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22 Feb 1999

Volume 74, Issue 8, pp. 1057-1183

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Optical properties of molecular organic semiconductor thin films under intense electrical excitation

V. G. Kozlov, P. E. Burrows, G. Parthasarathy, and S. R. Forrest

Appl. Phys. Lett. 74, 1057 (1999); http://dx.doi.org/10.1063/1.123480 (3 pages) | Cited 38 times

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Using electro-optical pump and probe measurements, we studied optical properties of a thin film of tris-(8-hydroxyquinoline) aluminum (Alq3) doped with DCM2 laser dye under pulsed injection currents as high as 300 A/cm2. Pump-induced transparency and absorption were observed in the spectral ranges of 570–610 nm and 620–705 nm, respectively. We attribute these optical effects to molecular polarons formed under electrical excitation. Polaron absorption dominates the optical properties of electrically pumped Alq3:DCM2 films in the spectral range where optical gain is anticipated (i.e., from 630 to 700 nm). Polaronic effects may present a significant obstacle for realization of organic diode lasers based on this material system. © 1999 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
42.70.Jk Polymers and organics
71.38.-k Polarons and electron-phonon interactions
78.40.Me Organic compounds and polymers
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

CaF2:Yb3++Pr3+ codoped waveguides grown by molecular beam epitaxy for 1.3 μm applications

F. Lahoz, E. Daran, G. Lifante, T. Balaji, and A. Muñoz-Yagüe

Appl. Phys. Lett. 74, 1060 (1999); http://dx.doi.org/10.1063/1.123481 (3 pages) | Cited 3 times

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CaF2:Yb3++Pr3+ codoped thin films grown by molecular beam epitaxy have been studied in order to determine their ability to be used for optical amplification in telecommunication devices. The guiding behavior of the layers has been demonstrated and an increase in the refractive index has been measured for increasing Pr3+ and Yb3+ doping levels. Energy transfer between Yb3+ and Pr3+ ions has also been observed with different pump wavelengths. Room temperature 1.3 μm emission of Pr3+ ions has been detected when pumping in the absorption band of Yb3+, where high performance laser diodes already exist. © 1999 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.55.Rz Doped-insulator lasers and other solid state lasers
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Development of a high-quantum-efficiency single-photon counting system

Shigeki Takeuchi, Jungsang Kim, Yoshihisa Yamamoto, and Henry H. Hogue

Appl. Phys. Lett. 74, 1063 (1999); http://dx.doi.org/10.1063/1.123482 (3 pages) | Cited 133 times

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A high-quantum-efficiency single-photon counting system has been developed. In this system, single photons were detected by a visible light photon counter operated at 6.9 K. The visible light photon counter is a solid state device that makes use of avalanches across a shallow impurity conduction band in silicon. Threefold tight shielding and viewports that worked as infrared blocking filters were used to eliminate the dark count caused by room-temperature radiation. Corrected quantum efficiencies as high as 88.2%±5% (at 694 nm) were observed, which we believe is the highest reported value for a single-photon detector. The dark count increased as the exponential of the quantum efficiency with changing temperature or bias voltage, and was 2.0×104 cps at the highest quantum efficiency. © 1999 American Institute of Physics.
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42.50.Ar Photon statistics and coherence theory
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Ci Filters, zone plates, and polarizers

Mode spacing “anomaly” in InGaN blue lasers

H. X. Jiang and J. Y. Lin

Appl. Phys. Lett. 74, 1066 (1999); http://dx.doi.org/10.1063/1.123483 (3 pages) | Cited 9 times

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An important experimental observation in InGaN laser diodes (LDs), which is not yet fully understood, is that the measured mode spacing of the lasing spectra could be one order of magnitude larger than that “calculated” from the known cavity length. The aim of this letter is to shed light on the nature of the mode spacing “anomaly” in InGaN LDs. We have derived a formula which accurately determines the mode spacing in InGaN LDs. Our analysis has shown that the discrepancy between the “expected” and observed mode spacing is due to the effect of carrier-induced reduction of the refractive index under lasing conditions and this discrepancy decreases and naturally disappears as the threshold carrier density required for lasing decreases. Since the carrier-induced reduction of the refractive index is expected only from an electron–hole plasma state, our results naturally imply that electron–hole plasma recombination provides the optical gain in InGaN LDs, like in all other conventional III–V semiconductor lasers. The implications of our results on the design of nitride optoelectronic devices are also discussed. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Mx High-frequency effects; plasma effects
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors

Angular filtering of spatial modes in a vertical-cavity surface-emitting laser by a Fabry–Perot étalon

Guoqiang Chen, James R Leger, and Anand Gopinath

Appl. Phys. Lett. 74, 1069 (1999); http://dx.doi.org/10.1063/1.123484 (3 pages) | Cited 3 times

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A low-finesse Fabry–Perot étalon is employed as an angularly selective filter to discriminate against the high-order spatial modes of a vertical-cavity surface-emitting laser (VCSEL) in the near field. Single-transverse-mode operation is obtained over a wide region for a 15 μm diam VCSEL. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Ci Filters, zone plates, and polarizers
07.60.Ly Interferometers

High-speed >90% quantum-efficiency p–i–n photodiodes with a resonance wavelength adjustable in the 795–835 nm range

Ekmel Özbay, Ïbrahim Kimukin, Necmi Biyikli, Orhan Aytür, Mutlu Gökkavas, Gökhan Ulu, M. Selim Ünlü, Richard P. Mirin, Kris A. Bertness, and David H. Christensen

Appl. Phys. Lett. 74, 1072 (1999); http://dx.doi.org/10.1063/1.123485 (3 pages) | Cited 15 times

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We report GaAs/AlGaAs-based high-speed, high-efficiency, resonant cavity enhanced p–i–n photodiodes. The devices were fabricated by using a microwave-compatible fabrication process. By using a postprocess recess etch, we tuned the resonance wavelength from 835 to 795 nm while keeping the peak efficiencies above 90%. The maximum quantum efficiency was 92% at a resonance wavelength of 823 nm. The photodiode had an experimental setup-limited temporal response of 12 ps. When the system response is deconvolved, the 3 dB bandwidth corresponds to 50 GHz, which is in good agreement with our theoretical calculations. © 1999 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
06.60.Jn High-speed techniques (microsecond to femtosecond)
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
42.86.+b Optical workshop techniques
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors

High-temperature continuous-wave 3–6.1 μm “W” lasers with diamond-pressure-bond heat sinking

W. W. Bewley, C. L. Felix, I. Vurgaftman, D. W. Stokes, E. H. Aifer, L. J. Olafsen, J. R. Meyer, M. J. Yang, B. V. Shanabrook, H. Lee, R. U. Martinelli, and A. R. Sugg

Appl. Phys. Lett. 74, 1075 (1999); http://dx.doi.org/10.1063/1.123486 (3 pages) | Cited 64 times

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Optically pumped type-II W lasers emitting in the mid-infrared exhibited continuous-wave (cw) operating temperatures of 290 K at λ = 3.0 μm and 210 K at λ = 6.1 μm. Maximum cw output powers for 78 K were 260 mW at λ = 3.1 μm and nearly 50 mW at λ = 5.4 μm. These high maximum temperatures were achieved through the use of a diamond-pressure-bonding technique for heat sinking the semiconductor lasers. The thermal bond, which is accomplished through pressure alone, permits topside optical pumping through the diamond at wavelengths that would be absorbed by the substrate. © 1999 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Polarization dynamics in vertical-cavity surface-emitting lasers with optical feedback through a quarter-wave plate

C. Masoller and N. B. Abraham

Appl. Phys. Lett. 74, 1078 (1999); http://dx.doi.org/10.1063/1.123487 (3 pages) | Cited 8 times

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Square-wave switching of the intensities of the orthogonal linearly polarized components of the output of a vertical-cavity surface-emitting laser (VCSEL) found previously in experiments with polarization-changing optical feedback, is not found in rate equation models incorporating only birefringence and gain anisotropy, but is found in the model for VCSELs developed by San Miguel, Feng, and Moloney [M. San Miguel, Q. Feng, and J. V. Moloney, Phys. Rev. A 52, 1729 (1995)]. The dynamics is sensitive to both the feedback strength and the relaxation rate of the magnetization in the quantum well sublevels. © 1999 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.25.Ja Polarization
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Damage threshold of HgCdTe induced by continuous-wave CO2 laser

Jianhua Zhao, Xiangyang Li, Hua Liu, Runqing Jiang, Zhaopeng Liu, Zhihan Hu, Haimei Gong, and Jiaxiong Fang

Appl. Phys. Lett. 74, 1081 (1999); http://dx.doi.org/10.1063/1.123488 (3 pages)

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We studied the interaction of p-type HgCdTe with a continuous-wave (cw) carbon dioxide (CO2) laser experimentally and theoretically and obtained an apparent damage threshold temperature, 670–680 K, which corresponds to the temperature of the solid–solid phase transition of HgCdTe. We proposed a two-dimensional thermal conducting model dealing with the thermal diffusion of cw laser processing of materials in this letter. The temperature distribution during the interaction between HgCdTe and the cw CO2 laser is also presented and discussed. All the theoretical calculations are in good agreement with the experimental results. © 1999 American Institute of Physics.
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61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.62.Cf Industrial applications
64.70.K- Solid-solid transitions
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Epitaxially ideal oxide–semiconductor interfaces: Silicate adlayers on hexagonal (0001) and (000math) SiC surfaces

J. Bernhardt, J. Schardt, U. Starke, and K. Heinz

Appl. Phys. Lett. 74, 1084 (1999); http://dx.doi.org/10.1063/1.123489 (3 pages) | Cited 40 times

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The preparation of hexagonal {0001} 4H and 6H silicon carbide surfaces by hydrogen plasma or etching in hydrogen flow produces highly ordered monolayers of silicon dioxide. Their structure and epitaxial relationship to the SiC substrate were analyzed by quantitative low-energy electron diffraction and Auger electron spectroscopy. The bond angles and distances retrieved agree with those of bulk SiO2. Due to the saturation of all dangling bonds the semiconductor surface is passivated and preserves its perfect order also in air. The practically ideal oxide monolayers may serve as a seed for growing epitaxial oxides with low defect density and only few structural distortions at the interface to the SiC substrate. © 1999 American Institute of Physics.
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68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.35.Ct Interface structure and roughness
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
79.20.Fv Electron impact: Auger emission
81.65.Rv Passivation

Phase separation in a two-dimensional Co–Cr alloy

S.-J. Kahng, Y. J. Choi, J.-Y. Park, and Y. Kuk

Appl. Phys. Lett. 74, 1087 (1999); http://dx.doi.org/10.1063/1.123490 (3 pages) | Cited 9 times

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Two-dimensional phase separation in a Co–Cr random binary alloy on a W(110) surface was confirmed with ultra-high-vacuum scanning tunneling microscopy. With 1.1 ML Co and 0.1 ML Cr co-deposited at room temperature, the film shows a kinetically limited structure. Upon annealing, phase separation between Co and Cr-rich phases of ∼100 Å size was observed. Evidence of compositional inhomogeneity was observed in Cr-rich phases but not in Co-rich phases. © 1999 American Institute of Physics.
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68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys
81.05.Bx Metals, semimetals, and alloys
81.30.Bx Phase diagrams of metals, alloys, and oxides
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Local electric-field-induced oxidation of titanium nitride films

S. Gwo, C.-L. Yeh, P.-F. Chen, Y.-C. Chou, T. T. Chen, T.-S. Chao, S.-F. Hu, and T.-Y. Huang

Appl. Phys. Lett. 74, 1090 (1999); http://dx.doi.org/10.1063/1.123491 (3 pages) | Cited 30 times

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Nanometer-scale patterning of TiN films grown on SiO2/Si(001) has been demonstrated using the local electric-field-induced oxidation process with a conductive-probe atomic force microscope. The chemical composition of the modified TiN region was determined by micro-Auger electron spectroscopy and was found to consist of Ti, some trace amount of N, and O, suggesting the formation of titanium oxynitride in the near surface region. The dependence of the oxide height on the sample bias voltage with a fixed scanning speed shows a nonlinear trend in the high electric field regime, indicating that the growth kinetics might be significantly different from previous studies using other film materials. © 1999 American Institute of Physics.
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81.65.Mq Oxidation
79.20.Fv Electron impact: Auger emission

Local density of states calculation for a discrete model of a diamond single atom tip

N. M. Miskovsky and Paul H. Cutler

Appl. Phys. Lett. 74, 1093 (1999); http://dx.doi.org/10.1063/1.123492 (3 pages) | Cited 3 times

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Recent studies of field emission from wide-band-gap semiconductors have concentrated on thin-film and needle geometries. It has been proposed that the emission originates from localized asperities (or crystallites) on the film (which can be of nanometer or even atomic size) or from very sharp tips approaching atomic size in the case of needle geometry. A quantity important in determining the origin of the tunneling electron states is the density of states function. In the present work we have calculated the local density of states at an atomically sharp diamond asperity (or tip) using a tight-binding model. A pyramidal-shaped cluster of 159 atoms is constructed to model the tip. The forces are calculated and used to optimize the atomic geometry of the top six layers of atoms. The bottom layers are fixed to simulate the bulk diamond. Results indicate that the local density of states of the topmost single atom on the tip is significantly different from that of the bulk and suggest that the discrete geometry of the structure plays a role in determining the field-emission characteristics. © 1999 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
71.20.Mq Elemental semiconductors
73.20.Fz Weak or Anderson localization
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
36.40.Cg Electronic and magnetic properties of clusters
79.70.+q Field emission, ionization, evaporation, and desorption

Near-field photoluminescence of microcrystalline arsenic oxides produced in anodically processed gallium arsenide

Christine M. Finnie and Paul W. Bohn

Appl. Phys. Lett. 74, 1096 (1999); http://dx.doi.org/10.1063/1.123454 (3 pages) | Cited 8 times

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Anodic processing of (100) GaAs in aqueous HCl results in the formation of a pitted surface hosting arsenic oxide microcrystals within a porous surface network. The composition of the microcrystalline features evolves from As(V) to As(III) with processing time. Spatially localized near-field photoluminescence (PL) spectroscopy of the microcrystalline and porous features demonstrates that the strong visible photoluminescence observed in the far field originates from the μm-sized crystalline features. The spatial localization of the PL on the arsenic oxide microcrystalline features argues that it does not arise from quantum confinement effects, but rather is due to luminescent features intrinsic to the arsenic oxide microcrystals on the pitted surface. © 1999 American Institute of Physics.
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78.55.Mb Porous materials
78.55.Cr III-V semiconductors
81.65.-b Surface treatments
81.05.Rm Porous materials; granular materials
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Band offsets at the ZnSe/CuGaSe2(001) heterointerface

A. Bauknecht, U. Blieske, T. Kampschulte, J. Albert, H. Sehnert, M. Ch. Lux-Steiner, A. Klein, and W. Jaegermann

Appl. Phys. Lett. 74, 1099 (1999); http://dx.doi.org/10.1063/1.123455 (3 pages) | Cited 14 times

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The formation of the ZnSe/CuGaSe2 heterointerface was studied by x-ray photoelectron spectroscopy (XPS). ZnSe was sequentially grown on CuGaSe2(001) epilayers. In situ photoemission spectra of the Ga 3d and Zn 3d core levels as well as XPS valence bands were acquired after each deposition step. The valence-band offset is determined to be ΔEV = 0.6±0.1 eV. As a consequence, a nearly symmetric “type-I” band alignment for the ZnSe/CuGaSe2 heterojunction with a conduction-band offset of ΔEC = 0.4±0.1 eV is found. Concerning the band alignment ZnSe can, therefore, be expected to be a suitable buffer material for CuGaSe2-based thin-film solar cells. © 1999 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
84.60.Jt Photoelectric conversion

Intermixing in strained InGaAs/GaAs quantum-well infrared photodetectors

Alex S. W. Lee, E. Herbert Li, and Gamani Karunasiri

Appl. Phys. Lett. 74, 1102 (1999); http://dx.doi.org/10.1063/1.123456 (3 pages) | Cited 3 times

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The effect of interdiffusion on strained InGaAs/GaAs quantum-well infrared photodetectors is investigated. Photoluminescence measurements of the interband transition indicate that there is minimal deterioration of the annealed heterostructures, as it is also evident from both the transverse electric and transverse magnetic infrared intersubband optical transitions. The absorption peak wavelength is redshifted from the as-grown 10.2 μm to 10.5 and 11.2 μm for 5 and 10 s annealing, respectively, at 850 °C without appreciable degradation in absorption strength. The peak responsivity of the as-grown and annealed spectra is of comparable amplitude, whereas the annealed spectra become narrower in shape. The dark current of the annealed devices is about an order of magnitude higher than the as-grown one at 77 K. © 1999 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing

Observation of tip-induced gap states in lightly doped Si(100) using scanning tunneling spectroscopy

Hai-An Lin, Ralph J. Jaccodine, and Michael S. Freund

Appl. Phys. Lett. 74, 1105 (1999); http://dx.doi.org/10.1063/1.123457 (3 pages) | Cited 2 times

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Scanning tunneling spectroscopy without shifts related to band bending was utilized to study tip-induced gap states in lightly doped Si(100) (ρ=12–25 Ω cm). The separation dependence of scanning tunneling spectroscopy revealed a reversible interaction between the tip and sample. A “U” shape curve of normalized differential conductivity versus sample bias in the band gap was also observed as the tip approached the sample, suggesting the evolution of a continuum of tip-induced gap states. These results can be explained in terms of an emission dominant-tunnel model where the tunneling current is controlled by electron emission from traps in the band gap. The experiments described herein demonstrate that scanning tunneling microscopy can be used as a powerful tool for probing the origin and evolution of the surface states. © 1999 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.25.+i Surface conductivity and carrier phenomena
73.40.Ns Metal-nonmetal contacts
71.20.Mq Elemental semiconductors
72.80.Cw Elemental semiconductors

Determination of energy levels of surface states in GaAs metal–semiconductor field-effect transistor using deep-level transient spectroscopy

Kyoung Jin Choi and Jong-Lam Lee

Appl. Phys. Lett. 74, 1108 (1999); http://dx.doi.org/10.1063/1.123458 (3 pages) | Cited 9 times

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The energy levels of surface states at the surface of GaAs were determined through capacitance deep-level transient spectroscopy of GaAs metal–semiconductor field-effect transistor with large gate periphery. Two types of hole-like traps are observed in the spectra. These originate from the surface states at the ungated regions between gate and source/drain electrodes. The activation energies of both surface states are determined to be 0.65±0.07 and 0.88±0.04 eV, which agree well with the energy levels of AsGa+ and AsGa++ within band gap of GaAs, responsible for the Fermi level pinning at the surface. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Eq III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.30.De Semiconductor-device characterization, design, and modeling

A narrow photoluminescence linewidth of 21 meV at 1.35 μm from strain-reduced InAs quantum dots covered by In0.2Ga0.8As grown on GaAs substrates

Kenichi Nishi, Hideaki Saito, Shigeo Sugou, and Jeong-Sik Lee

Appl. Phys. Lett. 74, 1111 (1999); http://dx.doi.org/10.1063/1.123459 (3 pages) | Cited 250 times

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InAs quantum dots with size fluctuations of less than 4% were grown on GaAs using the self-assembling method. By covering the quantum dots with In0.2Ga0.8As or In0.2Al0.8As, strain in InAs dots can be partly reduced due to relaxation of lattice constraint in the growth direction. This results in low-energy emission (about 1.3 μm) from the quantum dots. The photoluminescence linewidth can be reduced to 21 meV at room temperature. This width is completely comparable to the theoretical limit of a band-to-band emission from a quantum well at room temperature. Because the dots can be uniformly covered by the strain reducing layers, factors that degrade size uniformity during coverage, such as compositional mixing or segregation, will be suppressed, allowing for an almost ideal buried quantum dot structure. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Depth profiling of GaN by cathodoluminescence microanalysis

K. Fleischer, M. Toth, M. R. Phillips, J. Zou, G. Li, and S. J. Chua

Appl. Phys. Lett. 74, 1114 (1999); http://dx.doi.org/10.1063/1.123460 (3 pages) | Cited 35 times

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We present the results of a depth-resolved cathodoluminescence (CL) and transmission electron microscopy study of autodoped GaN grown on sapphire. Depth-resolved CL analysis can be used for depth profiling of the yellow luminescence (YL) center concentration which was found to increase with depth. The results are consistent with the (ON–VGa)2− complex model of YL centers [J. Neugebauer and C. G. Van de Walle, Appl. Phys. Lett. 69, 503 (1996) and T. Mattila and R. M. Nieminen, Phys. Rev. B 55, 9571 (1996)]. Depth profiling of the near-edge emission in GaN layers thicker than ∼0.5 μm is not possible due to strong self-absorption. © 1999 American Institute of Physics.
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71.55.Eq III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Valence-band structure of wurtzite GaN including the spin-orbit interaction

G. B. Ren, Y. M. Liu, and P. Blood

Appl. Phys. Lett. 74, 1117 (1999); http://dx.doi.org/10.1063/1.123461 (3 pages) | Cited 31 times

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We have investigated the effects of the spin-orbit interaction on the valence-band structure of wurtzite GaN in the k⋅p theory. The spin-orbit interaction is usually neglected in nitrides, which leads to three doubly degenerate bands: the heavy-hole, light-hole, and crystal-field split-off bands. Including the spin-orbit interaction, this degeneracy is removed to give six single bands. We obtained the Luttinger-like parameters in bulk wurtzite GaN by fitting data obtained from an empirical pseudopotential calculation obtaining a value for the parameter A7 of 93.7 meV/Å. We also used these results to calculate the valence-band structures of a GaN/AlGaN quantum well. Our result shows the spin-orbit interaction is important in GaN and associated quantum well structures. © 1999 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.70.Ch Crystal and ligand fields
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Direct observation of traps responsible for positive space charge in alternating-current thin-film electroluminescent devices

Alex N. Krasnov

Appl. Phys. Lett. 74, 1120 (1999); http://dx.doi.org/10.1063/1.123462 (3 pages) | Cited 4 times

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Space charge has significant influence on the operation of alternating-current thin-film electroluminescent displays. This letter introduces a relatively simple method for direct observation of the distribution of traps responsible for the space charge in the active layer of the devices. Contribution of native and dopant defects in the space charge formation is discussed. © 1999 American Institute of Physics.
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85.60.Pg Display systems
42.79.Kr Display devices, liquid-crystal devices
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
77.22.Jp Dielectric breakdown and space-charge effects
71.55.-i Impurity and defect levels

Dry etching of GaN substrates for high-quality homoepitaxy

M. Schauler, F. Eberhard, C. Kirchner, V. Schwegler, A. Pelzmann, M. Kamp, K. J. Ebeling, F. Bertram, T. Riemann, J. Christen, P. Prystawko, M. Leszczynski, I. Grzegory, and S. Porowski

Appl. Phys. Lett. 74, 1123 (1999); http://dx.doi.org/10.1063/1.123463 (3 pages) | Cited 18 times

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Chemically assisted ion-beam etching (CAIBE) was used to remove subsurface damage from polished GaN bulk substrates prior to growth. Subsequently, GaN layers were deposited by metalorganic vapor phase epitaxy. Only the CAIBE-treated areas reveal a mirror-like surface without trenches, scratches, or holes. A dramatic increase of crystal quality is determined by low-temperature cathodoluminescence (CL). Compared to not CAIBE-treated material, the CL intensity is improved by a factor of 1000 and the linewidth is ten times narrower. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.60.Hk Cathodoluminescence, ionoluminescence

On the origin of tunneling barriers in silicon single electron and single hole transistors

Hiroki Ishikuro and Toshiro Hiramoto

Appl. Phys. Lett. 74, 1126 (1999); http://dx.doi.org/10.1063/1.123464 (3 pages) | Cited 31 times

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To clarify the channel potential profiles, Coulomb blockades of single electron and single hole tunneling in Si nanosize narrow channel metal–oxide–semiconductor field-effect transistors are intensively studied. Devices with both n+ and p+ source/drain contacts were fabricated on silicon-on-insulator substrates. Transport properties of a hole system as well as an electron system induced in the same channel were investigated. It is found from the experimental results that potential fluctuations in the channel act as tunnel barriers for both electrons and holes. Lateral quantum confinement effects or silicon oxide (SiOx) are thought to be the cause of tunnel barriers. © 1999 American Institute of Physics.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices
73.23.Hk Coulomb blockade; single-electron tunneling
85.35.Ds Quantum interference devices

Visible cathodoluminescence of GaN doped with Dy, Er, and Tm

H. J. Lozykowski, W. M. Jadwisienczak, and I. Brown

Appl. Phys. Lett. 74, 1129 (1999); http://dx.doi.org/10.1063/1.123465 (3 pages) | Cited 105 times

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We reported the observation of visible cathodoluminescence of rare-earth Dy, Er, and Tm implanted in GaN. The implanted samples were given isochronal thermal annealing treatments at a temperature of 1100 °C in N2 or NH3, at atmospheric pressure to recover implantation damages and activated the rare-earth ions. The sharp characteristic emission lines corresponding to Dy3+, Er3+, and Tm3+ intra-4fn-shell transitions are resolved in the spectral range from 380 to 1000 nm, and observed over the temperature range of 8.5–411 K. The cathodoluminescence emission is only weakly temperature dependent. The results indicate that rare-earth-doped GaN epilayers are suitable as a material for visible optoelectronic devices. © 1999 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
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