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14 Oct 2002

Volume 81, Issue 16, pp. 2917-3103

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Depth profiling InGaN/GaN multiple quantum wells by Rutherford backscattering: The role of intermixing

S. Pereira, E. Pereira, E. Alves, N. P. Barradas, K. P. O’Donnell, C. Liu, C. J. Deatcher, and I. M. Watson

Appl. Phys. Lett. 81, 2950 (2002); http://dx.doi.org/10.1063/1.1513661 (3 pages) | Cited 6 times

Online Publication Date: 7 October 2002

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We report a detailed compositional analysis of InxGa1−xN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. Depth profiles of the InN fraction, x, in the MQWs were determined from grazing incidence Rutherford backscattering spectroscopy (RBS) analysis. Simulation of the RBS spectra provides precise estimations of individual well compositions, thickness, and the extent of In/Ga intermixing. It is ascertained that intermixing, and In segregation to the GaN cap layer, strongly increase with the value of x in the wells and with the number of periods in the MQW stack. Deleterious effects of intermixing on the spectral properties are apparent when comparing the photoluminescence spectra of two MQW structures with 8 and 18 wells, grown under the same nominal conditions. © 2002 American Institute of Physics.
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68.65.Fg Quantum wells
78.67.De Quantum wells
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.55.Cr III-V semiconductors

Optical and structural properties of InAsP ternary self-assembled quantum dots embedded in GaAs

E. Ribeiro, R. L. Maltez, W. Carvalho, D. Ugarte, and G. Medeiros-Ribeiro

Appl. Phys. Lett. 81, 2953 (2002); http://dx.doi.org/10.1063/1.1513215 (3 pages) | Cited 10 times

Online Publication Date: 7 October 2002

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We report on the growth of self-assembled ternary InAsP quantum dots embedded into GaAs. A comparison between average sizes and recombination energies for different dot species (InAs, InAsP, and InP) confirms the formation of the ternary alloy islands. By carefully changing the growth conditions, we determined a global growth map for InAs, InAsP, and InP dots, showing that it is possible to tailor the optical characteristics of the InAsP species, thus covering the energy range between InAs and InP quantum dot emission. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

High temperature stability of Al2O3 dielectrics on Si: Interfacial metal diffusion and mobility degradation

S. Guha, E. P. Gusev, H. Okorn-Schmidt, M. Copel, L.-Å Ragnarsson, N. A. Bojarczuk, and P. Ronsheim

Appl. Phys. Lett. 81, 2956 (2002); http://dx.doi.org/10.1063/1.1513662 (3 pages) | Cited 38 times

Online Publication Date: 7 October 2002

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We have examined the stability of Al2O3/Si heterostructures and show that significant Al diffusion occurs into the silicon for temperatures of 1000 °C and more. This may be caused by dissociation of small quantities of Al2O3 and subsequent dissolution of the Al into the silicon. Such diffusion may be reduced, though not eliminated via an interfacial silicon oxynitride diffusion barrier. Using long channel metal gate Al2O3/Si n field effect transistor data, we show that anneals at 1000 °C result in a degradation of the electron mobility by a factor of 2. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.35.Fx Diffusion; interface formation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing

Direct determination of free exciton binding energy from phonon-assisted luminescence spectra in GaN epilayers

S. J. Xu, W. Liu, and M. F. Li

Appl. Phys. Lett. 81, 2959 (2002); http://dx.doi.org/10.1063/1.1514391 (3 pages) | Cited 15 times

Online Publication Date: 7 October 2002

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Investigation of variable-temperature longitudinal optical (LO) phonon-assisted luminescence spectra of free excitons and free electrons in heteroepitaxial GaN thin films has been conducted. It is found that thermal broadening of the LO phonon-assisted photoluminescence peaks is much slower than those of the peaks of their parents so that the first-order LO peaks of the free exciton transition and the band-to-band transition can be well resolved even at room temperature, leading to a direct determination of the band A free exciton binding energy as 25.4±0.9 meV. At the same time, we demonstrate that the simple hydrogenlike model still is a good approximation to describe the energy level structure of free excitons in GaN. © 2002 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
63.20.kk Phonon interactions with other quasiparticles

Cathodoluminescence of Cu diffusion in CdTe thin films for CdTe/CdS solar cells

Manuel J. Romero, David S. Albin, Mowafak M. Al-Jassim, Xuanzhi Wu, Helio R. Moutinho, and Ramesh G. Dhere

Appl. Phys. Lett. 81, 2962 (2002); http://dx.doi.org/10.1063/1.1515119 (3 pages) | Cited 10 times

Online Publication Date: 7 October 2002

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We investigate the distribution of Cu acceptor states in CdTe thin films used in high-efficiency solar cells. These states are CuCd and Cui+–VCd− complexes, which are relatively deep and shallow acceptors, respectively. Cathodoluminescence spectroscopy and imaging show that, first, CuCd and Cui+–VCd− do not coexist and, second, the primary diffuser is represented by Cui+–VCd− complexes. Our results are used to discuss the effect of grain boundaries on Cu diffusion. © 2002 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Gs II-VI semiconductors
66.30.J- Diffusion of impurities
84.60.Jt Photoelectric conversion
78.66.Hf II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries

GaAs(311) templates for molecular beam epitaxy growth: surface morphologies and reconstruction

Z. M. Wang, V. R. Yazdanpanah, J. L. Shultz, and G. J. Salamo

Appl. Phys. Lett. 81, 2965 (2002); http://dx.doi.org/10.1063/1.1514822 (3 pages) | Cited 12 times

Online Publication Date: 7 October 2002

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Morphologies of GaAs(311) surfaces grown by molecular beam epitaxy were investigated by in situ reflection high-energy electron diffraction and scanning tunnelling microscope. In addition to the (8×1) reconstruction, two surface phases, GaAs(311)A-(4×1) and GaAs(311)B-(2×1) were observed. Both of these surfaces are characterized by wider, atomically smooth terraces with much lower structural anisotropy, when compared to the (8×1) reconstructed GaAs(311) surfaces. The observed surfaces have potential as templates for the growth of organized quantum dots, wires, and wells. © 2002 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Structural disorder and loss of piezoelectric properties in α-quartz at high temperature

J. Haines, O. Cambon, D. A. Keen, M. G. Tucker, and M. T. Dove

Appl. Phys. Lett. 81, 2968 (2002); http://dx.doi.org/10.1063/1.1515363 (3 pages) | Cited 10 times

Online Publication Date: 7 October 2002

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The piezoelectric properties of α-quartz-based resonators, characterized by the mechanical quality factor, Q, are found to degrade beginning above 300 °C. This is well below the transition at 573 °C to the β phase, which in principle limits the piezoelectric response of this material. This gradual loss of piezoelectric response can be linked to the increase in structural disorder in α-quartz found in total neutron scattering measurements. Analysis of these data by reverse Monte Carlo modeling indicates that between 200 and 400 °C, the local disorder in the instantaneous structure of α-quartz becomes comparable to that of β-quartz. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Fs Electromechanical resonance; quartz resonators
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.43.Bn Structural modeling: serial-addition models, computer simulation
64.70.K- Solid-solid transitions

Temporal and thermal studies of charge transportation in self-assembly organic photovoltaic devices

F. Ghebremichael

Appl. Phys. Lett. 81, 2971 (2002); http://dx.doi.org/10.1063/1.1514398 (3 pages) | Cited 3 times

Online Publication Date: 7 October 2002

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The charge transport of holes injected into organic nanostructure photovoltaic devices using the third harmonic of a pulsed infrared laser was studied. The devices were fabricated using the electrostatic self-assembly technique. From temporal and thermal time-of-flight studies, we determined the drift mobility to be in the range of 10−7–10−6 cm2/(V s) in 120 nm thick films. A model was adopted that accounts for the Pool–Freknel type effects to characterize the devices, including the electric-field coefficient and the activation energy. Using similar techniques, fill factor of 0.34±0.02 at 1 mW/cm2 intensity was determined for the devices. © 2002 American Institute of Physics.
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85.60.-q Optoelectronic devices
85.30.-z Semiconductor devices
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ht High-field and nonlinear effects

Influence of stacking faults on the performance of 4H–SiC Schottky barrier diodes fabricated on (11math0) face

K. Kojima, T. Ohno, T. Fujimoto, M. Katsuno, N. Ohtani, J. Nishio, T. Suzuki, T. Tanaka, Y. Ishida, T. Takahashi, and K. Arai

Appl. Phys. Lett. 81, 2974 (2002); http://dx.doi.org/10.1063/1.1512956 (3 pages) | Cited 13 times

Online Publication Date: 7 October 2002

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The influence of stacking faults (SFs) on the performance of 4H–SiC (11math0) Schottky barrier diodes fabricated on the epilayer grown on the substrate which was grown in [11math0] direction by the sublimation method was investigated. The number of SFs under the Schottky electrode was determined by KOH etching of (1math00) face cross section. SFs were found to have a severe influence on the leakage current of reverse characteristic and Schottky barrier height. The leakage current is increased even though a few SFs exist under the electrode. The Schottky barrier height is also affected by the SF under the electrode. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
61.72.Nn Stacking faults and other planar or extended defects
85.30.Hi Surface barrier, boundary, and point contact devices
81.65.Cf Surface cleaning, etching, patterning

Relationship between the Li ionic conduction and the local structures in B-site substituted perovskite compounds, (Li0.1La0.3)1+xMxNb1−xO3 (M = Zr, Ti; x = 0, 0.05)

Masanobu Nakayama, Hiromasa Ikuta, Yoshiharu Uchimoto, Masataka Wakihara, and Yasuko Terada

Appl. Phys. Lett. 81, 2977 (2002); http://dx.doi.org/10.1063/1.1515366 (3 pages) | Cited 5 times

Online Publication Date: 7 October 2002

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Generally, it is known that the activation energy for the Li+ conduction in the perovskite-type oxides such as (Li,La)NbO3 decreases with the expansion of the lattice. However, our previous results showed an increase in the activation energy with Zr doping at B site in spite of lattice expansion. In the present study, the local structure of B site substituted perovskite oxides, (Li0.1La0.3)1+xMxNb1−xO3 (M = Zr, Ti; x = 0, 0.05), has been investigated using the extended x-ray absorption fine structure (EXAFS) technique with a view to explore the divergence exerted by Zr-doped perovskites. The EXAFS measurement revealed that the Li+ migration pathway in the Zr-doped samples is subjected to contract due to the local lattice distortion around the Zr-doped site. © 2002 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
78.70.Dm X-ray absorption spectra
61.66.Bi Elemental solids
61.66.Dk Alloys
61.66.Fn Inorganic compounds

Dynamic etching of silicon for broadband antireflection applications

C. C. Striemer and P. M. Fauchet

Appl. Phys. Lett. 81, 2980 (2002); http://dx.doi.org/10.1063/1.1514832 (3 pages) | Cited 58 times

Online Publication Date: 7 October 2002

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An electrochemical etching technique has been developed that provides continuous control over the porosity of a porous silicon layer as a function of etching depth. Thin films with engineered porosity gradients, and thus a controllable gradient in the index of refraction, have been used to demonstrate broadband antireflection properties on silicon wafer and solar cell substrates. A simulation was also developed to examine the effects of specific porosity profiles on film reflectivity. © 2002 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
42.79.Wc Optical coatings
42.70.-a Optical materials
84.60.Jt Photoelectric conversion
78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Physical aging in a hyperquenched glass

Y. Z. Yue, S. L. Jensen, and J. deC. Christiansen

Appl. Phys. Lett. 81, 2983 (2002); http://dx.doi.org/10.1063/1.1514386 (3 pages) | Cited 20 times

Online Publication Date: 7 October 2002

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We report experimental data on the enthalpy relaxation of a hyperquenched silicate glass subjected to long-time aging (annealing) below the glass-transition temperature (Tg). The relaxation of a hyperquenched glass substantially differs from that of a normally cooled glass. Two mechanisms govern the relaxation of a hyperquenched glass. During relaxation of the first hyperquenched, and afterward aged glass, a relaxation endotherm occurs followed by an exotherm. This is reflected by the occurrence of crossover. By increasing the aging temperature and time, the endotherm becomes more pronounced, while the exotherm gradually disappears. The consequence of this is the shift of the crossover point to higher temperature. The relaxation of the hyperquenched glass at 0.66Tg with the aging time is highly nonexponential. © 2002 American Institute of Physics.
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65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
81.40.Gh Other heat and thermomechanical treatments
81.05.Kf Glasses (including metallic glasses)

Virtual surfaces, director domains, and the Fréedericksz transition in polymer-stabilized nematic liquid crystals

Pavel A. Kossyrev, Jun Qi, Nikolai V. Priezjev, Robert A. Pelcovits, and Gregory P. Crawford

Appl. Phys. Lett. 81, 2986 (2002); http://dx.doi.org/10.1063/1.1515136 (3 pages) | Cited 16 times

Online Publication Date: 7 October 2002

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The critical field of the Fréedericksz transition and switching dynamics are investigated for polymer-stabilized nematic liquid crystals as a function of polymer concentration. A simple phenomenological model is proposed to describe the observed critical field and dynamic response time behaviors as a function of concentration. In this model, the polymer fibrils form director domains, which are bounded by “virtual surfaces” with a finite anchoring energy. © 2002 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
64.70.M- Transitions in liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.70.Df Liquid crystals

Theoretical evidence for the kick-out mechanism for B diffusion in SiC

R. Rurali, P. Godignon, J. Rebollo, P. Ordejón, and E. Hernández

Appl. Phys. Lett. 81, 2989 (2002); http://dx.doi.org/10.1063/1.1515369 (3 pages) | Cited 15 times

Online Publication Date: 7 October 2002

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In this letter, we analyze by means of first-principles electronic structure calculations the diffusion of B impurities in 3C-SiC. We find, through molecular dynamics, that substitutional B at a Si lattice site is readily displaced by a nearby Si interstitial by the process known as a kick-out mechanism, in agreement with recent experimental results. This is in contrast to the situation in Si, where B has recently been shown to diffuse via an interstitialcy mechanism. © 2002 American Institute of Physics.
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66.30.J- Diffusion of impurities
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
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