Influence of different aspect ratios on the structural and electrical properties of GaN thin films grown on nanoscale-patterned sapphire substrates

Fang Wei Lee, Wen Cheng Ke*, Chun Hong Cheng, Bo Wei Liao, Wei-Kuo Chen

*Corresponding author for this work

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

This study presents GaN thin films grown on nanoscale-patterned sapphire substrates (NPSSs) with different aspect ratios (ARs) using a homemade metal-organic chemical vapor deposition system. The anodic aluminum oxide (AAO) technique is used to prepare the dry etching mask. The cross-sectional view of the scanning electron microscope image shows that voids exist between the interface of the GaN thin film and the high-AR (i.e. ∼2) NPSS. In contrast, patterns on the low-AR (∼0.7) NPSS are filled full of GaN. The formation of voids on the high-AR NPSS is believed to be due to the enhancement of the lateral growth in the initial growth stage, and the quick-merging GaN thin film blocks the precursors from continuing to supply the bottom of the pattern. The atomic force microscopy images of GaN on bare sapphire show a layer-by-layer surface morphology, which becomes a step-flow surface morphology for GaN on a high-AR NPSS. The edge-type threading dislocation density can be reduced from 7.1 × 10 8 cm -2 for GaN on bare sapphire to 4.9 × 10 8 cm -2 for GaN on a high-AR NPSS. In addition, the carrier mobility increases from 85 cm 2 /Vs for GaN on bare sapphire to 199 cm 2 /Vs for GaN on a high-AR NPSS. However, the increased screw-type threading dislocation density for GaN on a low-AR NPSS is due to the competition of lateral growth on the flat-top patterns and vertical growth on the bottom of the patterns that causes the material quality of the GaN thin film to degenerate. Thus, the experimental results indicate that the AR of the particular patterning of a NPSS plays a crucial role in achieving GaN thin film with a high crystalline quality.

Original languageEnglish
Pages (from-to)223-229
Number of pages7
JournalApplied Surface Science
Volume375
DOIs
StatePublished - 1 Jul 2016

Keywords

  • Anodic aluminum oxide
  • Aspect ratio
  • GaN
  • Nanoscale-patterned sapphire substrate

Fingerprint Dive into the research topics of 'Influence of different aspect ratios on the structural and electrical properties of GaN thin films grown on nanoscale-patterned sapphire substrates'. Together they form a unique fingerprint.

  • Cite this