Principal Investigators: Dr. Jaime Freitas, Dr. Evan Glaser

Wide bandgap semiconductors are of particular interest to the Navy because of their capability of operating at high power, high temperature and/or high frequency levels that far exceed the capabilities of Si-based technology. The development of high-voltage switching devices employing SiC is actively being pursued, while III-Nitride materials enable the fabrication of high-frequency, high output power microwave devices. Currently, the ability to integrate such devices into Navy systems is limited by device degradation due to material defects. Research is directed toward characterizing both point and extended defects in these systems, identifying those defects that limit device performance and understanding the microscopic mechanisms that lead to device degradation.

These studies are carried out in close connection to material growth facilities within the Laboratory and with outside commercial and academic institutions. Defects are investigated using several contactless optical probes, including steady-state and time-resolved photoluminescence, Raman spectroscopy and cathodo-luminescence, as well as magnetic resonance techniques and secondary electron and atomic force microscopy. Recent studies have focused on defects responsible for semi-insulating behavior and reduced minority carrier lifetimes in 4H-SiC, impurities associates with n-type conductivity in the nitrides and defects limiting nitride-based FET performance.

Selected Publications

2013 Freitas, J., B. N. Feigelson, and T. J. Anderson, "Efficient Incorporation of Mg in Solution Grown GaN Crystals", Applied Physics Express, vol. 6, issue 11, 2013. PDF icon 13-1231-2456.pdf (2.26 MB)
2012 Klein, P. B., U. Nwagwu, J. H. Edgar, and J. Freitas, "Photoluminescence investigation of the indirect band gap and shallow impurities in icosahedral B12As2", Journal of Applied Physics, vol. 112, issue 1, 07/2012. PDF icon 12-1231-0035.pdf (1.3 MB)
2012 Freitas, J., M. Mastro, E. R. Glaser, N. Y. Garces, S. K. Lee, J. H. Chung, O. D. K, and K. B. Shim, "Structural and optical studies of thick freestanding GaN films deposited by Hydride vapor phase epitaxy", Journal of Crystal Growth, vol. 350, issue 1, pp. 27-32, 07/2012. PDF icon 11-1226-2571.pdf (1.07 MB)
2012 Freitas, J., J. C. Culbertson, M. Mastro, Y. Kumagai, and A. Koukitu, "Structural and optical properties of thick freestanding AlN films prepared by hydride vapor phase epitaxy", Journal of Crystal Growth, vol. 350, issue 1, pp. 33-37, 07/2012. PDF icon 11-1226-3888.pdf (770.39 KB)
2010 Klein, P. B., R. L. Myers-Ward, K-K. Lew, B. L. VanMil, C. Eddy, D. K. Gaskill, A. Shrivastava, and T. S. Sudarshan, "Recombination processes controlling the carrier lifetime in n(-)4H-SiC epilayers with low Z(1/2) concentrations", Journal of Applied Physics, vol. 108, 2010. PDF icon 10-1226-1322.pdf (326.51 KB)
2010 Maximenko, S., J. Freitas, R. L. Myers-Ward, K-K. Lew, B. L. VanMil, C. Eddy, D. K. Gaskill, P. G. Muzykov, and T. S. Sudarshan, "Effect of threading screw and edge dislocations on transport properties of 4H-SiC homoepitaxial layers", Journal of Applied Physics, vol. 108, 2010. PDF icon 10-1226-0838.pdf (960.35 KB)
2010 Freitas, J., M. Mastro, E. A. Imhoff, M. J. Tadjer, C. Eddy, and F. J. Kub, "Thick homoepitaxial GaN with low carrier concentration for high blocking voltage", Journal of Crystal Growth, vol. 312, pp. 2616-2619, 2010. PDF icon 08-1226-0261.pdf (724.12 KB)
2010 Freitas, J., "Properties of the state-of-the-art of bulk III-V Nitrides substrates and homoepitaxial layers", Journal of Physics D: Applied Physics, vol. 43, 2010. PDF icon 09-1226-3017.pdf (1.6 MB)
2010 Freitas, J., J. G. Tischler, N. Y. Garces, and B. N. Feigelson, "Optical probing of low-pressure solution grown GaN crystal properties", Journal of Crystal Growth, vol. 312, pp. 2564-2568, 2010. PDF icon 10-1226-1111.pdf (595.86 KB)
2009 Klein, P. B., "Identification and carrier dynamics of the dominant lifetime limiting defect in n(-) 4H-SiC epitaxial layers", Phys. Status Solidi A: Applications and Materials Science, vol. 206, pp. 2257-2272, 10/2009. PDF icon 09-1226-0441.pdf (700.78 KB)
2009 Maximenko, S., L. Mazeina, Y. N. Picard, J. Freitas, V. M. Bermudez, and S. Prokes, "Cathodoluminescence studies of the inhomogeneities in Sn-doped Ga2O3 nanowires", Nano Letters, vol. 9, 2009. PDF icon 09-1226-1851.pdf (10.5 MB)
2009 Maximenko, S., J. Freitas, P. B. Klein, A. Shrivastava, and T. S. Sudarshan, "Cathodolumiensce study of the properties of stacking faults in 4H-SiC homoepitaxial layers", Applied Physics Letters, vol. 94, 2009. PDF icon 08-1226-3990.pdf (231.13 KB)
2008 Klein, P. B., "Carrier Lifetime Measurements in n 4H-SiC Epilayers", Journal of Applied Physics, vol. 103, 2008. PDF icon 07-1226-3321.pdf (384.81 KB)
2008 Freitas, J., M. Gowda, J. G. Tischler, J-H. Kim, L. Liu, and D. Hanser, "Semi-insulating GaN substrates for high-frequency device fabrication", Journal of Crystal Growth, vol. 310, pp. 3968-3972, 2008. PDF icon 08-1226-1056.pdf (878.13 KB)
2008 Silveira, E., J. Freitas, S. B. Schujman, and L. J. Schowalter, "AIN bandgap temperature dependence from its optical properties", Journal of Crystal Growth, vol. 310, 2008. PDF icon 08-1226-0573.pdf (256.89 KB)
2007 Mitchel, W. C., W. C. Mitchel, H. E. Smith, G. Landis, S. R. Smith, and E. R. Glaser, "Compensation Mechanism in High Purity Semi-Insulating 4H-SiC", Journal of Applied Physics, vol. 101, 2007. PDF icon 05-1226-3802.pdf (129.24 KB)
2007 Freitas, J., L. B. Rowland, J. Kim, and M. Fatemi, "Properties of epitaxial GaN on refractory metal substrates", Applied Physics Letters, vol. 90, 2007. PDF icon 07-1226-1832.pdf (171.51 KB)
2007 Mastro, M., J. Freitas, R. T. Holm, C. Eddy, J. Caldwell, K. Liu, O. Glembocki, R. L. Henry, and J. Kim, "Rare-earth chloride seeded growth of GaN nano- and micro-crystals", Applied Surface Science, vol. 253, pp. 6157-6161, 2007. PDF icon 06-1226-3187.pdf (1.47 MB)
2007 Glaser, E. R., M. Murthy, J. Freitas, D. Storm, L. Zhou, and D. J. Smith, "Optical and Magnetic Resonance Studies of Mg-doped GaN Homoepitaxial Layers Grown by Molecular Beam Epitaxy", Physica B, vol. 401-402, pp. 327-330, 2007. PDF icon 07-1226-2427.pdf (200.55 KB)
2006 Klein, P. B., B. V. Shanabrook, S. W. Huh, A. Y. Polyakov, M. Skowronski, J. J. Sumakeris, and M. J. O'Loughlin, "Lifetime limiting defects in n-4H-SiC epilayers", Applied Physics Letters, vol. 88, 2006. PDF icon 05-1226-4080.pdf (77.83 KB)
2006 Carlos, W. E., N. Y. Garces, E. R. Glaser, and M. A. Fanton, "Annealing of Multivacancy Defects in 4H-SiC", Physical Review B, vol. 74, 2006. PDF icon 06-1226-2387.pdf (1.06 MB)
2005 Glaser, E. R., B. V. Shanabrook, and W. E. Carlos, "Estimation of Residual Nitrogen Concentration in Semi-Insulating 4H-SiC Substrates via Low Temperature Photoluminescence", Applied Physics Letters, vol. 86, 2005. PDF icon 04-1226-2265.pdf (57.12 KB)
2003 Klein, P. B., and S. Binari, "Photoionization Spectroscopy of deep defects responsible for current collapse in nitride-based FETs", Journal of Physics: Condensed Matter, vol. 15, pp. R1641-R1667, 2003. PDF icon 03-1221.1-2043.pdf (464.06 KB)