Dept of Engineering Physics
Email: Robert Hengehold
Ph.D., Physics, University of Cincinnati, Cincinnati, Ohio, 1965
M.S., Physics, University of Cincinnati, Cincinnati, Ohio, 1960
A.B., Physics, Thomas More College, Fort Mitchell, Kentucky, 1956
Dr. Hengehold has been active in research in experimental physics since joining AFIT in 1961. He has initiated and conducted research programs in the following areas:
Surface and thin film studies of metals and semiconductors using electron energy loss spectroscopy (EELS), employing both low and medium energy electron beam probes in an ultra-high vacuum atmosphere.
Optical properties of semiconductors using vacuum ultraviolet reflectivity, depth-resolved cathodoluminescence, and visible and UV photoluminescence. This program has involved the use of these techniques for band structure determination in semiconductors and the study of the properties of ion-implanted materials and superlattices.
Laser and femtosecond spectroscopy of solids. Use of selective and pulsed laser excitation for the study of semiconductor materials and quantum wells for infrared and ultraviolet detectors, mid-infrared lasers, high-temperature electronics, etc.
CATHODOLUMINESCENCE
OPTICAL DIAGNOSTICS
SEMICONDUCTOR PHYSICS
SOLID STATE PHYSICS
SPECTROSCOPY
Dr. Hengehold's research has produced over 100 technical publications in refereed archival journals, such as The Physical Review, J. of Applied Physics, Applied Physics Letters, J. Vacuum Science and Technology, and J. of Crystal Growth, and 220 presentations at technical meetings, symposia, short courses, etc. His principal publications of the last 10 years are:
49. “Photoluminescence Studies of Epitaxial InAsSb and InAsSb:Be Grown on GaSb Substrates," M.A. Marciniak, R.L. Hengehold, Y.K. Yeo, G.W. Turner, and M.W. Prairie, Compound Semiconductors 1996, St. Petersburg, Russia, Inst. Phys. Conf. Ser. No. 155 (Institute of Physics, Bristol and Philadelphia, 1997), pp. 865-868
48. "Photoluminescence Study of p-type CdGeAs2 Ordered Semiconductor Crystals," J.E. McCrae, R.L. Hengehold, Y.K. Yeo, M.C. Ohmer, and P.G. Schunemann, Appl. Phys. Lett., 70, p. 455, 1997.
47. "Junction Characteristics of Electron-Irradiated Ga0.5In0.5P n+p Diodes and Solar Cells," K.C. Reinhardt, Y.K. Yeo, P.H. Ostdiek, and R.L. Hengehold, J. Appl. Phys., 81 p. 3700, 1997.
46. “Deep Level Capture Barrier in Molecular Beam Epitaxial Grown AlAsySb1-y Measured by Isothermal Capacitance Transient Spectroscopy," K. Johnstone, Y.K. Yeo, R.L. Hengehold, and G.W. Turner, Appl. Phys. Lett. 71, 506-508, 1997.
45. “Luminescence and Annealing Studies of Er-Implanted GaN with and without Oxygen Co-doping,” E. Silkowski, Y.K. Yeo, R.L. Hengehold, and L.R. Everitt, Mater. Sci. Forum 258-263, 1577-1582, 1997.
44. “Deep Level Defect Study of Ion Implanted (Ar, Mg, Cr) n-Type 6H-SiC by Deep Level Transient Spectroscopy,” M.B. Scott, J.D. Scofield, Y.K. Yeo, and R.L. Hengehold, Mater. Sci. Forum 264-268, 549-552, 1998.
43. "Optical Characterization of MBE-Grown InAs1-xSbx Nearly Lattice Matched to GaSb,” M.A. Marciniak, R.L. Hengehold, Y.K. Yeo, and G.W. Turner, J. Appl. Phys. 84, 480-488, 1998.
42. “Recombination Dynamics in InAsSb Quantum-Well Diode Lasers Measured Using Photoluminescence Upconversion,” W.T. Cooley, R.L. Hengehold, Y.K. Yeo, G.W. Turner, and J.P. Loehr, Appl. Phys. Lett. 73, 2890-2892, 1998.
41. “High Temperature (500 oC) Implantation Study of P+ and N+ Implanted Epitaxial N-Type 4H-SiC,” M.B. Scott, Y.K. Yeo, R.L. Hengehold, and J.D. Scofield, Compound Semiconductors 1998, Nara, Japan, Inst. Phys. Conf. Ser. No. 162 (Institute of Physics, Bristol and Philadelphia, 1999), pp. 763-768.
40. “Control of Surface States in GaSb/AlxGa1-xAsySb1-y/GaxIn1-xSb/AlxGa1-xAsySb1-y Quantum Well Structures,” D.K. Johnstone, Y.K. Yeo, R.L. Hengehold, and G.W. Turner, Appl. Phys. Lett. 75, 2779-2781, 1999.
39. “Cathodoluminescence, microstructure, and morphology of tensile-strained AlGaN epitaxial films grown by gas source molecular beam epitaxy,” J.E. Van Nostrand, R.L. Hengehold, K.D. Leedy, J.T. Grant, J.L. Brown, and Q.H. Xie, J. Applied Physics 86, 3120-3128, 1999.
38. “High Temperature (500 oC) Implantation Study of P+ and N+ Implanted Epitaxial N-Type 4H-SiC,” M.B. Scott, Y.K. Yeo, R.L. Hengehold, and J.D. Scofield, Compound Semiconductors 1998, Nara, Japan, Inst. Phys. Conf. Ser. No. 162 (Institute of Physics, Bristol and Philadelphia, 1999), pp. 763-768.
37. “Control of Surface States in GaSb/AlxGa1-xAsySb1-y/GaxIn1-xSb/AlxGa1-xAsySb1-y Quantum Well Structures,” D.K. Johnstone, Y.K. Yeo, R.L. Hengehold, and G.W. Turner, Appl. Phys. Lett. 75, 2779-2781, 1999.
36. “Hall coefficient singularity observed from p-SiGeC grown on n--Si substrate,” M. Ahoujja, Y.K. Yeo, M.R. Smith, R.L. Hengehold, G.S. Pomrenke, and Jim Huffman, Compound Semiconductors 1999, Berlin, Germany, Inst. Phys. Conf. Ser No. 166 (Institute of Physics, Bristol and Philadelphia, 2000), p. 161.
35. “Electrical properties of boron doped p-SiGeC grown on n--Si substrate,” M. Ahoujja, Y.K. Yeo, R.L. Hengehold, G.S. Pomrenke, D.C. Look, and Jim Huffman, Appl. Phys. Lett. 77, 1327-1329, 2000.
34. “Influence of arsenic doping on the electrical properties of GaN epitaxial layers grown by MOCVD,” M. Ahoujja, Y.K. Yeo, R.L. Hengehold, L.J. Guido, P. Mitev, D.K. Johnstone, and Y.K. Kim, Proceedings of the 2000 International Semiconducting and Insulating Materials Conference (SIMC-XI), pp. 27-30, edited by C. Jagadish and N.J. Welham.
33. “Hall coefficient singularity observed from p-SiGeC grown on n--Si substrate,” M. Ahoujja, Y.K. Yeo, M.R. Smith, R.L. Hengehold, G.S. Pomrenke, and Jim Huffman, Compound Semiconductors 1999, Berlin, Germany, Inst. Phys. Conf. Ser No. 166 (Institute of Physics, Bristol and Philadelphia, 2000), p. 161.
32. “Electrical properties of boron doped p-SiGeC grown on n--Si substrate,” M. Ahoujja, Y.K. Yeo, R.L. Hengehold, G.S. Pomrenke, D.C. Look, and Jim Huffman, Appl. Phys. Lett. 77, 1327-1329, 2000.
31. “Influence of arsenic doping on the electrical properties of GaN epitaxial layers grown by MOCVD,” M. Ahoujja, Y.K. Yeo, R.L. Hengehold, L.J. Guido, P. Mitev, D.K. Johnstone, and Y.K. Kim, Proceedings of the 2000 International Semiconducting and Insulating Materials Conference (SIMC-XI), pp. 27-30, edited by C. Jagadish and N.J. Welham.
29/30. “Optical Investigation of MBE Grown Si-Doped AlxGa1-xN as a Function of Nominal Al Mole Fraction up to 0.5,” J.L. McFall, R.L. Hengehold, Y.K Yeo, and J.E. Van Nostrand, J. Crystal Growth 227-228, 458-465, 2001.
28. “Electrical Properties of MBE grown Si-doped AlxGa1-xN as a Function of Nominal Al Mole Fraction up to 0.5,” M. Ahoujja, Y.K Yeo, R.L. Hengehold, and J.E. Van Nostrand, Material Research Soc. Symp. Proc. 680E, E3.5.1-E3.5.6, 2001.
27. “Effects of Process Parameter Variations on the Removal Rate in Chemical Mechanical Polishing of 4H-SiC," C.L. Neslen, W.C. Mitchell, and R.L. Hengehold, J. Electronic Materials 30, 1271-1275, 2001.
26. “Optical Characterization of Mg- and Si-Implanted GaN,” J.A. Fellows, Y.K Yeo, R.L. Hengehold, and L. Krasnobaev, Material Research Soc. Symp. Proc. 680E, E7.1.1-E7.1.6, 2001.
25. “Temperature-dependent Hall Measurements of MBE grown Si-doped AlxGa1-xN for Al Mole Fraction up to 0.5,” M. Ahoujja, Y.K Yeo, R.L. Hengehold, and J.E. Van Nostrand, Applied Physics Lett. 80, 1382-1384, 2002.
24. “Electrical and Optical Investigation of MBE Grown Si-doped AlxGa1-xN as a Function of Al Mole Fraction up to 0.5,” M. Ahoujja, J.L. McFall, Y.K. Yeo, R.L. Hengehold, and J.E. Van Nostrand, Materials Science and Engineering B, B91-92, 285-289, 2002.
23. “Deep Centers and Their Capture barriers in MOCVD-Grown GaN,” D. Johnstone, M. Ahoujja, Y.K Yeo, R.L. Hengehold, and L. Guido, Material Research Soc. Symp. Proc. 692, H2.7.1-11, 2002.
22. “Electrical and Optical Studies of Si-Implanted GaN,” J.A. Fellows, Y.K Yeo, R.L. Hengehold, and L. Krasnobaev, Material Research Soc. Symp. Proc. 693, I6.38.1-6, 2002.
21. “Electrical Activation Studies of GaN Implanted with Si from Low to High Dose,” J.A. Fellows, Y.K Yeo, R.L. Hengehold, and D. Johnstone, Applied Physics Lett. 80, 1930-1932, 2002.
20. “Inter-Subband Infrared Absorption Spectra of Si / Si1-x Gex Quantum Wells Grown in the [110] Direction,” D.E. Weeks, S.H. Yang, M.R. Gregg, S.J. Novotny, K.D. Greene, and R.L. Hengehold, Phys. Rev. B. 65, 195314-195322, 2002.
19. “Electrical Characterization of Defects Introduced in 4H-SiC during High Energy Proton Irradiation and Their Annealing Behavior,” Ahoujja M., H.C. Crocket, M.B. Scott, Y.K Yeo, and R.L. Hengehold, Mat. Res. Soc. Symp. Proc. 764 C3. 37, 2003.
18. “Annealing Studies of Si-Implanted GaN by Hall-Effect and Photoluminescence Measurements,” Fellows J.A., Y.K. Yeo, M.Y. Ryu, R.L. Hengehold, and Todd Steiner, Compound Semiconductors 2002, Inst. Phys. Conf. Ser. No. 174, 49-52 (Institute of Physics, Bristol and Philadelphia, 2003).
17. “Annealing Studies of Si-Implanted Al0.2Ga0.8N”, Ryu, Mee-Yi, E.A. Chitwood, E.N. Claunch, Y.K. Yeo, R.L. Hengehold, J.A. Fellows, and T.D. Steiner, Physica Status Solidi (c) No.7 2593-2596, 2003.
16. “Annealing Studies of Si-Implanted GaN by Hall-Effect and Photoluminescence Measurements,” J.A. Fellows, Y.K. Yeo, M.Y. Ryu, R.L. Hengehold, and Todd Steiner, Compound Semiconductors 2002, Lausanne, Switzerland, 2002, Inst. Phys. Conf. Ser. 174 (Institute of Physics, Bristol and Philadelphia, 2003), pp. 49-52.
15. “Electrical Characterization of Defects Introduced in 4H-SiC during High Energy Proton Irradiation and Their Annealing Behavior,” M. Ahoujja, H.C.Crocket, M.B. Scott, Y.K. Yeo, and R.L. Hengehold, Mat. Res. Soc. Symp. Proc.764, C3, 37-40, 2003.
14. “Annealing Studies of Si-Implanted Al0.2Ga0.8N,” Mee-Yi Ryu, E.A. Chitwood, E.N. Claunch, Y.K. Yeo, R.L. Hengehold, J.A. Fellows, and T.D. Steiner, Physica Status Solidi (c) No. 7, 2593-2596, 2003.
13. “Electrical and optical activation studies of Si-implanted AlxGa1-xN by Hall-effect and photoluminescence measurements,” M.Y. Ryu, Y.K. Yeo, E.A. Chitwood, R.L. Hengehold, and T. Steiner, 2003 International Symposium on Compound Semiconductors, San Diego, California, 2003, IEEE 22-27 (2004).
12. “Photoluminescence characterization of defects introduced in 4H-SiC during high energy proton irradiation and their annealing behavior,” Mo Ahoujja, H.C. Crocket, M.B. Scott, Y.K. Yeo, and R.L. Hengehold, Mat. Res. Soc. Symp. Proc. 815, J5.21, 2004.
11. “High electrical activation efficiency obtained from Si-implanted Al0.18Ga0.82N,” Mee-Yi Ryu, Y.K. Yeo, M.A. Marciniak, R.L. Hengehold, and T.D. Steiner, J. Appl. Phys. 96, 6277-6280, 2004.
10. “Electrical activation studies of Si-implanted AlxGa1-xN as a function of ion dose, anneal temperature, and anneal time,” M.Y. Ryu, Y.K. Yeo, E.A. Moore, R.L. Hengehold, and T. Steiner, J. Korean Phys. Soc. 45, S522-S525, 2004.
9.“Optical study of implantation damage recovery from Si-implanted GaN,” J.A. Fellows, Y.K. Yeo, Mee-Yi Ryu, and R.L. Hengehold, Solid State Commun. 133, 213-217, 2005.
8. “Electrical and optical properties of 1 MeV-electron irradiated AlxGa1-xN,” Michael R. Hogsed, M. Ahoujja, Mee-Yi Ryu, Y.K. Yeo, J.C. Petrosky, and R.L. Hengehold, Mater. Res. Soc. Symp. Proc. 831, E11.35.1, 2005.
7. “Electrical Characterization of As and [As+Si] doped GaN Grown by Metalorganic Chemical Vapor Deposition,” Mo Ahoujja, Said Elhamri, Rex Berney, Y.K. Yeo, and R.L. Hengehold, Mater. Res. Soc. Symp. Proc. 831, E3.19, 2005.
6. “Radiation-induced electron traps in Al0.14Ga0.86N by 1 MeV electron radiation,” Michael R. Hogsed, Y.K. Yeo, Mo Ahoujja, Mee-Yi Ryu, J.C. Petrosky, and R.L. Hengehold, Appl. Phys. Lett. 86, 261906, 2005.
5. “Electrical and optical activation studies of Si-implanted GaN,” J.A. Fellows, Y.K. Yeo, Mee-Yi Ryu, and R.L. Hengehold. J. Electronic Materials 34, 1157-1164, 2005.
4. “Electrical and optical characterization studies of lower dose Si-implanted AlxGa1-xN,” Mee-Yi Ryu, Y.K. Yeo, M.A. Marciniak, T.W. Zens, E.A. Moore, R.L. Hengehold, and T.D. Steiner, J. Electronic Materials 35, 647-653, 2006.
3. “Room temperature ferromagnetic properties of transition metal implanted Al0.35Ga0.65N,” Jeremy A. Raley, Y.K. Yeo, R.L. Hengehold, M.Y. Ryu, and T.D. Steiner, accepted and to be published in the Journal of Alloys and Compounds in 2006.
2. “Electrical characterization of Si-ion implanted AlxGa1-xN annealed at lower temperatures,” Mee-Yi Ryu, Y.K. Yeo, T.W. Zens, M.A. Marciniak, R.L. Hengehold, and T.D. Steiner, accepted and to be published in the Physica Status Solidi (a) in 2006.
1. “Electrical and optical activation studies of high dose Si-implanted Al0.18Ga0.82N,” Mee-Yi Ryu, Y.K. Yeo, M.A. Marciniak, and R.L. Hengehold, accepted and to be published in the Solid State Communications in 2006.