Center for Directed Energy (CDE)

Center for Directed Energy (CDE)
AFIT Faculty: Dr. Robert L. Hengehold
CONTACT INFORMATION
Name: Dr. Robert L. Hengehold
Title: Department of Engineering Physics
Commercial Phone: 937-255-3636 (4502)
DSN Phone: 785-3636 (4502)
EDUCATION

A.B., 1956, Thomas More College, Ft. Mitchell, KY, Physics & Math

M.S., 1960, Univ. of Cincinnati, Cincinnati, OH, Physics & Math

Ph.D., 1965, Univ. of Cincinnati, Cincinnati, OH, Physics (Experimental Solid State Physics)

RESEARCH INTERESTS

Dr. Hengehold's research and consulting activities have been primarily in the area of experimental solid state and optical physics. Past research activities have included surface studies of metals, electron energy loss spectroscopy of metals and semiconductors, vacuum ultraviolet spectroscopy, photoluminescence, selective excitation luminescence, cathode-luminescence, and time-resolved spectroscopy of semiconductors including rare-earth doped Si, GaAs and AlxGa1-xAs, Si/Ge superlattices, GaSb, the wide bandgap materials, GaN, AlN, and AlxGa1-xN, and femtosecond lifetime measurements of mid-infrared quantum well laser structures using time resolved photoluminescence and upconversion techniques He is currently carrying out optical studies of materials for neutron detection as well as photoemission studies of the actinides. He has directed the doctoral research of 18 Ph.D. students and over 80 M.S. students. This research has been carried out in collaboration with AF Research Laboratories, Naval Research Laboratory, Lincoln Laboratory, the University of Vermont, and the University of Nebraska.. Dr. Hengehold served as a Senior Research Associate at the Aerospace Research Laboratories from 1969-1975.

EXPERTISE
  • LASER DIAGNOSTICS
  • SPECTROSCOPY
  • CATHODOLUMINESCENCE
  • CHARACTERIZATION OF WIDE-BANDGAP OPTICALLY ACTIVATED HIGH-POWER SEMICONDUCTOR DEVICES
  • EXPERIMENTAL SOLID STATE PHYSICS
  • IMAGING SCIENCE
  • MATERIAL CHARACTERIZATION OF NARROW-GAP SEMICONDUCTORS FOR MID-INFRARED OPTO-ELECTRONIC DEVICES
  • MATERIALS CHARACTERIZATION
  • NARROW-BAND GAP MATERIAL STUDIES
  • OPTICAL DIAGNOSTICS
  • OPTICS
  • PHOTOLUMINESCENCE
  • RADIATION DETECTION
  • SEMICONDUCTOR PHYSICS
  • SOLID STATE PHYSICS
  • SPECTROSCOPY
  • VISIBLE AND THERMAL REMOTE SENSING
PUBLICATIONS & RESEARCH PAPERS

Books:

“Introduction to Laser Weapons Systems” by G.P. Perram, S.J. Cusumano, R.L. Hengehold, and S.T. Fiorino, Directed Energy Professional Society, 2010.
 
Archival Journal Papers:

1. C.R. Fraime and R.L. Hengehold, "Ultraviolet Reflectivity Spectra of CdSSe Single Crystals," Physical Review, 174, pp. 808-812, 1968.
 
2. R.J. Almassy, R.L. Hengehold and F.L. Pedrotti, "Electron Energy Loss and Ultra violet Reflectivity of Crystalline ZnO," Physical Review, B1, pp. 4784-4791, 1970.
 
3. C.J. Vesely, D.W. Langer and R.L. Hengehold, "UV Photoemission Measurements of the Upper d Levels in the IIB VIA Compounds," Physical Review, B5, pp. 2296-2301, 1972.
 
4. C.J. Vesely, D.W. Langer and R.L. Hengehold, "A Comparison of X Ray and UV Induced Electron Emission Studies of the Upper d Levels in IIB VIA Compounds," in Electron Spectroscopy, Edited by D. A. Shirley (North Holland 1972) pp. 535-539.
 
5. R.L. Hengehold and F.L. Pedrotti, "Electron Energy Loss Spectra of CdS, CdSe and CdTe," Physical Review, B6, pp. 2262-2268, 1972.
 
6. R.L. Hengehold and F.L. Pedrotti, "Electron Energy Loss Spectra of ZnS, ZnSe and ZnTe," Physical Review, B6, pp. 3026-3031, 1972.
 
7. T.T. Katonak and R.L. Hengehold, "Electron Energy Loss Study of the Mercury Chalcogenides," Journal of Applied Physics, 46, pp. 4294-4300, 1975.
 
8. R.L. Hengehold and F.L. Pedrotti, "Ultraviolet Reflectivity and Electron Energy Loss Spectra of AgGaS and CuGaS," Journal of Applied Physics, 46, pp. 5202-5204, 1975.
 
9. R.L. Hengehold and F.L. Pedrotti, "Plasmon Excitation Energies in ZnO, CdO and Mgo," Journal of Applied Physics, 46, pp. 287-291, 1976.
 
10. J.R. Pierce and R.L. Hengehold, "Depth Resolved Cathodoluminescence of Ion Implanted Layers in Zinc Oxide," Journal of Applied Physics 47, pp. 644-651, 1976.
 
11. O. Kim, Y.S. Park, R.S. Mason, T.E. Luke R.L. Hengehold and Y.K. Yeo, "Laser Annealing of Ion Implanted GaAs," Proceedings of Conference on Laser Solid Interactions and Laser Processing, AIP Conference Proceedings, 50, pp. 597-602, 1978.
 
12. G. Pomrenke, R.L. Hengehold and Y.S. Park, "Photoluminescence from Mg Implanted, Epitaxial, and Semi-Insulating InP," Journal of Applied Physics, 52, pp. 969-977, 1981.
 
13. G.S. Pomrenke, Y.S. Park, M. Maclin and R.L. Hengehold, "Luminescence Characteristics of the 1.4eV Silicon Related Complex in Gallium Arsenide," Physica B, 116, pp. 414-419, 1983.
 
14. M.L. Cone and R.L. Hengehold, "Characterization of Ion Implanted GaAs Using Cathodoluminescence," Journal Of Applied Physics, 54, pp. 6346-6351, 1983.
 
15. O. Swenson, R.L. Hengehold and T.E. Luke, "Luminescence Study of Thallium Implanted Silicon," Journal of Applied Physics, 54, pp. 6329-6335, 1983.
 
16. Y.K. Yeo, R. L. Hengehold. Y.Y. Kim, A. Ezis, Y.S. Park, and J.E. Ehret, "Substrate Dependent Electrical Properties of Low Dose Si Implants in GaAs," Journal of Applied Physics, 58, pp. 4083-4088, 1985.
 
17. Y.K. Yeo, D.W. Elsaesser and R.L. Hengehold, "Surface Depletion Effect Correction to Non Uniform Carrier Distributions by Hall Measurements," Journal of Applied Physics, 61, pp. 5070-5075, 1987.
 
18. J.R. Cavins, Y.K. Yeo and R.L. Hengehold, "Excited states of the Mg Acceptor in GaAs," Journal of Applied Physics, 64, pp. 6761-6766, 1988.
 
19. J.R. Cavins, Y.K. Yeo and R.L. Hengehold, "A Comparative Study of Photoluminescence and Selective Pair luminescence in GaAs," Proceedings of the Symposium on Luminescence Science and Technology, edited by C. W. Struck, B. DiBartolo, and W. M. Yen (The Electrochemical Society, Pennington, New Jersey, held in Chicago), Vol 88 24, pp. 258-270, 1988.
 
20. J.R. Cavins, Y.K. Yeo and R.L. Hengehold, "Characterization of Residual Acceptors in SI and VPE GaAs by Selective Pair Luminescence and Photoluminescence Methods," Journal of the Electrochemical Society, 136, pp. 2113-2119, 1989.
 
21. G.S. Pomrenke, R.L. Hengehold and Y.K. Yeo, "Excitation Mechanism of Rare Earth Emissions (Yb, Tm, Er, Pr) in GaAS and InP", Gallium Arsenide and Related Compounds 1989, Karuizawa, Japan, 1989; Inst. Phys. Conf. Ser. No. 106 (Institute of Physics, Bristol, UK and New York, 1990), pp. 339-344.
 
22. Y.K. Yeo, G.H. Gainer, Jr., J.H. Kim and R.L. Hengehold, "Evaluation of Carrier Distributions in a Depletion Region of a Semiconductor Measured by the Capacitance Voltage Profile Method," Applied Physics Letters, 56, pp. 75-77, 1990.
 
23. J.S. Solomon, G.S. Pomrenke, R.L. Hengehold and Y.K. Yeo, "SIMS and Photoluminescence Studies of Rare Earth Implants in InP," Proceedings of the Seventh International Conference on Secondary Ion Mass Spectrometry, SIMS VII, pp. 571-574, 1990.
 
24. G.S. Pomrenke, R.L. Hengehold, Y.K. Yeo, I.G. Brown, and J.S. Solomon, "Actinide Activated Luminescence in Uranium Implanted III V Semiconductors," Journal of Applied Physics, 67, pp. 2040-2043, 1990.
 
25. G.S. Pomrenke, R.L. Hengehold and Y.K. Yeo, "Lanthanide (Yb, Er, Tm, Pr, Ho) and Actinide (U) Activated Luminescence in III-V Semiconductors," European Journal of Solid State and Inorganic Chemistry, 28, p. 159, 1991.
 
26. Y.K. Yeo, G.S. Pomrenke and R.L. Hengehold, "Near IR Emission from Er, Tm, and Pr Implanted GaAs and A1GaAs," Materials Research Society Symp. Proc., 216, p. 415, 1991.
 
27. K.J. Keefer, Y.K. Yeo and R.L. Hengehold, "Study of the Broad Luminescence Bands in Ge-Implanted GaAs Centered at 1.44-1.46 eV," J. Appl. Phys., 70, p. 4634, 1991.
 
28. G.S. Pomrenke, E. Silkowski, J.E. Colon, D.J. Topp, Y.K. Yeo, and R.L. Hengehold, "Luminescence of Thulium in III-V Semiconductors and Silicon," J. Appl. Phys., 71, p. 1919, 1992.
 
29. J.E. Colon, D.W. Elsaesser, Y.K. Yeo, R.L. Hengehold and G.S. Pomrenke, "Excitation Mechanism of the Erbium 4f Emissions in GaAs," Mater. Sci. Forum, 83-87, pp. 671-676, 1992.
 
30. K.R. Evans, E.N. Taylor, C.E. Stutz, D.W. Elsaesser, J.E. Colon, Y.K. Yeo, R.L. Hengehold and J.S. Solomon, "Molecular Beam Epitaxial Growth and Characterization of Erbium-Doped GaAs and AlGaAs," J. Vac. Sci. Technol., B 10, Mar/Apr, 1992.
 
31. T.D. Steiner, R.L. Hengehold, Y.K. Yeo, D.J. Godbey, P.E. Thompson, and G.S. Pomrenke, "Near Band-Edge Photoluminescence from Si1-xGex/Si Superlattices Grown by Molecular Beam Epitaxy," J. Vac. Sci. Technol., B 10, p. 924, 1992.
 
32. T.D. Steiner, R.L. Hengehold, Y.K. Yeo, D.J. Godbey, P.E. Thompson, and G.S. Pomrenke, "A Study of Broad Band Photoluminescence from Si1-xGex/Si Superlattices," J. Crystal Growth, 127, p. 472, 1993.
 
33. D.W. Elsaesser, J.E. Colon, Y.K. Yeo, R.L. Hengehold, K.R. Evans, and J.S. Solomon, "Erbium Complexes and Defect Levels in MBE-Grown Erbium-Doped GaAs and AlGaAs," J. Crystal Growth, 127, p. 707, 1993.
 
34. J.E. Colon, D.W. Elsaesser, Y.K. Yeo, R.L. Hengehold, and G.S. Pomrenke, "Enhancement of the Er3+ Emissions from AlGaAs:Er Co-doped with Oxygen," Appl. Phys. Lett., 63, p. 216, 1993.
 
35. J.E. Colon, D.W. Elsaesser, Y.K. Yeo, R.L. Hengehold, and G.S. Pomrenke, "Luminescence Study of the Intra-4f Emissions from GaAs:(Er+O) and AlGaAs:(Er+O)," Mat. Res. Soc. Symp. Proc., 301, p. 169, 1993.
 
36. D.W. Elsaesser, J.E. Colon, Y.K. Yeo, R.L. Hengehold, and G.S. Pomrenke, "Annealing Studies of Er-Implanted GaAs and the Excitation Mechanism of Er in GaAs," Mat. Res. Soc. Symp. Proc., 301, p. 251, 1993.
 
37. P.L. Thee, Y.K. Yeo, R.L. Hengehold, and G.S. Pomrenke, "Pr-4f Luminescence Excitation in AlxGa1-xAsProceedings of the 22nd International Conference on the Physics of Semiconductors,” Vol 3, p. 2455, 1994.
 
38. D.W. Elsaesser, J.E. Colon, Y.K. Yeo, R.L. Hengehold, and G.S. Pomrenke, "Er-4f Luminescence Excitation and Quenching Mechanisms in GaAs," Mater. Sci. Forum, 143-147, p. 749, 1994.
 
39. P.L. Thee, Y.K. Yeo, R.L. Hengehold, and G.S. Pomrenke, "Excitation of the 4f-electron of Pr 3+ in GaAs:Pr and AlGaAs:Pr," Physica Scripta, T54, p. 24, 1994.
 
40. J.E. McCrae, Jr., M.R. Gregg, R.L. Hengehold, Y.K. Yeo, P.H. Ostdiek, M.C. Ohmer, P.G. Schunemann, and T.M. Pollack, "Polarized Luminescence Study of Ordered Nonlinear Optical Material ZnGeP," Appl. Phys. Lett., 64, p. 3142, 1994.
 
41. D.W. Elsaesser, Y.K. Yeo, R.L. Hengehold, K.R. Evans, and F.L. Pedrotti, "Er-related Deep Centers in GaAs Doped with Er by Ion Implantation and Molecular Beam Epitaxy," J. Appl. Phys., 77, p. 3919, 1995.
 
42. K.C. Reinhardt, Y.K. Yeo, and R.L. Hengehold, "Junction Characteristics of Ga0.5In0.5P n+p Diodes and Solar Cells," J. Appl. Phys., 77, p. 5763, 1995.
 
43. T.L. Kreifels, R.L. Hengehold, Y.K. Yeo, P.E. Thompson, and D.S. Simons. "Si1-xGex/Si Multiple Quantum Wells on Si (100) and Si (110) for Infrared Absorption," J. Vac. Sci. Technol, A13, p. 636, 1995.
 
44. P. L. Thee, Y. K. Yeo, R. L. Hengehold, and G. S. Pomrenke, "Pr3+ Luminescence in GaAs and AlxGa1-xAs Implanted with Pr," J. Appl. Phys. 78, p. 4651, 1995.
 
45. P.E. Thompson, T.L.Kreifels, M. Gregg, R.L. Hengehold, Y.K. Yeo, D.S. Simons, M.E. Twigg, M. Fatemi, and K. Hobart, "The Growth and Characterization of Si1-xGex Multiple Quantum Wells on Si(110) and Si(111)," J. Crystal Growth. 157, p. 21, 1995.
 
46. J.D. Scofield, Y.K. Yeo, and R.L. Hengehold, "Deep Level Study of As-Grown and Ion Implanted Bulk and MOCVD Grown Epitaxial 6H-SiC," Silicon Carbide and Related Materials 1995, Kyoto, Japan, 1995; Inst. Phys. Conf. Ser. No. 142 (Institute of Physics, Bristol and Philadelphia, 1996), p. 329.
 
47. D.K. Johnstone, M.A. Marciniak, Y.K. Yeo, R.L. Hengehold, and G.W. Turner, "Electrical and Optical Characterization of GaSb Based Diode Laser Material for 2-4 um Applications," Compound Semiconductors 1995, Cheju Island, Korea, 1995; Inst. Phys. Conf. Ser. No. 145 (Institute of Physics, Bristol and Philadelphia, 1996), p. 369.
 
48. J.D. Scofield, Y.K. Yeo, and R.L. Hengehold, "Deep Level Investigation of Bulk and Epitaxial 6H-SiC at High Temperatures," Compound Semiconductors 1995, Cheju Island, Korea, 1995; Inst. Phys. Conf. Ser. No. 145 (Institute of Physics, Bristol and Philadelphia, 1996), p. 511.
 
49. E. Silkowski, Y.K. Yeo, R.L. Hengehold, M.A. Khan, T. Lei, K. Evans, and C. Cerney. "Annealing Study of Ion Implanted MOCVD and MBE Grown GaN," Material Research Society Symposium Proceedings, 395, p. 813, 1996.
 
50. E. Silkowski, Y.K. Yeo, R.L. Hengehold, B.L. Goldenberg, and G.S. Pomrenke, "Neodymium and Erbium Implanted GaN," Mat. Res. Soc. Symp. Proc., 422, p. 69, 1996.
 
51. J.D. Scofield, Y.K. Yeo, and R.L. Hengehold, "Deep Level Studies Specific to 6H- and 4H-SiC Polytypes, " Proceedings of the 23rd International Conference on the Physics of Semiconductors, 4, p. 2657, 1996.
 
52. J.D. Scofield, M.E. Dunn, K.C. Reinhardt, Y.K. Yeo, and R.L. Hengehold, "Defect Dominant Junction Characteristics of 4H-SiC p+-n Diodes," Mat. Res. Soc. Symp. Proc., 423, p. 57, 1996.
 
53. E. Silkowski, G.S. Pomrenke, Y.K. Yeo, and R.L. Hengehold, "Optical Activation of Ion Implanted and Annealed GaN," Physica Scripta, T69, p. 276, 1997.
 
54. J.D. Scofield, M.E. Dunn, J.C. Wiemeri, K.C. Reinhardt, Y.K. Yeo, and R.L. Hengehold, “Comparative Study of the Junction Characteristics and Performance of SiC p+/n and Schottky Power Rectifiers,” Compound Semiconductors 1996, St. Petersburg, Russia, 1996; Inst. Phys. Conf. Ser. No. 155, (Institute of Physics, Bristol and Philadelphia, 1997), pp. 597-600.
 
55. M.A. Marciniak, R.L. Hengehold, Y.K. Yeo, G.W. Turner, and M.W. Prairie, “Photoluminescence Studies of Epitaxial InAsSb and InAsSb:Be Grown on GaSb Substrates,” Compound Semiconductors 1996, St. Petersburg, Russia, 1996; Inst. Phys. Conf. Ser. No. 155, (Institute of Physics, Bristol and Philadelphia, 1997), pp. 865-868
 
56. J.E. McCrae, R.L. Hengehold, Y.K. Yeo, M.C. Ohmer, and P.G. Schunemann, "Photoluminescence Study of p-type CdGeAs2 Ordered Semiconductor Crystals," Appl. Phys. Lett., 70, p. 455, 1997.
 
57. K.C. Reinhardt, Y.K. Yeo, P.H. Ostdiek, and R.L. Hengehold,"Junction Characteristics of Electron-Irradiated Ga0.5In0.5P n+p Diodes and Solar Cells," J. Appl. Phys., 81 p. 3700, 1997.
 
58. K. Johnstone, Y.K. Yeo, R.L. Hengehold, and G.W. Turner, “Deep Level Capture Barrier in Molecular Beam Epitaxial Grown AlAsySb1-y Measured by Isothermal Capacitance Transient Spectroscopy,” Appl. Phys. Lett. 71, 506-508 (1997).
 
59. “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).
 
60. “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).
 
61. “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).
 
62. “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).
 
63. “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, 1998; Inst. Phys. Conf. Ser. No. 162, (Institute of Physics, Bristol and Philadelphia, 1999), pp. 763-768.
 
64. “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).
 
65.“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)
 
66.   “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, 1998; Inst. Phys. Conf. Ser. No. 162, (Institute of Physics, Bristol and Philadelphia, 1999), pp. 763-768.
 
67. “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).
 
68. “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, 1999; Inst. Phys. Conf. Ser No. 166, (Institute of Physics, Bristol and Philadelphia, 2000), p. 161.
 
69. “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).
 
70. “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.
 
71. “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, 1999; Inst. Phys. Conf. Ser No. 166, (Institute of Physics, Bristol and Philadelphia, 2000), p. 161.
 
72. “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).
 
73. “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.
 
74. “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).
 
75. “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).
 
76. “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).
 
77. “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).
 
78. “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).
 
79. “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).
 
80. “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).
 
81. “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).
 
82. “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).
 
83. “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).
 
84. “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).
 
85. “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).
 
86. “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).
 
87. “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.
 
88. “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).
 
89. “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).
 
90. “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).
 
91. “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).
 
92. “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).
 
93. “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).
 
94. “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).
 
95. “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).
 
96. “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).
 
97. “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).
 
98. “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).
 
99. “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).
 
100.“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, J. Alloys and
Compounds 423, 184-187 (2006).
 
101. “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, Solid State Comm. 139, 284-288 (2006).
 
102. “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, Physica
Status Solidi (a) 203, 1650-1653 (2006).
 
103. “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).
 
104. “Ferromagnetic Properties of Nickel Implanted Al0.35Ga0.65N,” J.A. Raley, Y.K. Yeo, R.L.
Hengehold, Mee-Yi Ryu, Y. Lu, and Pan Wu, J. Korean Physical Society 51, 1707-1712 (2007).
 
105. “Implantation damage recovery and carrier activation studies of Si-implanted Al0.18Ga0.82N
by temperature dependent Hall-effect measurements,” Mee-Yi Ryu, Y. K. Yeo, and R. L. Hengehold,
Physica Status Solidi (c) 4, 2613-2616 (2007).
 
106. “Electroluminescence of n-Zn1-xMgxO/p-Zn1-xMgxO Heterostructures Grown on Si-Substrates,” Sh.U. Yuldashev, P.K. Khabibullaev, R.A. Nusretov, I.V. Khvan, Y.K. Yeo, R.L. Hengehold,
and T.W. Kang, J. Korean Phys. Soc. 53, 2913-2916 (2008).
 
107. “Magnetic Properties of Transition Metal Implanted ZnO Nanotips Grown on Sapphire and
Quartz,” J.A. Raley, Y.K. Yeo, R.L. Hengehold, and M.Y. Ryu, J. Magnetics 13, 19-22 (2008).
 
108. “Structural and Optical Characterization of Si-Implanted Al0.18Ga0.82N,” Mee-Yi Ryu,Y. K. Yeo, and R. L. Hengehold, Solid State Commun. 149, 319-321 (2009)
 
109. “Nearly Perfect Electrical Activation Efficiencies from Silicon-Implanted AlxGa1-xN with High Aluminum Mole fraction,” E.A. Moore, Y. K. Yeo, Mee-Yi Ryu, and R. L. Hengehold,
J. Electronic Materials 38, 153-158 (2009).
 
110. “Temperature-Dependent Studies of Si-Implanted Al0.33Ga0.67N with Different Annealing Temperature and Times,” E.A. Moore,* Y.K. Yeo, G.J. Gruen,* Mee-Yi Ryu, and R. L. Hengehold, J. Electronic Materials 39, 21-28 (2010).
 
111. “Activation Studies of Si-Implanted Al0.45Ga0.55N by Using Cathodoluminescence and Temperature-Dependent Hall-Effect Measurements,” E.A. Moore,* Y.K. Yeo, R. L. Hengehold, and Mee Yi Ryu, J. Korean Phys. Soc. 55, 2465-2469 (Dec. 2009).
112. “Electrical and Optical Characterization of Melt Grown Bulk InAs1-yPy Crystals,” J. Wei,* J. Barnes, S. Guha, L.P. Gonzalez, Y.K. Yeo, R.L. Hengehold, and G. Rajagopalan, J. Electronic Materials 40, 103-108 (Feb 2011).
 
113. “Electrical Activation Studies of Si-Implanted AlxGa1-xN with Aluminum Mole Fraction of 11% to 51%,” E.A. Moore,* Y.K. Yeo, Mee-Yi Ryu, and R.L. Hengehold, J. Electronic Materials 40, 11-16 (Jan 2011).
 
114. “Optical and Electrical Properties of Bulk-Grown Ternary InxGa1-xAs,” Y.K. Yeo, A.C. Bergstrom,* R.L. Hengehold, J.W. Wei,* S. Guha, G. Rajagopalan, and Mee-Yi Ryu, J. Korean Phys. Soc. 58, 1267-1273 (May 2011).
 
115. “Reversible Mn segregation at the polar surface of lithium tetraborate,”C. Dugan, R. L. Hengehold, S. R. McHale, J. A. Colón Santana, J. W. McClory, V. T. Adamiv, Y. V. Burak, Y. B. Losovyj, and P. A. Dowben, Appl. Phys. Lett. Vol 102, No. 13, 161602 (4 pages) (2013).
 
 
Other Articles:
 
1. "Graduate Optics Education at the AF Institute of Technology", R.L. Hengehold, T.E. Luke and S. Robinson, IEEE Transactions on Education, E?23, 87?91 (1980)
 
2. "Graduate Engineering Physics at the Air Force Institute of Technology", R.L. Hengehold and L.S. Pedrotti, ASEE Annual Conference Proceedings, Vol III, pp 934?937, 1981.
 
3. "A Comparative Study of Photoluminescence and Selective Pair luminescence in GaAs," Y.K. Yeo, J.R. Cavins, and R.L. Hengehold, Proceedings of the Symposium on Luminescence Science and Technology, edited by C.W. Struck, B.DiBartolo, and W.M. Yen (The Electrochemical Society, Pennington, New Jersey, held in Chicago), Vol 88?24, 258 (1988).
 
4. "Pr-4f Luminescence Excitation in AlxGa1-xAs," P.L. Thee, Y.K. Yeo, R.L. Hengehold, and G.S. Pomrenke, Proceedings of the 22nd International Conference on the Physics of Semiconductors, Vol 3, 2455 (1994).
 
5. "Deep Level Studies Specific to the 6H and 4H SiC Polytypes," J.D. Scofield, Y.K. Yeo, and R.L. Hengehold, Proceedings of the 23rd International Conference on the Physics of Semiconductors, Vol 4, 2657-2660 (1996).
 
6. “Activation of P+ and N+ Ions in Epitaxial N-Type 4H-SiC Implanted at High Temperature,” M.B. Scott, Y.K. Yeo, R.L. Hengehold, and J.D. Scofield, Proceedings of the 24th International Conference on the Physics of Semiconductors, World Scientific, Singapore, (1999).
 
7. “Mid-Infrared Quantum-Well, Opto-Electronic Devices,” R.L. Hengehold, D.E. Weeks, M.A. Marciniak, C.A. Bartholomew, and M.R. McKay, Solid State and Diode Laser Technology Review Technical Digest, Albuquerque NM, May 21-24, 2001.
 
8. “Time Resolved Photoluminescence Spectra of Mid-Infrared Quantum Well Lasers,” S.M. Gorski, M.A. Marciniak, R.L. Hengehold, and D.E. Weeks, Solid State and Diode Laser Technology Review Technical Digest, Albuquerque NM, 3-6 June 2002.
 
9. “Deviation of carrier dynamics in MWIR photonic structures from theoretical predictions,” P.M. Johnson, M.A. Marciniak, R.L. Hengehold and D.E. Weeks, Proceedings of the 2004 Great Lakes Photonics Symposium, (SPIE, 2004)

AWARDS & HONORS

Tau Beta Pi Outstanding Teacher of the Year Award for academic year 1967-1968.

Outstanding Instructor of the Quarter in 1995 and 1989.

Listed in Outstanding Educators in America 1973.
 
Listed in American Men of Science.
 
Senior Research Associate, Aerospace Research Laboratories, from 1969-1975.

AU Commanders Award for Faculty Achievement 1982

AF Meritorious Civilian Service Award 1990

Gage H. Crocker Outstanding Professor Award in 1996 for demonstrated excellence in teaching, curriculum development, educational innovation, consultation, and research.

Federal Laboratory Consortium Award in 1996 for excellence in technology transfer of advanced non-linear optical crystals

Outstanding Professional Achievement Award for 1997 from the Affiliate Society Council of the Engineering and Science Foundation of Dayton.

General Bernard A. Schriever Award for 1999 for major contributions to the advancement of aerospace power, technology, Air Force doctrine, and the military as a profession.

Air Education and Training Command Team Award Winner for 1996 for Graduate Engineering Reengineering Study Team.
 
Fellow, American Physical Society.

COURSES

Dr. Hengehold has taught a wide range of graduate courses in AFIT’s engineering physics, nuclear engineering, materials engineering, and electro-optics programs with emphasis on the areas of solid state physics, semiconductor device physics, optics, laser physics, optical detection, optical diagnostics and electro-optical systems with specific application to Air Force systems. He developed and taught one week short courses in High Energy Laser Systems, Infrared Technology, and Electro-optics to a wide range of Air Force officers and civilians at Air Force bases across the country. He has also developed and taught short courses in laser fundamentals, laser engineering, laser beam diagnostics, and infrared optical systems for the Laser Institute of America and the Engineering Technology Institute.

During the past five years, Dr. Hengehold has taught PHYS 556, Introduction to Quantum Physics, OENG 650, Optical Radiometry and Detection, PHYS 670, Introduction to Solid State Physics, and MATL 672, Optical Properties of Solids.

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