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28 Feb 2005

Volume 86, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 86, 093101 (2005); http://dx.doi.org/10.1063/1.1870108 (3 pages)

G. S. Paraoanu and A. M. Halvari
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Photoinduced generation of electron anions in H-doped nanoporous oxide 12CaO∙7Al2O3: Toward an optically controlled formation of electrides

Peter V. Sushko, Alexander L. Shluger, Katsuro Hayashi, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 86, 092101 (2005); http://dx.doi.org/10.1063/1.1871359 (3 pages) | Cited 12 times

Online Publication Date: 23 February 2005

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We suggest, on the basis of detailed ab initio calculations of both ground and photoexcited states of H-doped 12CaO∙7Al2O3 (C12A7:H), that stable high-conductivity regions can be optically generated in this insulating system. Each H− ion in C12A7:H can, under photoirradiation at 3.8–4.5 eV, produce up to two electrons and a proton that binds to the lattice network and forms OH−. Mobile electrons play a role of anions in this system. They move over subnanosized cages of the C12A7 lattice via polaron hopping. The insulating state is reversibly restored upon heating to 300 °C.
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73.22.-f Electronic structure of nanoscale materials and related systems
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
71.38.-k Polarons and electron-phonon interactions
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Strongly localized exciton luminescence in Cr-doped GaN

S. Shanthi, M. Hashimoto, Y. K. Zhou, S. Kimura, S. Emura, S. Hasegawa, N. Hasuike, H. Harima, and H. Asahi

Appl. Phys. Lett. 86, 092102 (2005); http://dx.doi.org/10.1063/1.1871365 (3 pages) | Cited 6 times

Online Publication Date: 23 February 2005

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Low-temperature photoluminescence spectrum of the transition metal Cr-doped GaN (GaCrN) shows unusual high-intensity emission lines at 3.365 and 3.311 eV. The spectrum also contains a weak neutral donor bound excitonic transition of wurtzite GaN at 3.47 eV, free excitonic transition of GaCrN at 3.29 eV, and two low-intensity lines at 3.24 and 3.17 eV. From our investigations, we attribute these high-intensity lines to the stacking faults which can bind excitons and are due to the coexistence of wurtzite and zinc blende phases of GaN. The 3.24 and 3.17 eV lines are interpreted as phonon replica lines of the 3.31 eV emission line.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.66.Fd III-V semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
78.55.Cr III-V semiconductors
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
61.72.Nn Stacking faults and other planar or extended defects
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Effect of electrical bias on metastability in hydrogenated nanocrystalline silicon solar cells

Guozhen Yue, Baojie Yan, Jeffrey Yang, and Subhendu Guha

Appl. Phys. Lett. 86, 092103 (2005); http://dx.doi.org/10.1063/1.1872212 (3 pages) | Cited 11 times

Online Publication Date: 23 February 2005

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The effect of electrical bias on metastability in hydrogenated nanocrystalline silicon (nc-Si:H) solar cells is studied. We find that forward bias current injection in the dark does not cause any degradation in nc-Si:H solar cells, while light soaking under reverse bias enhances the light-induced degradation in the cell performance. These phenomena are contrary to those found in hydrogenated amorphous silicon solar cells. We argue that the forward injected carriers mainly transport through the nanocrystallites where carrier recombination does not create metastable defects. The increased degradation under reverse bias is explained in terms of the heterogeneity of the material structure.
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84.60.Jt Photoelectric conversion
85.30.-z Semiconductor devices

Magnetocapacitance probing of the many-particle states in InAs dots

Oliver S. Wibbelhoff, Axel Lorke, Dirk Reuter, and Andreas D. Wieck

Appl. Phys. Lett. 86, 092104 (2005); http://dx.doi.org/10.1063/1.1872219 (3 pages) | Cited 17 times

Online Publication Date: 23 February 2005

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We use frequency-dependent capacitance-voltage spectroscopy to measure the tunneling probability into self-assembled InAs quantum dots. Using an in-plane magnetic field of variable strength and orientation, we are able to obtain information on the quasiparticle wave functions in momentum space for one to two electrons per dot. For the lowest two energy states, we find a good agreement with Gaussian functions for a harmonic potential. The high-energy orbitals exhibit signatures of anisotropic confinement and correlation effects.
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81.16.Dn Self-assembly
75.75.-c Magnetic properties of nanostructures
73.21.La Quantum dots
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment

Thickness scaling of the space-charge-limited current in poly(p-phenylene vinylene)

P. W. M. Blom, C. Tanase, D. M. de Leeuw, and R. Coehoorn

Appl. Phys. Lett. 86, 092105 (2005); http://dx.doi.org/10.1063/1.1868865 (3 pages) | Cited 38 times

Online Publication Date: 23 February 2005

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Charge transport in light-emitting diodes (LEDs) based on a poly(p-phenylene vinylene) (PPV) derivative is investigated as a function of sample thickness. Via the thickness dependence, the contributions from the electric field and charge carrier density to the mobility in space-charge-limited (SCL) diodes can be disentangled. It is demonstrated that a field-dependent mobility weakens the thickness dependence of the SCL current, whereas a carrier-density-dependent mobility gives rise to an enhanced thickness dependence. The enhanced thickness dependence of the experimental SCL current in PPV is in agreement with the predictions using a density-dependent mobility only. This observation confirms that in PPV-based LEDs, the hole transport is dominated by filling of the localized states.
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85.60.Jb Light-emitting devices
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
72.20.Fr Low-field transport and mobility; piezoresistance

Spectroscopic characterization of 1.3 μm GaInNAs quantum-well structures grown by metal-organic vapor phase epitaxy

H. D. Sun, A. H. Clark, S. Calvez, M. D. Dawson, Y. N. Qiu, J. M. Rorison, K. S. Kim, T. Kim, and Y. J. Park

Appl. Phys. Lett. 86, 092106 (2005); http://dx.doi.org/10.1063/1.1868866 (3 pages) | Cited 1 time

Online Publication Date: 23 February 2005

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We report optical studies of high-quality 1.3 μm strain-compensated GaInNAs/GaAs single-quantum-well structures grown by metalorganic vapor phase epitaxy. Photoluminescence excitation (PLE) spectroscopy shows clearly the electronic structure of the two-dimensional quantum well. The transition energies between quantized states of the electrons and holes are in agreement with theoretical calculations based on the band anti-crossing model in which the localized N states interact with the extended states in the conduction band. We also investigated the polarization properties of the luminescence by polarized edge-emission measurements. Luminescence bands with different polarization characters arising from the electron to heavy-hole and light-hole transitions, respectively, have been identified and verify the transition assignment observed in the PLE spectrum.
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78.67.De Quantum wells
73.21.Fg Quantum wells
68.65.Fg Quantum wells
81.07.St Quantum wells
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.20.Fz Weak or Anderson localization

Ti gate compatible with atomic-layer-deposited HfO2 for n-type metal-oxide-semiconductor devices

Hyundoek Yang, Yunik Son, Sungkwon Baek, Hyunsang Hwang, Hajin Lim, and Hyung-Seok Jung

Appl. Phys. Lett. 86, 092107 (2005); http://dx.doi.org/10.1063/1.1871362 (3 pages) | Cited 18 times

Online Publication Date: 24 February 2005

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The electrical characteristics were evaluated for the metal-oxide-semiconductor (MOS) devices with Ti and Pt gates on the atomic-layer-deposited (ALD) HfO2. The equivalent oxide thickness (EOT) of the Ti gate is shown to be nearly the same as that of the Pt gate, which means that a negligible chemical reaction occurs between the gate and dielectric. The values of the effective metal work function (Φm,eff), extracted from the conventional relations of flatband voltage versus EOT, were ∼ 4.2 eV for Ti and ∼ 5.4 eV for Pt, respectively. However, somewhat higher values of Φm,eff were extracted by considering the existence of an interfacial layer and the high negative charge at an interface between HfO2 and interfacial layer. The exact values of Φm,eff were ∼ 4.37 eV for Ti and ∼ 5.51 eV for Pt, respectively. Therefore, the Ti gate is compatible with ALD-HfO2 and can be a candidate for n-type MOS devices.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.30.+y Surface double layers, Schottky barriers, and work functions

Electrical and optical properties of Mg-doped Al0.7Ga0.3N alloys

M. L. Nakarmi, K. H. Kim, M. Khizar, Z. Y. Fan, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 86, 092108 (2005); http://dx.doi.org/10.1063/1.1879098 (3 pages) | Cited 24 times

Online Publication Date: 25 February 2005

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Mg-doped Al0.7Ga0.3N epilayers ( ∼ 1 μm) were grown on an AlN/sapphire template by metalorganic chemical vapor deposition and the electrical and optical properties of these epilayers were studied. For optimized Mg-doped Al0.7Ga0.3N epilayers, we have obtained a resistivity around 105 Ω cm at room temperature and confirmed p-type conduction at elevated temperatures(>700 K) with a resistivity of about 40 Ω cm at 800 K. From the temperature dependent Hall effect measurement, the activation energy of Mg acceptor is found to be around 400 meV for Al0.7Ga0.3N alloy. The optimized Mg-doped Al0.7Ga0.3N epilayers have been incorporated into the deep-ultraviolet (UV) (λ<300 nm) light-emitting diode (LED) structures as an electron blocking layer. An enhancement in the performance of the UV LEDs was obtained. LEDs with peak emission wavelengths at 280 nm were fabricated with a circular geometry (300 μm disk diameter). Output power reached 0.35 mW at 20 mA and 1.1 mW at 150 mA dc current. The importance of Mg-doped Al0.7Ga0.3N alloys to suppress the long-wavelength emission components in deep-UV LEDs and the fundamental limit for achieving p-type Al-rich AlGaN alloys are also discussed.
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81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
85.60.Jb Light-emitting devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Fi Electroluminescence
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
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