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2 Jun 2003

Volume 82, Issue 22, pp. 3811-3991

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Appl. Phys. Lett. 82, 3958 (2003); http://dx.doi.org/10.1063/1.1579125 (3 pages)

E. Zussman, D. Rittel, and A. L. Yarin
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High electron mobility of epitaxial ZnO thin films on c-plane sapphire grown by multistep pulsed-laser deposition

E. M. Kaidashev, M. Lorenz, H. von Wenckstern, A. Rahm, H.-C. Semmelhack, K.-H. Han, G. Benndorf, C. Bundesmann, H. Hochmuth, and M. Grundmann

Appl. Phys. Lett. 82, 3901 (2003); http://dx.doi.org/10.1063/1.1578694 (3 pages) | Cited 171 times

Online Publication Date: 27 May 2003

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A multistep pulsed-laser deposition (PLD) process is presented for epitaxial, nominally undoped ZnO thin films of total thickness of 1 to 2 μm on c-plane sapphire substrates. We obtain reproducibly high electron mobilities from 115 up to 155 cm2/V s at 300 K in a narrow carrier concentration range from 2 to 5×1016 cm−3. The key issue of the multistep PLD process is the insertion of 30-nm-thin ZnO relaxation layers deposited at reduced substrate temperature. The high-mobility samples show atomically flat surface structure with grain size of about 0.5–1 μm, whereas the surfaces of low-mobility films consist of clearly resolved hexagonally faceted columnar grains of only 200-nm size, as shown by atomic force microscopy. Structurally optimized PLD ZnO thin films show narrow high-resolution x-ray diffraction peak widths of the ZnO(0002) ω- and 2Θ-scans as low as 151 and 43 arcsec, respectively, and narrow photoluminescence linewidths of donor-bound excitons of 1.7 meV at 2 K. © 2003 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
81.05.Dz II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces
71.35.-y Excitons and related phenomena

Cyclotron resonance of terahertz photoresponse in two-dimensional polar semiconductors at high temperatures

X. L. Lei and S. Y. Liu

Appl. Phys. Lett. 82, 3904 (2003); http://dx.doi.org/10.1063/1.1579853 (3 pages) | Cited 2 times

Online Publication Date: 27 May 2003

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Far infrared photoresponse of magnetoresistivity ΔRxx of two-dimensional electron systems is investigated theoretically at high temperatures. Photon-assisted impurity and phonon scatterings, rather than the electron heating, are shown to be the dominant mechanisms for high-temperature photoresponse at cyclotron resonance. Based on the theory developed for electron magnetotransport driven by intense terahertz radiations, we have calculated the far infrared photoresistivity of a GaAs/AlGaAs heterostructure at temperature T = 150 K, predicting notable cyclotron resonance of ΔRxx, in agreement with the experimental finding. Contrary to low temperature case, where the electron heating is almost solely responsible for the cyclotron resonance of ΔRxx, at T = 150 K electron-heating contribute at most a small fraction of the total response. © 2003 American Institute of Physics.
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76.40.+b Diamagnetic and cyclotron resonances
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
72.40.+w Photoconduction and photovoltaic effects

Morphology and electronic transport of polycrystalline pentacene thin-film transistors

D. Knipp, R. A. Street, and A. R. Völkel

Appl. Phys. Lett. 82, 3907 (2003); http://dx.doi.org/10.1063/1.1578536 (3 pages) | Cited 108 times

Online Publication Date: 27 May 2003

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Temperature-dependent measurements of thin-film transistors were performed to gain insight in the electronic transport of polycrystalline pentacene. Devices were fabricated with plasma-enhanced chemical vapor deposited silicon nitride gate dielectrics. The influence of the dielectric roughness and the deposition temperature of the thermally evaporated pentacene films were studied. Although films on rougher gate dielectrics and films prepared at low deposition temperatures exhibit similar grain size, the electronic properties are different. Increasing the dielectric roughness reduces the free carrier mobility, while low substrate temperature leads to more and deeper hole traps. © 2003 American Institute of Physics.
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85.65.+h Molecular electronic devices
85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.37.Ps Atomic force microscopy (AFM)

Improved morphology for ohmic contacts to AlGaN/GaN high electron mobility transistors using WSix- or W-based metallization

B. Luo, F. Ren, R. C. Fitch, J. K. Gillespie, T. Jenkins, J. Sewell, D. Via, A. Crespo, A. G. Baca, R. D. Briggs, D. Gotthold, R. Birkhahn, B. Peres, and S. J. Pearton

Appl. Phys. Lett. 82, 3910 (2003); http://dx.doi.org/10.1063/1.1579845 (3 pages) | Cited 18 times

Online Publication Date: 27 May 2003

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A comparison was made of specific contact resistivity and morphology of Ti/Al/Pt/WSi/Ti/Au and Ti/Al/Pt/W/Ti/Au ohmic contacts to AlGaN/GaN heterostructures relative to the standard Ti/Al/Pt/Au metallization. The W- and WSi-based contacts show comparable specific resistivities to that of the standard contact on similar layer structures, reaching minimum values of ∼ 10−5 Ω cm2 after annealing in the range 850–900 °C. However, the W- and WSi-based contacts exhibit much smoother surface morphologies, even after 950 °C annealing. For example, the root-mean-square roughness of the Ti/Al/Pt/WSi/Ti/Au contact annealed at 950 °C was unchanged from the as-deposited values whereas the Ti/Al/Pt/Au contact shows significant deterioration of the morphology under these conditions. The improved thermal stability of the W- and WSix-based contacts is important for maintaining edge acuity during high-temperature operation. © 2003 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential
85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

Ion-implanted In0.53Ga0.47As for ultrafast optoelectronic applications

C. Carmody, H. H. Tan, C. Jagadish, A. Gaarder, and S. Marcinkevičius

Appl. Phys. Lett. 82, 3913 (2003); http://dx.doi.org/10.1063/1.1579565 (3 pages) | Cited 28 times

Online Publication Date: 27 May 2003

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Undoped In0.53Ga0.47As epilayers were implanted with 2-MeV Fe+ ions at doses of 1×1015 and 1×1016 cm−2 at room temperature and annealed at temperatures between 500 and 800 °C. Hall-effect measurements show that after annealing, layers with resistivities on the order of 105 Ω/square can be achieved. Carrier lifetimes as short as 300 fs are observed for samples annealed at 500 and 600 °C. For higher annealing temperatures, characteristic times of the optical response are on the order of a few picoseconds. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
61.80.Jh Ion radiation effects
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.82.Fk Semiconductors

Thickness-dependent stress effect in p-type metal–oxide–semiconductor structure investigated by substrate injection current

Chao-Chi Hong, Wei-Jian Liao, and Jenn-Gwo Hwu

Appl. Phys. Lett. 82, 3916 (2003); http://dx.doi.org/10.1063/1.1581004 (3 pages) | Cited 4 times

Online Publication Date: 27 May 2003

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The effects of oxide, Si wafer, and gate Al thicknesses on the substrate injection currents (Jsub) of p-type metal–oxide–semiconductor structures with ultrathin oxides are studied. Jsub is reported to be both trap-related (interface and Si bulk) and Si band gap-related (intrinsic carrier concentration). Both mechanisms have given rise to the stress near the Si/SiO2 interface. Current–voltage and capacitance–voltage characterizations reveal that Jsub increases with oxide thickness, which is suggested to be dominated by the trap-related mechanism. A stronger dependence of Jsub on a change in oxide thickness is observed for a thicker Si wafer, which is proposed to be mainly caused by the band gap-related mechanism. Furthermore, a thicker gate Al introduces a higher Jsub, which is proposed to be due to both the trap-related and the band gap-related mechanisms. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Observation of a scanning tunneling microscopy induced photocurrent during ballistic electron emission microscopy

E. R. Heller and J. P. Pelz

Appl. Phys. Lett. 82, 3919 (2003); http://dx.doi.org/10.1063/1.1579844 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2003

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We report that a scanning tunneling microscope induced photocurrent (STM–PC) can occur during ballistic electron emission microscopy (BEEM) measurements on Schottky-barrier samples with typical efficiency of 10−4–10−6 and apparent BEEM threshold slightly above the substrate semiconductor band gap. This STM–PC resembles normal BEEM current, and hence, can interfere with BEEM measurements of structures with intrinsically low signal and/or intrinsic BEEM threshold voltage larger than the substrate band gap. We discuss a simple test for the existence of STM–PC during BEEM measurements. © 2003 American Institute of Physics.
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68.37.Vj Field emission and field-ion microscopy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.30.+y Surface double layers, Schottky barriers, and work functions
73.50.Pz Photoconduction and photovoltaic effects

Hot-electron spectroscopy in parallel magnetic fields

M. Kast, W. Boxleitner, C. Pacher, G. Strasser, and E. Gornik

Appl. Phys. Lett. 82, 3922 (2003); http://dx.doi.org/10.1063/1.1579119 (3 pages) | Cited 1 time

Online Publication Date: 27 May 2003

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Hot-electron spectroscopy in the presence of magnetic fields applied parallel to the current direction is studied. Inter-Landau-level transitions are observed due to scattering processes in the drift region of the hot-electron transistor. In high magnetic fields, the reduced phase space of elastic/inelastic scattering is directly observed as a decrease of the energetic widths of ballistic/phonon-replica peaks. This results in an increased resolution of the hot-electron spectroscopy to be well below ΔE = 10 meV. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Determination of the electron capture time in quantum-well infrared photodetectors using time-resolved photocurrent measurements

S. Steinkogler, H. Schneider, M. Walther, and P. Koidl

Appl. Phys. Lett. 82, 3925 (2003); http://dx.doi.org/10.1063/1.1579855 (3 pages) | Cited 5 times

Online Publication Date: 27 May 2003

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We have investigated the transport properties of optically excited electrons in a 100 period InGaAs/GaAs-quantum well infrared photodetector. The electrons were excited by femtosecond-infrared laser pulses and the transient photocurrent was recorded in the picosecond regime. We have carefully analyzed the measured photocurrent transients taking into account both the capture time τc and the transit time τtrans. Our experimental results allow us to determine τc, which increases from 10 ps at 5 kV/cm to about 20 ps at 20 kV/cm. We have also measured the noise gain in order to determine the transit time and the drift velocity. The dynamic parameters extracted from our measurements are consistent with values from the literature. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Hs Quantum wells
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
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