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12 Feb 1996

Volume 68, Issue 7, pp. 879-1024

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Surface photovoltage spectroscopy of quantum wells and superlattices

N. Bachrach‐Ashkenasy, L. Kronik, Yoram Shapira, Y. Rosenwaks, M. C. Hanna, M. Leibovitch, and Prakhya Ram

Appl. Phys. Lett. 68, 879 (1996); http://dx.doi.org/10.1063/1.116217 (3 pages) | Cited 25 times

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Surface photovoltage spectroscopy (SPS) has been employed to monitor optical transitions in quantum well and superlattice structures at room temperature. Excellent agreement is found between theoretical predictions of heavy hole and electron energy level positions and the observed transitions. The results show that using this technique, the complete band diagram of the quantum structure may be constructed. SPS emerges as a powerful tool capable of monitoring optical transitions above the lowest one in a simple to interpret, contactless, and nondestructive way. © 1996 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Pz Photoconduction and photovoltaic effects

Electro‐optical structure with high speed and high reflectivity modulation

M. Levin, M. Rosenbluh, and V. Sandomirsky

Appl. Phys. Lett. 68, 882 (1996); http://dx.doi.org/10.1063/1.116218 (3 pages) | Cited 3 times

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A voltage controlled, multilayer electro‐optic structure is proposed. It is constructed from repeated Schottky‐like modules, which consist of layers of semiconductor‐dielectric‐semiconductor. The device reflectivity, in the range of incidence angles corresponding to surface plasmon excitation, is determined by the combined thickness and permittivity of the semiconductor space charge regions of all modules. A structure consisting of many modules allows for a large effective thickness of the voltage controlled space charge region which yields a high reflectivity modulation. Calculations show that fast (response time ∼ 10−10 s) and low‐voltage structures with reflectivity modulation depth of more than 80% can be constructed. © 1996 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.20.Jq Electro-optical effects
78.66.-w Optical properties of specific thin films

Radially and azimuthally oriented liquid crystal alignment patterns fabricated by linearly polarized ultraviolet exposure process

J. Chen, D. L. Johnson, P. J. Bos, S. Sprunt, J. Lando, and J. A. Mann

Appl. Phys. Lett. 68, 885 (1996); http://dx.doi.org/10.1063/1.116219 (3 pages) | Cited 11 times

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Radially and azimuthally oriented liquid crystal (LC) alignment patterns, which are hard to achieve by conventional LC alignment techniques, have been realized by exposure of polyimide surfaces to linearly polarized ultraviolet radiation. These surfaces can be used to realize some special LC configurations which are useful for LC basic research and applications. © 1996 American Institute of Physics.
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61.30.-v Liquid crystals

Observation of internal field in LiTaO3 single crystals: Its origin and time‐temperature dependence

Venkatraman Gopalan and Mool C. Gupta

Appl. Phys. Lett. 68, 888 (1996); http://dx.doi.org/10.1063/1.116220 (3 pages) | Cited 51 times

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The measured polarization hysteresis loop for a Z‐cut LiTaO3 crystal was found to be asymmetric about the field axis indicating the presence of an in‐built internal field in the crystal of 5 kV/mm in the direction of the original polarization in the virgin crystal. Upon polarization reversal under electric field, the internal field tends to realign along the new polarization direction. Systematic time–temperature dependence of this realignment process was carried out. At room temperature, this realignment process was incomplete even after many days, while above 200 °C, the recovery process takes less than 30 s. Conductivity measurements also indicate an exponential increase in the dc conductivity of the sample above 200 °C with an activation energy of 1.55 eV. Further experiments related to the behavior of the internal field with change in sample thickness and surface removal revealed that the internal field is a volume effect. Possible origins of this field based on point defect chemistry of the crystal are discussed. © 1996 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Wide and continuous wavelength tuning in a vertical‐cavity surface‐emitting laser using a micromachined deformable‐membrane mirror

M. C. Larson and J. S. Harris

Appl. Phys. Lett. 68, 891 (1996); http://dx.doi.org/10.1063/1.116221 (3 pages) | Cited 35 times

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Continuous wavelength tuning of 15 nm was achieved micro‐electromechanically in an InGaAs/AlGaAs vertical‐cavity surface‐emitting laser operating near 960 nm. The device utilizes a micromachined deformable‐membrane top mirror suspended by an air gap above a p‐i‐n diode quantum well active region and bottom mirror. Applied membrane‐substrate bias produces an electrostatic force which reduces the air gap thickness and therefore tunes the lasing wavelength. Typical tuning bias ranged between 15 and 23 V, and the minimum threshold current was 35 mA for pulsed room‐temperature operation. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Alternating‐current light‐emitting devices based on conjugated polymers

Y. Z. Wang, D. D. Gebler, L. B. Lin, J. W. Blatchford, S. W. Jessen, H. L. Wang, and A. J. Epstein

Appl. Phys. Lett. 68, 894 (1996); http://dx.doi.org/10.1063/1.116222 (3 pages) | Cited 78 times

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Most polymer electroluminescent devices to date are represented as tunnel diodes and operate under direct‐current (dc) driving field. Here we report the fabrication of symmetrically configured alternating‐current (ac) light‐emitting (SCALE) devices based on conjugated polymers. The new devices consist of an emissive polymer layer sandwiched between two redox polymer layers. This configuration enables the SCALE devices to work under both forward and reverse dc bias as well as in ac modes. The nearly ohmic electrode/redox polymer contacts improve the charge injection efficiency significantly and make the SCALE device operation insensitive to electrode work functions. Symmetric operation supports the key role of redox polymer/emissive polymer interface states. © 1996 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
85.60.Jb Light-emitting devices

Photoluminescence and micro‐Raman studies of as‐grown and high‐temperature‐annealed KTiOPO4

K. T. Stevens, N. C. Giles, and L. E. Halliburton

Appl. Phys. Lett. 68, 897 (1996); http://dx.doi.org/10.1063/1.116223 (3 pages) | Cited 1 time

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An emission band has been observed near 820 nm in a series of KTiOPO4 crystals grown by the flux technique. Photoluminescence spectra were obtained at room temperature using an excitation wavelength of 457 nm and a power density of 1.9 kW/cm2. When a crystal was held for 1 h in air at 1000 °C, the intensity of the emission increased by two orders of magnitude. Micro‐Raman spectra taken at the same location as the photoluminescence revealed that the high‐temperature anneal caused significant decomposition at the KTiOPO4 surface. Potassium, phosphorus, and oxygen evolved from the surface and left TiO2 (anatase). The increase in emission correlated with the amount of anatase created. This enhanced near‐infrared emission arises from Ti3+ ions which are formed by reduction in the TiO2 surface layer during the decomposition process. Since the 820‐nm emission is observed in as‐grown crystals, our data suggest that some reduced TiO2 (rutile or anatase) is formed in the bulk of KTiOPO4 crystals during growth. © 1996 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Characterization of photoinduced birefringence change in optical fiber rocking filters

D. C. Psaila, F. Ouellette, and C. Martijn de Sterke

Appl. Phys. Lett. 68, 900 (1996); http://dx.doi.org/10.1063/1.116224 (3 pages) | Cited 4 times

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We investigate the effects of UV exposure on the growth of optical fiber rocking filters written in hydrogen‐loaded germanosilicate elliptical core fibers. We find that with increasing exposure, the rocking angle (induced birefringence) increases rapidly then begins to decrease, eventually erasing completely. With further exposure, the rocking angle is seen to increase again, reaching values of 3.5°. This corresponds to a photoinduced birefringence almost four times larger than previously recorded in optical fiber rocking filters. Furthermore, we show that at high UV fluences, the direction of rotation of the birefringent axes is opposite to that at low fluences. © 1996 American Institute of Physics.
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42.81.Gs Birefringence, polarization

Ion drag effects in inductively coupled plasmas for etching

Wenli Z. Collison and Mark J. Kushner

Appl. Phys. Lett. 68, 903 (1996); http://dx.doi.org/10.1063/1.116225 (3 pages) | Cited 30 times

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Ion drag refers to Coulomb momentum transfer collisions between a directed flux of charged particles and a second charged species. It is an important force in determining the motion of negatively charged dust particles in plasma processing reactors. The same ion drag mechanism acts between the directed flux of positive ions moving towards the boundaries of a plasma etching reactor and negative ions being accelerated by electrostatic forces towards the center of the plasma. In this letter, we discuss the parameter space for inductively coupled plasma etching reactors in which ion drag forces on negative ions influence their transport using results from a two‐dimensional plasma equipment model. We find that ion drag forces on negative ions are important at high plasma densities and low ion temperatures. Under these conditions, the large positive ion flux, coupled with a large Coulomb cross section, creates an ion drag force which may dominate the electrostatic forces on negative ions. The end result is that negative ions may accumulate near the sheath edge. © 1996 American Institute of Physics.
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52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Microstructure of AlGaAs‐oxide heterolayers formed by wet oxidation

S. Guha, F. Agahi, B. Pezeshki, J. A. Kash, D. W. Kisker, and N. A. Bojarczuk

Appl. Phys. Lett. 68, 906 (1996); http://dx.doi.org/10.1063/1.116226 (3 pages) | Cited 38 times

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We have carried out a transmission electron microscopy based study of AlGaAs–Al(oxide) heterolayers created by lateral sidewall wet oxidation and identify the oxide phase formed as a consequence of the oxidation of AlAs to be γ‐Al2O3, with the cubic Fd 3m structure. The oxide‐semiconductor interface is weak and porous, possibly due to the high stress loads developed during oxidation, and we propose that the fast oxidation rates are a consequence of reactants transported to the oxidation front along the porous interface. © 1996 American Institute of Physics.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
81.65.Mq Oxidation

Preparation of cubic boron nitride films by radio frequency magnetron sputtering and radio frequency ion plating

S. Ulrich, J. Scherer, J. Schwan, I. Barzen, K. Jung, M. Scheib, and H. Ehrhardt

Appl. Phys. Lett. 68, 909 (1996); http://dx.doi.org/10.1063/1.116227 (3 pages) | Cited 42 times

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Cubic boron nitride (c‐BN) thin films have been deposited by unbalanced rf (13.56 MHz) magnetron sputtering of a hexagonal boron nitride target in a pure argon discharge. Deposition parameters have been 300 W rf target power, 8×10−4 mbar argon pressure, 3.5 cm target substrate distance, and 800 K substrate temperature. Under these conditions the ion current density is 2.25 mA/cm2 and the growth rate is ∼1.1 Å/s. By applying a rf substrate bias the ion plating energy is varied from plasma potential of 37 eV up to 127 eV. The films have been characterized by infrared (IR) and Auger electron spectroscopy (AES), x‐ray diffraction (XRD), x‐ray reflectivity, elastic recoil detection (ERD), Rutherford backscattering (RBS), nuclear resonance analysis (NRA), and stress measurements. The subplantation model proposed by Lifshitz and Robertson can be applied to the c‐BN formation. An energy of about 85±5 eV is found where the stress (25 GPa, 200 nm film thickness) and the c‐BN content (≳90%) have a maximum. The grain size of the crystalline c‐BN phase was estimated to be in the range of 5 nm. Below an energy of 67±5 eV no c‐BN could be detected. An excellent adhesion has been obtained by a special interface treatment. © 1996 American Institute of Physics.
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81.05.Hd Other semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Evidence of two‐species nucleation of InAs islands on (100) and (111)B GaAs substrates

R. E. Welser and L. J. Guido

Appl. Phys. Lett. 68, 912 (1996); http://dx.doi.org/10.1063/1.116228 (3 pages) | Cited 6 times

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The nucleation of InAs islands on (100) and (111)B GaAs substrates during metalorganic chemical vapor deposition has been investigated via scanning electron microscopy. The measured values of island density are 4–5 orders of magnitude smaller than those predicted using conventional one‐species nucleation theory. In addition, the effect of an increase in arsine flow on island density is opposite in sense for the two substrate orientations. To explain these observations, we further develop a two‐species picture of nucleation—originally proposed by Stoyanov [Appl. Phys. A 50, 349 (1990)]—in which the InAs island density is an explicit function of both the indium flux and the arsenic partial pressure at the growth interface. This more realistic physical model is in good agreement with the complete set of experimental data. © 1996 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

On the mechanically driven rapid crystallization of amorphous Si3N4 ceramics

G. J. Fan, M. X. Quan, Z. Q. Hu, Y. L. Li, and Y. Liang

Appl. Phys. Lett. 68, 915 (1996); http://dx.doi.org/10.1063/1.116229 (2 pages) | Cited 6 times

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The effect of high‐energy ball milling on the structure of nanometer sized amorphous ceramics, a‐Si3N4 and a‐Si–N–C, respectively, has been investigated. At high milling intensity, a‐Si3N4 may rapidly crystallize into a mixture of α‐Si3N4 and β‐Si3N4 after the initial 4 s of milling whereas no structural changes were observed at low milling intensity. For a‐Si–N–C, mechanical milling does not cause structural changes at both low and high intensity. It was found that extension of mechanical milling of these hard ceramics can introduce large volume fractions of contamination fragments from the milling media. We conclude that the observed structural changes occurring in a‐Si3N4 may be due to mechanical effect, rather than local heating and/or impurity effect. © 1996 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Homoepitaxy of GaN on polished bulk single crystals by metalorganic chemical vapor deposition

F. A. Ponce, D. P. Bour, W. Götz, N. M. Johnson, H. I. Helava, I. Grzegory, J. Jun, and S. Porowski

Appl. Phys. Lett. 68, 917 (1996); http://dx.doi.org/10.1063/1.116230 (3 pages) | Cited 64 times

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Bulk single crystals of GaN were used for epitaxial growth of GaN by metalorganic chemical vapor deposition. Photoluminescence (at 2 K) from polished substrates yields a broad near‐band‐edge emission band centered at 3.32 eV and the commonly observed yellow luminescence band. In contrast, the epitaxial layer displays a strong, sharp bound exciton line at 3.458 eV and a weak yellow band. Transmission electron microscopy reveals a sharp, planar interface between substrate and epilayer: The substrate contains small Ga inclusions, and the epilayer consists of less than 108 dislocations per cm2, mostly in the form of dislocation loops, which originate at the interface. © 1996 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Shock‐induced polarization in normal‐hexane

Kanchan Saxena, Yoichiro Hironaka, Hisako Hirai, and Ken‐ichi Kondo

Appl. Phys. Lett. 68, 920 (1996); http://dx.doi.org/10.1063/1.116231 (3 pages) | Cited 1 time

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The shock‐induced electromotive force has been observed in normal‐hexane as dielectric in a short circuited capacitor in the pressure range between 2.47 and 6.22 GPa. The induced current is inversely proportional to the initial thickness of the dielectric and is in accordance with Allison’s theory to some extent. The magnitude of polarization is of the order of 10−6–10−5 C/m2 and proportional to particle velocity in the pressure range studied. © 1996 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
77.22.Ej Polarization and depolarization
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals

Ultralow friction behavior of borided steel surfaces after flash annealing

C. Bindal and A. Erdemir

Appl. Phys. Lett. 68, 923 (1996); http://dx.doi.org/10.1063/1.116232 (3 pages) | Cited 22 times

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In this letter, we describe the ultralow friction mechanism of borided steel surfaces subjected to a short‐duration, or ‘‘flash,’’ annealing procedure. In this procedure, a borided steel surface is exposed to high temperature (600 to 800 °C) for a short time (3 to 5 min) and then cooled to room temperature in open air. During the high‐temperature exposure, boron atoms within the borided layer diffuse to the surface and react spontaneously with oxygen in air. The reaction product is a thin boron oxide film. During cooling, the boron oxide reacts spontaneously with moisture in the surrounding air to form a thin boric acid film. The sliding friction coefficient of a Si3N4 ball against this flash‐annealed surface is about 0.06, but is 0.5 and higher against the unborided or borided‐only surfaces. Mechanistically, we propose that the ultralow friction behavior of the borided and flash‐annealed surface is due mainly to the layered‐crystal structure of the boric acid film that forms on the sliding surface. © 1996 American Institute of Physics.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Pulsed laser deposition of SrCuO2/CaCuO2 superlattices

C. Aruta, G. Balestrino, R. Desfeux, S. Martellucci, A. Paoletti, and G. Petrocelli

Appl. Phys. Lett. 68, 926 (1996); http://dx.doi.org/10.1063/1.116233 (3 pages) | Cited 12 times

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We have shown that the pulsed laser deposition (PLD) technique, with no in situ diagnostic, can be used to grow good quality superlattices based on the infinite layer compounds SrCuO2 and CaCuO2. We demonstrated that the major source of disorder in these superlattices, grown at temperatures lower than 600 °C, comes from random discrete thickness fluctuations. However the random discrete thickness fluctuations affect essentially only one unit cell. This makes the PLD technique very attractive for the growth of new artificial high‐Tc structures based on the infinite layers compounds. © 1996 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.15.Fg Pulsed laser ablation deposition

Laser ablation: Selective unzipping of addition polymers

Graciela B. Blanchet and C. R. Fincher

Appl. Phys. Lett. 68, 929 (1996); http://dx.doi.org/10.1063/1.116234 (3 pages) | Cited 3 times

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These studies show that laser ablation, a technique widely used to deposit thin films of inorganic materials is also a simple and highly versatile tool for studying polymer decomposition. The use of laser ablation and fast resistive heating to control the degradation kinetics of vinyl polymers is illustrated here. Although polypropylene and polyvinyl fluoride are commonly believed to pyrolyze via random scission producing little monomer, our results demonstrate that in ablative decomposition they unzip with large monomer yields. We propose heating rate and final temperature to be the controlling factors in determining the thermodynamics and kinetics of decomposition reactions. © 1996 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena

Growth of n‐ and p‐type Al(As)Sb by metalorganic chemical vapor deposition

R. M. Biefeld, A. A. Allerman, and M. W. Pelczynski

Appl. Phys. Lett. 68, 932 (1996); http://dx.doi.org/10.1063/1.116235 (3 pages) | Cited 15 times

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AlSb and AlAsxSb1−x epitaxial films grown by metalorganic chemical vapor deposition were successfully doped p‐ or n‐type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500 ° C and 76 Torr using trimethylamine alane and triethylantimony. AlAs0.16Sb0.84 films lattice matched to InAs were grown at 600 ° C and 76 Torr by adding arsine. Secondary ion mass spectroscopy showed C and O levels below 2×1018 and 6×1018 cm−3, respectively, for undoped AlSb. Similar levels of O were found in AlAs0.16Sb0.84 films but C levels were an order of magnitude less in undoped and Sn‐doped AlAs0.16Sb0.84 films. Hall measurements of AlAs0.16Sb0.84 showed hole concentrations between 1×1017 to 5×1018 cm−3 for Zn‐doped material and electron concentrations in the low to mid‐ 1018 cm−3 for Sn‐doped material. © 1996 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Highly resistive CH‐doped GaN grown by plasma‐assisted metalorganic chemical vapor deposition

Michio Sato

Appl. Phys. Lett. 68, 935 (1996); http://dx.doi.org/10.1063/1.116236 (3 pages) | Cited 5 times

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Highly resistive (≳106 Ω cm) GaN thin films were grown on (0001) sapphire substrates by plasma‐assisted metalorganic chemical vapor deposition using triethylgallium and N radicals. Considerable amounts of C and H were incorporated in the GaN films and the incorporated C was electrically inactive after annealing in N2 up to 900 °C, suggesting that thermally stable CH complex made the GaN films highly resistive. The C concentrations were reduced when the Ga and N sources were alternately supplied. © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effect of channeling of halo ion implantation on threshold voltage shift of metal oxide semiconductor field‐effect transistor

Hyunsang Hwang, Dong Hoon Lee, Jae‐Gyung Ahn, Jeong Soo Byun, and Dooyoung Yang

Appl. Phys. Lett. 68, 938 (1996); http://dx.doi.org/10.1063/1.116237 (2 pages) | Cited 2 times

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In this letter, we report threshold voltage shift of metal oxide semiconductor field effect transistor (MOSFET) after the halo ion implantation process. Although halo implantation can significantly reduce the short channel effect, it causes a threshold voltage shift of a long channel device due to dopant channeling through polycrystalline silicon grain boundary. Although the chemical vapor deposited (CVD) cap oxide on polycrystalline silicon gate was used as a blocking layer of dopant, threshold voltages shift clearly indicate dopant channeling through polycrystalline silicon. To avoid a channeling problem, a thicker cap oxide layer or lower halo implantation energy is necessary. © 1996 American Institute of Physics.
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61.80.Jh Ion radiation effects
85.30.Tv Field effect devices

1.2 K Shubnikov–de Haas measurements and self‐consistent calculation of silicon spreading in δ‐ and slab‐doped In0.53Ga0.47As grown by molecular beam epitaxy

M. McElhinney, B. Vögele, M. C. Holland, C. R. Stanley, E. Skuras, A. R. Long, and E. A. Johnson

Appl. Phys. Lett. 68, 940 (1996); http://dx.doi.org/10.1063/1.116105 (3 pages) | Cited 7 times

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Magnetotransport measurements are reported for In0.53Ga0.47As layers grown by molecular beam epitaxy (MBE) at different substrate temperatures (Ts) and either δ‐ or slab‐doped with Si. Multiple subband densities deduced from the Fourier analysis of 1.2 K Shubnikov–de Haas measurements are compared with those derived from self‐consistent calculations which include nonparabolicity and the doping profile width wSi as a fitting parameter. Significant spreading of the Si donors away from the doping plane is deduced for deposition at Ts≊520 °C, while no measurable migration is inferred for Ts≤470 °C, leading to near‐ideal δ‐doping behavior. Contrary to previous results [McElhinney et al., J. Cryst. Growth 150, 266 (1995)], no evidence for amphoteric behavior has been found for Si areal densities up to 4×1012 cm−2. © 1996 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Photoluminescence study of C60 doped polystyrene

Chun Zhang, Xudong Xiao, Weikun Ge, M. M. T. Loy, Wang Dazhi, Zhang Qijin, and Zuo Jian

Appl. Phys. Lett. 68, 943 (1996); http://dx.doi.org/10.1063/1.116106 (3 pages) | Cited 14 times

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We report here a new phenomenon in photoluminescence of C60 doped in polystyrene. Under 488 nm cw laser radiation, the PL intensity of the sample was found to increase with time. With 10 h of irradiation, the PL signal strength increased by 10 times, comparable to that from porous Si. The peak of the PL was found to shift to high frequency as well. More detailed studies showed that such an irreversible change of the sample might be a result of the lowering symmetry of oxidized C60 fullerene in the polystyrene. © 1996 American Institute of Physics.
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78.66.Tr Fullerenes and related materials

II–VI quantum confined Stark effect waveguide modulators

P. J. Thompson, S. Y. Wang, G. Horsburgh, T. A. Steele, K. A. Prior, and B. C. Cavenett

Appl. Phys. Lett. 68, 946 (1996); http://dx.doi.org/10.1063/1.116107 (3 pages) | Cited 5 times

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Quantum confined Stark effect p‐i‐n waveguide modulators, grown on GaAs substrates by molecular beam epitaxy and using an undoped ZnSe/ZnCdSe multiquantum well structure as the guiding layer, have exhibited intensity modulation at wavelengths of 496 and 501 nm with extinction ratios of 6 and 4, respectively. These same devices have also demonstrated a transverse linear electro‐optic effect observed as a superimposed secondary effect on the lateral intensity modulation at 514 nm in the form of phase modulation in the output of the same device. Intensity modulation has also been observed in quaternary laser waveguide structures, indicating that this is a device structure which is suitable for monolithic integration. © 1996 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.66.Hf II-VI semiconductors

Direct observation of oxygen‐induced luminescent states in porous silicon by tunable excitation time‐resolved spectroscopy

Shuji Komuro, Takashi Kato, Takitaro Morikawa, Patrick O’Keeffe, and Yoshinobu Aoyagi

Appl. Phys. Lett. 68, 949 (1996); http://dx.doi.org/10.1063/1.116108 (3 pages) | Cited 12 times

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Time‐resolved photoluminescence (TRPL) using a dye laser pumped by a N2 laser has been employed to clarify the recombination processes of carriers selectively excited to energy levels ranging from 3.68 to 1.94 eV in oxidized porous silicon (PS). Selective excitation of carriers to energy levels around 2.7±0.4 eV significantly enhances the radiative recombination probability. The decay time of this enhanced PL is estimated to be about 4 ns. This PL enhancement is considered to be due to the creation of oxygen‐induced defect states which are located at the oxidized surface layer and/or the interface between the Si bulk and the SiOx layer. © 1996 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.47.-p Spectroscopy of solid state dynamics
78.55.Mb Porous materials
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