Self-assembled Multilayers of Silica Nanospheres for Defect Reduction in Non- and Semipolar Gallium Nitride Epitaxial Layers.

Tongtong Zhu,Fengzai Tang,Stoyan K Smoukov,Andrew J Shields,Yisong Han,Menno J Kappers,Rachel A Oliver,Muhammad Ali,Tao Ding,Tom Badcock

doi:10.1021/acs.cgd.5b01560

Tongtong Zhu, Fengzai Tang + Show 8 more

Open Access

https://doi.org/10.1021/acs.cgd.5b01560

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Abstract

Non- and semipolar GaN have great potential to improve the efficiency of light emitting devices due to much reduced internal electric fields. However, heteroepitaxial GaN growth in these crystal orientations suffers from very high dislocation and stacking faults densities. Here, we report a facile method to obtain low defect density non- and semipolar heteroepitaxial GaN via selective area epitaxy using self-assembled multilayers of silica nanospheres (MSN). Nonpolar (11–20) and semipolar (11–22) GaN layers with high crystal quality have been achieved by epitaxial integration of the MSN and a simple one-step overgrowth process, by which both dislocation and basal plane stacking fault densities can be significantly reduced. The underlying defect reduction mechanisms include epitaxial growth through the MSN covered template, island nucleation via nanogaps in the MSN, and lateral overgrowth and coalescence above the MSN. InGaN/GaN multiple quantum wells structures grown on a nonpolar GaN/MSN template show more than 30-fold increase in the luminescence intensity compared to a control sample without the MSN. This self-assembled MSN technique provides a new platform for epitaxial growth of nitride semiconductors and offers unique opportunities for improving the material quality of GaN grown on other orientations and foreign substrates or heteroepitaxial growth of other lattice-mismatched materials.

Highlights

GaN-based light emitting diodes (LEDs) have attracted a significant amount of attention over the past decade, owing to their high optical efficiency in the blue to UV spectral range.Most research and commercial products utilize the conventional polar c-plane orientation
Silica nanospheres (d = ∼180 nm) dispersed in ethanol were subsequently coated onto the GaN seed layer using convective assembly with a varying deposition rate, which can result in the controlled formation of a monolayer (ML) or multilayers of silica nanospheres.[15]
Epitaxial integration of self-assembled multilayers of silica nanospheres in heteroepitaxial growth of non- and semipolar GaN is demonstrated as a new defect reduction technique, which reduces the dislocations down to cm−2 and ∼3 × cm−2, respectively, and allows us to significantly reduce the basal plane stacking faults (BSFs) density by more than an order of magnitude in both cases

Summary

INTRODUCTION

GaN-based light emitting diodes (LEDs) have attracted a significant amount of attention over the past decade, owing to their high optical efficiency in the blue to UV spectral range. In situ defect reduction schemes, such as the application of low-temperature GaN nucleation layers (NLs)[6] or AlN NLs,[7] the use of silicon nitride[8] or scandium nitride interlayers,[9] followed by three-dimensional (3D) growth and coalescence, direct growth without a lowtemperature NL,[10] and very high silicon doping[11] can only reduce the dislocation density down to the 109 cm−2 regime, while the BSF density remains well above 105 cm−1 Ex situ methods, such as epitaxial lateral overgrowth (ELOG) or the Received: November 4, 2015 Revised: December 22, 2015 Published: December 29, 2015. The MSN masking technique is applied to the epitaxial growth of semipolar (11−22) GaN, and, here too, significant defect reduction is achieved

RESULTS AND DISCUSSION

CONCLUSION

EXPERIMENTAL SECTION

■ ACKNOWLEDGMENTS

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