The Surface Morphology Evolution of GaN Nucleation Layer during Annealing and Its Influence on the Crystal Quality of GaN Films

Lin Shang,Bingshe Xu,Hengsheng Shan,Bin Han,Huican Ouyang,Qingming Liu,Shufang Ma,Xiaodong Hao

doi:10.3390/coatings11020188

Lin Shang, Bingshe Xu + Show 6 more

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https://doi.org/10.3390/coatings11020188

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Abstract

The surface morphology evolution of GaN nucleation layer (NL) after different annealing time has been investigated by atomic force microscope. The surface morphologies of GaN NL after different annealing time are island-like. It is observed that for 0-min annealing time sample nucleation islands (NIs) are high density and small in size which results in high dislocation density GaN films, while the samples with longer annealing time have low density and large size NIs which results in low dislocation density GaN films. The crystal structure of GaN NLs after different annealing time investigated by high-resolution X-ray diffraction indicates GaN NL is polycrystalline. During annealing, GaN nanocrystals misaligned with sapphire gradually disappear and GaN nanocrystals aligned with sapphire survive and grow up. Thus, the GaN NL surface has different NIs’ densities and sizes after different annealing time. The NL annealing time can effectively control the density and size of the NIs and further determine the GaN films crystal quality.

Highlights

The third-generation semiconductor GaN film materials have been widely used in solid-state lighting, semiconductor blue-green laser, transistor and microwave devices since a high-quality GaN film was successfully grown on sapphire substrate [1,2,3]
GaN grown on sapphire involves a nucleation layer (NL) grown at low temperature and the growth of a thick GaN grown at high temperature (HT) which is called two-step growth [4]
The GaN films with different NL annealing time were grown on c-plane sapphire substrate by TS300 metal organic chemical vapor deposition (MOCVD) system (Aixtron, Herzogenrath, Germany)

Summary

Introduction

The third-generation semiconductor GaN film materials have been widely used in solid-state lighting, semiconductor blue-green laser, transistor and microwave devices since a high-quality GaN film was successfully grown on sapphire substrate [1,2,3]. The role of GaN NL during annealing is to provide nucleation islands (NIs) for the GaN crystallites and to promote the lateral growth of the film. After the anealing of NL, the GaN NL will transform to three-dimensional (3D) NIs. Threading dislocations (TDs) are usually generated at the boundaries of NIs and inside the NIs. low density NIs are beneficial to reduce the TD density in GaN film during the lateral growth of 3D islands. High performance GaN coatings with low dislocation density are used as high-efficiency light emitting diodes and laser diodes.

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