Flat GaN Epitaxial Layers Grown on Si(111)by Metalorganic Vapor Phase Epitaxy Using Step-Graded AIGaN Intermediate Layers

摘要

In this work,we report on the growth by metalorganic vapor phase epitaxy (MOVPE)of GaN layers on AlN/Si(111)templates with step-graded AlGaN intermediate layers.First,we will discuss the optimization of the AlN/Si(lll)templates and then we will discuss the incorporation of step-graded AIGaN intermediate layers.It is found that the growth stress in GaN on high-temperature (HT)AlN/Si(lll)templates is compressive,although,due to relaxation,the stress we have measured is much lower than the theoretical value.In order to prevent the stress relaxation,step-graded AlGaN layers are introduced and a crack-free GaN epitaxial layer of thickness > 1 mu m is demonstrated.Under optimized growth conditions,the total layer stack,exceeding 2 mum in total,is kept under compressive stress,and the radius of the convex wafer bowing is as large as 119 m.The crystalline quality of the GaN layers is examined by high-resolution x-ray diffraction (HR-XRD),and the full-width-at-half maximums (FWHMs)of the x-ray rocking curve (0002)omega-scan and (-1015)omega-scan are 790 arc sec and 730 arc sec,respectively.It is found by cross-sectional trans-mission electron microscopy (TEM)that the step-graded AIGaN layers termi-nate or bend the dislocations at the interfaces.