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16 Oct 2000

Volume 77, Issue 16, pp. 2437-2616

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GaAs/AlGaAs quantum-well photodetector for visible and middle infrared dual-band detection

H. C. Liu, C. Y. Song, A. Shen, M. Gao, Z. R. Wasilewski, and M. Buchanan

Appl. Phys. Lett. 77, 2437 (2000); http://dx.doi.org/10.1063/1.1318232 (3 pages) | Cited 18 times

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We present experimental results on quantum-well photodetectors for visible and infrared dual-band detection. Large band gap top contacts were used on a standard GaAs/AlGaAs quantum-well infrared photodetector so that visible light could reach the quantum-well region and be absorbed via interband transitions. Two designs were investigated, using a high Al fraction AlGaAs and a short period GaAs/AlAs superlattice contact layer. The dual-band response spectral regions are 0.55–0.7 and 7–10 μm. Measured responsivities are about 0.7 A/W at 8.3 μm and 0.1 A/W at 0.63 μm under −6 V bias voltage. © 2000 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
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors

Strong modification of photoluminescence in erbium-doped porous silicon microcavities

Y. Zhou, P. A. Snow, and P. St. J. Russell

Appl. Phys. Lett. 77, 2440 (2000); http://dx.doi.org/10.1063/1.1318230 (3 pages) | Cited 4 times

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A microcavity composed of porous silicon multilayer mirrors was electrochemically etched and doped with erbium. Measurements of the reflectivity and photoluminescence spectra are presented. Thermal processing under a nitrogen atmosphere optically activated the erbium ions. Photopumping yielded room temperature emission around 1.54 μm from the erbium-doped samples with the emitted light strongly modified by the microcavity structure. Emission spectra with a peak at 1.536 μm had a full width at half maximum of ∼6 nm. © 2000 American Institute of Physics.
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78.55.Mb Porous materials
81.05.Rm Porous materials; granular materials
42.79.Bh Lenses, prisms and mirrors
78.55.Ap Elemental semiconductors
42.79.Wc Optical coatings
78.30.Am Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors

Photoluminescence from pendant dye molecules mediated by exciton transport on helical polysilane chains

Hiroaki Tachibana, Hideo Kishida, and Yoshinori Tokura

Appl. Phys. Lett. 77, 2443 (2000); http://dx.doi.org/10.1063/1.1318395 (3 pages) | Cited 5 times

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We have synthesized helical polysilanes on which the pendant groups are partly substituted by dye molecules. The introduction of a few percent of dye molecules into the substituents enhances the luminescent efficiency of the visible region, by behaving as luminescence centers. We have demonstrated that the excitation energy is transferred efficiently by free excitons on the Si backbones to reach the luminescence centers, where energy transfer occurs from the exciton to the dye molecule, and as a result sensitized luminescence occurs. The exciton transfer is found to occur over 50–100 monomer units on the polysilane backbone. This approach will open the way to fabricating a wavelength-tunable luminous device by utilizing the exciton transport on Si chains. © 2000 American Institute of Physics.
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78.55.Kz Solid organic materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
71.35.-y Excitons and related phenomena
61.41.+e Polymers, elastomers, and plastics
71.55.Jv Disordered structures; amorphous and glassy solids

Luminescence enhancement from hydrogen-passivated self-assembled quantum dots

E. C. Le Ru, P. D. Siverns, and R. Murray

Appl. Phys. Lett. 77, 2446 (2000); http://dx.doi.org/10.1063/1.1318931 (3 pages) | Cited 23 times

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We have measured a large increase (by a factor of up to 50) in the room-temperature emission of InAs/GaAs self-assembled quantum dots subjected to a hydrogen-passivation treatment. Smaller enhancements were measured at low temperatures. We tentatively attribute the improved optical signal to passivation of defects within the GaAs matrix and wetting layer adjacent to the dots. Annealing studies show that these benefits are lost following annealing at temperatures above 600 °C for 5 min. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.55.Eq III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing

Amplification of picosecond optical pulses in midinfrared intersubband semiconductor optical amplifiers

J. M. Tang, P. S. Spencer, and K. A. Shore

Appl. Phys. Lett. 77, 2449 (2000); http://dx.doi.org/10.1063/1.1318932 (3 pages) | Cited 1 time

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A comprehensive theoretical model describing the amplification of picosecond optical pulses in midinfrared intersubband semiconductor optical amplifiers is developed, taking into account gain dispersion, short carrier relaxation time and ultrafast nonlinear refraction. It is shown that these factors are extremely important in determining the amplified optical pulse characteristics in both the time and frequency domains. The calculations also indicate that gain dispersion can be significantly enhanced by fast carrier relaxations, short pulse widths, and high pulse energies. © 2000 American Institute of Physics.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Px Semiconductor lasers; laser diodes
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.60.Fc Modulation, tuning, and mode locking

Electrical characterization of conducting polypyrrole by THz time-domain spectroscopy

Tae-In Jeon, D. Grischkowsky, A. K. Mukherjee, and Reghu Menon

Appl. Phys. Lett. 77, 2452 (2000); http://dx.doi.org/10.1063/1.1319188 (3 pages) | Cited 34 times

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Using an optoelectronic THz beam system for THz time-domain spectroscopy (THz TDS), we have measured the absorption and index of refraction of a conducting polypyrrole film from low frequencies to 2.5 THz. From these measurements, the dc conductivity of 215/(Ω cm) and the complex conductance were obtained over this frequency range. All of the results were well fit by Drude theory, which gives a carrier scattering time of only 12.6 fs, less than 1/10 that of the semiconductors, thereby illustrating the disorder and low mobility of the polymer. © 2000 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
78.70.Gq Microwave and radio-frequency interactions
72.15.Nj Collective modes (e.g., in one-dimensional conductors)
72.30.+q High-frequency effects; plasma effects
73.50.Mx High-frequency effects; plasma effects
77.22.Ch Permittivity (dielectric function)

Co2+:LiGa5O8 saturable absorber passive Q switch for 1.34 μm Nd3+:YAlO3 and 1.54 μm Er3+:glass lasers

I. A. Denisov, M. I. Demchuk, N. V. Kuleshov, and K. V. Yumashev

Appl. Phys. Lett. 77, 2455 (2000); http://dx.doi.org/10.1063/1.1319179 (3 pages) | Cited 21 times

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Passive Q switching of a Nd3+:YAlO3 laser at 1.34 μm and an Er3+: glass laser at 1.54 μm was demonstrated using a Co2+:LiGa5O8 crystal as a saturable absorber. Q-switched pulses at 1.34 μm of 13 mJ energy and 90 ns duration and at 1.54 μm of 8 mJ energy and 70 ns duration were obtained. The ground state absorption cross section of the Co2+:LiGa5O8 was estimated to be (2.6±0.4)×10−19 cm2 and (2.5±0.5)×10−19 cm2 at 1.34 and 1.54 μm, respectively. The 4T1(4F)→4A2 relaxation time of the Co2+ ion in the LiGa5O8 crystal was measured to be ∼130 ns. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.70.Hj Laser materials

Color engineering by modified oligothiophene blends

M. Anni, G. Gigli, V. Paladini, R. Cingolani, G. Barbarella, L. Favaretto, G. Sotgiu, and M. Zambianchi

Appl. Phys. Lett. 77, 2458 (2000); http://dx.doi.org/10.1063/1.1314886 (3 pages) | Cited 31 times

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Fully tunable light emission is demonstrated with combinations of binary blends of modified oligothiophenes of high efficiency, covering the entire spectrum of colors according to the standards of the Commission International de l’Eclairage. The emission spectrum of each blend is determined by the Forster transfer when the energy separation between the highest occupied molecular orbital–lowest unoccupied molecular orbital gap of the constituent molecules is smaller than 0.56 eV. For larger energy separation, the blend emission is just given by the superposition of the emission spectra of the constituent molecules. © 2000 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics

Enhanced photoinduced birefringence in polymer microcavities

Rozenn Piron, Eric Toussaere, Dominique Josse, and Joseph Zyss

Appl. Phys. Lett. 77, 2461 (2000); http://dx.doi.org/10.1063/1.1316072 (3 pages) | Cited 5 times

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We investigate photoinduced birefringence in functionalized polymer microcavities illuminated by a visible polarized cw laser beam. The cavity studied in this experiment consists of an assembly of two Bragg mirrors embedding a polymer film with tethered azobenzene dyes. Linearly polarized light induces orientationally selective excitation of the chromophore guests, resulting in optical anisotropy of the film. The mechanism of the phenomenon is based on random-to-axial statistical reorientation of the azochromophores following repetitive trans-cis-trans photoisomerization cycles. The resulting birefringence is inferred from analysis of the spectral shifts of the cavity Fabry–Pérot longitudinal modes as a result of illumination. A large value of the birefringence of the order of 10−2 is noted after currently unoptimized durations of the order of 30′ in the 1.3–1.5 μm range with possible applications in optical storage at WDM telecom-compatible wavelengths. © 2000 American Institute of Physics.
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78.20.Fm Birefringence
78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
42.25.Lc Birefringence
42.55.Sa Microcavity and microdisk lasers
82.30.Qt Isomerization and rearrangement
82.50.-m Photochemistry
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Initiation of an early-stage plasma during picosecond laser ablation of solids

Samuel S. Mao, Xianglei Mao, Ralph Greif, and Richard E. Russo

Appl. Phys. Lett. 77, 2464 (2000); http://dx.doi.org/10.1063/1.1318239 (3 pages) | Cited 40 times

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Picosecond time-resolved images of plasma initiation were recorded during pulsed-laser ablation of metal targets in an air atmosphere. An early-stage plasma was observed to form before the release of a material vapor plume. Close to the target surface, interferometry measurements indicate that the early-stage plasma has an electron number density on the order of 1020 cm−3. The longitudinal expansion of the ionization front for this plasma has a velocity 109 cm/s, during the laser pulse. In contrast, a material–vapor plume forms approximately 200 ps after the laser pulse, and it moves away from the target at 106 cm/s. The experimental observations of the early-stage plasma were simulated by using a theoretical model based on a two-fluids description of laser plasmas. The results indicate that the initiation of the plasma is due to air breakdown assisted by electron emission from the target. © 2000 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
81.05.Bx Metals, semimetals, and alloys
79.20.Ds Laser-beam impact phenomena
52.65.Kj Magnetohydrodynamic and fluid equation
52.25.-b Plasma properties
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
81.65.-b Surface treatments

Diagnostics of inductively coupled chlorine plasmas: Measurements of the neutral gas temperature

V. M. Donnelly and M. V. Malyshev

Appl. Phys. Lett. 77, 2467 (2000); http://dx.doi.org/10.1063/1.1318727 (3 pages) | Cited 68 times

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We report measurements of the bulk, neutral gas temperature in a chlorine transformer-coupled plasma. A trace amount (2%–5%) of N2 was added to the discharge and the rotational temperature of the C3Πu state was determined from the C3Πu→B3Πg emission in the ultraviolet. This temperature has been shown by others to be equal to the rotational temperature of ground-state N2, which is the thermally equilibrated (translational and rotational) gas temperature (Tg). The gas temperature 3 cm above the wafer is equal to, or only slightly above the wall temperature (300 K) throughout the low-power, capacitively coupled regime (<60 W, 0.024 W/cm3). Between the lowest (130 W, 0.053 W/cm3) and highest (900 W, 0.36 W/cm3) inductively coupled mode powers investigated, Tg increases sublinearly with power (and electron density). The high-power (900 W) Tg increases with increasing pressure (650, 750, 900, and 1250 K at 2, 5, 10, and 20 mTorr, respectively). Mechanisms of neutral gas heating are discussed. The energy released in dissociation of Cl2 appears to be the dominant heating mechanism. © 2000 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges
33.20.Sn Rotational analysis
52.40.Hf Plasma-material interactions; boundary layer effects
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Probing capped and uncapped mesoporous low-dielectric constant films using positron annihilation lifetime spectroscopy

Mihail P. Petkov, Marc H. Weber, Kelvin G. Lynn, and Kenneth P. Rodbell

Appl. Phys. Lett. 77, 2470 (2000); http://dx.doi.org/10.1063/1.1318238 (3 pages) | Cited 21 times

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We have measured uncapped mesoporous low-dielectric-constant films using positron annihilation lifetime spectroscopy (PALS), a nondestructive technique, which yields both pore-size distributions and the threshold for pore interconnectivity. Pairs of fully cured capped and uncapped identical films, initially containing 5%–50% porogen additions, exhibited similar signatures in PALS, establishing a technique in which film capping is unnecessary. We also found that it was possible to distinguish between closed and percolated pores, without film capping, by comparing lifetime spectra of a film taken using different detector configurations. Interconnected pores were observed in cured samples, which had greater than 20% porogen additions. © 2000 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
78.70.Bj Positron annihilation
85.40.Ls Metallization, contacts, interconnects; device isolation
77.55.-g Dielectric thin films
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials

Efficient photovoltaic energy conversion in pentacene-based heterojunctions

J. H. Schön, Ch. Kloc, and B. Batlogg

Appl. Phys. Lett. 77, 2473 (2000); http://dx.doi.org/10.1063/1.1318234 (3 pages) | Cited 25 times

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We have prepared heterojunction devices based on ZnO and both pentacene single crystals and thin films. Their photovoltaic properties have been studied. Bromine doping is found to improve significantly the performance of such devices and solar-energy conversion efficiencies up to 4.5% are achieved for single-crystal devices. In addition, efficiencies exceeding 2% are realized in thin-film devices on flexible plastic substrates. These results demonstrate that efficient photovoltaic energy conversion is possible with organic semiconductors. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.61.Ph Polymers; organic compounds
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Pz Photoconduction and photovoltaic effects
72.40.+w Photoconduction and photovoltaic effects

Effect of Sb doping on the thermoelectric properties of Ti-based half-Heusler compounds, TiNiSn1−xSbx

S. Bhattacharya, A. L. Pope, R. T. Littleton, Terry M. Tritt, V. Ponnambalam, Y. Xia, and S. J. Poon

Appl. Phys. Lett. 77, 2476 (2000); http://dx.doi.org/10.1063/1.1318237 (3 pages) | Cited 53 times

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Half-Heusler alloys (MgAgAs type) with the general formula MNiSn where M is a group IV transition metal (Hf, Zr, or Ti) are currently under investigation for potential thermoelectric materials. These materials exhibit a high negative thermopower (−40 to −250 μV/K) and low electrical resistivity values (0.1–8 mΩ cm) both of which are necessary for a potential thermoelectric material. Results are presented in this letter regarding the effect of Sb doping on the Sn site (TiNiSn1−xSbx). The Sb doping leads to a relatively large power factor of (0.2–1.0) W/m K at room temperature for small concentrations of Sb. These values are comparable to that of Bi2Te3 alloys, which are the current state-of-the-art thermoelectric materials. The power factor is much larger at T ≈ 650 K where it is over 4 W/m K making these materials very attractive for potential power generation considerations. © 2000 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Ga Transition-metal compounds
72.20.Fr Low-field transport and mobility; piezoresistance

Faceted inversion domain boundary in GaN films doped with Mg

L. T. Romano, J. E. Northrup, A. J. Ptak, and T. H. Myers

Appl. Phys. Lett. 77, 2479 (2000); http://dx.doi.org/10.1063/1.1318731 (3 pages) | Cited 51 times

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Homoepitaxial GaN films, doped with Mg, were grown by rf-plasma molecular-beam epitaxy on Ga-polarity (0001) templates. Convergent-beam electron diffraction analysis establishes that the film polarity changes from [0001] to [000math] when the Mg flux during growth is approximately 1 ML/s. Secondary ion mass spectrometry indicates a doping concentration of ∼ 1020 cm−3 in the film where the inversion occurs, and a reduced Mg incorporation in the [000math] material. Transmission electron microscopy shows that the inversion domain boundary is faceted predominantly along the {0001} and {h,h,−2h,l} planes, with l/h approximately equal to 3. Using first-principles total energy calculations, we show that the {h,h,−2h,l} segments of the boundary are stabilized by the incorporation of Mg in threefold coordinated lattice sites. © 2000 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.uj III-V and II-VI semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors

Comparison of nitrogen incorporation in molecular-beam epitaxy of GaAsN, GaInAsN, and GaAsSbN

J. C. Harmand, G. Ungaro, L. Largeau, and G. Le Roux

Appl. Phys. Lett. 77, 2482 (2000); http://dx.doi.org/10.1063/1.1318228 (3 pages) | Cited 49 times

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The incorporation of nitrogen in the low percentage range is investigated in a different III–V compound matrix. The materials are grown by molecular-beam epitaxy with a nitrogen radio-frequency plasma source. For equivalent growth conditions, the same rate of N incorporation is found for GaAsN and GaInAsN. However, this N incorporation rate is significantly enhanced in the GaAsSbN alloy. These observations support a discussion on the reactive nitrogen species. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology

Molecular beam epitaxial growth of atomically smooth scandium nitride films

Hamad Al-Brithen and Arthur R. Smith

Appl. Phys. Lett. 77, 2485 (2000); http://dx.doi.org/10.1063/1.1318227 (3 pages) | Cited 31 times

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High quality scandium nitride films have been grown on magnesium oxide (001) substrates by molecular beam epitaxy using a rf plasma source for nitrogen. Both reflection high energy electron diffraction and x-ray diffraction confirm that these films have (001)-orientation. Atomic force microscopy reveals a surface morphology consisting of large plateaus and pyramids. The plateaus are found to be atomically smooth and have a 1×1 surface structure, as revealed by in situ scanning tunneling microscopy. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Domain mapping of periodically poled lithium niobate via terahertz wave form analysis

Y.-S. Lee, T. Meade, M. L. Naudeau, T. B. Norris, and A. Galvanauskas

Appl. Phys. Lett. 77, 2488 (2000); http://dx.doi.org/10.1063/1.1318725 (3 pages) | Cited 12 times

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We demonstrate a nondestructive probing technique to investigate the inner crystal domain structure of ferroelectric crystals by analyzing the terahertz wave forms generated by optical rectification. Quantitative analysis of the domain structure has been performed for the domain width in periodically poled lithium niobate. Simulation results show that the terahertz wave form analysis reproduces root-mean-square domain width fluctuations. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
42.70.Mp Nonlinear optical crystals
77.22.Ej Polarization and depolarization

Molecular beam epitaxy growth of GaN on C-terminated 6H–SiC (000math) surface

Z. P. Guan, A. L. Cai, J. S. Cabalu, H. L. Porter, and S. Huang

Appl. Phys. Lett. 77, 2491 (2000); http://dx.doi.org/10.1063/1.1318723 (3 pages) | Cited 9 times

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We report the results of successful growth of GaN on the C-terminated surface of SiC. A combination of direct heating and hydrogen plasma treatment was employed for surface preparation. High-quality epitaxy was achieved in epilayers as thin as 2000 Å, as evidenced by the x-ray diffraction full width at half maximum of 90 arc sec and 4.2 K donor-bound exciton peak width of 1.4 meV. The epilayers exhibit clear signatures of compressive strain, suggesting a more favorable growth mode than can be achieved on the Si-terminated surface. © 2000 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Photorefraction in LiNbO3 as a function of [Li]/[Nb] and MgO concentrations

Y. Furukawa, K. Kitamura, S. Takekawa, A. Miyamoto, M. Terao, and N. Suda

Appl. Phys. Lett. 77, 2494 (2000); http://dx.doi.org/10.1063/1.1318721 (3 pages) | Cited 69 times

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Photorefractive damage, photoconductivities, and photogalvanic currents of LiNbO3 single crystals have been investigated as a function of [Li]/[Nb] and MgO concentrations. Near stoichiometric LiNbO3 single crystal, having large [Li]/[Nb] ratios of 0.993, shows lower photorefractive damage resistance than congruent LiNbO3. However, crystals doped with a small amount of MgO (>0.78 mol %) exhibit no measurable photorefractive damage at 532 nm to intensities of as much as 2 MW/cm2. This remarkable decrease of photorefraction that was found can be attributed to the decrease of saturated space charge field results from a combination of the increased photoconductivity and the decreased photogalvanic current of the crystal. © 2000 American Institute of Physics.
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42.70.Gi Light-sensitive materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.40.+w Photoconduction and photovoltaic effects
77.22.Jp Dielectric breakdown and space-charge effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
61.66.Bi Elemental solids
61.66.Dk Alloys

Influence of growth direction on order–disorder transition in (GaAs)1−x(Ge)2x semiconductor alloys

A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal

Appl. Phys. Lett. 77, 2497 (2000); http://dx.doi.org/10.1063/1.1318722 (3 pages) | Cited 6 times

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We provide direct evidence of the dependence of the critical concentration of IV-type atoms at the order–disorder transition in ternary metastable (III–V)–IV, zincblende–diamond semiconductor alloys on the growth direction. The excellent agreement between the experimental and model predicted critical concentrations is evidence that the atomic ordering in these alloys is ruled almost entirely by substrate geometry. In this letter, we report the observation of the critical concentration dependence on substrate orientation in (GaAs)1−x(Ge2)x metastable alloys, epitaxially grown on (001), (111), (112), and (113) oriented GaAs. A different long-range order parameter behavior with Ge concentration is obtained for each growth direction. The Ge critical concentrations observed are 0.36, 0.96, 0.59, and 0.50±0.03, for the orientations listed above, values that compare well with those obtained from a Monte Carlo simulation of the growth, 0.33, 1.0, 0.64, and 0.54, respectively. © 2000 American Institute of Physics.
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64.70.K- Solid-solid transitions
68.55.Nq Composition and phase identification
64.60.Cn Order-disorder transformations
64.60.My Metastable phases
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
02.70.Rr General statistical methods

Optical microcavities using highly luminescent films of semiconductor nanocrystals

Chris E. Finlayson, David S. Ginger, and Neil C. Greenham

Appl. Phys. Lett. 77, 2500 (2000); http://dx.doi.org/10.1063/1.1318720 (3 pages) | Cited 23 times

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Colloidally grown CdSe nanocrystals with epitaxial ZnS shells show highly efficient, size-tunable luminescence. We report the incorporation of films of these core-shell nanocrystals into wavelength-scale, high-Q, planar microcavities. Under optical excitation, we find that emission from the nanocrystals couples to the discrete optical modes of the microcavity. The broad free-space emission spectrum of the nanocrystals is modified by the presence of the microcavity, giving a series of sharp emission lines with wavelengths determined by the cavity dimension. Our experiments demonstrate that microcavities with semiconductor emitters can be conveniently fabricated using spin-coating techniques. We find that, at room temperature, the microcavity emission spectrum is independent of excitation intensity for excitation densities up to approximately one electron–hole pair per nanocrystal. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
42.79.Wc Optical coatings
81.05.Dz II-VI semiconductors

Observation of long photoluminescence decay times for high-quality GaN grown by metalorganic chemical vapor deposition

Ho Ki Kwon, C. J. Eiting, D. J. H. Lambert, M. M. Wong, R. D. Dupuis, Z. Liliental-Weber, and M. Benamara

Appl. Phys. Lett. 77, 2503 (2000); http://dx.doi.org/10.1063/1.1318396 (3 pages) | Cited 12 times

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GaN epitaxial layers with different crystalline quality grown on sapphire substrates by metalorganic chemical vapor deposition are investigated using time-resolved photoluminescence at 300 K. It is found that the time-dependent photoluminescence of low-quality GaN decays faster than that of the high-quality GaN films. The time constants for the dual-exponential decay of the photoluminescence are calculated to be 50 and 250 ps for high-quality undoped GaN and 30 ps for low-quality undoped GaN. For high-quality Si-doped GaN, time constants of 150 and 740 ps are extracted while corresponding time constants of 40 and 200 ps are measured for low-quality Si-doped GaN. We believe that the time constant of 740 ps measured for our high-quality Si-doped GaN is the longest ever reported for thin GaN/sapphire films. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Strong blue emission from As doped GaN grown by molecular beam epitaxy

A. J. Winser, S. V. Novikov, C. S. Davis, T. S. Cheng, C. T. Foxon, and I. Harrison

Appl. Phys. Lett. 77, 2506 (2000); http://dx.doi.org/10.1063/1.1318394 (3 pages) | Cited 22 times

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Arsenic doped GaN grown by molecular beam epitaxy has been studied by room temperature photoluminescence. In addition to the wurzite band edge transition, luminescence from the cubic phase and very strong blue emission at ∼2.6 eV are observed. The intensities of the blue and the cubic band edge emissions have a power law dependence on the As2 flux. The formation of the cubic phase has been explained by the initial formation of GaAs before substitution of the As by the more reactive N. The intensity of the blue emission at room temperature of the As doped samples is more than an order of magnitude stronger than the band edge emission in undoped samples. © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Effect of overgrowth temperature on the photoluminescence of Ge/Si islands

O. G. Schmidt, U. Denker, K. Eberl, O. Kienzle, and F. Ernst

Appl. Phys. Lett. 77, 2509 (2000); http://dx.doi.org/10.1063/1.1318729 (3 pages) | Cited 47 times

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Ge/Si islands grown with molecular-beam epitaxy at 630 °C are overgrown with Si at different temperatures Tcap, and their photoluminescene spectra are recorded. Both the island-related and wetting-layer-related energy transitions redshift with lowered Tcap, which is explained by reduced material intermixing. The mandatory growth interruption, which is introduced during the temperature drop, causes island ripening and shifts the island (wetting layer) photoluminescence peaks slightly to lower (higher) energies. The growth interruption quenches the quantum efficiency of the wetting layer by more than an order of magnitude, whereas the island-related photoluminescence intensity even slightly increases. The island’s superior resistance against growth interruptions, and hence interface contamination, is explained by effective carrier localization in the Ge nanostructures. Room-temperature photoluminescence is reported for Ge islands overgrown at 460 °C. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
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