high-quality GaN micro-rods and coaxial quantum structures on graphene films, and transferring these structures onto polymer substrates.

Results

Conclusion