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- HETEROSTRUCTURES; POLARIZATION; HEMTS; GAN (1)
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Articles 1 - 15 of 15
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Normal And Inverse Spin-Valve Effect In Organic Semiconductor Nanowires And The Background Monotonic Magnetoresistance, Sandipan Pramanik, Supriyo Bandyopadhyay, Kalyan Garre, Marc Cahay
Normal And Inverse Spin-Valve Effect In Organic Semiconductor Nanowires And The Background Monotonic Magnetoresistance, Sandipan Pramanik, Supriyo Bandyopadhyay, Kalyan Garre, Marc Cahay
Electrical and Computer Engineering Publications
We have observed both peaks and troughs in the magnetoresistance of organic nanowires consisting of three layers—cobalt, 8-hydroxy-quinolinolato aluminum (Alq3), and nickel. They always occur between the coercive fields of the ferromagnetic layers, and we attribute them to the normal and inverse spin-valve effect. The latter is caused by resonant tunneling through localized impurity states in the organic material. Peaks are always found to be accompanied by a positive monotonic background magnetoresistance, while troughs are accompanied by a negative monotonic background magnetoresistance. This curious correlation suggests that the background magnetoresistance, whose origin has hitherto remained unexplained, is probably caused by …
Band Offset Measurements Of Zno∕6h-Sic Heterostructure System, Ya. I. Alivov, Bo Xiao, Q. Fan, Hadis Morkoç, D. Johnstone
Band Offset Measurements Of Zno∕6h-Sic Heterostructure System, Ya. I. Alivov, Bo Xiao, Q. Fan, Hadis Morkoç, D. Johnstone
Electrical and Computer Engineering Publications
The conduction band offset of n-ZnO∕n-6H-SiCheterostructures fabricated by rf-sputtered ZnO on commercial n-type 6H-SiC substrates has been measured by a variety of methods. Temperature dependent current-voltage characteristic, photocapacitance, and deep level transient spectroscopy measurements showed the conduction band offsets to be 1.25, 1.1, and 1.22eV, respectively.
Near-Infrared Wavelength Intersubband Transitions In Gan∕Aln Short Period Superlattices, E. D. Decuir Jr., Emil Fred, B. S. Passmore, A. Muddasani, M. O. Manasreh, Jinqiao Xie, Hadis Morkoç, M. E. Ware, G. J. Salamo
Near-Infrared Wavelength Intersubband Transitions In Gan∕Aln Short Period Superlattices, E. D. Decuir Jr., Emil Fred, B. S. Passmore, A. Muddasani, M. O. Manasreh, Jinqiao Xie, Hadis Morkoç, M. E. Ware, G. J. Salamo
Electrical and Computer Engineering Publications
Intersubband transitions in GaN∕AlN short period superlattices prepared by molecular beam epitaxy were investigated using the optical absorption technique. The peak position wavelengths of these transitions are found to span the spectral range of 1.35–2.90μm for samples cut into 45° waveguides with GaNquantum well thicknesses ranging between 1.70 and2.41nm. The Fermi energy levels are estimated from the carrier concentrations, which were measured using an electrochemical capacitance-voltage profiler. The well widths were inferred from comparing the measured peak position energy of the intersubband transitions and the bound state energy levels calculated using the transfer matrix method.
Subpicosecond Time-Resolved Raman Studies Of Lo Phonons In Gan: Dependence On Photoexcited Carrier Density, K. T. Tsen, Juliann G. Kiang, D. K. Ferry, Hadis Morkoç
Subpicosecond Time-Resolved Raman Studies Of Lo Phonons In Gan: Dependence On Photoexcited Carrier Density, K. T. Tsen, Juliann G. Kiang, D. K. Ferry, Hadis Morkoç
Electrical and Computer Engineering Publications
Subpicosecond time-resolved Raman spectroscopy has been used to measure the lifetime of the LO phonon mode in GaN for photoexcited electron-hole pair density ranging from1016to2×1019cm−3 . The lifetime has been found to decrease from 2.5ps , at low density, to0.35ps , at the highest density. The experimental findings should help resolve the recent controversy over the lifetime of LO phonon mode in GaN.
Quantitative Mobility Spectrum Analysis Of Algan∕Gan Heterostructures Using Variable-Field Hall Measurements, N. Biyikli, J. Xie, Y.-T. Moon, F. Yun, C.-G. Stefanita, S. Bandyopadhyay, Hadis Morkoç, I. Vurgaftman
Quantitative Mobility Spectrum Analysis Of Algan∕Gan Heterostructures Using Variable-Field Hall Measurements, N. Biyikli, J. Xie, Y.-T. Moon, F. Yun, C.-G. Stefanita, S. Bandyopadhyay, Hadis Morkoç, I. Vurgaftman
Electrical and Computer Engineering Publications
Carrier transport properties of AlGaN∕GaNheterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally undoped Al0.08Ga0.92N∕GaN sample was grown by plasma-assisted molecular beam epitaxy on a GaN/sapphire template prepared with hydride vapor phase epitaxy. Variable-magnetic-field Hall measurements were carried out in the temperature range of 5–300K and magnetic field range of 0.01–7T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility two-dimensional electron gas and the relatively low-mobility bulk electrons for the temperature range investigated. The mobilities at T=80K are found to be 7100 and 880cm2/Vs, respectively, …
In Situ Pendeoepitaxy Of Gan Using Heteroepitaxial Algan∕Gan Cracks, Y. T. Moon, C. Liu, J. Xie, X. Ni, Y. Fu, Hadis Morkoç, Lin Zhou, David J. Smith
In Situ Pendeoepitaxy Of Gan Using Heteroepitaxial Algan∕Gan Cracks, Y. T. Moon, C. Liu, J. Xie, X. Ni, Y. Fu, Hadis Morkoç, Lin Zhou, David J. Smith
Electrical and Computer Engineering Publications
Pendeoepitaxy on patterned templates has been proven to be efficient for reducing threading dislocation densities in GaN thin films. In this letter, we report on in situ crack-assisted pendeoepitaxy of GaN using spontaneously formed cracks in AlGaN∕GaNheterostructures. Our approach involves the growth of an AlGaN∕GaNtemplate followed by in situ thermal etching and deposition of an amorphous silicon nitride mask in a low pressure metal organic chemical vapor deposition system. Microwirelike GaN seeds are then formed along the crack lines during the initial stage of GaN overgrowth, which act as nucleation stripes for epitaxial lateral overgrowth. Transmission electron microscopy revealed that …
Fabrication And Current-Voltage Characterization Of A Ferroelectric Lead Zirconate Titanate/Algan∕Gan Field Effect Transistor, Youn-Seon Kang, Qian Fan, Bo Xiao, Ya. I. Alivov, Jinqiao Xie, Norio Onojima, Sang-Jun Cho, Yong-Tae Moon, Hosun Lee, D. Johnstone, Hadis Morkoç, Young-Soo Park
Fabrication And Current-Voltage Characterization Of A Ferroelectric Lead Zirconate Titanate/Algan∕Gan Field Effect Transistor, Youn-Seon Kang, Qian Fan, Bo Xiao, Ya. I. Alivov, Jinqiao Xie, Norio Onojima, Sang-Jun Cho, Yong-Tae Moon, Hosun Lee, D. Johnstone, Hadis Morkoç, Young-Soo Park
Electrical and Computer Engineering Publications
We demonstrated ferroelectricfield effect transistors (FFETs) with hysteretic I-V characteristics in a modulation-doped field effect transistors(MODFET)AlGaN∕GaN platform with ferroelectricPb(Zr,Ti)O3 between a GaN channel and a gate metal. The pinch-off voltage was about 6–7V comparable to that of conventional Schottky gate MODFET. Counterclockwise hysteresis appeared in the transfer characteristics with a drain current shift of ∼5mA for zero gate-to-source voltage. This direction is opposite and much more pronounced than the defect induced clockwise hysteresis in conventional devices, which suggests that the key factor contributing to the counterclockwise hysteresis of the FFET is the ferroelectric switching effect of the lead zirconate titanate …
Effect Of Hydrostatic Pressure On The Dc Characteristics Of Algan∕Gan Heterojunction Field Effect Transistors, Y. Liu, P. P. Ruden, J. Xie, Hadis Morkoç, K.-A. Son
Effect Of Hydrostatic Pressure On The Dc Characteristics Of Algan∕Gan Heterojunction Field Effect Transistors, Y. Liu, P. P. Ruden, J. Xie, Hadis Morkoç, K.-A. Son
Electrical and Computer Engineering Publications
We report the effect of compressive hydrostatic pressure on the current-voltage characteristics ofAlGaN∕GaNheterojunction field effect transistors (HFETs) on a sapphire substrate. The drain current increases with hydrostatic pressure and the maximum relative increase occurs when the gate bias is near threshold and drain bias is slightly larger than saturation bias. The increase of the drain current is associated with a pressure induced shift of the threshold voltage by −8.0mV∕kbar that is attributed to an increase of the polarizationcharge density at the AlGaN∕GaN interface due to the piezoelectric effect. The results demonstrate the considerable potential of AlGaN∕GaNHFETs for strain sensor applications.
Admittance Of Cds Nanowires Embedded In Porous Alumina Template, A. Varfolomeev, D. Zaretsky, V. Pokalyakin, S. Tereshin, S. Pramanik, S. Bandyopadhyay
Admittance Of Cds Nanowires Embedded In Porous Alumina Template, A. Varfolomeev, D. Zaretsky, V. Pokalyakin, S. Tereshin, S. Pramanik, S. Bandyopadhyay
Electrical and Computer Engineering Publications
CdSnanowires of 10nm diameter, electrodeposited in porous alumina films, had shown a conductance bistability in the past [Appl. Phys. Lett.76, 460 (2000)]. The conductance has a high (ON) and a low (OFF) state. In the ON state, different sets of nanowires display qualitatively different relation between the conductance and capacitance. We propose a model to explain this anomalous behavior. Based on this model, we predict that the inelastic mean free path of electrons in the nanowires is 3–3.5nm at room temperature. This short mean free path may be a consequence of acoustic phonon confinement.
Spin Relaxation Of “Upstream” Electrons In Quantum Wires: Failure Of The Drift Diffusion Model, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay
Spin Relaxation Of “Upstream” Electrons In Quantum Wires: Failure Of The Drift Diffusion Model, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay
Electrical and Computer Engineering Publications
The classical drift diffusion (DD) model of spin transport treats spin relaxation via an empirical parameter known as the “spin diffusion length.” According to this model, the ensemble averaged spin of electrons drifting and diffusing in a solid decays exponentially with distance due to spin dephasing interactions. The characteristic length scale associated with this decay is the spin diffusion length. The DD model also predicts that this length is different for “upstream” electrons traveling in a decelerating electric field than for “downstream” electrons traveling in an accelerating field. However, this picture ignores energy quantization in confined systems (e.g., quantum wires) …
Dislocation Reduction In Gan Grown On Porous Tin Networks By Metal-Organic Vapor-Phase Epitaxy, Y. Fu, F. Yun, Y. T. Moon, Ü. Özgür, J. Q. Xie, X. F. Ni, N. Biyikli, H. Morkoç, Lin Zhou, David J. Smith, C. K. Inoki, T. S. Kuan
Dislocation Reduction In Gan Grown On Porous Tin Networks By Metal-Organic Vapor-Phase Epitaxy, Y. Fu, F. Yun, Y. T. Moon, Ü. Özgür, J. Q. Xie, X. F. Ni, N. Biyikli, H. Morkoç, Lin Zhou, David J. Smith, C. K. Inoki, T. S. Kuan
Electrical and Computer Engineering Publications
We report on the effectiveness of porous TiN nanonetworks on the reduction of threading dislocations (TDs) in GaN grown by metal-organic vapor-phase epitaxy (MOVPE). The porous TiN networks were formed by in situ annealing of thin-deposited Ti films deposited ex situ on GaN templates within the MOVPE growth chamber. Different annealing parameters in relation to surface porosity of TiN networks were investigated. Transmission electron micrographs indicated dislocation reduction by factors of up to 10 in GaN layers grown on the TiN nanonetwork, compared with a control sample. TiN prevented many dislocations present in the GaN templates from penetrating into the …
Effect Of Hydrostatic Pressure On The Current-Voltage Characteristics Of Gan∕Algan∕Gan Heterostructure Devices, Y. Liu, M. Z. Kauser, D. D. Schroepfer, P. P. Ruden, J. Xie, Y. T. Moon, N. Onojima, H. Morkoç, K.-A. Son, M. I. Nathan
Effect Of Hydrostatic Pressure On The Current-Voltage Characteristics Of Gan∕Algan∕Gan Heterostructure Devices, Y. Liu, M. Z. Kauser, D. D. Schroepfer, P. P. Ruden, J. Xie, Y. T. Moon, N. Onojima, H. Morkoç, K.-A. Son, M. I. Nathan
Electrical and Computer Engineering Publications
The current-voltage characteristics of n-GaN∕u-AlGaN∕n-GaN heterostructure devices are investigated for potential pressure sensor applications. Model calculations suggest that the current decreases with pressure as a result of the piezoelectric effect, and this effect becomes more significant with thicker AlGaN layers and increasing AlN composition. The change in current with pressure is shown to be highly sensitive to the change in interfacial polarization charge densities. The concept is verified by measuring the current versus voltage characteristics of an n-GaN∕u-Al0.2Ga0.8N∕n-GaN device under hydrostatic pressure over the range of 0–5 kbars. The measured current is found to decrease approximately linearly with applied pressure …
Growth Optimization And Structural Analysis For Ferromagnetic Mn-Doped Zno Layers Deposited By Radio Frequency Magnetron Sputtering, M. Abouzaid, P. Ruterana, C. Liu, H. Morkoç
Growth Optimization And Structural Analysis For Ferromagnetic Mn-Doped Zno Layers Deposited By Radio Frequency Magnetron Sputtering, M. Abouzaid, P. Ruterana, C. Liu, H. Morkoç
Electrical and Computer Engineering Publications
The effect of the deposition temperature on the crystalline quality of (Zn,Mn)O is investigated in thin films prepared by radio frequency magnetronsputtering on c-plane sapphire and GaN substrates. The layers are made of a 0.5μm Mn-doped layer towards the surface on top of a 150nm pure ZnO buffer. Depending on the deposition temperature, the layers can exhibit a columnar structure; the adjacent domains are rotated from one another by 90°, putting [101¯0]and [11¯20] directions face to face. At high Mn concentration the columnar structure is blurred by the formation of Mn rich precipitates. Only one variety of domains is observed …
Spectroscopic Ellipsometry And Absorption Study Of Zn1-Xmnxo/Al2o3 (0 <= X <= 0.08) Thin Films, Ghil Soo Lee, Ho Suk Lee, Tae Dong Kang, Hosun Lee, C. Liu, B. Xiao, Ü. Özgür, H. Morkoç
Spectroscopic Ellipsometry And Absorption Study Of Zn1-Xmnxo/Al2o3 (0 <= X <= 0.08) Thin Films, Ghil Soo Lee, Ho Suk Lee, Tae Dong Kang, Hosun Lee, C. Liu, B. Xiao, Ü. Özgür, H. Morkoç
Electrical and Computer Engineering Publications
We grow Zn1−xMnxO∕Al2O3 (0⩽x⩽0.08)thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5eV. Using the model of Holden et al. [T. Holden et al., Phys. Rev. B56, 4037 (1997)], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gapenergy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large …
Illumination And Annealing Characteristics Of Two-Dimensional Electron Gas Systems In Metal-Organic Vapor-Phase Epitaxy Grown Alxga1-Xn/Aln/Gan Heterostructures, N. Biyikli, Ü. Özgür, X. Ni, Y. Fu, H. Morkoç, Ç. Kurdak
Illumination And Annealing Characteristics Of Two-Dimensional Electron Gas Systems In Metal-Organic Vapor-Phase Epitaxy Grown Alxga1-Xn/Aln/Gan Heterostructures, N. Biyikli, Ü. Özgür, X. Ni, Y. Fu, H. Morkoç, Ç. Kurdak
Electrical and Computer Engineering Publications
We studied the persistent photoconductivity (PPC) effect in AlxGa1−xN∕AlN∕GaN heterostructures with two different Al compositions (x=0.15and x=0.25). The two-dimensional electron gas formed at the AlN∕GaN heterointerface was characterized by Shubnikov-de Haas and Hall measurements. Using optical illumination, we were able to increase the carrier density of the Al0.15Ga0.85N∕AlN∕GaN sample from 1.6×1012 to 5.9×1012cm−2, while the electron mobility was enhanced from 9540 to 21400cm2/Vs at T=1.6K. The persistent photocurrent in both samples exhibited a strong dependence on illumination wavelength, being highest close to the band gap and decreasing at longer wavelengths. The PPC effect became fairly weak for illumination wavelengths longer …