Morphological and microstructural evolution in the two-step growth of nonpolar a -plane GaN on r -plane sapphire

Qian Sun, Bo Hyun Kong, Christopher D. Yerino, Tsung Shine Ko, Benjamin Leung, Hyung Koun Cho, Jung Han

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Abstract

In this paper, we report a detailed study on the evolution of surface morphology and microstructure of nonpolar a -plane GaN (a-GaN) through controlled growth interruptions. Microscopy imaging shows that the two-step a-GaN growth went through a roughening-recovery process. The first-step growth (under high V/III and high pressure) produced a rough surface with tall mesas separated by voids. The second-step growth (under low V/III and low pressure) promoted the lateral growth and filled up the voids. Striations that formed during the island coalescence persisted throughout the second-step growth, but could be relieved by an additional third-step growth. The morphological evolution was explained according to the kinetic Wulff plots. The microstructure of the a-GaN films was investigated by transmission electron microscopy (TEM) and x-ray rocking curve analysis. Most of the extended defects observed in the plan-view TEM images were I1 type basal-plane stacking faults (BSFs) and their associated partial dislocations (PDs). It is found that the bending of PDs (at the inclined/vertical growth fronts) within the basal plane toward the m -axes was responsible for the substantial reduction in threading PDs and the increase in BSF dimension. Based on a careful correlation between the morphological evolution and the microstructure development, we proposed a model explaining the possible mechanisms for the great reduction in defect density during the two-step growth process.

Original languageEnglish
Article number123519
JournalJournal of Applied Physics
Volume106
Issue number12
DOIs
Publication statusPublished - 2009 Dec 1

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All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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