Growth, Doping and Characterization of Al x Ga 1-x N Thin Film Alloys on 6H-SiC(0001) Substrates
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Internet Journal o f
Nitride S emiconductor Research
Volume 1, Article 8
Growth, Doping and Characterization of AlxGa1-xN Thin Film Alloys on 6H-SiC(0001) Substrates M. D. Bremser, W. G. Perry, T. Zheleva, N. V. Edwards, O. H. Nam Department of Materials Science and Engineering, North Carolina State University N. Parikh University of North Carolina at Chapel Hill Department of Physics and Astronomy D. E. Aspnes Department of Physics, North Carolina State University Robert F. Davis Department of Materials Science and Engineering, North Carolina State University This article was received on July 23, 1996 and accepted on September 10, 1996.
Abstract Thin films of Alx Ga1-xN (0.05 ≤ x ≤ 0.96) having smooth surfaces were deposited directly on both vicinal and on-axis 6H-SiC(0001) substrates. Cross-sectional TEM of Al 0.13Ga0.87N revealed stacking faults near the SiC/Nitride alloy interface and numerous threading dislocations. EDX, AES and RBS were used to determine the compositions, which were paired with their respective CL near band-edge emission energies. A negative bowing parameter was determined. The CL emission energies were similar to the bandgap energies obtained by SE. FE-AES of the initial growth of Al0.2Ga0.8N revealed an aluminum rich layer near the interface. N-type (silicon) doping was achieved for Alx Ga1-xN for 0.12 ≤ x ≤ 0.42. Al0.2Ga0.8N/GaN superlattices were fabricated with coherent interfaces. Additionally, HEMT structures using an AlN/GaN/AlN buffer structure were fabricated.
1. Introduction The potential and employment of III-Nitride materials for both optoelectronic and microelectronic applications has stimulated significant research. [1] The wurtzitic phase of GaN forms continuous solid solutions with InN and AlN such that bandgap engineering is possible from 1.95 eV to 6.2 eV. When alloyed solely with AlN, materials having bandgaps from 3.4 eV to 6.2 eV are possible. This makes Alx Ga1-xN attractive for both ultraviolet emitters and detectors as well as high-power and high-frequency microelectronic applications. Single crystal GaN substrates are currently available in very limited quantities only via high pressure, high temperature processes. [2] As such, heteroepitaxy is the dominant growth process, and c-plane sapphire is the most commonly employed substrate. In order to accommodate the large lattice mismatch between GaN and sapphire, nitridation of the latter followed by the deposition of a low temperature amorphous GaN or AlN buffer layer is conducted prior to GaN film growth. [3] [4] This buffer layer is subsequently annealed to form a textured polycrystalline template upon which the GaN is deposited. Grain orientation competition in the GaN film occurs during the first 0.5 microns of growth which results in the formation of low angle grain boundaries which persist throughout the entire epitaxial layer. [5] Substantial concentrations of threading dislocations exist near the film/buffer layer interface, some of which are annihilated by intersection within the film. As such, the growth
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