Integrated Nanostructured Systems

iMagnetic field dependence of optical circular polarization for a spin-LED with a wide InAs quantum well as the at the emitting medium. The upper left inset shows the band diagram for the spin LED; spin polarized electrons are injected from the right (a (CdMn)Se:I giant g-factor layer; unpolarized holes are injected from p-type InAs on the left over a narrow (AlAs)Sb barrier that confines the electrons. The solid squares are the experimental data. The three curves are simulation based on a rate equation model: blue-a best fit with spin polarized injection (P_inj) between 74% and 95%, a recombination lifetime/spin lifetime (τ_rτ_S = x) ratio of 0.43, and a carrier temperature (T_e) of 25K. For comparison the black curve shows a simulation with P_inj = 100%, x = 0.5 and T_e = 20K (black) and T_e = 30K (red).

Electronic states of III-V and II-VI quantum dots; spin injection into narrow gap semiconductors and spin lifetimes; understanding the anomalous Hall effect in ferromagnetic diluted magnetic semiconductors; the optical Aharonov-Bohm effect in columnar type II quantum dots in the AnTe/ZnSe system; vibrational properties of nanoparticles.

McCombe’s group is primarily interested in optical (far IR/(THz) to the UV) and electrical magnetotransport properties of semiconductor nanostructures and diluted magnetic semiconductors and using spectroscopic techniques to unravel the basic physics of these materials and structure. The basic understanding thus derived is used to explore device structures. Recent work has focused on: photoluminescence and optically detected resonance (ODR) spectroscopy of Interface Fluctuation Quantum Dots in the GaAs/AlGaAs system; low temperature magnetotransport (magnetoresistance and Anomalous Hall Resistance) properties of digital and random alloys of (GaMn)As and (GaMn)Sb; spin injection in the CdMnSe/InAs heterostructure system, high frequency spin manipulation based on Electric Dipole Spin Resonance in InAs and HgTe quantum wells; measurements of robust Aharonov Bohm oscillations in type-II columnar ZnTe/ZnSe quantum dots; and IR and Raman measurements of the "surface" modes of InP and InMnP colloidal nanoparticles.

Bomem FTIR with associated beam splitters and detectors (10 cm^-1 to 25,000 cm^-1); Edinburgh Instruments and Apollo THz laser systems, three superconducting magnet variable temperature systems- maximum field capability of 17 T; 3/4m grating spectrometer with high sensitivity CCD detector and PMT for the near IR and visible region; electrical (magneto) transport system; C-V system.

"Internal Transitions of Negatively Charged Magneto-excitons and Many Body Effects in a Two-dimensional Electron Gas," H. A. Nickel, T. M. Yeo, B. D. McCombe, A. B. Dzyubenko, A. Petrou, A. Yu. Sivachenko, W. Schaff and V. Umansky, Phys. Rev. Letters 88, 056801-1 to 4 (2002).

"Optically Detected Resonance Spectroscopy of Interface Fluctuation Quantum Dots", C.J. Meining, V.R. Whiteside, A. Petrou, B.D. McCombe, J.G. Tischler, A.S. Bracker and D. Gammon, Physica E 26, 158-162 (2005).

"Spin Polarization Measurements of InAs-Based LEDs", C. J. Meining, K. A. Korolev, B. D. McCombe, P. Grabs, I. Chado, G. Schmidt, and L. W. Molenkamp, Journal of Superconductivity: Incorporating Novel Magnetism, 18, 391- 397(2005).

"Above Room Temperature Ferromagnetism in GaSb/Mn Digital Alloys", X. Chen, M. Na, M. Cheon, S. Wang, H. Luo, B. D. McCombe, X. Liu, Y. Sasaki, T. Wojtowicz, J. K. Furdyna, S. J. Potashnik and P. Schiffer, Appl. Phys. Lett. 81, 511-513 (2002).

"Internal transitions of quasi-2D charged magneto-excitons in the presence of purposely introduced weak lateral potential energy variations", C. J. Meining, V. R. Whiteside, B. D. McCombe, A. B. Dzyubenko, J. G. Tischler, A. S. Bracker, D. Gammon, Phys. Rev. B 75, 165301 (2007).

"Internal Transitions of Confined Neutral Magneto-excitons in GaAs/AlGaAs Quantum Wells," G. Kioseoglou, H. A. Nickel, M. Salib, G. Herold, T. Yeo, H. D. Cheong, R. A. Lewis, A. Petrou and B. D. McCombe, Phys. Rev. B 62 2773-2779 (2000).

"Optical Phonon Spectra of GaP Nanoparticles Prepared by Nanochemistry," F. S. Manciu, Y. Sahoo, D. J. MacRae, M. Furis, B. D. McCombe, and P. N. Prasad, Appl. Phys. Lett. 82, 4059 - 61 (2003).

"Internal Transitions of Excitons and Hole Cyclotron Resonance in Undoped GaAs/AlGaAs Quantum Wells by Optically Detected Resonance Spectroscopy," H. A. Nickel, G. S. Herold, M. S. Salib, G. Kiosioglu, A. Petrou, B.D. McCombe and D. Broido, Physica B, 251, 598-602 (1998).

"Donor Impurities as a Probe of Electron Correlations in 2DEG in High Magnetic Fields," Z.X. Jiang, B.D.McCombe, and P. Hawrylak.. Phys. Rev. Lett., 81, 3499-3502 (1998).