Abstract
This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.
Highlights
GaN is a direct wide band gap (3.4 eV) semiconductor with high electronic mobility and high melting temperature (2,500 oC)[1]
A new reactive sputtering setup dedicated to GaN and related compounds is presented
Its special features allowed the growth of GaN films onto Si substrates kept at relatively low temperature (400°C), using a liquid Ga target and Ar + N2 plasma
Summary
GaN is a direct wide band gap (3.4 eV) semiconductor with high electronic mobility and high melting temperature (2,500 oC)[1]. Temperatures below 600 oC strongly favor a preferential growth of the crystalline axis c, that is, in the direction[10] This is a great advantage since obtaining high-quality crystalline and electronic-grade GaN is almost always linked to the use of sapphire (Al2O3) and/or silicon carbide (SiC) substrates, which are offered in small sizes and at extremely high prices. In this sense, the growth of GaN onto silicon substrates[11,12,13,14] stands out among efforts to reduce costs and increase compatibility with current technologies[15]. Known to obtain generally amorphous or polycrystalline films, the reactive sputtering has recently achieved GaN and AlN epitaxial films[16,17,18,19,20,21]
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