Magnesium Doping of GaN by Metalorganic Chemical Vapor Deposition
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MAGNESIUM DOPING OF GaN BY METALORGANIC CHEMICAL VAPOR DEPOSITION Hongqiang Lu and Ishwara Bhat ECSE department, Rensselaer Polytechnic Institute, Troy, NY12180, [email protected] ABSTRACT P-type GaN films were grown on sapphire substrates in a horizontal metalorganic chemical vapor deposition system using (C5H5 )2Mg (Cp 2Mg) as the p-dopant source. It is found that the acceptor concentration in the post-growth annealed GaN samples increases with the Mg flow rate and reaches a peak value of lxlO19 cm-3 at Mg flow rate of 0.84 }Lmo!/min. The films remain semi-insulating even after annealing when the Mg flow rate is higher than 1.08 jimol/min. The effects of annealing temperature and duration on the electrical properties of GaN are also investigated. The results confirm that a 800 'C, 30 minutes postgrowth annealing in N2 ambient is sufficient to activate most of the Mg atoms. In addition, study of rapid thermal annealing of Mg-doped GaN was carried out and the results show that the p-type acceptor concentration obtained is comparable to the results obtained using furnace annealing process. Finally, GaN light emitting diodes (LEDs) are demonstrated using undoped layer as the n-type base layer in a p-on-n structure. The light emission spectra are dominated by the 430 nm peak, accompanied with two relatively weak peaks located at 380nm and 550nm. INTRODUCTION Wide band-gap GaN and related III-V nitrides are promising materials for applications in UV and blue light emitting diodes (LEDs) and in high temperature electronics." 2' For a long time, the main obstacle to the realization of these devices has been the poor material quality, such as the high background n-type carrier concentration and the lack of p-type conductivity. Recently high qualit unintentionally doped n-type GaN thin films with low carrier concentration (
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