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20 Sep 2004

Volume 85, Issue 12, pp. 2157-2437

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Appl. Phys. Lett. 85, 2390 (2004); http://dx.doi.org/10.1063/1.1796520 (3 pages)

Stas Polonsky and Alan Weger
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Electromodulation of photoinduced charge transfer in polyfluorene bilayer devices

A. S. Dhoot, J. A. Hogan, A. C. Morteani, and N. C. Greenham

Appl. Phys. Lett. 85, 2256 (2004); http://dx.doi.org/10.1063/1.1793337 (3 pages) | Cited 4 times

Online Publication Date: 24 September 2004

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Photoinduced charge transfer at a conjugated polymer donor-acceptor heterojunction controls the ultimate photogeneration efficiency in photovoltaic devices. We have studied this charge transfer by measurements of electric-field-induced photoluminescence (PL) modulation in polyfluorene-based bilayer devices at room and low temperatures. Depending on the field direction across the interface we observe field-induced quenching or enhancement of the PL, which we ascribe to modulation of the exciton dissociation rate through modification of the energy of the charge-transfer state formed after charge separation.
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85.60.-q Optoelectronic devices
78.66.Qn Polymers; organic compounds
78.55.Qr Amorphous materials; glasses and other disordered solids
71.55.Ht Other nonmetals
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Palladium Schottky barrier contacts to hydrothermally grown n-ZnO and shallow electron states

Ulrike Grossner, Stig Gabrielsen, Thomas Moe Børseth, Joachim Grillenberger, Andrej Yu. Kuznetsov, and Bengt G. Svensson

Appl. Phys. Lett. 85, 2259 (2004); http://dx.doi.org/10.1063/1.1790592 (3 pages) | Cited 34 times

Online Publication Date: 24 September 2004

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Schottky barrier contacts have been formed by electron beam evaporation of Pd on the (000math)-face of hydrothermally grown n-type single-crystalline ZnO. The contacts can be operated under reverse bias voltages up to −5 V and in the temperature range between 130 and 350 K. A barrier height of 0.83 eV is deducted at room temperature, which is in reasonable agreement with the value predicted by fundamental theory. The ideality factor for the current-voltage characteristics varies between 1.01 and 1.03 in the voltage range of −5.0 to +0.5 V, indicating that thermionic emission is a dominant mechanism for charge-carrier transport. Thermal admittance measurements were performed between 15 and 350 K, and two prominent levels were resolved at 0.05(1) and 0.33(2) eV below the conduction band edge, respectively. The origin of these levels is not known, but possible candidates are complexes involving hydrogen, Zn interstitials, and vacancy-oxygen centers.
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85.30.Hi Surface barrier, boundary, and point contact devices
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
79.40.+z Thermionic emission
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Coherent states in a coupled quantum dot nanocrystalline silicon transistor

M. A. H. Khalafalla, Z. A. K. Durrani, and H. Mizuta

Appl. Phys. Lett. 85, 2262 (2004); http://dx.doi.org/10.1063/1.1795974 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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We investigate the coherent coupling of electronic states in a nanocrystalline silicon quantum dot transistor. The device consists of a nanometer-scale point-contact containing only a few silicon grains. The grains form quantum dots, tunnel-coupled across thin silicon sub-oxide grain boundaries. At 4.2 K, we observe a pattern of single-electron conductance peaks versus two gate voltages, caused by electrostatic coupling between the quantum dots. Additional peaks are observed when the energy levels from two adjacent quantum dots are resonant, which may be associated with “quasi-molecular” states formed by coherent coupling of the levels. The tunnel splitting obtained from the peak separation is ∼0.4 meV, which is from a few times to an order-of-magnitude larger than reported previously in GaAs∕AlGaAs quantum dots.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.35.Gv Single electron devices
61.72.Mm Grain and twin boundaries
71.20.Mq Elemental semiconductors
73.20.At Surface states, band structure, electron density of states

Ballistic hole emission luminescence

Ian Appelbaum, K. J. Russell, I. Shalish, V. Narayanamurti, M. P. Hanson, and A. C. Gossard

Appl. Phys. Lett. 85, 2265 (2004); http://dx.doi.org/10.1063/1.1793347 (3 pages) | Cited 2 times

Online Publication Date: 24 September 2004

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Using a method complementary to ballistic electron emission luminescence (BEEL), we demonstrate tunnel-junction injection of sub-band-gap hot holes into the valence band of a semiconductor heterostructure to generate band-gap luminescence. This mechanism can be used in a scanning-probe geometry for the development of a simultaneous hole transport and luminescence microscopy of p-type Schottky devices.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Jb Light-emitting devices
72.20.Ht High-field and nonlinear effects

Electrical activation phenomena induced by excimer laser annealing in B-implanted silicon

G. Fortunato, L. Mariucci, A. La Magna, P. Alippi, M. Italia, V. Privitera, B. Svensson, and E. Monakhov

Appl. Phys. Lett. 85, 2268 (2004); http://dx.doi.org/10.1063/1.1793352 (3 pages) | Cited 9 times

Online Publication Date: 24 September 2004

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The activation process induced by excimer laser annealing (ELA) has been investigated in 10 keV B-implanted samples. It is found that for energy densities inducing melt depths of the order or larger of the implanted region the junction depth is controlled by the melt depth, with activation approaching 100% and box-shaped carrier density distributions with abrupt junction profile. For energy densities inducing a melting shallower than the implanted region, two different activation mechanisms have been identified: the first occurring in the molten region and leading to complete B activation; the second occurring in the region immediately below the molten zone and leading to thermal activation of B, induced by the heat wave propagating into the Si wafer. This last process is characterized by an activation energy of 5 eV and is not accompanied by B diffusion. As a consequence, a deep tail of active B is produced, preventing the possibility to form abrupt and ultrashallow junctions. These results suggest that for the formation of ultrashallow junctions it is essential to combine ELA with ultralow energy ion implantation.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
66.30.J- Diffusion of impurities
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.70.D- Solid-liquid transitions
81.40.Gh Other heat and thermomechanical treatments
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Acceptor-bound exciton transition in Mg-doped AlN epilayer

N. Nepal, M. L. Nakarmi, K. B. Nam, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 85, 2271 (2004); http://dx.doi.org/10.1063/1.1796521 (3 pages) | Cited 8 times

Online Publication Date: 24 September 2004

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Mg-doped AlN epilayers grown by metalorganic chemical-vapor deposition have been studied by deep ultraviolet time-resolved photoluminescence (PL) spectroscopy. A PL emission line at 6.02 eV has been observed at 10 K in Mg-doped AlN, which is about 40 meV below the free-exciton transition in undoped AlN epilayer. Temperature dependence of the PL intensity of this emission line also reveals a binding energy of 40 meV. This transition line is believed to be due to the recombination of an exciton bound to neutral Mg acceptor (I1) with a binding energy of Ebx=40 meV. This value is also about 10% of the energy level of Mg impurity in AlN satisfying Haynes’ rule. The recombination lifetime of the I1 transition in Mg-doped AlN has been measured to be 130 ps, which is close to the expected value. The larger Ebx of the acceptor-bound exciton in AlN than that in GaN is due to large effective masses of the electrons and holes, as well as the energy level of Mg impurity.
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71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

Depletion-mode ZnO nanowire field-effect transistor

Y. W. Heo, L. C. Tien, Y. Kwon, D. P. Norton, S. J. Pearton, B. S. Kang, and F. Ren

Appl. Phys. Lett. 85, 2274 (2004); http://dx.doi.org/10.1063/1.1794351 (3 pages) | Cited 119 times

Online Publication Date: 24 September 2004

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Single ZnO nanowire metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated using nanowires grown by site selective molecular-beam epitaxy. When measured in the dark at 25°C, he depletion-mode transistors exhibit good saturation behavior, a threshold voltage of ∼−3 V, and a maximum transconductance of order 0.3 mS∕mm. Under ultraviolet (366 nm) illumination, the drain–source current increase by approximately a factor of 5 and the maximum transconductance is ∼5 mS∕mm. The channel mobility is estimated to be ∼3 cm2∕V s, which is comparable to that reported for thin film ZnO enhancement mode MOSFETs, and the on∕off ratio was ∼25 in the dark and ∼125 under UV illumination.
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85.30.Tv Field effect devices
81.07.Bc Nanocrystalline materials
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Magnetotransport in C-doped AlGaAs heterostructures

B. Grbić, C. Ellenberger, T. Ihn, K. Ensslin, D. Reuter, and A. D. Wieck

Appl. Phys. Lett. 85, 2277 (2004); http://dx.doi.org/10.1063/1.1781750 (3 pages) | Cited 15 times

Online Publication Date: 24 September 2004

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High-quality C-doped p-type AlGaAs heterostructures with mobilities exceeding 150 000 cm2∕V s are investigated by low-temperature magnetotransport experiments. We find features of the fractional quantum Hall effect as well as a highly resolved Shubnikov–de Haas oscillations at low magnetic fields. This allows us to determine the densities, effective masses, and mobilities of the holes populating the spin-split subbands arising from the lack of inversion symmetry in these structures.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.43.Qt Magnetoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
73.61.Ey III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

An n- to p-type conductivity transition induced by oxygen adsorption on α-Fe2O3

A. Gurlo, N. Bârsan, A. Oprea, M. Sahm, T. Sahm, and U. Weimar

Appl. Phys. Lett. 85, 2280 (2004); http://dx.doi.org/10.1063/1.1794853 (3 pages) | Cited 34 times

Online Publication Date: 24 September 2004

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The simultaneous measurements of conductance and work function changes induced by gaseous ambient have been performed on α-Fe2O3 thick film polycrystalline samples kept at 280 °C and exposed to different gaseous atmospheres. The switching from n- to p-type conductivity on α-Fe2O3 is shown to have an electronic origin, which is due to the oxygen adsorption and formation of a surface inversion layer and, therefore, to the inversion of the surface conduction type. The modeling of the n–p switching is described in terms of conductance dependence on the band bending induced by gaseous ambient.
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72.60.+g Mixed conductivity and conductivity transitions
73.25.+i Surface conductivity and carrier phenomena
68.43.Mn Adsorption kinetics
71.30.+h Metal-insulator transitions and other electronic transitions
75.50.Gg Ferrimagnetics
73.40.Cg Contact resistance, contact potential
71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states
71.55.Ht Other nonmetals

Cooperative polymer gate dielectrics in organic thin-film transistors

S. Young Park, Mikyung Park, and Hong H. Lee

Appl. Phys. Lett. 85, 2283 (2004); http://dx.doi.org/10.1063/1.1794857 (3 pages) | Cited 41 times

Online Publication Date: 24 September 2004

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A concept is introduced in which two polymer dielectrics are made cooperative in acting as the gate insulator for organic thin-film transistors. The bilayer insulator consists of a thin polymer dielectric in contact with the active layer that can induce good electrical properties and a much thicker dielectric with good dielectric properties. These dielectrics are cooperative in combining the best each can offer for a high mobility and a negligible hysteresis.
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85.30.Tv Field effect devices
77.55.-g Dielectric thin films
73.61.Ng Insulators
85.65.+h Molecular electronic devices
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