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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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Experimental studies of the internal Goos–Hänchen shift for self-collimated beams in two-dimensional microwave photonic crystals

Aaron Matthews and Yuri Kivshar

Appl. Phys. Lett. 93, 131901 (2008); http://dx.doi.org/10.1063/1.2980033 (3 pages) | Cited 5 times

Online Publication Date: 29 September 2008

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We study experimentally the Goos–Hänchen effect observed at the reflection of a self-collimated beam from the surface of a two-dimensional photonic crystal and describe a method for controlling the beam reflection through surface engineering. The microwave photonic crystal, fabricated from alumina rods, allows control of the output position of a reflected beam undergoing an internal Goos–Hänchen shift by changing the rod diameter at the reflection surface. The experimental data are in good agreement with the results of the finite-difference time-domain numerical calculations.
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42.70.Qs Photonic bandgap materials
42.79.Ag Apertures, collimators
02.70.Bf Finite-difference methods

Evaluation of growth rate equations of three-dimensional grains using large-scale Monte Carlo simulation

Hao Wang and Guoquan Liu

Appl. Phys. Lett. 93, 131902 (2008); http://dx.doi.org/10.1063/1.2983746 (3 pages) | Cited 7 times

Online Publication Date: 29 September 2008

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Three-dimensional normal grain growth process was simulated in scale of 300×300×300 on the basis of Monte Carlo–Potts model to study topology-dependent growth rate equations for individual grains. The results show that those growth rate equations solely dependent on the grain face number (f) are not applicable for grains with face number f<8; however, Glazier’s equation [ J. A. Glazier, Phys. Rev. Lett. 70, 2170 (1993) ], MacPherson–Srolovitz’s topology-dependent equation [ R. D. MacPherson and D. J. Srolovitz, Nature (London) 446, 1053 (2007) ], and Yu–Liu’s equation [ G. Q. Liu and H. B. Yu, Chin. Sci. Bull. 41, 2000 (1996) ] describe the simulation data well for grains with face number f>8.
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61.72.-y Defects and impurities in crystals; microstructure
02.50.Ng Distribution theory and Monte Carlo studies

Submicrometer periodic patterns fixed by photopolymerization of dissipative structures

A. Hoischen, S. A. Benning, and H.-S. Kitzerow

Appl. Phys. Lett. 93, 131903 (2008); http://dx.doi.org/10.1063/1.2990762 (3 pages) | Cited 4 times

Online Publication Date: 29 September 2008

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In photoreactive liquid crystals, spontaneous pattern formation can be used to fabricate phase gratings or polymer films with a periodic surface modulation. Typically, the periodicity of such structures is comparable to the sample thickness, and thus in the range between several micrometers and about 100 μm. Here, attempts to create and to investigate smaller structures are presented. For a chevron pattern, periodicities as small as 800 nm could be detected.
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42.70.Df Liquid crystals
42.70.Gi Light-sensitive materials
42.70.Jk Polymers and organics
82.35.-x Polymers: properties; reactions; polymerization
42.79.Dj Gratings

Toward the existence of ultrafast diffusion paths in Cu with a gradient microstructure: Room temperature diffusion of Ni

Z. B. Wang, K. Lu, G. Wilde, and S. Divinski

Appl. Phys. Lett. 93, 131904 (2008); http://dx.doi.org/10.1063/1.2992628 (3 pages) | Cited 2 times

Online Publication Date: 29 September 2008

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Room temperature diffusion of 63Ni in Cu with a gradient microstructure prepared by surface mechanical attrition treatment (SMAT) was investigated by applying the radiotracer technique. The results reveal significant penetration of Ni into the nanostructured layer. The relevant diffusivity is higher than that along the conventional high-angle grain boundaries by about six orders of magnitude. This behavior is associated with a higher energy state of internal interfaces produced via plastic deformation. The diffusivity in the top surface layer is somewhat smaller than that in the subsurface layer. This fact is related to nanotwin formation in the former during SMAT.
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66.30.Pa Diffusion in nanoscale solids
66.30.J- Diffusion of impurities
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep
61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals

Measurement of the optical absorption spectra of epitaxial graphene from terahertz to visible

Jahan M. Dawlaty, Shriram Shivaraman, Jared Strait, Paul George, Mvs Chandrashekhar, Farhan Rana, Michael G. Spencer, Dmitry Veksler, and Yunqing Chen

Appl. Phys. Lett. 93, 131905 (2008); http://dx.doi.org/10.1063/1.2990753 (3 pages) | Cited 50 times

Online Publication Date: 30 September 2008

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We present experimental results on the optical absorption spectra of epitaxial graphene from the visible to the terahertz frequency range. In the terahertz range, the absorption is dominated by intraband processes with a frequency dependence similar to the Drude model. In the near-IR range, the absorption is due to interband processes and the measured optical conductivity is close to the theoretical value of e2/4ℏ. We extract values for the carrier densities, the number of carbon atom layers, and the intraband scattering times from the measurements.
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78.70.Gq Microwave and radio-frequency interactions
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
78.40.Ri Fullerenes and related materials
78.66.Tr Fullerenes and related materials
78.30.Na Fullerenes and related materials
73.61.Wp Fullerenes and related materials

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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