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30 Aug 1999

Volume 75, Issue 9, pp. 1189-1337

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Red light emission by photoluminescence and electroluminescence from Eu-doped GaN

J. Heikenfeld, M. Garter, D. S. Lee, R. Birkhahn, and A. J. Steckl

Appl. Phys. Lett. 75, 1189 (1999); http://dx.doi.org/10.1063/1.124686 (3 pages) | Cited 103 times

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Visible light emission has been obtained at room temperature by photoluminescence (PL) and electroluminescence (EL) from Eu-doped GaN thin films. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga and Eu) and a plasma source for N2. X-ray diffraction shows the GaN:Eu to be a wurtzitic single crystal film. Above GaN band gap photoexcitation with a He–Cd laser at 325 nm resulted in strong red emission. Observed Eu3+ PL transitions consist of a dominant narrow red line at 621 nm and several weaker emission lines were found within the green through red (543 to 663 nm) range. Below band gap PL by Ar laser pumping at 488 nm also resulted in red emission, but with an order of magnitude lower intensity. EL was obtained through use of transparent indium–tin–oxide contacts to the GaN:Eu film. Intense red emission is observed in EL operation, with a spectrum similar to that seen in PL. The dominant red line observed in PL and EL has been identified as the Eu3+ 4f shell transition from the 5D0 to the 7F2 state. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.60.Fi Electroluminescence

Room-temperature photopumped InGaN/GaN/AlGaN vertical-cavity surface-emitting laser

I. L. Krestnikov, W. V. Lundin, A. V. Sakharov, V. A. Semenov, A. S. Usikov, A. F. Tsatsul’nikov, Zh. I. Alferov, N. N. Ledentsov, A. Hoffmann, and D. Bimberg

Appl. Phys. Lett. 75, 1192 (1999); http://dx.doi.org/10.1063/1.124638 (3 pages) | Cited 40 times

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We report photopumped room-temperature surface-mode lasing at 401 nm in a InGaAlN vertical-cavity surface-emitting laser grown on a sapphire substrate using metal–organic vapor-phase epitaxy. A 2λ cavity was formed by a quarter-wave Al0.15Ga0.85N/GaN distributed Bragg reflector on the one side of the active layer and a GaN–air interface on the other. A multilayer structure composed of 12-fold-stacked ultrathin InGaN insertions in a GaN matrix served as an active layer providing ultrahigh material gain and making possible vertical lasing without use of the upper Bragg reflector. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Experimental investigation of wavelength conversion based on four-wave mixing in a three-electrode distributed feedback laser

Ioannis Tomkos, Ioannis Zacharopoulos, Eugenia Roditi, and Dimitris Syvridis

Appl. Phys. Lett. 75, 1195 (1999); http://dx.doi.org/10.1063/1.124639 (3 pages) | Cited 1 time

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A wavelength converter based on four-wave mixing in a three-electrode distributed feedback laser is experimentally investigated. The output power and the signal to background noise ratio characteristics of the converted waves were measured for highly nondegenerate conditions, up to 2 THz detuning frequency. The dependence of the converted wave power on the pump and probe input power has been also investigated. Moreover, a comparison with a highly performing converter based on four-wave mixing in a 1.5-mm-long semiconductor optical amplifier has been carried out. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Wavelength shifting of optical pulses through cascaded second-order processes in a lithium–niobate channel waveguide

I. Cristiani, G. P. Banfi, V. Degiorgio, and L. Tartara

Appl. Phys. Lett. 75, 1198 (1999); http://dx.doi.org/10.1063/1.124640 (3 pages) | Cited 11 times

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We investigate the efficiency of wavelength shifting (generation of a pulse at the wavelength λp−Δλ from a signal at λp+Δλ under the action of a pump at λp) through a cascaded second-order process in a lithium–niobate channel waveguide. With a 58-mm-long Ti-diffused channel waveguide, λp = 1.1 μm (the wavelength of phase matching for the first step of the second-harmonic generation), Δλ of several nanometers and 20 ps pulse duration, wavelength conversion with unit efficiency is obtained with a pump pulse energy of the order of 102 pJ. © 1999 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Gn Optical waveguides and couplers
42.79.Nv Optical frequency converters

Two-dimensional metallodielectric photonic crystal with a large band gap

Chongjun Jin, Bingying Cheng, Baoyuan Man, Daozhong Zhang, Shouzheng Ban, Bo Sun, Lieming Li, Xiangdong Zhang, and Zhaoqing Zhang

Appl. Phys. Lett. 75, 1201 (1999); http://dx.doi.org/10.1063/1.124641 (3 pages) | Cited 18 times

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Three kinds of square metallodielectric photonic crystals have been fabricated. In these crystals, a very small metal cylinder is inserted into the center of each unit cell, while the dielectric cylinders are located at the corners of each unit cell. The transmissions of these photonic crystals have been measured in the microwave region. Compared with dielectric photonic crystals, the first photonic band gap is enlarged by a factor of 2. The experimental results agree well with the simulation obtained by the multiscattering approach. This method may be valuable for the design of photonic crystals with a large band gap. © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.70.Gq Microwave and radio-frequency interactions

AgGaS2 optical parametric oscillator continuously tunable from 3.9 to 11.3 μm

K. L. Vodopyanov, J. P. Maffetone, I. Zwieback, and W. Ruderman

Appl. Phys. Lett. 75, 1204 (1999); http://dx.doi.org/10.1063/1.124642 (3 pages) | Cited 28 times

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This is the experimental realization of a silver gallium sulfide (AgGaS2) optical parametric oscillator (OPO) with a wide mid-IR tuning range. The singly resonant angle-tuned AgGaS2 type-II OPO was pumped by 1.06 μm pulses from a nanosecond Nd:YAG laser and yielded idler wave continuously tunable from 3.9 to 11.3 μm with a linewidth of 1 cm−1. The OPO threshold was 0.03 J/cm2 corresponding to sub-MW/cm2 pump intensity and sub-100 μJ pump energy. The slope and absolute quantum conversion efficiencies reached 41% and 22%, respectively. © 1999 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers
78.66.Li Other semiconductors

Terahertz optical gain based on intersubband transitions in optically pumped semiconductor quantum wells: Coherent pump–probe interactions

Ansheng Liu and C. Z. Ning

Appl. Phys. Lett. 75, 1207 (1999); http://dx.doi.org/10.1063/1.124643 (3 pages) | Cited 15 times

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Terahertz optical gain due to intersubband transitions in optically pumped semiconductor quantum wells (QWs) is calculated nonperturbatively. We solve the pump-field-induced nonequilibrium distribution function for each subband of the QW system from a set of rate equations that include both intrasubband and intersubband relaxation processes. The gain arising from population inversion and stimulated Raman processes is calculated in a unified manner. We show that the coherent pump and signal wave interactions contribute significantly to the tetrahertz gain. Because of the optical Stark effect and pump-induced population redistribution, optical gain saturation at larger pump intensities is predicted. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering

Efficient channel-waveguide laser in Nd:GGG at 1.062 μm wavelength

R. Gerhardt, J. Kleine-Börger, L. Beilschmidt, M. Frommeyer, H. Dötsch, and B. Gather

Appl. Phys. Lett. 75, 1210 (1999); http://dx.doi.org/10.1063/1.124644 (3 pages) | Cited 23 times

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Channel waveguide lasers in crystals of neodymium-doped gadolinium-gallium-garnet are realized. They are based on single-mode rib waveguides prepared by liquid phase epitaxy. By this growth technique the incorporation of certain impurities, which may cause severe quenching, is inevitable. The dominant quenching process could be identified and eliminated. Channel waveguides with extremely low losses, down to 0.25 dB/cm for both TE and TM modes, are fabricated by ion-beam etching. As a result, low thresholds of 5 mW and high slope efficiencies of 48% at the laser wavelength of 1.062 μm could be achieved when pumping at a wavelength of 807 nm. © 1999 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.Cf Surface cleaning, etching, patterning

Effect of external feedback on lasing in random media

H. Cao, Y. G. Zhao, X. Liu, E. W. Seelig, and R. P. H. Chang

Appl. Phys. Lett. 75, 1213 (1999); http://dx.doi.org/10.1063/1.124645 (3 pages) | Cited 20 times

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We have studied the effect of external feedback on random laser action in ZnO polycrystalline thin films. Reinjection of light into scattering-formed cavities strongly influences modes, intensity, and threshold of random lasers. We have compared the effect of external feedback from the side of the film and that from the film surface. Our study opens the possibility of controlling random laser frequencies by external feedback. © 1999 American Institute of Physics.
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42.70.Hj Laser materials
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.25.Dd Wave propagation in random media
78.66.Hf II-VI semiconductors
78.45.+h Stimulated emission
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Nonlinear changes in plasma and crater properties during laser ablation of Si

H. C. Liu, X. L. Mao, J. H. Yoo, and R. E. Russo

Appl. Phys. Lett. 75, 1216 (1999); http://dx.doi.org/10.1063/1.124646 (3 pages) | Cited 9 times

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A dramatic change in plasma characteristics, as well as a significant increase in the quantity of ablated mass were observed at a laser power density threshold of 20 GW/cm2. The electron number density and temperature of the laser-induced plasma show dramatic changes in their nonlinear behavior in the range of 2–80 GW/cm2. The crater volume undergoes some type of phase explosion at the threshold. Mechanisms such as inverse bremsstrahlung and self-regulation were used to describe the behavior below threshold. Self-focusing and critical temperature are discussed to explain the dramatic changes at the threshold. © 1999 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
81.05.Cy Elemental semiconductors
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Defects in thermal oxide studied by photoluminescence spectroscopy

Hiroyuki Nishikawa, James H. Stathis, and E. Cartier

Appl. Phys. Lett. 75, 1219 (1999); http://dx.doi.org/10.1063/1.124647 (3 pages) | Cited 3 times

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Defects in as-grown thermal oxide were investigated by photoluminescence (PL) spectroscopy using synchrotron radiation as a light source. A PL band at 3.3 eV was observed under excitation at 5 eV for dry thermal oxide at room temperature. The PL band was also observed for forming-gas annealed oxide, in which the 3.3 eV PL was either enhanced by subsequent vacuum annealing or suppressed by hydrogen exposure. The PL measurements on oxynitride films show that effect of nitrogen incorporation on the 3.3 eV PL is less significant than that of hydrogen. Wide observability of the 3.3 eV PL band for oxide films prepared under various conditions indicates the intrinsic nature of the defects in thermal oxide introduced during thermal oxidation of silicon. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals
61.72.Cc Kinetics of defect formation and annealing

Optical and structural studies of Ge nanocrystals embedded in AlN matrix fabricated by pulsed laser deposition

K. M. Hassan, A. K. Sharma, J. Narayan, J. F. Muth, C. W. Teng, and R. M. Kolbas

Appl. Phys. Lett. 75, 1222 (1999); http://dx.doi.org/10.1063/1.124648 (3 pages) | Cited 19 times

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We have fabricated Ge nanostructures buried in a matrix of AlN grown on Si(111) by pulsed laser deposition at the substrate temperature of 500 °C. The characterization of these structures was performed using high-resolution transmission electron microscopy (HRTEM), photoluminescence, and Raman spectroscopy. The HRTEM results show that the Ge islands are single crystal with a pyramidal shape. The average size of Ge islands was determined to be ∼15 nm, which could be varied by controlling laser deposition and substrate parameters. The Raman spectrum showed a peak of the Ge–Ge vibrational mode downward shifted up to 295 cm−1 which is caused by quantum confinement of phonons in the Ge dots. The photoluminescence of the Ge dots (size ∼15 nm) was blueshifted by ∼0.266 eV from the bulk Ge value of 0.73 eV at 77 K, resulting in a distinct peak at ∼1.0 eV. The transmission measurements carried out on different samples having Ge dot sizes of 7, 8, and 13 nm deposited on sapphire substrate showed the above band edge transitions of Ge, which were also blueshifted in accordance with the quantum confinement effect. The importance of pulsed laser deposition in fabricating novel nanostructures is emphasized. © 1999 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Fg Pulsed laser ablation deposition
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.05.Cy Elemental semiconductors

Optimized configuration for reflective bistable twisted nematic displays

Zhizhong Zhuang, Young Jin Kim, and J. S. Patel

Appl. Phys. Lett. 75, 1225 (1999); http://dx.doi.org/10.1063/1.124649 (3 pages) | Cited 9 times

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In this letter, we experimentally verify the operation of a single-polarizer reflective bistable twisted nematic (BTN) liquid-crystal display using an optimized geometry. Based on the polarization optimization using the Poincaré sphere representation, several optimized operating modes, which can simultaneously optimize both bistable states, are possible. One of these optimized configurations, the 67.38° and −292.62° twisted bistable states with 310.69 nm birefringence and a 24.25° incident polarization angle, is studied in detail. The evolution of the state of polarization of light passing through this reflective BTN structure is numerically studied, and the electro-optic property of the reflective BTN structure is experimentally demonstrated. Our results show that, using these optimum configurations, a high-contrast display is possible. © 1999 American Institute of Physics.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
78.20.Fm Birefringence
42.65.Pc Optical bistability, multistability, and switching, including local field effects
85.60.Pg Display systems

Field-emission studies of smooth and nanostructured carbon films

Vladimir I. Merkulov, Douglas H. Lowndes, and Larry R. Baylor

Appl. Phys. Lett. 75, 1228 (1999); http://dx.doi.org/10.1063/1.124650 (3 pages) | Cited 25 times

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Electron field-emission measurements of carbon films prepared by pulsed-laser deposition (PLD) and hot-filament chemical-vapor deposition (HF-CVD) are reported. Smooth PLD carbon films, with both high- and low-sp3 contents, appear to be poor field emitters. In contrast, HF-CVD carbon exhibits very good field-emission properties, including the emission turn-on field as low as 9 V/μm, high emission site density, and excellent durability. In addition, HF-CVD was carried out at temperatures below 600 °C, compatible with the use of glass substrates. The promising field-emission properties of HF-CVD carbon are attributed to the nanostructured nature of this material. © 1999 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology

Kinetics of radiative recombination in strongly excited ZnSe/BeTe superlattices with a type-II band alignment

A. A. Maksimov, S. V. Zaitsev, I. I. Tartakovskii, V. D. Kulakovskii, D. R. Yakovlev, W. Ossau, M. Keim, G. Reuscher, A. Waag, and G. Landwehr

Appl. Phys. Lett. 75, 1231 (1999); http://dx.doi.org/10.1063/1.124651 (3 pages) | Cited 16 times

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We report results of a detailed investigation of type-II superlattices under high density photoexcitation. A strong spectral shift ( ≈ 0.5 eV) of the recombination band corresponding to the indirect transition from the ZnSe conduction band to the BeTe valence band in ZnSe/BeTe superlattices with increasing carrier density has been found at T = 300 K. The dynamical characteristics of this transition are studied by time-resolved spectroscopy. A model which accounts for the dependence of band bending and lifetimes of spatially separated electrons and holes on the concentration of the photoexcited carriers is developed. Numerical simulations of the photoluminescence kinetics are in very good agreement with experimental results. It turns out that despite the huge band offsets involved, the radiative recombination under high excitation conditions can be nearly as fast as in spatially direct quantum wells. © 1999 American Institute of Physics.
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78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.40.+w Photoconduction and photovoltaic effects

A regime of the yield point of silicon at high temperatures

Hans Siethoff, Hans Georg Brion, and Wolfgang Schröter

Appl. Phys. Lett. 75, 1234 (1999); http://dx.doi.org/10.1063/1.124652 (3 pages) | Cited 9 times

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We present measurements of the lower yield point of undoped floating-zone silicon at temperatures between 800 and 1300 °C. The knowledge of the defect structure in this temperature range is of considerable importance for the numerical simulation of dislocation generation in various solar silicon materials. Above about 1050 °C, we find marked deviations from the well-known low-temperature behavior, thus establishing a further deformation regime. It is characterized by an activation energy of 4.1 eV. Comparison to preliminary work indicates that this effect depends on the as-grown dislocation density, but not on the ambient during deformation. We tentatively assume that it may reflect the change in the mechanism of self-diffusion typical for silicon at high temperatures. © 1999 American Institute of Physics.
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62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
84.60.Jt Photoelectric conversion
66.30.H- Self-diffusion and ionic conduction in nonmetals

Kelvin probe and scanning tunneling microscope characterization of Langmuir–Blodgett sapphyrin films

C. Goletti, A. Sgarlata, N. Motta, P. Chiaradia, R. Paolesse, A. Angelaccio, M. Drago, C. Di Natale, A. D’Amico, M. Cocco, and V. I. Troitsky

Appl. Phys. Lett. 75, 1237 (1999); http://dx.doi.org/10.1063/1.124653 (3 pages) | Cited 7 times

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The work function of solid layers of increasing thicknesses of E2M8− sapphyrin, deposited on a gold substrate by the Langmuir–Blodgett method, has been measured by the Kelvin-probe technique. The results show that the contact-potential-difference values depend upon the layer thickness, reaching saturation after a certain amount of deposited sapphyrin. Scanning tunneling microscope images taken at the same coverages show that corresponding with this threshold, sapphyrin forms a true continuous layer on gold, completely covering the substrate. Evolution of the layer towards its completion is accompanied by a continuous variation of the work-function value, consistent with an increasing dipole term due to the interaction of sapphyrin with the metal substrate. © 1999 American Institute of Physics.
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68.18.-g Langmuir-Blodgett films on liquids
73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Ph Polymers; organic compounds
73.40.Cg Contact resistance, contact potential
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.50.Pz Photoconduction and photovoltaic effects

High spatial resolution thermal conductivity of lateral epitaxial overgrown GaN/sapphire (0001) using a scanning thermal microscope

V. M. Asnin, Fred H. Pollak, J. Ramer, M. Schurman, and I. Ferguson

Appl. Phys. Lett. 75, 1240 (1999); http://dx.doi.org/10.1063/1.124654 (3 pages) | Cited 35 times

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We have performed high spatial resolution thermal conductivity (κ) measurements at room temperature on different patterned sections of GaN/sapphire (0001) fabricated by lateral epitaxial overgrowth using a scanning thermal microscope. In a number of regions we find κ ≈ 1.7–1.8 W/cm K, values that are substantially higher than κ ≈ 1.3 W/cm K previously reported by Sichel and Pankove [J. Phys. Chem. Solids 38, 330 (1977)] on “bulk” material and comparable to the theoretical estimate of 1.7 W/cm K deduced by Slack [J. Phys. Chem. Solids 34, 321 (1973)]. The implications of these findings for device applications will be discussed. © 1999 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.60.Dv Thermal stability; thermal effects
07.20.-n Thermal instruments and apparatus
07.79.Lh Atomic force microscopes
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The role of potential fluctuations in continuous-wave donor–acceptor pair luminescence of heavily doped materials

I. Kuskovsky, D. Li, G. F. Neumark, V. N. Bondarev, and P. V. Pikhitsa

Appl. Phys. Lett. 75, 1243 (1999); http://dx.doi.org/10.1063/1.124655 (3 pages) | Cited 7 times

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It has recently become apparent that “standard” (low-concentration and low-compensation) theory for donor–acceptor pair (DAP) photoluminescence (PL) is totally incapable of explaining results in highly doped and compensated material. It can be noted that such material is often of high technological interest. It has been argued, mainly qualitatively, that the discrepancies result from potential fluctuations due to random ionic charges. We here present a quantitative theory for cw DAP PL, using an approximate model. We also present data for the concentration and intensity dependence of DAP PL in heavily doped ZnSe:N, and show that the results are explained very satisfactorily by our fluctuation model. © 1999 American Institute of Physics.
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78.55.Et II-VI semiconductors
71.55.Eq III-V semiconductors
71.55.Gs II-VI semiconductors
78.55.Cr III-V semiconductors

Ultra-high-finesse IV–VI microcavities for the midinfrared

T. Schwarzl, W. Heiß, and G. Springholz

Appl. Phys. Lett. 75, 1246 (1999); http://dx.doi.org/10.1063/1.124656 (3 pages) | Cited 17 times

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IV–VI semiconductor-based midinfrared microcavities with very high-quality factors were grown by molecular-beam epitaxy. The structures consist of PbTe/EuTe Bragg mirrors with three to five layer pairs rendering reflectivities in excess of 99.7%. The PbTe resonator layer between the reflectors has an optical length of λ/2, which yields a first-order cavity. The transmission spectra of the microcavities show a very narrow Lorentzian-shaped Fabry–Perot resonance at 1877 cm−1 (λ = 5.32 μm) with a full width at half maximum of 0.63 cm−1 78 μeV. This corresponds to an ultrahigh effective cavity finesse of 1700. © 1999 American Institute of Physics.
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78.66.Li Other semiconductors
78.30.Hv Other nonmetallic inorganics
42.55.Sa Microcavity and microdisk lasers

Large coherent acoustic-phonon oscillation observed in InGaN/GaN multiple-quantum wells

Chi-Kuang Sun, Jian-Chin Liang, Christopher J. Stanton, Amber Abare, Larry Coldren, and Steven P. DenBaars

Appl. Phys. Lett. 75, 1249 (1999); http://dx.doi.org/10.1063/1.124657 (3 pages) | Cited 25 times

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We have observed coherent acoustic-phonon oscillation in InGaN/GaN multiple-quantum wells. With femtosecond pulse excitation, photogenerated carriers screen out the strained-induced piezoelectric field and initiate the coherent acoustic-phonon oscillation. The resulted modulation of the piezoelectric field will then cause large optical property oscillation through the quantum-confined Stark effect. © 1999 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
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
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
77.65.Ly Strain-induced piezoelectric fields
78.20.Jq Electro-optical effects

Electro-optic recovery of the photoquenching effect

R. M. Rubinger, A.G. de Oliveira, G. M. Ribeiro, J. C. Bezzera, M. V. B. Moreira, and H. Chacham

Appl. Phys. Lett. 75, 1252 (1999); http://dx.doi.org/10.1063/1.124658 (3 pages) | Cited 3 times

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We have carried out dynamic low-temperature measurements of the current density for a semi-insulating GaAs sample grown at 300 °C. The standard photoquenching (PQ) effect was observed at low temperatures. We found that high electric fields inhibit the PQ effect and that the recovery of the PQ effect was made possible by simultaneous application of a high electric field and illuminating the sample with infrared light. © 1999 American Institute of Physics.  
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73.50.Pz Photoconduction and photovoltaic effects
78.20.Jq Electro-optical effects
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
72.20.Ht High-field and nonlinear effects
73.50.Fq High-field and nonlinear effects

Observation of critical gate oxide thickness for substrate-defect related oxide failure

Twan Bearda, Michel Houssa, Paul W. Mertens, Jan Vanhellemont, and Marc Heyns

Appl. Phys. Lett. 75, 1255 (1999); http://dx.doi.org/10.1063/1.124659 (3 pages) | Cited 1 time

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The presence of crystal originated particles in silicon substrates leads to gate oxide failures in metal–oxide–semiconductor devices. A nonlinear relationship is known to exist between the oxide defect density and the oxide thickness, but the mechanism behind this remains unclear. In this work, we evaluate the gate oxide integrity for oxide thicknesses ranging from 2.5 to 26.5 nm. The results show no appreciable oxide degradation below an oxide thickness of approximately 5 nm; above this threshold value, the defect density depends strongly on the presence of crystal originated particles. Oxide thinning is unlikely to be responsible for this behavior. © 1999 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices

Cooling of a semiconductor by luminescence up-conversion

E. Finkeißen, M. Potemski, P. Wyder, L. Viña, and G. Weimann

Appl. Phys. Lett. 75, 1258 (1999); http://dx.doi.org/10.1063/1.124660 (3 pages) | Cited 34 times

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We report the observation of phonon-mediated up-conversion of luminescence in a GaAs quantum well. This opens the possibility of light-induced lattice cooling in a semiconductor. Under appropriate conditions, pumping the sample with light at the energy of the heavy-hole exciton, we observe light-hole exciton emission, which lies ∼10 meV above the excitation energy. The use of an external magnetic field together with the resolution of excited excitonic states provides an internal thermometer to monitor the sample temperature. Temperature drops as large as 10% of the initial temperature are observed for pump densities of 4 W cm−2. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Characteristics of dielectric layers grown on Ge by low temperature vacuum ultraviolet-assisted oxidation

Valentin Craciun, Ian W. Boyd, Bernie Hutton, and David Williams

Appl. Phys. Lett. 75, 1261 (1999); http://dx.doi.org/10.1063/1.124661 (3 pages) | Cited 21 times

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The growth of thin dielectric layers on (100) Ge samples at temperatures lower than 450 °C by photoassisted oxidation with vacuum ultraviolet radiation emitted by a Xe silent discharge lamp has been investigated. The thickness of the grown layers increased with both the oxidation time and processing temperature. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy (XPS) indicated that the layers are mainly stoichiometric GeO2. XPS investigations also indicated the presence of a several-nanometer-thick substoichiometric oxide layer at the interface region for samples irradiated for short periods of time. Capacitance– and current–voltage measurement showed that layers thicker than 15 nm exhibited good electrical characteristics. © 1999 American Institute of Physics.
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78.66.Li Other semiconductors
77.55.-g Dielectric thin films
78.30.Hv Other nonmetallic inorganics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
81.65.Mq Oxidation
79.60.Dp Adsorbed layers and thin films
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