Abstract
GaN-based light-emitting diodes (LEDs) have been widely accepted as highly efficient solid-state light sources capable of replacing conventional incandescent and fluorescent lamps. However, their applications are limited to small devices because their fabrication process is expensive as it involves epitaxial growth of GaN by metal-organic chemical vapor deposition (MOCVD) on single crystalline sapphire wafers. If a low-cost epitaxial growth process such as sputtering on a metal foil can be used, it will be possible to fabricate large-area and flexible GaN-based light-emitting displays. Here we report preparation of GaN films on nearly lattice-matched flexible Hf foils using pulsed sputtering deposition (PSD) and demonstrate feasibility of fabricating full-color GaN-based LEDs. It was found that introduction of low-temperature (LT) grown layers suppressed the interfacial reaction between GaN and Hf, allowing the growth of high-quality GaN films on Hf foils. We fabricated blue, green, and red LEDs on Hf foils and confirmed their normal operation. The present results indicate that GaN films on Hf foils have potential applications in fabrication of future large-area flexible GaN-based optoelectronics.
Highlights
GaN and the related group III nitrides are key materials in high-efficiency LEDs1, 2
Recent progress in the epitaxial growth process based on pulsed sputtering deposition (PSD) has made it possible to grow high-quality group III nitride epitaxial films even at room temperature (RT)[14,15,16,17,18] because of the highly energetic group III atoms during PSD growth
X-ray diffraction (XRD) measurements were performed to investigate the structural properties of the Hf foil before and after annealing
Summary
The annealed Hf foils were introduced into a PSD chamber with a background pressure below 5 × 10−10 torr for nitride film growth. We prepared 1-μm-thick GaN films at 700 °C with LT-grown reaction barrier layers composed of 100-nm-thick AlN and 50-nm-thick HfN layers. The structural properties of the GaN films were characterized by XRD using a Bruker D8 diffractometer and by EBSD using an INCA Crystal EBSD system connected to the SEM apparatus. Five periods of InGaN (3 nm)/GaN (10 nm) MQWs were grown on a 1-μm-thick n-type GaN layer and topped by a 0.2-μm-thick Mg-doped p-type GaN layer. These layers were grown in a temperature range from 400 to 700 °C16. In and Pd/Au electrodes were deposited on the n- and p-GaN layers, respectively, by e-beam evaporation to form ohmic contacts
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