Plasma-Assisted MOCVD Growth of Non-Polar GaN and AlGaN on Si(111) Substrates Utilizing GaN-AlN Buffer Layer

Pepen Arifin,Agus Subagio,Sugianto Sugianto,Heri Sutanto

doi:10.3390/coatings12010094

Pepen Arifin, Agus Subagio + Show 2 more

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https://doi.org/10.3390/coatings12010094

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Abstract

We report the growth of non-polar GaN and AlGaN films on Si(111) substrates by plasma-assisted metal-organic chemical vapor deposition (PA-MOCVD). Low-temperature growth of GaN or AlN was used as a buffer layer to overcome the lattice mismatch and thermal expansion coefficient between GaN and Si(111) and GaN’s poor wetting on Si(111). As grown, the buffer layer is amorphous, and it crystalizes during annealing to the growth temperature and then serves as a template for the growth of GaN or AlGaN. We used scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) characterization to investigate the influence of the buffer layer on crystal structure, orientation, and the morphology of GaN. We found that the GaN buffer layer is superior to the AlN buffer layer. The thickness of the GaN buffer layer played a critical role in the crystal quality and plane orientation and in reducing the cracks during the growth of GaN/Si(111) layers. The optimum GaN buffer layer thickness is around 50 nm, and by using the optimized GaN buffer layer, we investigated the growth of AlGaN with varying Al compositions. The morphology of the AlGaN films is flat and homogenous, with less than 1 nm surface roughness, and has preferred orientation in a-axis.

Highlights

The unique properties of GaN and related III-nitrides, such as direct wide-bandgap, high thermal stability, and high voltage breakdown, have attracted interest
The buffer layer was deposited with different growth times, resulting in different GaN and AlN thicknesses
The morphology of GaN without a buffer layer appears to be dominated by hexagonal islands separated by about 0.2–0.6 μm

Summary

Introduction

The unique properties of GaN and related III-nitrides, such as direct wide-bandgap, high thermal stability, and high voltage breakdown, have attracted interest. These properties make them suitable for use as visible and ultraviolet optoelectronic devices and high-power and high-frequency electronic devices [1,2,3]. GaN-based devices are usually made on sapphire substrates and grown in a c-axis oriented wurtzite epilayer using various techniques such as molecular-beam epitaxy (MBE) and MOCVD. Heat generated in GaN-based devices with sapphire as a substrate cannot be dissipated quickly, causing degrading device performance and shortening of a lifetime. Internal spontaneous and piezoelectric polarization processes in GaNbased heterostructures can generate a significant electric field at the nitrides interface causes increasing the radiative lifetime [5] and lowering quantum efficiency [6]

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