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6 Sep 2004

Volume 85, Issue 10, pp. 1659-1861

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1793 (2004); http://dx.doi.org/10.1063/1.1790588 (3 pages)

Hyunsik Yoon, Kyoung Mi Lee, Dahl-Young Khang, Hong H. Lee, and Se-Jin Choi
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Laser threshold reduction in an all-spiro guest–host system

D. Schneider, T. Rabe, T. Riedl, T. Dobbertin, M. Kröger, E. Becker, H.-H. Johannes, W. Kowalsky, T. Weimann, J. Wang, and P. Hinze

Appl. Phys. Lett. 85, 1659 (2004); http://dx.doi.org/10.1063/1.1792794 (3 pages) | Cited 22 times

Online Publication Date: 13 September 2004

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We report on stimulated emission in an all-spiro guest–host (G–H) system. Different doping concentrations of the guest molecule 2,2′,7,7′-tetrakis(2,2-diphenylvinyl)spiro-9,9′-bifluorene in the host material 2,7-bis(biphenyl-4-yl)-2′, 7′-di-tert-butyl-9,9′-spirobifluorene were investigated for amplified spontaneous emission (ASE) and distributed feedback (DFB) lasing. The ASE maximum could be shifted over 20 nm by variation of the doping concentration. DFB lasing is observed in the pure host, the pure guest material, and in the G–H system. The laser wavelength can be tuned from 401.5 to 529.3 nm by changing the grating period of the Bragg reflector and the doping concentration. A minimum threshold energy density of 6 μJ∕cm2 was observed in second-order DFB structures for a doping concentration of 1.1%. In first-order DFB operation the threshold value could be further lowered to 320 nJ∕cm2. These results render this material system an excellent candidate for stable and widely tunable lasers in the visible spectrum.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials

Replica-molded electro-optic polymer Mach–Zehnder modulator

George T. Paloczi, Yanyi Huang, Amnon Yariv, Jingdong Luo, and Alex K.-Y. Jen

Appl. Phys. Lett. 85, 1662 (2004); http://dx.doi.org/10.1063/1.1787944 (3 pages) | Cited 27 times

Online Publication Date: 13 September 2004

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A Mach–Zehnder electro-optic polymer amplitude modulator is fabricated by a simple and high-throughput soft-stamp replica-molding technique. The modulator structure incorporates the highly nonlinear and stable chromophore, AJL8, doped in amorphous polycarbonate. Single-arm phase-retardation results in a halfwave voltage (Vπ) of 8.4 V at 1600 nm. The on/off extinction ratio is better than 19 dB, resulting from precise Y-branch power splitters and good waveguide uniformity. These results indicate that the simple fabrication process allows for good optical performance from high-fidelity replicas of the original master devices.
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07.60.Ly Interferometers
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Jk Polymers and organics
81.10.Fq Growth from melts; zone melting and refining
42.65.Wi Nonlinear waveguides

Photodimerization in dipeptides for high capacity optical digital storage

P. S. Ramanujam and Rolf H. Berg

Appl. Phys. Lett. 85, 1665 (2004); http://dx.doi.org/10.1063/1.1787948 (3 pages) | Cited 7 times

Online Publication Date: 13 September 2004

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We have developed peptide materials with chromophores that undergo cycloaddition, suitable for terabit optical digital storage in a 5.25 in. disc. The rationale behind this design is that the length and rigidity of the backbone can be adjusted to facilitate the formation of a photodimer without large physical movements of the chromophores on exposure to UV light. Initially strongly absorbing films transmit up to 50% of light on irradiation at dimerizing wavelengths. This property can be utilized to record grey levels. An intensity-dependent transmission behavior has been observed that may enable data to be written and read at the same wavelength.
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82.30.Nr Association, addition, insertion, cluster formation
78.66.Qn Polymers; organic compounds
61.82.Pv Polymers, organic compounds
42.70.Jk Polymers and organics
78.40.Me Organic compounds and polymers
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
82.50.-m Photochemistry
42.79.Vb Optical storage systems, optical disks

InGaAs-on-Si single photon avalanche photodetectors

Y. Kang, Y.-H. Lo, M. Bitter, S. Kristjansson, Z. Pan, and A. Pauchard

Appl. Phys. Lett. 85, 1668 (2004); http://dx.doi.org/10.1063/1.1788882 (3 pages) | Cited 8 times

Online Publication Date: 13 September 2004

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In this letter, an InGaAs-on-Si single photon avalanche diode (SPAD) for telecommunication wavelengths is presented. This SPAD demonstrates high-single-photon quantum efficiency and low-dark-count probability under gated mode operation. We attributed the good performance of this device to the high absorption coefficient of InGaAs and low noise avalanche multiplication of Si.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
72.40.+w Photoconduction and photovoltaic effects
85.30.Kk Junction diodes
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Zero voltage Freedericksz transition in periodically aligned liquid crystals

James N. Eakin, Yunhe Xie, Robert A. Pelcovits, Marc D. Radcliffe, and Gregory P. Crawford

Appl. Phys. Lett. 85, 1671 (2004); http://dx.doi.org/10.1063/1.1789578 (3 pages) | Cited 39 times

Online Publication Date: 13 September 2004

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Patterned alignment layers have been created through an approach using polarization holography and a photopolymerizable alignment layer. This technique enables continuously periodic boundary conditions on planar surfaces. Polarization gratings have been created using polarization interference from incident right-handed and left-handed circular polarization exposure conditions. A simple phenomenological model is derived to show that the Freedericksz threshold voltage vanishes when the cell gap and grating pitch are comparable.
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42.40.Eq Holographic optical elements; holographic gratings
64.70.M- Transitions in liquid crystals
42.79.Dj Gratings
42.70.Jk Polymers and organics
42.25.Hz Interference
42.70.Df Liquid crystals
61.30.Vx Polymer liquid crystals

2.9 THz quantum cascade lasers operating up to 70 K in continuous wave

S. Barbieri, J. Alton, H. E. Beere, J. Fowler, E. H. Linfield, and D. A. Ritchie

Appl. Phys. Lett. 85, 1674 (2004); http://dx.doi.org/10.1063/1.1784874 (3 pages) | Cited 80 times

Online Publication Date: 13 September 2004

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We report the operation of a quantum cascade laser emitting at a 103 μm wavelength (2.9 THz). The active region is based on a bound-to-continuum design allowing a low parasitic leakage current, and a high upper-to-lower-state lifetime ratio. The latter is demonstrated by a pronounced decrease of the differential resistance at threshold, which is visible up to high temperatures, and by a weak temperature dependence of the slope efficiency. At 4 K, we report a threshold current density of only 105 A∕cm2 both in pulsed and continuous-wave operation, and an emitted peak power of 15 mW independent of the duty cycle. Maximum operating temperatures of 95 K and 70 K are observed in pulsed and continuous wave modes, respectively.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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Reduction of the electrostatic coupling in a large-area internal inductively coupled plasma source using a multicusp magnetic field

Y. J. Lee, K. N. Kim, G. Y. Yeom, and M. A. Lieberman

Appl. Phys. Lett. 85, 1677 (2004); http://dx.doi.org/10.1063/1.1784877 (3 pages) | Cited 5 times

Online Publication Date: 13 September 2004

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A large area (1020 mm×830 mm) inductively coupled plasma (ICP) source has been developed using an internal-type linear antenna with permanent magnets forming a multicusp magnetic field. The large rf antenna voltages, which cause the electrostatic coupling between the antenna and the plasma in a large area internal-type linear-antenna ICP source, were decreased significantly by applying the magnetic field near and parallel to the antenna. Through the application of the magnetic field, an approximately 20% higher plasma density, with a value of close to 1.0×1011 cm−3 at a rf power of 2000 W, and about three times higher photoresist etch rates were observed, while maintaining the plasma nonuniformity at less than 9%.
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52.50.Dg Plasma sources
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.-b Plasma properties
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n-type conductivity in ultrananocrystalline diamond films

Oliver A. Williams, Stephane Curat, Jennifer E. Gerbi, Dieter M. Gruen, and Richard B. Jackman

Appl. Phys. Lett. 85, 1680 (2004); http://dx.doi.org/10.1063/1.1785288 (3 pages) | Cited 66 times

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Hall effect measurements have been carried out to determine the carrier density and mobilities in ultrananocrystalline diamond films grown with added nitrogen. The results show clear n-type conductivity with very low thermal activation energy. Mobility values of 1.5 cm2 V−1 s−1 are found for a sheet carrier concentration of 2×1017 cm−2. These measurements indicate that ultrananocrystalline films grown with high nitrogen levels in the growth gas mixture can have bulk carrier concentrations of up to 1021, which is very high for diamond films. The n-type nature of this material was also confirmed by Seebeck effect measurements.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Cw Elemental semiconductors
73.50.Lw Thermoelectric effects
81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
68.55.A- Nucleation and growth
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.S- Impurities in crystals
61.72.up Other materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Transmission electron microscopy study of blisters in high-temperature annealed He and H co-implanted single-crystal silicon

S. Frabboni, G. C. Gazzadi, L. Felisari, R. Tonini, F. Corni, and G. Ottaviani

Appl. Phys. Lett. 85, 1683 (2004); http://dx.doi.org/10.1063/1.1790031 (3 pages) | Cited 4 times

Online Publication Date: 13 September 2004

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Transmission electron microscopy has allowed us to draw the three-dimensional structure of blisters formed after high-temperature annealing of He-H co-implanted silicon by combining the unique capability of site-selective cross sectioning of the focused ion beam with conventional plan view images. It has been shown that blisters are formed by crystalline lamellae strongly bended, plastically deformed, and suspended over buried empty cavities. The volume of the protruding blister surface is almost equal to the buried empty volumes, thus suggesting a mechanism for blister formation based on H and He precipitation and migration of silicon atoms toward the surface.
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68.47.Fg Semiconductor surfaces
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
61.72.uf Ge and Si
61.66.Bi Elemental solids

Influence of overlayer thickness on the density of Lomer dislocations in nanoscale Ni–Cu bilayer thin films

D. Mitlin, A. Misra, T. E. Mitchell, R. G. Hoagland, and J. P. Hirth

Appl. Phys. Lett. 85, 1686 (2004); http://dx.doi.org/10.1063/1.1779343 (3 pages) | Cited 5 times

Online Publication Date: 13 September 2004

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We report on the evolution of the spacing and the character of misfit dislocations with increasing Ni overlayer thickness at an (001) Ni–Cu interface. At low Ni overlayer thicknesses (3 and 5 nm), most of the interface dislocations are 60° 1∕2〈110〉 glide dislocations, while Lomer edge dislocations constitute only about 5% of the total interface dislocation content. At a 13 nm Ni overlayer thickness, the fraction of Lomer dislocations increases to approximately 40% of the total content. This dramatic increase in the fraction of Lomer dislocations is likely related to a “rebound mechanism” which initiates at some critical thickness between 5 and 13 nm.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Near-infrared electroluminescence at room temperature from neodymium-doped gallium nitride thin films

Joo Han Kim and Paul H. Holloway

Appl. Phys. Lett. 85, 1689 (2004); http://dx.doi.org/10.1063/1.1781745 (3 pages) | Cited 13 times

Online Publication Date: 13 September 2004

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Strong near-infrared (NIR) electroluminescence (EL) at room temperature from neodymium (Nd)-doped gallium nitride (GaN) thin films is reported. The Nd-doped GaN films were grown by radio-frequency planar magnetron cosputtering of separate GaN and metallic Nd targets in a pure nitrogen ambient. X-ray diffraction data did not identify the presence of any secondary phases and revealed that the Nd-doped GaN films had a highly textured wurtzite crystal structure with the c-axis normal to the surface of the film. The EL devices were fabricated with a thin-film multilayered structure of Al∕Nd-doped GaN∕Al2O3–TiO2∕indium-tin oxide and tested at room temperate. Three distinct NIR EL emission peaks were observed from the devices at 905, 1082, and 1364 nm, arising from the radiative relaxation of the 4F3∕2 excited-state energy level to the 4I9∕2, 4I11∕2, and 4I13∕2 levels of the Nd3+ ion, respectively. The threshold voltage for all the three emission peaks was ∼150 V. The external power efficiency of the fabricated EL devices was ∼1×10−5 measured at 40 V above the threshold voltage.
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85.60.Jb Light-emitting devices
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.65.Ac Multilayers
73.21.Ac Multilayers
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Mechanisms of nitrogen incorporation in GaAsN alloys

M. Reason, H. A. McKay, W. Ye, S. Hanson, R. S. Goldman, and V. Rotberg

Appl. Phys. Lett. 85, 1692 (2004); http://dx.doi.org/10.1063/1.1789237 (3 pages) | Cited 23 times

Online Publication Date: 13 September 2004

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We have investigated nitrogen incorporation mechanisms in dilute nitride GaAsN alloys grown by plasma-assisted molecular-beam epitaxy. A comparison of nuclear reaction analysis and Rutherford backscattering spectrometry in channeling and nonchanneling conditions reveals significant composition-dependent incorporation of N into nonsubstitutional sites, presumably as either N–N or N–As split interstitials. Furthermore, we identify the (2×1) reconstruction as the surface structure which leads to the highest substitutional N incorporation, likely due to the high number of group V sites per unit area available for N–As surface exchange.
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81.05.Ea III-V semiconductors
68.47.Fg Semiconductor surfaces
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.J- Point defects and defect clusters
61.72.S- Impurities in crystals
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition

Nanoindentation of polycrystalline silicon-carbide thin films studied by acoustic emission

X.-G. Ma, K. Komvopoulos, and D. B. Bogy

Appl. Phys. Lett. 85, 1695 (2004); http://dx.doi.org/10.1063/1.1784880 (3 pages) | Cited 1 time

Online Publication Date: 13 September 2004

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Nanoindentation experiments and in situ monitoring of acoustic emission (AE) were used to investigate the evolution of deformation in polycrystalline silicon-carbide thin films. An acoustic sensor attached to the holder of the indenter tip was used to continuously record the AE signal during nanoindentation. The amplitudes of the AE wave forms were used to analyze the response of the indented films in the time domain. In addition, a hybrid time-frequency analysis of the AE events was performed in order to determine the dominant frequencies of the deformation events encountered during nanoindentation. The effects of the film thickness and microstructure and the indenter tip radius on the film deformation behavior are interpreted in terms of the AE response and associated deformation mechanisms. The findings of this study demonstrate that in situ AE monitoring provides potentially useful information about microstructure changes associated with nanoscale deformation processes, such as grain boundary cracking, in thin films subjected to normal contact loading.
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68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
61.72.Mm Grain and twin boundaries
62.20.Qp Friction, tribology, and hardness
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing

Cobalt valence in epitaxial Ti0.93Co0.07O2 anatase

M. L. Cui, J. Zhu, X. Y. Zhong, Y. G. Zhao, and X. F. Duan

Appl. Phys. Lett. 85, 1698 (2004); http://dx.doi.org/10.1063/1.1784885 (3 pages) | Cited 16 times

Online Publication Date: 13 September 2004

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Anatase Ti0.93Co0.07O2 films, synthesized by pulsed-laser deposition, have been investigated in the transmission electron microscope using selected area electron diffraction, energy dispersive x-ray analysis, and electron-energy-loss spectroscopy (EELS), and by x-ray diffraction measurements. It is found that Co ions are soluble in anatase, and that the unit-cell c-axis parameter is shortened, in some areas to even less than that in pure TiO2 anatase films. This observation was ascribed to substitution of the smaller Co3+ ions into the TiO2 anatase lattice. The EELS data confirm that Co is in either a +2 or +3 formal oxidation state in ferromagnetic Ti0.93Co0.07O2 films.
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81.15.Fg Pulsed laser ablation deposition
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
68.55.A- Nucleation and growth

Spectroscopic ellipsometry characterization of HfxSiyOz films using the Cody–Lorentz parameterized model

J. Price, P. Y. Hung, T. Rhoad, B. Foran, and A. C. Diebold

Appl. Phys. Lett. 85, 1701 (2004); http://dx.doi.org/10.1063/1.1784889 (3 pages) | Cited 26 times

Online Publication Date: 13 September 2004

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A parameterized, Kramers–Kronig consistent, Cody–Lorentz optical model is used to simulate the dielectric response of thin HfxSiyOz films. Optical constants are determined in the range 0.75–8.35 eV. The Cody–Lorentz model has three specific differences when compared to the previously employed Tauc–Lorentz model: (1) weak exponential absorption below the band gap, (2) a modified joint density-of-states, and (3) a restriction on the ε1(∞) parameter. These three differences allow the Cody–Lorentz model to have an improved fit to experimental data. As a result of a more accurate optical model for HfxSiyOz, we were able to identify an interfacial layer with thickness in close agreement with transmission electron microscopy measurements. Use of the Tauc–Lorentz model when fitting the same experimental data could not identify an interfacial layer. Results are also discussed in which the Cody–Lorentz model shows sensitivity to varying degrees of silicate composition.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators
77.55.-g Dielectric thin films

Self-assembling in AlxGa1−xNyAs1−y alloys

V. A. Elyukhin, V. M. Sánchez-R., and O. V. Elyukhina

Appl. Phys. Lett. 85, 1704 (2004); http://dx.doi.org/10.1063/1.1789574 (3 pages) | Cited 11 times

Online Publication Date: 13 September 2004

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The self-assembling of the isoelectronic cation impurities in lightly anion-doped AlxGa1−xNyAs1−y alloys with the zinc blende structure is predicted. The tetrahedral surroundings of Ga (Al) impurity atoms should be formed around As (N) impurity atoms in AlN-enriched (GaAs-enriched) alloys. The cation impurity concentrations for the complete Ga (Al) surroundings of all As (N) atoms are estimated at the higher growth and lower annealing temperatures. The advantage of the Al–N and Ga–As bonding over the Al–As and Ga–N bonding is an origin of the self-assembling in lightly isoelectronically-doped AlxGa1−xNyAs1−y alloys.
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81.05.Ea III-V semiconductors
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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Gate-controlled resonant interband tunneling in silicon

S. Sedlmaier, Krishna K. Bhuwalka, A. Ludsteck, M. Schmidt, J. Schulze, W. Hansch, and I. Eisele

Appl. Phys. Lett. 85, 1707 (2004); http://dx.doi.org/10.1063/1.1783023 (3 pages) | Cited 7 times

Online Publication Date: 13 September 2004

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We present gate-controlled resonant interband tunneling on silicon 〈111〉. The investigated structure principally consists of a vertical, gated p-i-n diode grown by molecular beam epitaxy. We evaluated the surface tunnel current from a gate-induced two-dimensional electron channel into the quantized hole states of a degenerately doped δp+ layer. This current reveals a negative differential resistance due to resonant interband tunneling in the forward biased p-i-n diode at 200 K. Even at room temperature the influence of this tunnel mechanism is observed. The experimental results are in good agreement with simulated band diagrams and their dependence on the applied voltages.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
68.55.A- Nucleation and growth
71.20.Mq Elemental semiconductors
73.40.Gk Tunneling
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

High-electron-mobility AlGaN∕AlN∕GaN heterostructures grown on 100-mm-diam epitaxial AlN/sapphire templates by metalorganic vapor phase epitaxy

M. Miyoshi, H. Ishikawa, T. Egawa, K. Asai, M. Mouri, T. Shibata, M. Tanaka, and O. Oda

Appl. Phys. Lett. 85, 1710 (2004); http://dx.doi.org/10.1063/1.1790073 (3 pages) | Cited 40 times

Online Publication Date: 13 September 2004

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Al0.26Ga0.74N∕AlN∕GaN heterostructures with 1-nm-thick AlN interfacial layers were grown on 100-mm-diam epitaxial AlN/sapphire templates and sapphire substrates by metalorganic vapor phase epitaxy. It was found that AlN/sapphire templates significantly enhanced the electron mobility of the two-dimensional electron gas (2DEG) confined at the GaN channel. This can be explained by the high-crystal-quality GaN channel realized by the use of epitaxial AlN/sapphire templates as substrates. The very high Hall mobilities of approximately 2100 cm2∕V s at room temperature and approximately 17 000 cm2∕V s at 77 K with a 2DEG density of approximately 1×1013∕cm2 were uniformly obtained for AlGaN∕AlN∕GaN heterostructures on 100-mm-diam epitaxial AlN/sapphire templates. The Hall mobility of AlGaN∕AlN∕GaN heterostructures on epitaxial AlN/sapphire templates reached a very high value of 25 500 cm2∕V s at 15 K.
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81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Deep subsurface electronic defect image contrast and resolution amplification in Si wafers using infrared photocarrier radiometry

Jerias Batista, Andreas Mandelis, Derrick Shaughnessy, and Bincheng Li

Appl. Phys. Lett. 85, 1713 (2004); http://dx.doi.org/10.1063/1.1785289 (3 pages) | Cited 5 times

Online Publication Date: 13 September 2004

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A photocarrier radiometry technique using a secondary subband-gap dc light source is introduced, along with the applications to deep subsurface electronic defect analysis in Si wafers. It is shown that the use of a dc light source, in addition to the modulated laser beam, drastically enhances the potential of the technique in resolving low-level damage otherwise virtually indistinguishable by conventional photothermal techniques. Using this methodology, the overall contrast enhancement was about 386% for amplitude and 5586% in phase over conventional photocarrier radiometry.
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71.55.Cn Elemental semiconductors
42.30.Va Image forming and processing
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.72.-g Optical sources and standards
42.60.Fc Modulation, tuning, and mode locking
73.20.Hb Impurity and defect levels; energy states of adsorbed species
07.60.Dq Photometers, radiometers, and colorimeters

Stability of deep centers in 4H-SiC epitaxial layers during thermal annealing

Y. Negoro, T. Kimoto, and H. Matsunami

Appl. Phys. Lett. 85, 1716 (2004); http://dx.doi.org/10.1063/1.1790032 (3 pages) | Cited 22 times

Online Publication Date: 13 September 2004

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N-type epitaxial 4H-SiC layers grown by hot-wall chemical vapor deposition were investigated with regard to deep centers by capacitance-voltage measurements and deep level transient spectroscopy (DLTS). The DLTS spectra revealed that the concentrations of deep centers were reduced by one order of magnitude by annealing at 1700 °C, compared to those in an as-grown material. The Z1∕2 center with an energy level of 0.59±0.03 eV and the EH6∕7 center with an energy level of 1.66±0.11 eV below the conduction band edge are annealed out at a temperature of 1700 °C or higher.
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71.55.Ht Other nonmetals
73.40.Ns Metal-nonmetal contacts
71.20.Nr Semiconductor compounds
61.72.Cc Kinetics of defect formation and annealing
85.30.Hi Surface barrier, boundary, and point contact devices

Schottky emission at the metal polymer interface and its effect on the polarization switching of ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer thin films

Feng Xia and Q. M. Zhang

Appl. Phys. Lett. 85, 1719 (2004); http://dx.doi.org/10.1063/1.1786364 (3 pages) | Cited 14 times

Online Publication Date: 13 September 2004

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In metal/insulator/metal sandwich structure, the interface between the metal and the insulator thin films plays significant roles in the functional performance of the thin films. In ferroelectric poly(vinylidene fluoride-trifluoroethylene) copylmer thin films metallized by different metals, it is found that the polarization switching is asymmetric due to the work function difference of the metal electrodes, and the degree of asymmetry increases with the increasing work function difference. For the samples with high work function metals as both or at least one of the electrodes, the polarization switching is much faster. The current–voltage curves at various temperatures indicated the interface-controlled asymmetric phenomena are mainly determined by the Schottky emission and charge injection at the metal/insulator polymer interface.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Rw Metal-insulator-metal structures
61.41.+e Polymers, elastomers, and plastics
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
73.61.-r Electrical properties of specific thin films
68.35.Ct Interface structure and roughness
77.80.Dj Domain structure; hysteresis

Electron mobility in very low density GaN∕AlGaN∕GaN heterostructures

M. J. Manfra, K. W. Baldwin, A. M. Sergent, R. J. Molnar, and J. Caissie

Appl. Phys. Lett. 85, 1722 (2004); http://dx.doi.org/10.1063/1.1784887 (3 pages) | Cited 15 times

Online Publication Date: 13 September 2004

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We report on the transport properties of a tunable two-dimensional electron gas (2DEG) confined at the lower interface of a GaN∕Al0.06Ga0.94N∕GaN heterostructure grown by plasma-assisted molecular beam epitaxy on semi-insulating GaN templates prepared by hydride vapor phase epitaxy. Using an insulated gate Hall bar structure, the electron density is continuously tuned from ∼2×1012 down to 1.5×1011 cm−2. At T=300 mK, the 2DEG displays a maximum mobility of 80 000 cm2∕V s at a sheet density of 1.75×1012 cm−2. At low densities, the mobility exhibits a power law dependence on density −μ∼neα, with α∼1.0, over the range of 2×1011–1×1012 cm−2. In this density regime, the mobility is no longer limited by alloy scattering and long-range Coulomb scattering dominates. We discuss the dominant scattering mechanisms that presently limit low temperature mobility at electron densities below 1×1012 cm−2.
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81.05.Ea III-V semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition

Level crossing conductance spectroscopy of molecular bridges

F. Remacle and R. D. Levine

Appl. Phys. Lett. 85, 1725 (2004); http://dx.doi.org/10.1063/1.1791745 (3 pages) | Cited 5 times

Online Publication Date: 13 September 2004

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A possible mechanism for negative differential resistance is discussed. The level crossing is induced by the source-drain voltage applied across the bridge. The effect is most dramatic when the zero field levels that are resonant with the electrodes are almost degenerate. It is suggested that such degeneracies can arise often when the junctions on either side are weakly coupled by the bridge. Quantitative results for I–V curves are reported on the basis of high-level electronic structure computations for the junction–bridge–junction region and where the electric field is included in the Hamiltonian.
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31.10.+z Theory of electronic structure, electronic transitions, and chemical binding
33.80.Be Level crossing and optical pumping
36.40.Cg Electronic and magnetic properties of clusters

Room temperature sensing of ozone by transparent p-type semiconductor CuAlO2

X. G. Zheng, K. Taniguchi, A. Takahashi, Y. Liu, and C. N. Xu

Appl. Phys. Lett. 85, 1728 (2004); http://dx.doi.org/10.1063/1.1784888 (2 pages) | Cited 28 times

Online Publication Date: 13 September 2004

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A transparent p-type semiconductor, CuAlO2, shows selective and reversible response to ozone gas at room temperature. All existing commercial semiconductor ozone sensors are of n type. This study demonstrates the feasibility of developing an inexpensive p type and transparent ozone sensor. Types of transparent p–n junction ozone sensors may be fabricated using the p-type semiconductor CuAlO2 and existing n-type transparent materials such as In2O3.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Electrical characterization of Cd∕CdTe Schottky barrier diodes

Whitney Mason, L. A. Almeida, A. W. Kaleczyc, and J. H. Dinan

Appl. Phys. Lett. 85, 1730 (2004); http://dx.doi.org/10.1063/1.1784873 (3 pages) | Cited 6 times

Online Publication Date: 13 September 2004

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We have deposited Cd metal contacts on molecular-beam epitaxy CdTe(112)B on Si(112) and have made electronic transport measurements to deduce the properties of the Schottky barrier diode thus formed. We find a room-temperature barrier height ϕB=0.92 eV and an ideality factor n≈2. We suggest that the high value of n is due to generation–recombination currents associated with dislocations in the CdTe epilayer.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
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