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1 Sep 2003

Volume 83, Issue 9, pp. 1689-1898

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 1710 (2003); http://dx.doi.org/10.1063/1.1605792 (3 pages)

G. D. Chern, H. E. Tureci, A. Douglas Stone, R. K. Chang, M. Kneissl, and N. M. Johnson
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Optical properties of the ZnO nanotubes synthesized via vapor phase growth

Y. J. Xing, Z. H. Xi, Z. Q. Xue, X. D. Zhang, J. H. Song, R. M. Wang, J. Xu, Y. Song, S. L. Zhang, and D. P. Yu

Appl. Phys. Lett. 83, 1689 (2003); http://dx.doi.org/10.1063/1.1605808 (3 pages) | Cited 227 times

Online Publication Date: 26 August 2003

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A large quantity of nanosized ZnO tubular structures was prepared using a very simple thermal evaporation of mixed Zn–ZnO powders under a wet oxidation condition. The ZnO nanotubes have a hollow core with crystalline wall of 8–20 nm in thickness. Optical properties of ZnO nanotubes were studied at room temperature. Raman peaks arising from the ZnO nanotubes were analyzed, which correspond well to that of the bulk ZnO sample. The photoluminescence measurements of ZnO nanotubes revealed an intensive UV peak at 377 nm corresponding to the free exciton emission, and a broad peak at about 500 nm arising from defect-related emission. © 2003 American Institute of Physics.
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78.67.Ch Nanotubes
81.07.De Nanotubes
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

“Plug and play” quantum key distribution system with differential phase shift

Chunyuan Zhou, Guang Wu, Xiuliang Chen, and Heping Zeng

Appl. Phys. Lett. 83, 1692 (2003); http://dx.doi.org/10.1063/1.1606874 (3 pages) | Cited 7 times

Online Publication Date: 26 August 2003

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We propose a “plug and play” scheme for the long-distance fiber-based cryptosystem based on the differential phase shift quantum key distribution, where any birefringence effects and polarization-dependent losses in the transmission fiber are automatically compensated by using a Faraday mirror. This system not only has stable performance but also creates keys 8/3 times more efficiently than the conventional cryptosystem based on the BB84 protocol. © 2003 American Institute of Physics.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
03.67.Dd Quantum cryptography and communication security

Effects of power truncation on the insertion loss and crosstalk of arrayed-waveguide grating devices

A. A. Bernussi, L. Grave de Peralta, S. Frisbie, and H. Temkin

Appl. Phys. Lett. 83, 1695 (2003); http://dx.doi.org/10.1063/1.1605802 (3 pages) | Cited 3 times

Online Publication Date: 26 August 2003

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A measurement of the insertion loss and crosstalk in folded, 100 GHz, arrayed waveguide multiplexers as a function of the number of grating waveguides is described. The number of grating waveguides can be varied in a single device to evaluate power truncation effects with high accuracy. We show that the central peak insertion loss decreases exponentially with the number of grating waveguides. The crosstalk decreases with increased number of waveguides and the measured dependence shows valleys and peaks associated with the passband spectrum of individual channels. These observations are in good agreement with simulation results. With the arrayed waveguide design used in this work the crosstalk performance becomes phase error limited for the number of waveguides greater than 250. © 2003 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Birefringence of GaN/AlGaN optical waveguides

R. Hui, Y. Wan, J. Li, S. X. Jin, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 83, 1698 (2003); http://dx.doi.org/10.1063/1.1606103 (3 pages) | Cited 2 times

Online Publication Date: 26 August 2003

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We have experimentally studied the birefringence of wurtzite GaN grown on a sapphire substrate. The measurements were done with single-mode GaN/AlGaN planar optical waveguides on c-plane grown heterostructure films. The refractive indices were found to be different for signal optical field perpendicular or parallel to the crystal c axis (n⊥ ≠ n∥). More importantly, we found an approximately 10% change in index difference Δn = n∥−n⊥ with variation of the waveguide orientation in the a–b plane, and a 60° periodicity was clearly observed. This is attributed to the hexagonal structure of nitride materials. © 2003 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
78.20.Fm Birefringence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Super-resolution by elliptical bubble formation with PtOx and AgInSbTe layers

Jooho Kim, Inoh Hwang, Duseop Yoon, Insik Park, Dongho Shin, Takashi Kikukawa, Takayuki Shima, and Junji Tominaga

Appl. Phys. Lett. 83, 1701 (2003); http://dx.doi.org/10.1063/1.1605794 (3 pages) | Cited 29 times

Online Publication Date: 26 August 2003

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The recording and retrieval of signals below 100 nm mark length were attempted with elliptical bubble-type super-resolution technology with platinum oxide (PtOx) and ductile AgInSbTe layers, using the same optical system as that of a digital versatile disk (a 635 nm wavelength red laser system). The carrier-to-noise ratio (CNR) of over 47 dB for 100 nm mark length signals (over 43 dB for 80 nm mark length signals) was obtained, which can be considered as a commercially acceptable level of CNR. The recording mechanism of the sample disk was shown through the transmission electron microscopy cross-section image observation to be by rigid elliptical bubble formation at the PtOx layer located between the AgInSbTe layers. The results of this report represent the potential for a much higher-density storage using the red laser system and a subterabyte optical storage using the blue laser system. © 2003 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
42.70.Ln Holographic recording materials; optical storage media
81.15.Cd Deposition by sputtering
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
68.37.Lp Transmission electron microscopy (TEM)

Lasing characteristics of InAs quantum-dot lasers on (001) InP substrate

Yueming Qiu, David Uhl, Rebecca Chacon, and Rui Q. Yang

Appl. Phys. Lett. 83, 1704 (2003); http://dx.doi.org/10.1063/1.1606501 (3 pages) | Cited 33 times

Online Publication Date: 26 August 2003

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Single-stack InAs self-assembled quantum-dot (QD) lasers based on (001) InP substrates have been grown by metalorganic vapor-phase epitaxy. The narrow ridge waveguide lasers lased up to 260 K in continuous-wave operation, and near room temperature in pulsed mode, with emission wavelengths between 1.59 to 1.74 μm. Above 200 K, a very low wavelength temperature sensitivity of 0.09 nm/K was observed. Lasing spectra at different temperatures suggests that the ground states and the excited states almost overlap, and form a quasicontinuous band due to the large size of the InAs dots and their inhomogeneous broadening. These results will provide guidance for further development of long wavelength InAs QD lasers based on InP substrates. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Proton beam writing of low-loss polymer optical waveguides

T. C. Sum, A. A. Bettiol, J. A. van Kan, F. Watt, E. Y. B. Pun, and K. K. Tung

Appl. Phys. Lett. 83, 1707 (2003); http://dx.doi.org/10.1063/1.1606502 (3 pages) | Cited 23 times

Online Publication Date: 26 August 2003

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Proton beam writing is a direct-write micromachining technique capable of producing three-dimensional microstructures with straight and smooth sidewalls. Low-loss channel waveguides in SU-8, a chemically amplified negative tone resist, were fabricated using a focused submicron beam of 2.0 MeV protons with a dose of 30 nC/mm2 and a beam current of approximately 2 pA. Propagation losses of approximately (0.19±0.03) dB/cm were measured at 632.8 nm wavelength. Waveguides of arbitrary design can be easily fabricated using proton beam writing, making the technique ideal for the rapid prototyping of optical circuits. © 2003 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Unidirectional lasing from InGaN multiple-quantum-well spiral-shaped micropillars

G. D. Chern, H. E. Tureci, A. Douglas Stone, R. K. Chang, M. Kneissl, and N. M. Johnson

Appl. Phys. Lett. 83, 1710 (2003); http://dx.doi.org/10.1063/1.1605792 (3 pages) | Cited 84 times

Online Publication Date: 26 August 2003

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We report unidirectional emission from lasing in In0.09Ga0.91N/In0.01Ga0.99N multiple-quantum-well spiral micropillars. Our imaging technique shows that the maximum emission comes from the notch of the spiral microcavities at an angle about 40° from the normal of the notch. At room temperature, the spiral microcavity lases near 400 nm when optically pumped with 266 or 355 nm light. A reduction in the lasing threshold and an improvement in unidirectionality occurs when the microcavity is selectively pumped near its boundary. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Sa Microcavity and microdisk lasers

Terahertz electroluminescence from boron-doped silicon devices

T. N. Adam, R. T. Troeger, S. K. Ray, P.-C. Lv, and J. Kolodzey

Appl. Phys. Lett. 83, 1713 (2003); http://dx.doi.org/10.1063/1.1605263 (3 pages) | Cited 24 times

Online Publication Date: 26 August 2003

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Terahertz emission was observed from electrically pumped boron-doped p-type silicon structures at cryogenic temperatures. At a current of 1.5 A and temperature of 4.4 K, we achieved a pulsed peak power of 31 μW from a single mesa facet, integrated over three closely spaced spectral lines centered about 8.1 THz. The radiation was slightly transverse magnetically polarized with respect to the plane of the substrate and was still detectable at temperatures as high as 150 K. These findings suggest that moderate power THz sources can be fabricated without epitaxially grown quantum wells using techniques compatible with silicon integrated circuit technology. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices

Regulating the size and position of deposited Zn nanoparticles by optical near-field desorption using size-dependent resonance

T. Yatsui, S. Takubo, J. Lim, W. Nomura, M. Kourogi, and M. Ohtsu

Appl. Phys. Lett. 83, 1716 (2003); http://dx.doi.org/10.1063/1.1606883 (3 pages) | Cited 9 times

Online Publication Date: 26 August 2003

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We report that optical near-field desorption can dramatically regulate the growth of Zn nanoparticles during optical chemical vapor deposition. The trade off between the deposition due to 3.81 eV optical near-field light and desorption due to 2.54 eV optical near-field light allowed the fabrication of a single 15 nm Zn dot, while regulating its size and position. © 2003 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.-w Structure of nanoscale materials
68.43.Tj Photon stimulated desorption
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Ultrafast and highly sensitive photodetectors fabricated on high-energy nitrogen-implanted GaAs

M. Mikulics, M. Marso, P. Kordoš, S. Stanček, P. Kováč, X. Zheng, S. Wu, and Roman Sobolewski

Appl. Phys. Lett. 83, 1719 (2003); http://dx.doi.org/10.1063/1.1606879 (3 pages) | Cited 10 times

Online Publication Date: 26 August 2003

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We have fabricated and tested metal–semiconductor–metal (MSM) photodetectors based on nitrogen-ion-implanted GaAs. Nitrogen ions with energy of 700 and 880 keV, respectively, were implanted into epitaxial GaAs films at an ion concentration of 3×1012 cm−2. Ti/Au MSM photodetectors with 1-μm-wide fingers were fabricated on top of the implanted GaAs. In comparison to low-temperature-grown GaAs photodetectors, produced in parallel in identical MSM geometry, the 880 keV N+-implanted photodetectors exhibited almost two orders of magnitude lower dark current (10 nA at 1 V bias) and the responsivity more than doubled (>20 mA/W at 20 V bias). Illumination with 100-fs-wide, 810 nm wavelength laser pulses, generated ∼2.5-ps-wide photoresponse signals with amplitudes as high as 2 V. The 2.5 ps relaxation time was the same for both the ion-implanted and low-temperature-grown devices and was limited by the MSM capacitance time constant. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Optical parametric spectral broadening of picosecond laser pulses in β-barium borate

Seung Mook Lee, Bum Ku Rhee, Moongoo Choi, and Seung-Han Park

Appl. Phys. Lett. 83, 1722 (2003); http://dx.doi.org/10.1063/1.1609054 (3 pages) | Cited 1 time

Online Publication Date: 26 August 2003

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We present that optical parametric luminescence generated near the degenerate point of a type I optical parametric tuning curve in β-BaB2O4 can be used as a spectrally broadened probe beam for a picosecond pump-probe spectroscopy. In particular, we show that it is possible to change the position of the central peak and spectral range in visible and infrared wavelengths by varying the incident angle of pump pulse with respect to the optical axis of barium borate crystal. The picosecond time-resolved diffuse-reflectance experiment is also performed in order to demonstrate usefulness of these spectrally broadened pulses as a probe source. © 2003 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Self-developing aspherical chalcogenide-glass microlenses for semiconductor lasers

A. Saitoh and K. Tanaka

Appl. Phys. Lett. 83, 1725 (2003); http://dx.doi.org/10.1063/1.1598650 (3 pages) | Cited 15 times

Online Publication Date: 26 August 2003

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A principle of self-developing microlenses for semiconductor lasers has been demonstrated using a photosensitive glass, As2S3. The glass film is placed in front of a semiconductor laser, the light from which increases the refractive index and thickness of the film. If its position and thickness are properly selected, the illuminated film operates as an aspherical microlens which can focus an elliptical laser beam to a circular spot. © 2003 American Institute of Physics.
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42.60.By Design of specific laser systems
42.79.Bh Lenses, prisms and mirrors
42.55.Px Semiconductor lasers; laser diodes
42.70.Gi Light-sensitive materials
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Transition from island formation to pseudomorphic growth in the submonolayer CdSe/ZnSe multilayer system

M. Kim, J. K. Furdyna, M. Dobrowolska, S. Lee, M. Cheon, and H. Luo

Appl. Phys. Lett. 83, 1728 (2003); http://dx.doi.org/10.1063/1.1605234 (3 pages) | Cited 1 time

Online Publication Date: 26 August 2003

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Transmission electron microscopy and photoluminescence measurements have been performed on samples with submonolayer (0.3 up to 0.9 ML) CdSe insertions in ZnSe in both single- and multilayer geometries. We observe a significant difference in Cd distribution in the layer plane between these two geometries for the same Cd coverage. While Cd-rich islands can be seen for a single layer of Cd, a layered growth is achieved in the multilayer samples. This effect is attributed to the reduction of lattice mismatch in the multilayer samples due to a high level of diffusion of Cd atoms along the growth direction. © 2003 American Institute of Physics.
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68.65.Cd Superlattices
81.05.Dz II-VI semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Mechanical characterization of trilayer thin films by the microbridge testing method

Wei-Hua Xu and Tong-Yi Zhang

Appl. Phys. Lett. 83, 1731 (2003); http://dx.doi.org/10.1063/1.1605799 (3 pages) | Cited 14 times

Online Publication Date: 26 August 2003

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Microbridge tests were conducted on two sets of trilayer samples, consisting of SiO2/Si3N4/SiO2 and Si3N4/SiO2/Si3N4, which were fabricated on 4 in. p-type (100) silicon wafers by means of the microelectromechanical fabrication technique. The experimental results were analyzed using the small deformation formula including substrate deformation. By changing the sample length, we determined the bending stiffness and the resultant residual force per unit width in each of the trilayer thin films. A simplification is proposed to estimate residual stress and Young’s modulus in each layer. Young’s moduli and residual stresses are estimated to be 54.59 GPa and −429.49 MPa for the silicon oxide films and 270.54 GPa and 550.75 MPa for the silicon nitride films, respectively. The microbridge testing method enables us to characterize the mechanical properties of each layer of sandwich-structured thin films. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
07.10.Cm Micromechanical devices and systems
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Isotopically enriched designer-diamond anvil

Paul A. Baker, Yogesh K. Vohra, Randolph S. Peterson, and Samuel T. Weir

Appl. Phys. Lett. 83, 1734 (2003); http://dx.doi.org/10.1063/1.1606877 (3 pages) | Cited 4 times

Online Publication Date: 26 August 2003

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Isotopically enriched (42 at. % 13C) designer-diamond anvils were grown by microwave plasma chemical vapor deposition using methane/hydrogen/oxygen chemistry. These isotopically enriched diamond layers can modify the thermal properties of the culet of high-pressure anvils and also allow the use of a 13C/12C Raman pressure sensor system for high-pressure, high-temperature measurements. Raman spectroscopy clearly revealed the isotopically mixed nature of the culet while the photoluminescence spectra at 80 K demonstrate the nitrogen-based defect center near the culet of the diamond anvil. The ability to isotopically modify the diamond culets offers yet another functionality for the embedded electric and magnetic sensors in a designer-diamond anvil. © 2003 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals
81.05.U- Carbon/carbon-based materials

Exciton diffusion in light-emitting organic thin films studied by photocurrent spectra

C. L. Yang, Z. K. Tang, W. K. Ge, J. N. Wang, Z. L. Zhang, and X. Y. Jian

Appl. Phys. Lett. 83, 1737 (2003); http://dx.doi.org/10.1063/1.1606880 (3 pages) | Cited 20 times

Online Publication Date: 26 August 2003

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Photocurrent spectroscopy is employed to obtain the exciton diffusion coefficient and diffusion length in two typical light-emitting organic thin films, the hole transport material [N,N′-diphenyl-N,N′-bis(3-methyl-phenyl)-1,1′biphenyl-4,4′diamine] (TPD) and the electron transport material tris(8-hydroxyquinolinolato) aluminum III (Alq3). The photocurrent spectra of both films at higher biases exhibit either symbatic or antibatic responses. However, complicated responses are observed for smaller biases. At certain small biases, the direction of the photocurrent even alters with the energy of illuminating photons. A model based on exciton diffusion and dissociation at film/electrode interfaces is used to explain these experimental results. Good agreement is achieved between experiments and theory by taking into account both symbatic and antibatic responses, especially at zero or small biases. The diffusion coefficient and the diffusion length of excitons derived are 1.53×10−3 cm2 s−1 and 17 nm for TPD and 4×10−5 cm2 s−1 and 8 nm for Alq3, respectively. © 2003 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.66.Qn Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects

Temperature dependent spectroscopic studies of the electron delocalization dynamics of excited Ce ions in the wide band gap insulator, Lu2SiO5

E. van der Kolk, S. A. Basun, G. F. Imbusch, and W. M. Yen

Appl. Phys. Lett. 83, 1740 (2003); http://dx.doi.org/10.1063/1.1603337 (3 pages) | Cited 28 times

Online Publication Date: 26 August 2003

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Electron delocalization processes of optically excited states of Ce3+ impurities in Lu2SiO5 were investigated by means of a temperature and spectrally resolved photoconductivity study. By monitoring separately the strength of the photocurrent resulting from excitation into each of the Ce3+ 5d absorption bands, over a broad temperature region, three different delocalization processes, namely direct photoionization, thermal ionization, and tunneling, have been identified. The relative probabilities and temperature dependencies of each of these processes are discussed. The observed exponential temperature increase in the photocurrent, which spans six orders of magnitude, allows for the exact placement of the lowest energy 5d levels of the Ce3+ ions within the band gap. For Lu2SiO5:Ce3+, the lowest 5d state is determined to be 0.45 eV below the conduction band edge. © 2003 American Institute of Physics.
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71.55.Ht Other nonmetals
72.40.+w Photoconduction and photovoltaic effects
71.20.Ps Other inorganic compounds
72.20.Fr Low-field transport and mobility; piezoresistance

Heteroepitaxial growth of CuInS2 thin films on sapphire by radio frequency reactive sputtering

Y. B. He, W. Kriegseis, B. K. Meyer, A. Polity, and M. Serafin

Appl. Phys. Lett. 83, 1743 (2003); http://dx.doi.org/10.1063/1.1606505 (3 pages) | Cited 7 times

Online Publication Date: 26 August 2003

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Direct heteroepitaxial growth of uniform stoichiometric CuInS2 (CIS) thin films on sapphire (0001) substrates has been achieved by radio frequency reactive sputtering. X-ray ω–2θ scans reveal that the sputtered layers grow in a (112) orientation with a chalcopyrite structure. A rocking curve full width at half maximum of about 0.05° (180 arc sec) for the (112) peak demonstrates a nearly perfect out-of-plane arrangement of CIS (112)∥sapphire (0001). X-ray diffraction Phi scans further illustrate an excellent in-plane ordering of CIS [math10]∥sapphire (10math0). The sputtered thin CIS epilayers had a smooth surface with a typical root-mean-square roughness of about 3.3 nm as evaluated by atomic force microscopy. The epitaxial growth of tetragonal CIS on hexagonal sapphire provides evidence that heteroepitaxial growth may be realized between structures of different symmetry, such as films of cubic or tetragonal structures on hexagonal substrates or vice versa. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Discontinuous tracks in relaxed Si0.5Ge0.5 alloy layers: A velocity effect

P. I. Gaiduk, A. Nylandsted Larsen, J. Lundsgaard Hansen, C. Trautmann, and M. Toulemonde

Appl. Phys. Lett. 83, 1746 (2003); http://dx.doi.org/10.1063/1.1605240 (3 pages) | Cited 8 times

Online Publication Date: 26 August 2003

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Strain-relaxed crystalline Si0.5Ge0.5 layers were irradiated with U ions of various energies (0.8–2.64 GeV) but of approximately identical electronic stopping power. Transmission electron microscopy reveals tracks of different morphology depending on the velocity of the projectiles. For decreasing beam energy, individual dotted defect structures form aligned discontinuous tracks including a large number of dislocation loops. No indication for track amorphization is found. © 2003 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
81.05.Hd Other semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
61.82.Fk Semiconductors
61.72.Lk Linear defects: dislocations, disclinations

Morphology evolution during strained (In,Ga)As epitaxial growth on GaAs vicinal (100) surfaces

Z. M. Wang, J. L. Shultz, and G. J. Salamo

Appl. Phys. Lett. 83, 1749 (2003); http://dx.doi.org/10.1063/1.1606891 (3 pages) | Cited 15 times

Online Publication Date: 26 August 2003

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Molecular-beam-epitaxy growth of strained (In,Ga)As on GaAs vicinal (100) surfaces is investigated by scanning tunneling microscopy. Surface roughing as the consequence of step bunching driven by strain is explored. By tuning the In content over the range from 0.05 to 0.2, the step bunching is observed to exhibit considerable uniformity and order. These results experimentally demonstrate that strain-driven step bunching is a viable approach to provide templates for nanostructure growth. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Nanoheteroepitaxy of GaN on a nanopore array Si surface

J. Liang, S.-K. Hong, N. Kouklin, R. Beresford, and J. M. Xu

Appl. Phys. Lett. 83, 1752 (2003); http://dx.doi.org/10.1063/1.1604175 (3 pages) | Cited 37 times

Online Publication Date: 26 August 2003

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We report the growth by molecular beam epitaxy and the optical characterization of GaN films nucleated on a Si(111) surface that has been patterned by dry etching an ordered array of nanometer-scale pores prior to the growth. The etching is performed using an anodized aluminum oxide membrane as a mask. The nanopore array surface with the pore diameter of 60 nm and periodicity of 110 nm exhibits significant effects on emissivity and the optical properties of the resulting film. Room-temperature photoluminescence intensity increases by a factor of 5 for GaN grown on nanoporous Si. Peak shifts in photoluminescence and Raman spectroscopy suggest that the material grown on nanopores may be more relaxed than films grown on flat substrates. The effects of nanopore topography on the nucleation of GaN films offer a potential path to significant improvement of III-nitride heteroepitaxy for device applications. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
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Field-effect transistor on SrTiO3 with sputtered Al2O3 gate insulator

K. Ueno, I. H. Inoue, H. Akoh, M. Kawasaki, Y. Tokura, and H. Takagi

Appl. Phys. Lett. 83, 1755 (2003); http://dx.doi.org/10.1063/1.1605806 (3 pages) | Cited 39 times

Online Publication Date: 26 August 2003

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A field-effect transistor has been constructed that employs a perovskite-type SrTiO3 single crystal as the semiconducting channel. This device functions as an n-type accumulation-mode device. The device was fabricated at room temperature by sputter-deposition of amorphous Al2O3 films as a gate insulator on the SrTiO3 substrate. The field-effect (FE) mobility is 0.1 cm2/V s and on-off ratio exceeds 100 at room temperature. The temperature dependence of the FE mobility down to 2 K shows a thermal-activation-type behavior with an activation energy of 0.6 eV. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering

Indication of hysteresis in AlMnN

R. Frazier, G. Thaler, M. Overberg, B. Gila, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 83, 1758 (2003); http://dx.doi.org/10.1063/1.1604465 (3 pages) | Cited 49 times

Online Publication Date: 26 August 2003

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AlN films grown by gas-source molecular beam epitaxy were doped with different levels of Mn during growth. High resolution x-ray diffraction characterization revealed good crystallinity in single phase material, with lattice constant decreasing with increasing Mn concentration. Single phase AlMnN was found to be p type while AlMnN/AlMn mixed phase material was found to be highly conductive n type. Magnetization measurements performed with a superconducting quantum interference device magnetometer indicated ferromagnetism in single phase material persisting to 300 K and showed no evidence of room temperature magnetization in multiphase material. In particular, it was shown that Mn4N second phases are not contributing to the magnetization in the AlMnN under optimized growth conditions. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification

Spin lifetimes of electrons injected into GaAs and GaN

Srinivasan Krishnamurthy, Mark van Schilfgaarde, and Nathan Newman

Appl. Phys. Lett. 83, 1761 (2003); http://dx.doi.org/10.1063/1.1606873 (3 pages) | Cited 55 times

Online Publication Date: 26 August 2003

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The spin relaxation times of electrons in GaAs and GaN are determined with a model that includes momentum scattering by phonons and ionized impurities, and spin scattering by the Elliot–Yafet, D’yakonov–Perel, and Bir–Aronov–Pikus mechanisms. Accurate bands generated using a long-range tight-binding Hamiltonian obtained from empirical pseudopotentials are used. The inferred temperature dependence of the spin relaxation lifetime agrees well with measured values in GaAs. We further show that the spin lifetimes decrease rapidly with injected electron energy and reach a local maximum at the longitudinal optical phonon energy. Our calculation predicts that electron spin lifetime in pure GaN is about three orders of magnitude longer than in GaAs at all temperatures, primarily as a result of the lower spin-orbit interaction and higher conduction band density of states. © 2003 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
72.25.Hg Electrical injection of spin polarized carriers
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.20.Nr Semiconductor compounds
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