Quarternary Matalorganic Vapor Phase Epitaxy system – QMOVPE

Principal Investigator: Dr. Tim Anderson

The deposition of thin films is central to the fabrication of electronic and optoelectronic devices. A commonly used method for depositing such films is chemical vapor deposition, CVD. The column III nitrides are wide band gap semiconductor that offers the most promise for providing both electronic (transistors) and optoelectronic (blue and ultraviolet light-emitting and laser diodes) devices with properties that exceed those of any other material. The University of Florida has several programs directed at the development of wide bandgap semiconductors. Metalorganic chemical vapor deposition, MOCVD, has been the preferred technique for he growth of GaN and related compounds. Quarternary Matalorganic Vapor Phase Epitaxy system – QMOVPE is used for thin films growth. This is RF heated low-pressure horizontal cold wall reactor with a tilted susceptor. The machine has the ability to accommodate four bubblers and five gas sources.

A summary of typical growth conditions is given below

• Growth Reactor - Water-cooled Reactor with a tilted horizontal susceptor
• Substrates - LiGaO2 (100), LiAlO2 (100), Si (111), AlN, SiC, ScMgAlO4 and (0001) a-Al2O3
• Precursors - TEGa, NH3
• Carrier gases - N2, H2 2.5-3.0 slm<
• Flow rates - TEGa- 50 sccm and NH3- 500 to 3000 sccm
• V/III Inlet molar ratio - 1000 to 5000
• Growth pressure - 40 to 760 Torr
• Growth temperature - 500 to 900°C
• Growth rate - 0.30 to 0.80 mm/h

Since a commercially available substrate matched in both lattice parameter and thermal expansion is not available, heteroepitaxially grown GaN films typically contain a dislocation density of approximately 10¹⁰ cm^-2. The most widely used substrates for III-V nitride epitaxy are sapphire and silicon carbide. A poor lattice match and difference in thermal expansion coefficients for these substrates usually leads to high dislocation densities, formation of threading defects, and residual strains which may affect both optical and electrical properties of devices. The ongoing effort to improve the GaN film properties has driven the research community to find better and alternative substrate materials. LiGaO₂ – lithium gallate and LiAlO₂ - lithium aluminate are gaining increasing attention as a potential substrates for GaN growth. Recently great interest has developed into the low cost alternative of silicon. In addition to the cost advantages, silicon is available in large quantities with high quality. The use of new substrates such as LiGaO₂ and LiAlO₂, as well as Si, are being investigated.

For more information, contact Dr. Tim Anderson: (352) 392-0882
http://www.che.ufl.edu/faculty/anderson/index.html

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