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Optical properties of AlGaN/GaN epitaxial layers grown on free-standing Ga-face and N-face GaN substrates
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.ORCID-id: 0000-0002-2597-3322
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska högskolan.
Visa övriga samt affilieringar
2015 (Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

Comparative studies have been made on AlGaN/GaN epitaxial layers grown by metalorganic chemical vapor deposition on both Ga- and N-face free-standing GaN substrates fabricated by halide vapor phase epitaxy. By time-resolved photoluminescence studies, we conclude that two-dimensional electron gas (2DEG) only appears for heterostructures grown on Ga-face. We studied the temporal behavior of the 2DEG emission, which correlates well with recombination processes in an asymmetric triangular potential well formed by an AlGaN/GaN structure grown in [0001] direction.

Ort, förlag, år, upplaga, sidor
2015.
Nationell ämneskategori
Fysik Fysikalisk kemi
Identifikatorer
URN: urn:nbn:se:liu:diva-118114OAI: oai:DiVA.org:liu-118114DiVA, id: diva2:813234
Tillgänglig från: 2015-05-22 Skapad: 2015-05-22 Senast uppdaterad: 2015-09-22Bibliografiskt granskad
Ingår i avhandling
1. CVD solutions for new directions in SiC and GaN epitaxy
Öppna denna publikation i ny flik eller fönster >>CVD solutions for new directions in SiC and GaN epitaxy
2015 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis aims to develop a chemical vapor deposition (CVD) process for the new directions in both silicon carbon (SiC) and gallium nitride (GaN) epitaxial growth. The properties of the grown epitaxial layers are investigated in detail in order to have a deep understanding.

SiC is a promising wide band gap semiconductor material which could be utilized for fabricating high-power and high-frequency devices. 3C-SiC is the only polytype with a cubic structure and has superior physical properties over other common SiC polytypes, such as high hole/electron mobility and low interface trap density with oxide. Due to lack of commercial native substrates, 3C-SiC is mainly grown on the cheap silicon (Si) substrates. However, there’s a large mismatch in both lattice constants and thermal expansion coefficients leading to a high density of defects in the epitaxial layers. In paper 1, the new CVD solution for growing high quality double-position-boundaries free 3C-SiC using on-axis 4H-SiC substrates is presented. Reproducible growth parameters, including temperature, C/Si ratio, ramp-up condition, Si/H2 ratio, N2 addition and pressure, are covered in this study.

GaN is another attractive wide band gap semiconductor for power devices and optoelectronic applications. In the GaN-based transistors, carbon is often exploited to dope the buffer layer to be semi-insulating in order to isolate the device active region from the substrate. The conventional way is to use the carbon atoms on the gallium precursor and control the incorporation by tuning the process parameters, e.g. temperature, pressure. However, there’s a risk of obtaining bad morphology and thickness uniformity if the CVD process is not operated in an optimal condition. In addition, carbon source from the graphite insulation and improper coated graphite susceptor may also contribute to the doping in a CVD reactor, which is very difficult to be controlled in a reproducible way. Therefore, in paper 2, intentional carbon doping of (0001) GaN using six hydrocarbon precursors, i.e. methane (CH4), ethylene (C2H4), acetylene (C2H2), propane (C3H8), iso-butane (i-C4H10) and trimethylamine (N(CH3)3), have been explored. In paper 3, propane is chosen for carbon doping when growing the high electron mobility transistor (HEMT) structure on a quarter of 3-inch 4H-SiC wafer. The quality of epitaxial layer and fabricated devices is evaluated. In paper 4, the behaviour of carbon doping using carbon atoms from the gallium precursor, trimethylgallium (Ga(CH3)3), is explained by thermochemical and quantum chemical modelling and compared with the experimental results.

GaN is commonly grown on foreign substrates, such as sapphire (Al2O3), Si and SiC, resulting in high stress and high threading dislocation densities. Hence, bulk GaN substrates are preferred for epitaxy. In paper 5, the morphological, structural and luminescence properties of GaN epitaxial layers grown on N-face free-standing GaN substrates are studied since the N-face GaN has advantageous characteristics compared to the Ga-face GaN. In paper 6, time-resolved photoluminescence (TRPL) technique is used to study the properties of AlGaN/GaN epitaxial layers grown on both Ga-face and N-face free-standing GaN substrates. A PL line located at ~3.41 eV is only emerged on the sample grown on the Ga-face substrate, which is suggested to associate with two-dimensional electron gas (2DEG) emission.

Ort, förlag, år, upplaga, sidor
Linköping: Linköping University Electronic Press, 2015. s. 50
Serie
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1654
Nyckelord
CVD, SiC, GaN, epitaxy
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:liu:diva-117878 (URN)10.3384/diss.diva-117878 (DOI)978-91-7519-084-6 (ISBN)
Disputation
2015-06-11, Schrödinger, Fysikhuset, Campus Valla, Linköping, 10:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2015-05-22 Skapad: 2015-05-12 Senast uppdaterad: 2019-11-15Bibliografiskt granskad

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