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10 Nov 1997

Volume 71, Issue 19, pp. 2725-2857

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Cooperative effects in blue light emission of poly-(para-phenylene)-type ladderpolymer

G. Kranzelbinder, M. Nisoli, S. Stagira, S. De Silvestri, G. Lanzani, K. Müllen, U. Scherf, W. Graupner, and G. Leising

Appl. Phys. Lett. 71, 2725 (1997); http://dx.doi.org/10.1063/1.120118 (3 pages) | Cited 24 times

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A hyperlinear increase of radiative quantum efficiencies of poly(para-phenylene)-type ladderpolymer in the blue–green region as a function of subpicosecond excitation intensity is reported. The light emission in the range from 485 to 495 nm undergoes a change from linear behavior to a second order response; the two regimes are separated by a distinct threshold of 3.1 mJ/cm2. Above this threshold, investigation by femtosecond excitation–correlation measurements indicate that the hyperlinear blue emission is associated with a characteristic excitonic depopulation of 2 ps. © 1997 American Institute of Physics.
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78.55.Kz Solid organic materials
42.70.Jk Polymers and organics
85.60.Jb Light-emitting devices
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Resonant excitation of visible photoluminescence from an erbium-oxide overlayer on Si

A. Kasuya and M. Suezawa

Appl. Phys. Lett. 71, 2728 (1997); http://dx.doi.org/10.1063/1.120119 (3 pages) | Cited 23 times

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A thin Er2O3 layer grown on a Si surface by vapor doping of Er exhibits intense photoluminescence in the green and red regions excited by laser beams in the 800 nm and 450–490 nm ranges. These intense light emissions take place via resonant two or one step photoexcitations of the 4f levels in Er3+ ions. Our sample fabrication procedure is integrated circuit compatible and produces Er2O3 layers of excellent homogeneity and quality as demonstrated in the optical measurements. © 1997 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Frequency locking of tunable Er:Yb microlasers to absorption lines of 13C2H2 in the 1540–1550 nm wavelength interval

P. Laporta, S. Taccheo, S. Longhi, C. Svelto, and P. De Natale

Appl. Phys. Lett. 71, 2731 (1997); http://dx.doi.org/10.1063/1.120120 (3 pages) | Cited 9 times

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We demonstrate frequency stabilization of widely tunable erbium–ytterbium microlasers in the wavelength interval between 1540 and 1550 nm by locking the oscillators to nine different absorption lines of 13C2H2, spaced by approximately 150 GHz. Frequency stability is evaluated by measuring the two-sample Allan variance of the heterodyne beat-note signal between two identical lasers. The square root of the Allan variance is 7×10−10 for integration times between 10−3 and 102 s. © 1997 American Institute of Physics.
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42.55.Wd Fiber lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.60.By Design of specific laser systems

Coherent phonons in alkali metal-doped C60

S. B. Fleischer, B. Pevzner, D. J. Dougherty, H. J. Zeiger, G. Dresselhaus, M. S. Dresselhaus, E. P. Ippen, and A. F. Hebard

Appl. Phys. Lett. 71, 2734 (1997); http://dx.doi.org/10.1063/1.120121 (3 pages) | Cited 13 times

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We report the femtosecond impulsive excitation of coherent phonons in alkali metal-doped fullerenes. These excitations appear as small oscillations of the reflectivity (ΔR/R ∼ 10−7) produced by the pump in an optical pump-probe experiment. The observed phonons include previously unobserved highly damped modes near 150 cm−1 as well as long-lived Ag(1) modes near 490 cm−1. © 1997 American Institute of Physics.
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78.40.Ri Fullerenes and related materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.47.-p Spectroscopy of solid state dynamics

Properties of ion exchanged planar and channel optical waveguides fabricated in Cu doped KTiOPO4 substrates

L. P. Shi, T. C. Chong, Z. Zhuo, W. X. Hou, and P. F. Hu

Appl. Phys. Lett. 71, 2737 (1997); http://dx.doi.org/10.1063/1.120122 (3 pages) | Cited 3 times

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Planar and channel optical waveguides were fabricated in Cu doped KTiOPO4 (KTP) substrates using Rb+:K+ ion exchange process and annealing process. The effective refractive indices were measured using the m-line method and the refractive index profiles of these waveguides were calculated using the inverse WKB method. For waveguides in Cu:KTP substrates the difference of diffusion depth d and index change Δn at the z− and z+ surfaces can hardly be observed. This observation is different from KTP. Compared with undoped KTP substrates the diffusion depth d at the z− surfaces is larger, whereas the index change Δn is smaller. At the z+ surfaces both d and Δn are larger. The light induced effective index changes in Cu doped KTP channel waveguides were measured at 0.476, 0.488, 0.514, 0.6328, and 0.83 μm wavelengths. No changes were observed at the power flow of 1×108 W/m2, revealing that Cu ion does not play an important role in photorefractive effect of KTP crystals. © 1997 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Gn Optical waveguides and couplers
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
42.86.+b Optical workshop techniques
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Visible luminescence from Pr-doped sulfide glasses

V. K. Tikhomirov, K. Iakoubovskii, P. W. Hertogen, and G. J. Adriaenssens

Appl. Phys. Lett. 71, 2740 (1997); http://dx.doi.org/10.1063/1.120549 (3 pages) | Cited 8 times

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Room-temperature visible luminescence from Pr3+ ions embedded in germaniumsulfide glass hosts is reported along with edge luminescence from these hosts. The important role of energy transfer processes between the host and Pr ions is demonstrated experimentally through the dependencies of photoluminescence on excitation wavelength, temperature, and polarization. © 1997 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.40.Pg Disordered solids

Optical and terahertz power limits in the low-temperature-grown GaAs photomixers

S. Verghese, K. A. McIntosh, and E. R. Brown

Appl. Phys. Lett. 71, 2743 (1997); http://dx.doi.org/10.1063/1.120445 (3 pages) | Cited 59 times

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Optical heterodyne conversion, or photomixing, occurs in an epitaxial low-temperature-grown GaAs layer with voltage-biased metal electrodes on which two laser beams are focused with their frequencies offset by a desired difference frequency. Difference-frequency power couples out of the photomixer through a log-spiral antenna at THz frequencies. Pumping such a device with the maximum optical power of ∼90 mW at 77 K led to a measured output power of 0.2 μW at 2.5 THz, approximately twice the maximum output power of a photomixer operated near 300 K. Photomixers that were operated above the maximum optical power were destroyed, often because of a thermally induced fracture in the GaAs substrate. The fracture seemed to occur at high pump power when the temperature of the photomixer active area was elevated by roughly 110 K, independent of the bath temperature. © 1997 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
85.60.-q Optoelectronic devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.40.-x Radiowave and microwave (including millimeter wave) technology

Prospects of new planar optical waveguides based on eutectic microcomposites of insulating crystals: The ZrO2(c)-CaZrO3 erbium doped system

V. M. Orera, J. I. Peña, R. I. Merino, J. A. Lázaro, J. A. Vallés, and M. A. Rebolledo

Appl. Phys. Lett. 71, 2746 (1997); http://dx.doi.org/10.1063/1.120200 (3 pages) | Cited 18 times

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A new approach to produce structured optical materials is described. The method relies on the capability of growing eutectic crystals of wide optical band gap materials by directional solidification procedures. The laser float zone technique was used to produce ordered arrays of alternate lamellae with thickness of the order of microns of erbium doped CaZrO3 and calcia stabilized zirconia single crystals. The later, having a higher refractive index, exhibited planar waveguiding effects as it has been proved experimentally. The possibility of producing waveguides from eutectic crystals promises the fabrication of hundreds of planar waveguides integrated into a crystal grown at a speed of several tenths of cm/h. © 1997 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
81.30.Fb Solidification
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Video rate near-field scanning optical microscopy

S. J. Bukofsky and R. D. Grober

Appl. Phys. Lett. 71, 2749 (1997); http://dx.doi.org/10.1063/1.120123 (3 pages) | Cited 15 times

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The enhanced transmission efficiency of chemically etched near-field optical fiber probes makes it possible to greatly increase the scanning speed of near-field optical microscopes. This increase in system bandwidth allows sub-diffraction limit imaging of samples at video rates. We demonstrate image acquisition at 10 frames/s, rate-limited by mechanical resonances in our scanner. It is demonstrated that the optical signal to noise ratio is large enough for megahertz single pixel acquisition rates. © 1997 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
07.60.Vg Fiber-optic instruments
42.81.Pa Sensors, gyros

Pulsed laser deposition of liquid crystals

J. Gonzalo, P. E. Dyer, and M. Hird

Appl. Phys. Lett. 71, 2752 (1997); http://dx.doi.org/10.1063/1.120124 (3 pages) | Cited 14 times

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Thin films of 4-cyano-4’-pentylbiphenyl (5CB) liquid crystal have been fabricated by pulsed laser deposition. The suitability of different lasers (ArF, KrF and CO2) has been investigated over a range of fluence using visible-UV and infrared absorption and optical microscopy to characterise the films. High performance liquid chromatography (HPLC) and matrix assisted laser desorption ionization mass spectroscopy (MALDI-MS) were used to assess the extent of decomposition of the films. The results suggest that the CO2 laser acts as a quasi-steady heat source, while for ArF laser irradiation severe photodecomposition is observed. However, use of the KrF laser allows the production of excellent quality submicron films, showing properties similar to the 5CB target with only slight photodecomposition. © 1997 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.15.+e Liquid thin films
61.30.-v Liquid crystals
78.66.Qn Polymers; organic compounds
78.30.C- Liquids
78.40.Dw Liquids

Correlation between the pretilt angle of liquid crystal and the inclination angle of the polyimide backbone structure

R. Arafune, K. Sakamoto, and S. Ushioda

Appl. Phys. Lett. 71, 2755 (1997); http://dx.doi.org/10.1063/1.119566 (3 pages) | Cited 26 times

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We have determined the inclination angle of the backbone structure of polyimide with alkyl side-chains in rubbed films. Four different polyimides with the same backbone structure but different lengths of alkyl side-chains were used in this study. The inclination angle of the backbone structure increases with the number of carbon atoms in the alkyl side-chains. We found a linear relation between the inclination angle of the backbone structure and the pretilt angle of liquid crystal (LC) that is in contact with the polyimide films. We conclude that the inclination of the polyimide backbone structure determines the pretilt angle of LC. © 1997 American Institute of Physics.  
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Jf Defects in liquid crystals

Direct writing of conductive aluminum line on aluminum nitride ceramics by transversely excited atmospheric CO2 laser

Hiroyuki Yabe, Akihisa Takahashi, Tetsumi Sumiyoshi, Minoru Obara, and Katsunori Ishii

Appl. Phys. Lett. 71, 2758 (1997); http://dx.doi.org/10.1063/1.120125 (3 pages)

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The fabrication of very low resistance aluminum conductor line on the aluminum nitride (AlN) by transversely excited atmospheric (TEA) CO2 laser writing was demonstrated. A minimum electrical resistance was measured to be less than 0.1 Ω/mm with a linewidth of 500 μm. The electrical resistance measured is lower than those of conventional conductor lines used for electronic circuits. The x-ray photoelectron spectroscopy depth profile analysis of aluminum layers can explain the resistance of the metallic aluminum layer formed. Compared to the experimental data by KrF laser, TEA CO2 laser writing is found to be a more effective process for fabricating a low resistance conductor line on AlN than the KrF excimer laser. © 1997 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
42.62.-b Laser applications
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Thermal conductivity and heat transfer in superlattices

G. Chen and M. Neagu

Appl. Phys. Lett. 71, 2761 (1997); http://dx.doi.org/10.1063/1.120126 (3 pages) | Cited 82 times

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Understanding the thermal conductivity and heat transfer processes in superlattice structures is critical for the development of thermoelectric materials and optoelectronic devices based on quantum structures. This letter reports modeling of the heat transfer and thermal conductivity of superlattice structures based on solving the Boltzmann transport equation. Both diffuse and specular phonon scattering processes at interfaces are considered. The modeling results could explain recent experimental data on the cross-plane thermal conductivity of Si/Ge superlattices. Below the critical thickness, thermal conductivity is strongly influenced by diffuse interface scattering of phonons while above the critical thickness, dislocations are the dominant scattering centers in superlattices. © 1997 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.35.Ja Surface and interface dynamics and vibrations

SiO2 film thickness metrology by x-ray photoelectron spectroscopy

Z. H. Lu, J. P. McCaffrey, B. Brar, G. D. Wilk, R. M. Wallace, L. C. Feldman, and S. P. Tay

Appl. Phys. Lett. 71, 2764 (1997); http://dx.doi.org/10.1063/1.120438 (3 pages) | Cited 86 times

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Silicon dioxide films grown by industrial thermal furnace, rapid thermal, and low-pressure thermal methods were measured by x-ray photoelectron spectroscopy, transmission electron microscopy (TEM), spectroscopic ellipsometry, and capacitance–voltage analysis. Based on TEM measurements, the photoelectron effective attenuation lengths in the SiO2 and Si are found to be 2.96±0.19 and 2.11±0.13 nm, respectively. The oxide physical thicknesses (range from 1.5 to 12.5 nm) as measured by all above techniques are in good agreement. The electrical thickness is noted to be slightly thicker than the physical thickness. © 1997 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
77.55.-g Dielectric thin films

Ion-cut silicon-on-insulator fabrication with plasma immersion ion implantation

Xiang Lu, S. Sundar Kumar Iyer, Chenming Hu, Nathan W. Cheung, Jing Min, Zhineng Fan, and Paul K. Chu

Appl. Phys. Lett. 71, 2767 (1997); http://dx.doi.org/10.1063/1.120127 (3 pages) | Cited 29 times

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We report the implementation of ion-cut silicon-on-insulator (SOI) wafer fabrication technique with plasma immersion ion implantation (PIII). The hydrogen implantation rate, which is independent of the wafer size, is considerably higher than that of conventional implantation. The simple PIII reactor setup and its compatibility with cluster-tools offer other ion-cut process optimization opportunities. The feasibility of the PIII ion-cut process is demonstrated by successful fabrication of SOI structures. The hydrogen plasma can be optimized so that only one ion species is dominant. The feasibility of performing ion-cut using helium PIII is also demonstrated. © 1997 American Institute of Physics.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.uf Ge and Si
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Highly ordered nanochannel-array architecture in anodic alumina

Hideki Masuda, Haruki Yamada, Masahiro Satoh, Hidetaka Asoh, Masashi Nakao, and Toshiaki Tamamura

Appl. Phys. Lett. 71, 2770 (1997); http://dx.doi.org/10.1063/1.120128 (3 pages) | Cited 453 times

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The development of the ordered channel array in the anodic porous alumina was initiated by the textured pattern of the surface made by the molding process, and growth of an almost defect-free channel array can be achieved throughout the textured area. The long-range-ordered channel array with dimensions on the order of millimeters with a channel density of 1010 cm−2 was obtained, and the aspect ratio was over 150. The master for molding could be used many times, which makes it possible to overcome problems in the conventional nanolithographic technique, such as low through-put and high cost. © 1997 American Institute of Physics.
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81.65.-b Surface treatments
82.45.-h Electrochemistry and electrophoresis
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Rm Porous materials; granular materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

A new mechanism for spontaneous nanostructure formation on bottom-patterned compliant substrates

Carrie Carter-Coman, April S. Brown, Robert A. Metzger, Nan Marie Jokerst, Jason Pickering, and Lawrence A. Bottomley

Appl. Phys. Lett. 71, 2773 (1997); http://dx.doi.org/10.1063/1.120129 (3 pages) | Cited 6 times

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Bottom-patterned compliant substrates can be used to laterally modulate the properties of a mismatched epilayer. At temperatures where strain-dependent growth kinetics are significant, the GaAs bottom pattern compliant substrates affected the growth of strained InGaAs epilayers by causing lateral modulation in material height. Spatially aligned mounds and quantum dots were observed on the samples grown at high temperatures. A new mounding mechanism was observed on InGaAs layers grown on the compliant substrates. Strain-dependent growth kinetics and the bottom patterned compliant substrate are used to explain these effects. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.07.-b Nanoscale materials and structures: fabrication and characterization
68.35.Ct Interface structure and roughness
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Effect of surface polarity on gallium adsorption on 6H-SiC surfaces

L. Li, C. Tindall, Y. Hasegawa, and T. Sakurai

Appl. Phys. Lett. 71, 2776 (1997); http://dx.doi.org/10.1063/1.120130 (3 pages) | Cited 3 times

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We have performed the first scanning tunneling microscopy (STM) study of gallium adsorption on both the Si-terminated 6H-SiC(0001) (√×√) and C-terminated 6H-SiC(0001) (2√×2√) surfaces. The structure of the Ga terminated 6H-SiC surface showed strong polarity dependence. On the Si-terminated √×√ surface, parallel rows of Ga atoms arranged in three different domains oriented at 120° with respect to each other at 1 ML coverage were observed. On the C-terminated 2√×2√ surface, sets of two concentric rings formed an overall 4√×4√ reconstruction at 1 ML coverage. We propose a structural model for the 4√×4√ structure which explains the STM image. © 1997 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
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
68.35.B- Structure of clean surfaces (and surface reconstruction)

Energy resolved ultrafast relaxation dynamics close to the band edge of low-temperature grown GaAs

G. Segschneider, T. Dekorsy, H. Kurz, R. Hey, and K. Ploog

Appl. Phys. Lett. 71, 2779 (1997); http://dx.doi.org/10.1063/1.120131 (3 pages) | Cited 24 times

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We investigate the relaxation dynamics of photogenerated carriers in low-temperature grown GaAs by femtosecond pump-probe measurements. The carrier dynamics in the vicinity of the band edge is disentangled in a two-color technique. The filling of shallow bound states close beneath the band edge is resolved. A temporal delay in the occupation of these states as well as a large optical nonlinearity points towards microscopic potential fluctuations forming these states. © 1997 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
73.50.Pz Photoconduction and photovoltaic effects
78.66.Fd III-V semiconductors
42.65.-k Nonlinear optics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Cu crystallographic texture control in Cu/refractory-metal layered structure as interconnects

Kazuhide Abe, Yusuke Harada, and Hiroshi Onoda

Appl. Phys. Lett. 71, 2782 (1997); http://dx.doi.org/10.1063/1.120132 (3 pages) | Cited 5 times

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The effect of underlayer texture on Cu film orientation has been studied. The crystallographic orientation of sputter-deposited Cu film depends strongly on the underlayer refractory-materials. Cu (111) orientation can be controlled by changing the preferred orientation of the TiN underlayer that has the same cubic structure as Cu. TEM observation of the Cu/RTN–TiN interface has revealed that the Cu (111) plane grows epitaxially on the TiN (111) plane. It has been also clarified that the atomic arrangement between the Cu (111) and TiN (111) planes has a rotational angle within ±10° around the 〈111〉 axis. © 1997 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Intraband absorption in n-doped InAs/GaAs quantum dots

S. Sauvage, P. Boucaud, F. H. Julien, J.-M. Gérard, and V. Thierry-Mieg

Appl. Phys. Lett. 71, 2785 (1997); http://dx.doi.org/10.1063/1.120133 (3 pages) | Cited 80 times

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We have investigated the intraband absorption within the conduction band of InAs/GaAs quantum dots. The islands obtained by self-organized epitaxy are modulation doped with a silicon planar doping 2 nm below the dot layer plane. The dots exhibit infrared absorption polarized along the growth axis in the midinfrared spectral range. The absorption is maximum around 150 meV with a large broadening around 130 meV. This broadening is attributed to size fluctuations within the one dot layer plane and the consequent variation of the electron confinement energy with the dot size. The magnitude of the absorption along the growth axis for the one dot layer plane is ≈ 2.5×10−2% which corresponds to an equivalent absorption cross section σz ≈ 3.1×10−15 cm2. We show that the intraband absorption can also be clearly observed using a photoinduced infrared absorption technique with the doped quantum dots. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.30.Fs III-V and II-VI semiconductors

Fourier transform analysis of electromodulation spectra: Effects of the modulation amplitude

V. L. Alperovich, A. S. Jaroshevich, H. E. Scheibler, A. S. Terekhov, and Richard L. Tober

Appl. Phys. Lett. 71, 2788 (1997); http://dx.doi.org/10.1063/1.120134 (3 pages) | Cited 5 times

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Fourier transform analysis of Franz-Keldysh oscillations is applied to electroreflectance spectra of GaAs p–i–n diode structures in order to elucidate the role of the modulation amplitude in electric-field-modulated spectroscopies. The effects of modulation amplitude are quantitatively evaluated by considering the imaginary and real parts of the complex Fourier transform in addition to its modulus. The experimentally measured electroreflectance spectra and their Fourier transforms are in good agreement with model calculations. © 1997 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.66.Fd III-V semiconductors
85.30.Kk Junction diodes

Effect of phonon bottleneck on quantum-dot laser performance

Mitsuru Sugawara, Kohki Mukai, and Hajime Shoji

Appl. Phys. Lett. 71, 2791 (1997); http://dx.doi.org/10.1063/1.120135 (3 pages) | Cited 58 times

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The effect of phonon bottleneck on quantum-dot laser performance is examined by solving the carrier-photon rate equations including the carrier relaxation process into the quantum-dot ground state. We show that the retarded carrier relaxation due to phonon bottleneck degrades the threshold current and the external quantum efficiency. We also show that quantum-dot lasers are quite sensitive to the crystal quality outside as well as inside quantum dots. Our results clarified that the relaxation lifetime should be less than about 10 ps to fully utilize the laser potential originating from the quantum-dot discrete energy states. © 1997 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Measurement of piezoelectrically induced charge in GaN/AlGaN heterostructure field-effect transistors

E. T. Yu, G. J. Sullivan, P. M. Asbeck, C. D. Wang, D. Qiao, and S. S. Lau

Appl. Phys. Lett. 71, 2794 (1997); http://dx.doi.org/10.1063/1.120138 (3 pages) | Cited 159 times

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Electron concentration profiles have been obtained for AlxGa1−xN/GaN heterostructure field-effect transistor structures. Analysis of the measured electron distributions demonstrates the influence of piezoelectric effects in coherently strained layers on III-V nitride heterostructure device characteristics. Characterization of a nominally undoped Al0.15Ga0.85N/GaN transistor structure reveals the presence of a high sheet carrier density in the GaN channel which may be explained as a consequence of piezoelectrically induced charges present at the Al0.15Ga0.85N/GaN interface. Measurements performed on an Al0.15Ga0.85N/GaN transistor structure with a buried Al0.15Ga0.85N isolation layer indicate a reduction in electron sheet concentration in the transistor channel and accumulation of carriers below the Al0.15Ga0.85N isolation layer, both of which are attributable to piezoelectric effects. © 1997 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Tv Field effect devices
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.65.Bn Piezoelectric and electrostrictive constants

Does a dipole layer at the p–i interface reduce the built-in voltage of amorphous silicon p–i–n solar cells?

A. Nuruddin and J. R. Abelson

Appl. Phys. Lett. 71, 2797 (1997); http://dx.doi.org/10.1063/1.120139 (3 pages) | Cited 3 times

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The open-circuit voltage of amorphous silicon p–i–n solar cells is 0.1–0.3 V less than the total Fermi level shift in the p- and n-type layers. It was hypothesized that a dipole layer at the p–i interface reduces the potential drop across the i-layer. We determine the electrostatic potential profile using an in situ Kelvin probe during incremental depositions of p-type a-Si,C:H and undoped a-Si:H layers by direct current reactive magnetron sputtering. We confirm the existence of a dipole layer, but which produces a potential loss of only ∼ 20 mV. Thus, most of the “missing” voltage in solar cells must have other origins. © 1997 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.61.Jc Amorphous semiconductors; glasses
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