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29 Sep 2008

Volume 93, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 132101 (2008); http://dx.doi.org/10.1063/1.2988720 (3 pages)

Yueh-Nan Chen and Lukas Gilz
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Wavelength controlled multilayer-stacked linear InAs quantum dot arrays on InGaAsP/InP (100) by self-organized anisotropic strain engineering: A self-ordered quantum dot crystal

N. Sritirawisarn, F. W. M. van Otten, T. J. Eijkemans, and R. Nötzel

Appl. Phys. Lett. 93, 131906 (2008); http://dx.doi.org/10.1063/1.2993178 (3 pages) | Cited 2 times

Online Publication Date: 30 September 2008

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Multilayer-stacked linear InAs quantum dot (QD) arrays are created on InAs/InGaAsP superlattice templates formed by self-organized anisotropic strain engineering on InP (100) substrates in chemical beam epitaxy. Stacking of the QD arrays with identical emission wavelength in the 1.55 μm region at room temperature is achieved through the insertion of ultrathin GaAs interlayers beneath the QDs with increasing interlayer thickness in successive layers. The increment in the GaAs interlayer thickness compensates the QD size/wavelength increase during strain correlated stacking. This is the demonstration of a three-dimensionally self-ordered QD crystal with fully controlled structural and optical properties.
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68.55.ag Semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
85.40.Sz Deposition technology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Cd Superlattices
78.66.Fd III-V semiconductors

Al-based metallic glass composites containing fcc Pb-rich crystalline spheres

Jie He, Haiquan Li, Jiuzhou Zhao, and Chunli Dai

Appl. Phys. Lett. 93, 131907 (2008); http://dx.doi.org/10.1063/1.2993342 (3 pages) | Cited 6 times

Online Publication Date: 30 September 2008

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Liquid immiscible systems present a unique opportunity in designing composites with sphere-dispersed microstructure. The authors report here phase formation of a multicomponent Al82.87Pb2.5Ni4.88Y7.8Co1.95 alloy upon melt spinning. The alloy undergoes liquid-liquid phase transformation in the liquid immiscibility gap and subsequently solidifies into Pb-rich crystalline phase and Al-rich amorphous phase. The Pb-rich phase with sphere shape is dispersed in the Al-based metallic glass matrix. The average diameter of the Pb-rich spheres is ∼ 0.62 μm near the free side and ∼ 0.03 μm near the wheel side of the ribbon.
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81.05.Pj Glass-based composites, vitroceramics
81.20.-n Methods of materials synthesis and materials processing
81.30.Fb Solidification
64.70.D- Solid-liquid transitions
64.70.Ja Liquid-liquid transitions
61.72.-y Defects and impurities in crystals; microstructure

Localized heating and thermal characterization of high electrical resistivity silicon-on-insulator sensors using nematic liquid crystals

Oguz H. Elibol, Bobby Reddy, Jr., and Rashid Bashir

Appl. Phys. Lett. 93, 131908 (2008); http://dx.doi.org/10.1063/1.2993350 (3 pages) | Cited 4 times

Online Publication Date: 30 September 2008

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We present a method for localized heating of media at the surface of silicon-on-insulator field-effect sensors via application of an ac voltage across the channel and the substrate and compare this technique with standard Joule heating via the application of dc voltage across the source and drain. Using liquid crystals as the medium to enable direct temperature characterization, our results show that under comparable bias conditions, heating of the medium using an alternating field results in a greater increase in temperature with a higher spatial resolution. These features are very attractive as devices are scaled to the nanoscale dimensions.
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07.20.Hy Furnaces; heaters
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
61.30.-v Liquid crystals

Deep/shallow levels in arsenic-doped HgCdTe determined by modulated photoluminescence spectra

Fangyu Yue, Jun Wu, and Junhao Chu

Appl. Phys. Lett. 93, 131909 (2008); http://dx.doi.org/10.1063/1.2983655 (3 pages) | Cited 10 times

Online Publication Date: 2 October 2008

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The modulated photoluminescence spectra have been performed on as-grown and in situ annealed arsenic-doped Hg1−xCdxTe grown by molecular beam epitaxy. Besides the discussions about shallow levels including VHg, AsHg, VHg–AsHg complex, and TeHg, two deep levels have been observed in as-grown with an ionization energy of ∼ 77.0 and ∼ 95.0 meV, respectively, which can be completely eliminated by annealing and temporarily ascribed to As-related clusters or interstitials.
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71.55.Gs II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
61.72.jj Interstitials

Optical properties of heavily boron-doped nanocrystalline diamond films studied by spectroscopic ellipsometry

A. Zimmer, O. A. Williams, K. Haenen, and H. Terryn

Appl. Phys. Lett. 93, 131910 (2008); http://dx.doi.org/10.1063/1.2990679 (3 pages) | Cited 6 times

Online Publication Date: 2 October 2008

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The optical properties of heavily boron-doped nanocrystalline diamond films grown by microwave plasma enhanced chemical vapor deposition on silicon substrates are presented. The diamond films are characterized by spectroscopic ellipsometry within the midinfrared, visible, and near-ultraviolet regions. The ellipsometric spectra are also found to be best described by a four-phase model yielding access to the optical constants, which are found distinct from previous nanocrystalline diamond literature values. The presence of a subgap absorption yielding high extinction coefficient values defined clearly the boron incorporated films in comparison to both undoped and composite films, while refractive index values are relatively comparable.
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78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.ag Semiconductors

Carbon-hydrogen bonding in near-frictionless carbon

J. A. Johnson, J. B. Woodford, D. Rajput, A. I. Kolesnikov, J. A. Schleuter, O. L. Eryilmaz, and A. Erdemir

Appl. Phys. Lett. 93, 131911 (2008); http://dx.doi.org/10.1063/1.2990757 (3 pages) | Cited 2 times

Online Publication Date: 2 October 2008

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The uniquely low friction behavior of near-frictionless carbon (NFC) as compared to conventional diamondlike carbon (DLC) is determined by the bonding within the film. Inelastic neutron scattering (INS) and Fourier transform infrared (FTIR) spectroscopy were used to probe the bonding environment of carbon and hydrogen; both INS and FTIR can probe the whole sample. Previous work has focused on surface studies; the present results show that in the film as a whole the majority of the hydrogen is adjacent to sp3-bonded carbon. In addition this work has determined the absence of any molecular hydrogen in NFC.
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81.05.U- Carbon/carbon-based materials
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
78.30.Hv Other nonmetallic inorganics

Nitrogen-polar GaN growth evolution on c-plane sapphire

Q. Sun, Y. S. Cho, I.-H. Lee, J. Han, B. H. Kong, and H. K. Cho

Appl. Phys. Lett. 93, 131912 (2008); http://dx.doi.org/10.1063/1.2993333 (3 pages) | Cited 18 times

Online Publication Date: 2 October 2008

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This letter presents a study on N-polar GaN growth evolution on sapphire using a low-temperature GaN buffer, which is distinctly different from the two-step growth of Ga-polar GaN according to both in situ reflectance and ex situ microscopy. Annealed N-polar GaN buffer exhibits densely packed tiny grains, serving as a template for the subsequent high-temperature GaN growth, which starts in a quasi-two-dimensional mode without any roughening-recovery process. Atomically smooth N-polar GaN has been achieved with no stacking fault or inversion domain observed. The mosaic microstructure, electrical, and optical properties of N-polar GaN are compared with those of Ga-polar GaN.
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72.80.Ey III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.40.Gh Other heat and thermomechanical treatments

Process induced mechanical stress in InP ridge waveguides fabricated by inductively coupled plasma etching

M. Avella, J. Jiménez, F. Pommereau, J. P. Landesman, and A. Rhallabi

Appl. Phys. Lett. 93, 131913 (2008); http://dx.doi.org/10.1063/1.2994691 (3 pages) | Cited 3 times

Online Publication Date: 2 October 2008

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Inductively coupled plasma (ICP) etching is suitable for producing semiconductor structures with a high aspect ratio. While the morphology of the structures is very satisfactory, less is known about other aspects related to the process, but with potential influence in the optical performance of the devices. We present herein a study of the mechanical stresses produced by the ICP process in the fabrication of ridge waveguides in InP. Stresses purely induced by the process are revealed by the spectral analysis of the cathodoluminescence. A dependence of the stress distribution on the aspect ratio of the waveguides is demonstrated.
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52.77.Bn Etching and cleaning
78.60.Hk Cathodoluminescence, ionoluminescence
84.40.Az Waveguides, transmission lines, striplines

Evolution of infrared photoreflectance lineshape with temperature in narrow-gap HgCdTe epilayers

Jun Shao, Lili Ma, Xiang Lü, Wei Lu, Jun Wu, F.-X. Zha, Y.-F. Wei, Z.-F. Li, S.-L. Guo, J.-R. Yang, Li He, and J.-H. Chu

Appl. Phys. Lett. 93, 131914 (2008); http://dx.doi.org/10.1063/1.2996030 (3 pages) | Cited 4 times

Online Publication Date: 2 October 2008

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Temperature-dependent (11–290 K) infrared photoreflectance (PR) measurements are performed on as-grown arsenic-doped HgCdTe epilayers in a midinfrared spectral region. Main PR features near bandedge manifest clear evolution of lineshape with temperature, of which the fittings identify besides a band-band process several below-gap processes. Analyses show that these features are due to photomodulation-induced screening of donor-acceptor pairs and photomodulation of band- impurity and band-band reflectance, their intensities correlate to the joint concentration of the involved energetic states. Temperature-dependent infrared PR may be a right optical spectroscopy for identifying impurity levels in semiconductors such as HgCdTe with high-density impurities.
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78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

Structural investigation of GaAs1−xBix/GaAs multiquantum wells

Yoriko Tominaga, Yusuke Kinoshita, Kunishige Oe, and Masahiro Yoshimoto

Appl. Phys. Lett. 93, 131915 (2008); http://dx.doi.org/10.1063/1.2993343 (3 pages) | Cited 14 times

Online Publication Date: 3 October 2008

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GaAs1−xBix/GaAs multiquantum wells (MQWs) have been grown in the layer-by-layer mode of molecular beam epitaxy. A well-defined multilayered structure of the MQWs has been confirmed by cross-sectional transmission microscopy and high-resolution x-ray diffraction measurements. Photoluminescence has been observed from GaAs1−xBix/GaAs MQW at room temperature. The MQW structures have been confirmed to be thermally stable even after annealing up to 800 °C, although they need to be grown at a low temperature (350–400 °C) for Bi incorporation.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Optical constants of silicon in near infrared region

V. Ya. Mendeleyev, S. N. Skovorodko, E. N. Lubnin, and V. M. Prosvirikov

Appl. Phys. Lett. 93, 131916 (2008); http://dx.doi.org/10.1063/1.2994669 (3 pages)

Online Publication Date: 3 October 2008

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Refractive index (n) and extinction coefficient (χ) spectra for n-type silicon with impurity concentrations Ni = 2.3×1012 cm−3 and Ni = 4.5×1018 cm−3 are determined from measured reflectance and transmittance of silicon samples in the 0.7–1.8 μm range. In the 0.81–0.92 μm range, the spectra have a region of the anomalous dispersion and peaks, which are associated with interband transitions. It was found that the increase in Ni leads to increasing n and χ in the ranges of 0.70–0.81 and 0.90–1.80 μm, respectively, and decreasing n in the 0.86–1.80 μm range. For Ni = 2.3×1012 cm−3, χ depends slightly on wavelength in the 1.15–1.8 μm range.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.sd Impurity concentration
78.30.Am Elemental semiconductors and insulators

Photoreflectance of InN and InN:Mg layers: An evidence of Fermi level shift toward the valence band upon Mg doping in InN

R. Kudrawiec, T. Suski, J. Serafińczuk, J. Misiewicz, D. Muto, and Y. Nanishi

Appl. Phys. Lett. 93, 131917 (2008); http://dx.doi.org/10.1063/1.2995989 (3 pages) | Cited 7 times

Online Publication Date: 3 October 2008

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Photoreflectance (PR) has been applied to study the energy-gap related absorption in undoped and Mg-doped InN layers. This technique, due to its sensitivity to built-in electric fields, enables studies of the Fermi level position inside an InN bulk. Narrow PR resonance at 0.68 eV has been observed in the unintentionally doped n-InN layer at 10 K. Due to Mg doping this resonance broadens drastically and exhibits the Franz–Keldysh oscillations typical for band-to-band absorption in a region with strong band bending. Such changes in PR spectra are evidences of a strong Fermi level shift toward the valence band due to Mg doping in the probed bulklike region of a sample.
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71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
78.20.-e Optical properties of bulk materials and thin films

A percolation model for insulator-metal transition in polymer-conductor composites

Q. Q. Yang and J. Z. Liang

Appl. Phys. Lett. 93, 131918 (2008); http://dx.doi.org/10.1063/1.2995992 (3 pages) | Cited 3 times

Online Publication Date: 3 October 2008

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In order to reveal the important influence of the aggregate structure of conductive component to the percolation behavior of polymer-conductor composites, a percolation model, which is based on the percolation theory and the equivalent sphere of aggregate that acts as a basic cell, is proposed. A formula, describing the relationship of the conductivity and the volume fraction of conductive component, and an expression, estimating percolation threshold of the composites, are derived. Based on these expressions, the electrical conductivity and percolation threshold of some composites are predicted. The results show that the predictions are reasonably consistent with the experimental data.
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64.60.ah Percolation
73.40.Ns Metal-nonmetal contacts
72.80.Le Polymers; organic compounds (including organic semiconductors)

Crystallographically oriented Zn nanocrystals formed in ZnO by Mn+-implantation

Y. J. Li, B. Zhang, W. Lu, Y. Wang, and J. Zou

Appl. Phys. Lett. 93, 131919 (2008); http://dx.doi.org/10.1063/1.2996028 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2008

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The nanostructural characteristics of ZnO implanted with Mn+ to doses ranging from 1×1015 to 1×1017 cm−2 are systematically studied for both as-implanted and postannealed cases. The detailed structural characterizations confirmed that the Mn+ implantation and postannealing result in (1) the formation of crystallographically orientated Zn nanocrystals in the ZnO matrix and (2) Mn atoms occupy the Zn sites in ZnO.
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81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
81.16.-c Methods of micro- and nanofabrication and processing
61.72.uj III-V and II-VI semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.72.Cc Kinetics of defect formation and annealing

The correlation between pentatomic and heptatomic carbon rings and stress of hydrogenated amorphous carbon films prepared by dc-pulse plasma chemical vapor deposition

Qi Wang, Chengbing Wang, Zhou Wang, Junyan Zhang, and Deyan He

Appl. Phys. Lett. 93, 131920 (2008); http://dx.doi.org/10.1063/1.2996273 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2008

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Hydrogenated diamondlike carbon films were prepared at different reactive times by dc-pulse plasma chemical vapor deposition technique. The thickness of the film increased significantly with the reactive time, and the stress is just 0.9 GPa when the thickness of the film increased to 2 μm. The structure analysis by high resolution transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and Fourier transform infrared spectra revealed a close relationship between the residual compressive stress and the microstructure of the films, which nanometer scale curved graphite sheets with pentatomic and heptatomic rings bestowed the film lower stress.
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81.05.U- Carbon/carbon-based materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.at Other materials
79.60.Ht Disordered structures
78.30.Na Fullerenes and related materials
78.66.Tr Fullerenes and related materials

Nanotip formation on a carbon nanotube pillar array for field emission application

Padmnabh Rai, Dipti R. Mohapatra, K. S. Hazra, D. S. Misra, and S. P. Tiwari

Appl. Phys. Lett. 93, 131921 (2008); http://dx.doi.org/10.1063/1.2996283 (3 pages) | Cited 9 times

Online Publication Date: 3 October 2008

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The field emission of a carbon nanotube (CNT) pillar array has been improved significantly by plasma treatment in a mixture of hydrogen and nitrogen gases. The plasma treatment for 30 s on a pillar array decreased the turn-on electric field from 0.48 to 0.37 V/μm and increased the field enhancement factor from 6200 to 6900. The emission current density increased by a factor of ≈ 40. We report in this letter the technique of generating nanotips on CNT pillars with an enormous potential to become a tool for the control and manipulation of CNTs and nanostructures.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing

Different optical absorption edges in AlN bulk crystals grown in m- and c-orientations

P. Lu, R. Collazo, R. F. Dalmau, G. Durkaya, N. Dietz, and Z. Sitar

Appl. Phys. Lett. 93, 131922 (2008); http://dx.doi.org/10.1063/1.2996413 (3 pages) | Cited 5 times

Online Publication Date: 3 October 2008

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AlN single crystals were grown on m-plane (10math0) and c-plane (000math) AlN seeds under identical growth conditions. The m-plane AlN crystals exhibited substantially lower oxygen incorporation, ∼ 1018 cm−3, than the c-plane crystals, ∼ 1019 cm−3. By investigating optical transmission spectra, m-plane AlN had absorption bands at 4.05 and 4.35 eV, while c-plane AlN had an absorption band edge at 4.85 eV. These below bandgap absorption bands strongly correlate with the reported transitions related to Al vacancy-impurity complexes, such as the complex of an Al vacancy and two oxygen atoms, (VAl–2ON)1− and the complex of an Al vacancy and one oxygen atom, (VAl–ON)2−, becoming the major cause for the poor, below bandgap optical transparency (α>200 cm−1) of these crystals.
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61.50.-f Structure of bulk crystals
71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
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Proposal for observation of retardation effect between two quantum dots via current noise

Yueh-Nan Chen and Lukas Gilz

Appl. Phys. Lett. 93, 132101 (2008); http://dx.doi.org/10.1063/1.2988720 (3 pages)

Online Publication Date: 29 September 2008

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We propose to observe the retardation effect between two quantum dots in a one-dimensional waveguide. The effect of retardation is more pronounced comparing to that in free space. If the photons are to be reflected by a mirror at one of the ends, the interference role played by the reflecting photon is found to be destructive. With the combination of p-i-n junction, the retardation effect can be read out via current-noise spectrums.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.79.Gn Optical waveguides and couplers

Single-valley high-mobility (110) AlAs quantum wells with anisotropic mass

S. Dasgupta, S. Birner, C. Knaak, M. Bichler, A. Fontcuberta i Morral, G. Abstreiter, and M. Grayson

Appl. Phys. Lett. 93, 132102 (2008); http://dx.doi.org/10.1063/1.2991448 (3 pages) | Cited 6 times

Online Publication Date: 29 September 2008

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We studied a doping series of (110)-oriented AlAs quantum wells (QWs) and observed transport evidence of single anisotropic-mass valley occupancy for the electrons in a 150 Å wide QW. Our calculations of strain and quantum confinement for these samples predict single anisotropic-mass valley occupancy for well widths W greater than 53 Å. Below this, double-valley occupation is predicted such that the longitudinal mass axes are collinear. We observed mobility anisotropy in the electronic transport along the crystallographic directions in the ratio of 2.8, attributed to the mass anisotropy as well as anisotropic scattering of the electrons in the X-valley of AlAs.
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73.63.Hs Quantum wells
73.21.Fg Quantum wells
72.20.Fr Low-field transport and mobility; piezoresistance
81.05.Ea III-V semiconductors
81.07.St Quantum wells

Achieving high Curie temperature in (Ga,Mn)As

M. Wang, R. P. Campion, A. W. Rushforth, K. W. Edmonds, C. T. Foxon, and B. L. Gallagher

Appl. Phys. Lett. 93, 132103 (2008); http://dx.doi.org/10.1063/1.2992200 (3 pages) | Cited 42 times

Online Publication Date: 29 September 2008

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We study the effects of growth temperature, Ga:As ratio, and postgrowth annealing procedure on the Curie temperature TC of (Ga,Mn)As layers grown by molecular beam epitaxy. We achieve the highest TC values for growth temperatures very close to the two-dimensional–three-dimensional phase boundary. The increase in TC, due to the removal of interstitial Mn by postgrowth annealing, is counteracted by a second process, which reduces TC and which is more effective at higher annealing temperatures. Our results show that it is necessary to optimize the growth parameters and postgrowth annealing procedure to obtain the highest TC.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors

Carrier transport mechanisms of nonvolatile memory devices based on nanocomposites consisting of ZnO nanoparticles with polymethylmethacrylate nanocomposites sandwiched between two C60 layers

Kyu Ha Park, Jae Hun Jung, Fushan Li, Dong Ick Son, and Tae Whan Kim

Appl. Phys. Lett. 93, 132104 (2008); http://dx.doi.org/10.1063/1.2992203 (3 pages) | Cited 10 times

Online Publication Date: 29 September 2008

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Transmission electron microscope images showed that ZnO nanoparticles were formed in a polymethylmethacrylate (PMMA) layer. Current-voltage (I-V) curves for the Al/C60/ZnO nanoparticles embedded in the PMMA layer/C60/indium tin oxide (ITO) device at 300 K showed a current bistability with a large on/off ratio of 104, which was much larger than the on/off ratio of the device without C60 layers, indicative of significant enhancement of memory storage. Carrier transport mechanisms of the memory effects for the Al/C60/ZnO nanoparticles embedded in the PMMA layer/C60/ITO device are described on the basis of the I-V results.
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84.30.Sk Pulse and digital circuits

Enhanced oscillator strength of interband transitions in coupled Ge/Si quantum dots

A. I. Yakimov, A. A. Bloshsin, and A. V. Dvurechenskii

Appl. Phys. Lett. 93, 132105 (2008); http://dx.doi.org/10.1063/1.2988469 (3 pages) | Cited 8 times

Online Publication Date: 30 September 2008

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We report a calculation of oscillator strength for the Δ1−Γ25′ interband transition in two vertically coupled pyramidal Ge quantum dots embedded in Si. A six-band k⋅p formalism was used to study the Γ25′ hole states, and a single-band approach was used to obtain the Δ1 electron state interacting with the hole. The elastic strain due to the lattice mismatch between Ge and Si was included into the problem via the Bir–Pikus Hamiltonian. We find that when two dots are brought closely together, the oscillator strength may enlarge by a factor of about 2 as compared to the single-dot system.
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73.21.La Quantum dots
71.15.-m Methods of electronic structure calculations

Fabrication and microstructure of p-type transparent conducting CuS thin film and its application in dye-sensitized solar cell

K. D. Yuan, J. J. Wu, M. L. Liu, L. L. Zhang, F. F. Xu, L. D. Chen, and F. Q. Huang

Appl. Phys. Lett. 93, 132106 (2008); http://dx.doi.org/10.1063/1.2991441 (3 pages) | Cited 16 times

Online Publication Date: 30 September 2008

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By reducing film thickness to a few nanometers, the narrow-band-gap CuS turns highly transparent. Surface modification by a self-assembled monolayer is the key factor to obtain a thin, dense, and continuous film. The film growth mechanism is identified as “layer-by-layer growth followed by islanding.” After annealing, a p-type conductivity of ∼ 2×103 S cm−1 is achieved at room temperature, and the thinnest conductive film has an average transparency of 92% between 400 and 800 nm. Using p-type CuS films as front contact layers, a dye-sensitized solar cell was fabricated with a significant photoelectric response.
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81.16.Dn Self-assembly
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
61.72.Cc Kinetics of defect formation and annealing
72.40.+w Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion

Carbon clusters in N-doped ZnO by metal-organic chemical vapor deposition

Kun Tang, Shulin Gu, Shunming Zhu, Wei Liu, Jiandong Ye, Jianmin Zhu, Rong Zhang, Youdou Zheng, and Xiaowei Sun

Appl. Phys. Lett. 93, 132107 (2008); http://dx.doi.org/10.1063/1.2992197 (3 pages) | Cited 14 times

Online Publication Date: 30 September 2008

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We employed transmission electron microscopy and Raman spectra to investigate the behavior of impurity carbon usually unintentionally introduced in N-doped ZnO by metal-organic chemical vapor deposition. Unintentional doped carbon may form graphite clusters along grain boundaries resulting in n-type domains and possibly be a big obstacle for the realization of p-type conductivity. The enhanced desorption rate of hydrocarbon radicals by high temperature and oxygen atom will significantly suppress carbon incorporation rate. The results provide understandings of the formation mechanism of carbon clusters and help us find some available routines to minimize carbon impurity for realization of p-type N-doped ZnO.
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61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
61.72.Mm Grain and twin boundaries
68.43.Nr Desorption kinetics
78.30.Fs III-V and II-VI semiconductors

Carrier wave-packet transport under the influence of charged quantum dot in small-area resonant tunneling diode

Y. Hou, W.-P. Wang, N. Li, W.-L. Xu, W. Lu, and Y. Fu

Appl. Phys. Lett. 93, 132108 (2008); http://dx.doi.org/10.1063/1.2993339 (3 pages) | Cited 4 times

Online Publication Date: 30 September 2008

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It was shown experimentally that charging InAs quantum dots (QDs) embedded in a small-area GaAs/AlAs double-barrier resonant tunneling diode (RTD) effectively modified the carrier transport properties of the RTD. By adopting and comparing the one-dimensional plane-wave and three-dimensional (3D) wave-packet transport theories we show that the electron transports in the QDRTD device are in the form of 3D wave packets, which are strongly affected by the 3D long-range Coulomb potential induced by charged InAs QDs. This explains well experimental data and indicates that the 3D wave-packet transport model is more appropriate for the QDRTD device.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling
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