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8 May 1995

Volume 66, Issue 19, pp. 2451-2593

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Macroparticle distribution and chemical composition of laser deposited apatite coatings

V. N. Bagratashvili, E. N. Antonov, E. N. Sobol, V. K. Popov, and S. M. Howdle

Appl. Phys. Lett. 66, 2451 (1995); http://dx.doi.org/10.1063/1.113992 (3 pages) | Cited 24 times

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We have studied the effect of pulsed laser ablation conditions on the deposition of biocompatible apatite coatings on Ti and Ti–6Al–4V alloy at room temperature. We have made detailed analyses of the spatial distribution of the macroparticles (MP) and of the Ca/P ratio in the coatings. We find that (i) two types of MP are observed, differing in size, shape, and stoichiometry, and (ii) the size distribution of the MP has a maximum depending on the laser fluence and gas pressure in the deposition chamber. Manipulation of the laser deposition conditions allows fine control over both morphology and stoichiometry of coatings. Experimental results are explained on the basis of a theoretical model which includes the analysis of cluster‐type ablation mechanisms due to the high pressures of gas evolved in thermal decomposition of the target material under laser irradiation. © 1995 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition

Upconverting Tm‐doped BaYYbF8 optical waveguides epitaxially grown on GaAs

L. S. Hung, G. R. Paz‐Pujalt, T. N. Blanton, and D. D. Tuschel

Appl. Phys. Lett. 66, 2454 (1995); http://dx.doi.org/10.1063/1.113993 (3 pages) | Cited 2 times

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TM‐doped BaYYbF8 films were epitaxially grown on both (100) and (111) GaAs substrates using CaF2 or LiF as intermediate layers. The BaYYbF8 phase was found to be a previously unreported cubic phase with a lattice constant of 0.5711 nm, which is different from a monoclinic phase reported for bulk crystals. The films produced UV and visible radiation with wavelengths at 360 nm (UV), 450–480 nm (blue), and 500–550 nm (green) when pumped by laser radiation at 647 nm. © 1995 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Hj Laser materials
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Gn Optical waveguides and couplers

High‐repetition operation of a symmetric Mach–Zehnder all‐optical switch

S. Nakamura, K. Tajima, and Y. Sugimoto

Appl. Phys. Lett. 66, 2457 (1995); http://dx.doi.org/10.1063/1.113994 (3 pages) | Cited 11 times

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The high‐repetition switching capabilities of a recently developed symmetric Mach–Zehnder (SMZ) all‐optical switch are experimentally investigated. Using a series of four control pulses at intervals of 100 or 25 ps, nearly full switching is achieved at the corresponding intervals. The results experimentally show that the repetition rate, as well as the switching speed, of the SMZ all‐optical switch is not restricted by the slow relaxation of the utilized high‐efficiency band‐filling effect. © 1995 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Many body effects in the temperature dependence of threshold in a vertical‐cavity surface‐emitting laser

W. W. Chow, S. W. Corzine, D. B. Young, and L. A. Coldren

Appl. Phys. Lett. 66, 2460 (1995); http://dx.doi.org/10.1063/1.113995 (3 pages) | Cited 14 times

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The temperature dependence of the threshold in a vertical‐cavity surface‐emitting laser is investigated. Comparison of theory with experiment indicates that many‐body Coulomb interactions play an important role. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Intracavity frequency doubling of a continuous wave Ti:sapphire laser with over 70% conversion efficiency

W.‐L. Zhou, Y. Mori, T. Sasaki, S. Nakai, K. Nakano, S. Niikura, and B. Craig

Appl. Phys. Lett. 66, 2463 (1995); http://dx.doi.org/10.1063/1.113996 (3 pages) | Cited 3 times

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Efficient tunable ultraviolet generation by intracavity frequency doubling of a continuous wave Ti:sapphire laser was demonstrated. Maximum output is obtained of 460 mW at 398 nm corresponding to a total infrared‐to‐ultraviolet conversion efficiency over 70%. High conversion efficiency was resulted from a critically phase‐matched, temperature‐tuned lithium triborate crystal and a novel resonator design. The observed laser damage of the crystal coatings is also discussed. © 1995 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.-v Laser optical systems: design and operation
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Monolithic integration of multiple wavelength vertical‐cavity surface‐emitting lasers by mask molecular beam epitaxy

Hideaki Saito, Ichiro Ogura, Yoshimasa Sugimoto, and Kenichi Kasahara

Appl. Phys. Lett. 66, 2466 (1995); http://dx.doi.org/10.1063/1.113997 (3 pages) | Cited 13 times

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Mask molecular beam epitaxy has been used to monolithically integrate vertical‐cavity surface‐emitting lasers (VCSELs) emitting at two wavelengths. This technique allows successive selective and nonselective growth in a chamber by using a movable mask. Varying the cavity thickness at selected areas enables the growth of VCSELs spaced 500 μm apart and emitting at wavelengths 10 nm apart. Both lasers have threshold current densities of 1.3–1.4 kA/cm2, a range comparable to that of typical VCSELs grown by conventional molecular beam epitaxy. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Potassium titanyl phosphate thin films on fused quartz for optical waveguide applications

P. M. Lundquist, H. Zhou, D. N. Hahn, J. B. Ketterson, G. K. Wong, M. E. Hagerman, K. R. Poeppelmeier, H. C. Ong, F. Xiong, and R. P. H. Chang

Appl. Phys. Lett. 66, 2469 (1995); http://dx.doi.org/10.1063/1.113998 (3 pages) | Cited 6 times

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Thin films of potassium titanyl phosphate (KTiOPO4) for photonic applications have been fabricated on fused quartz substrates by pulsed excimer laser ablation. The textured films were optically uniaxial with the symmetry axis oriented normal to the film surface. The principle component of the second order electric susceptibility was oriented parallel to this symmetry axis and was determined to be about 16 times the magnitude of quartz for the fundamental wavelength of 1.064 μm. This configuration, with the largest nonlinear optical response for polarizations perpendicular to the film surface, is desirable in TM guided wave applications. Planar optical waveguide measurements were performed and the linear waveguide loss was measured. The frequency dependence of χ(2)(ω) was determined and found to be uniform for visible second harmonic wavelengths. © 1995 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Thin‐film temperature rise estimates during low energy ion bombardment in a plasma reactor

M. D. Naeem and D. Chidambarrao

Appl. Phys. Lett. 66, 2472 (1995); http://dx.doi.org/10.1063/1.113999 (3 pages) | Cited 2 times

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Theoretical estimates of the temperature distributions are obtained in structures where thin copper films mounted on special membrane wafer transmission electron microscopy (TEM) specimens are exposed to low energy (63–114 eV) ion bombardment in a magnetically enhanced (ME) plasma reactor. The substrate temperatures are experimentally measured as a function of rf power in the plasma reactor and of time. The temperature rise in the copper films is obtained based on a two‐dimensional heat transfer finite element analysis with input of a heat flux at the surface due to ion bombardment. The results indicate that copper heating due to ion bombardment is minimal because of rapid heat transfer through the underlying structure and the observed microstructural changes in copper films during plasma processing must be attributed to other causes. © 1995 American Institute of Physics.
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61.80.Jh Ion radiation effects
68.60.Dv Thermal stability; thermal effects
73.50.Mx High-frequency effects; plasma effects

Low energy electron‐enhanced etching of Si(100) in hydrogen/helium direct‐current plasma

H. P. Gillis, D. A. Choutov, P. A. Steiner, J. D. Piper, J. H. Crouch, P. M. Dove, and K. P. Martin

Appl. Phys. Lett. 66, 2475 (1995); http://dx.doi.org/10.1063/1.114000 (3 pages) | Cited 13 times

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Low energy electron‐enhanced etching of Si(100) has been achieved by placing the sample on the anode of a dc discharge in hydrogen/helium mixtures. Over a broad range of gas composition, gas pressure, and discharge current, nonpatterned samples gave etch yields of 0.01–0.02 atoms/electron, and average etch rates of 2000–3000 Å/min. Postetch examination by atomic force microscopy revealed surface roughness of 2–3 nm. These results are related to incident flux of H atoms and electrons through a simple model of the anode sheath layer above the sample. © 1995 American Institute of Physics.
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81.65.-b Surface treatments

Conducting atomic force microscopy of alkane layers on graphite

David L. Klein and Paul L. McEuen

Appl. Phys. Lett. 66, 2478 (1995); http://dx.doi.org/10.1063/1.114001 (3 pages) | Cited 17 times

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We have used an atomic force microscope with a conducting tip to investigate the layering of hexadecane on graphite. Discrete jumps were observed in both the tip–sample conductance and separation as individual liquid layers are penetrated. These conductance measurements extend solvation studies to higher force scales than have been previously achieved, and can be used to determine when the tip makes contact with the substrate. The layering also enables the formation of stable tunneling junctions. © 1995 American Institute of Physics.
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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
07.79.Lh Atomic force microscopes
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Pulsed excimer (KrF) laser induced crystallization of PbZr0.44Ti0.56O3 amorphous films

X. M. Lu, J. S. Zhu, W. S. Hu, Z. G. Liu, and Y. N. Wang

Appl. Phys. Lett. 66, 2481 (1995); http://dx.doi.org/10.1063/1.114002 (3 pages) | Cited 18 times

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Amorphous PZT thin films 600 nm thick were rf sputtered from a PbZr0.44Ti0.56O3 ceramic target with excess PbO onto glass substrates maintained at room temperature. After irradiation with a 248 nm KrF pulsed excimer laser with a power density of 2.3×107 W/m2 at a frequency of 50 Hz and a pulsed width of 30 ns for 2 min, the films crystallized into the PZT perovskite structure to a depth of about 120 nm. Comparisons of this work with PZT crystallization obtained from a traditional oven and 488 nm Ar+ laser postdeposition treatments are also given. © 1995 American Institute of Physics.
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81.15.Cd Deposition by sputtering
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Formation of Al‐Cu via/interconnect by low‐pressure collimated sputtering

R. V. Joshi, H. M. Dalal, and R. Filippi

Appl. Phys. Lett. 66, 2484 (1995); http://dx.doi.org/10.1063/1.114003 (3 pages) | Cited 1 time

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This paper describes the effect of low‐pressure collimated sputtering (LPCS) on deposition rates, step coverages, and electrical properties of Al‐Cu. The LPCS deposition is achieved in a magnetron sputter deposition system with a hollow cathode and collimator. The deposition results show that as the via or line size reduces, a complete fill requires a monotonic increase in the aspect ratio of the collimator which limits the throughput for a thick deposition, especially at high pressures (≳1 mT). The benefit of the LPCS is the improved deposition rate (scaled to power) of 1.5–2× compared to the conventional high‐pressure collimated deposition. The integration of LPCS process to fabricate a two‐level Al‐Cu metal structure with submicron Al‐Cu studs (aspect ratio of 2) shows excellent via and electromigration resistances. © 1995 American Institute of Physics.
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81.15.Cd Deposition by sputtering
85.40.Ls Metallization, contacts, interconnects; device isolation

Thermogravimetric analysis to determine the lithium to manganese atomic ratio in Li1+xMn2−xO4

Yuan Gao and J. R. Dahn

Appl. Phys. Lett. 66, 2487 (1995); http://dx.doi.org/10.1063/1.113143 (3 pages) | Cited 6 times

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Li1+xMn2−xO4 samples show reversible oxygen intercalation and deintercalation upon heating in the temperature range between 700 and 950 °C which can be monitored using thermal gravimetric analysis. There are two kinks, due to phase transitions, in the weight‐temperature curve observed on heating. The temperature of the low‐temperature kink depends linearly on x and therefore can be used to infer the sample stoichiometry. This provides a simple and straightforward quality control check on Li1+xMn2−xO4 samples for the lithium battery industry. © 1995 American Institute of Physics.
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61.50.Nw Crystal stoichiometry
82.47.-a Applied electrochemistry
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Direct observation of hexagonal boron nitride at the grain boundary of cubic boron nitride by high resolution electron microscopy

Wei‐Lie Zhou, Yuichi Ikuhara, Masao Murakawa, Syuichi Watanabe, and Tetsuya Suzuki

Appl. Phys. Lett. 66, 2490 (1995); http://dx.doi.org/10.1063/1.113142 (3 pages) | Cited 26 times

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Cubic boron nitride (c‐BN) film deposited on a Si substrate was observed by high resolution electron microscopy. Thin layers, 1–2 nm, of hexagonal boron nitride (h‐BN) phase were often found at the boundaries of c‐BN grains. The observed interplanar spacing was about 0.33 nm, which coincided with that of the (0002) plane of h‐BN. The nucleation mechanism of c‐BN film is briefly discussed based on the formation of the h‐BN phase at the grain boundaries. The existence of the h‐BN phase at the boundaries of c‐BN grains may be the reason for the occurrence of compressive stress and cracks in c‐BN thin films. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.Mm Grain and twin boundaries

Thickness dependence of the coercive electric field of laser ablated niobium‐doped lead‐zirconium‐titanate films

C. Björmander, K. Sreenivas, M. Duan, A. M. Grishin, and K. V. Rao

Appl. Phys. Lett. 66, 2493 (1995); http://dx.doi.org/10.1063/1.113144 (3 pages) | Cited 14 times

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Thickness dependence (over the range d=1.05 to 0.02 μm) of the coercive electric fields, Ec, of niobium‐doped lead‐zirconium‐titanate (PNZT) films has been investigated in pulsed laser ablated c‐axis‐oriented PNZT/YBa2Cu3O7−x heterostructures deposited on LaAlO3 substrates. Our studies show that Ec has a d−2/3 dependence in good agreement with the domain nucleation model developed for ferroelectric single crystals by Kay and Dunn [Philos. Mag. 7, 2027 (1962)]. Reproducible structural properties as well as ferroelectric properties with rather high polarization which is independent of the film thickness have been obtained in these Nd:YAG pulsed laser ablated films. © 1995 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Fabrication of highly concentrated Er3+ doped aluminosilicate films via sol‐gel processing

Choon Kun Ryu, Hyungsoo Choi, and Kyekyoon Kim

Appl. Phys. Lett. 66, 2496 (1995); http://dx.doi.org/10.1063/1.113145 (3 pages) | Cited 25 times

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Optically active highly concentrated Er3+–Al3+ codoped silica thin films were fabricated on fused silica substrates by sol‐gel method. The synthesis of the Er3+–Al3+ double alkoxide was intended to prevent the optically harmful Er clustering by the selective coordination of Al3+ around Er3+ ions. The molar Er ion concentration was varied from 3811 to 23719 ppm. Photoluminescence (PL) measurements indicated that Er ions were optically active in all films of different Er concentrations. A broadband peak was observed at 1531 nm with the full width at half‐maximum (FWHM) of 42 nm, which corresponds to the 4I13/2→4I15/2 transition. The shape, peak position, and FWHM of the PL signals from the sol‐gel derived Er3+ doped silica were quite comparable to those prepared by other methods. The PL peak showed maximum intensity at an Er concentration of 8535 ppm. This implies the concentration quenching at higher Er concentrations. © 1995 American Institute of Physics.
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42.70.Ce Glasses, quartz
78.55.Hx Other solid inorganic materials
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
61.72.up Other materials

Nanometer‐scale modification of the tribological properties of Si(100) by scanning force microscope

T. Teuschler, K. Mahr, S. Miyazaki, M. Hundhausen, and L. Ley

Appl. Phys. Lett. 66, 2499 (1995); http://dx.doi.org/10.1063/1.113146 (3 pages) | Cited 14 times

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Hydrogen‐terminated Si(100) surfaces were patterned on the nanometer scale using a conducting‐probe scanning force microscope (SFM) operating in air ambient. To generate the nanostructures, negative voltages were applied to the conductive SFM tip with respect to the sample while scanning in contact mode. After structuring, the same SFM tip was used to measure simultaneously the sample topography and the friction force between tip and sample. An increase in height by about three nanometers resulting from field‐enhanced oxidation is observed in areas where the tip had been negatively biased with constant voltages above 7 V. The topographical change is accompanied by a relative increase of the friction force of about 20% over the structured areas. © 1995 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.-b Surface treatments
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

Observation of enhanced lateral confinement of excitons in GaAs quantum wires with various sizes (7–30 nm) by magnetophotoluminescence measurements

Y. Nagamune, T. Tanaka, T. Kono, S. Tsukamoto, M. Nishioka, Y. Arakawa, K. Uchida, and N. Miura

Appl. Phys. Lett. 66, 2502 (1995); http://dx.doi.org/10.1063/1.113147 (3 pages) | Cited 7 times

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We investigated magnetophotoluminescence spectra up to 40 T of GaAs quantum wires with various lateral widths (7–30 nm) grown by the selective metalorganic chemical vapor deposition. The photoluminescence peak shift due to the magnetic fields is more suppressed with decreasing the wire width. The observed energy shift was in good agreement with the calculation based on a variation method. These results clearly demonstrate existence of the two‐dimensional confinement effect and enhanced binding energy of excitons. In the narrowest wire (7 nm), however, comparison of the experimental results with the calculation indicates penetration of exciton wavefunction from the two‐dimensional potential to the barrier region. © 1995 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.20.Ls Magneto-optical effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Characteristics of graded‐like multiple‐delta‐doped GaAs field effect transistors

M. J. Kao, W. C. Hsu, R. T. Hsu, Y. H. Wu, T. Y. Lin, and C. Y. Chang

Appl. Phys. Lett. 66, 2505 (1995); http://dx.doi.org/10.1063/1.113148 (2 pages) | Cited 4 times

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Multiple‐δ‐doped GaAs field effect transistors using graded‐like δ‐doping profile are demonstrated and investigated. An extremely high carrier density of 1.2×1013 (7.9×1012) cm−2 along with an enhanced Hall mobility of 1700 (3300) cm2/v s at 300 (77) K for a triple‐δ‐doped GaAs structure are achieved. The dc characteristic reveals an extrinsic transconductance as high as 110 mS/mm at room temperature with a gate length of 2 μm. Three separated peaks in the transconductance versus gate bias curve are observed. Meanwhile, a broad and flat transconductance region is obtained. © 1995 American Institute of Physics.
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85.30.Tv Field effect devices
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Impact of the substrate on the low‐frequency noise of silicon n+p junction diodes

E. Simoen, G. Bosman, J. Vanhellemont, and C. Claeys

Appl. Phys. Lett. 66, 2507 (1995); http://dx.doi.org/10.1063/1.113149 (3 pages) | Cited 19 times

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This letter describes the low‐frequency noise characteristics in forward operation of near‐ideal n+p junction diodes fabricated in different p‐type silicon substrates. The highest noise is found typically in Czochralski substrates, while float‐zone and epitaxial diodes yield a lower noise magnitude. The spectra are 1/fβ‐like for low‐frequency f and frequency independent for larger f, whereby the frequency exponent β changes from slightly below to slightly above 1 with increasing forward bias. The spectral density SI at constant frequency shows a Iν dependence, with ν close to 1.5 for near‐ideal diodes. Furthermore, there exists a close relationship between the static diode characteristics (the ideality factor) and the low‐frequency noise magnitude. The experimental observations are not in agreement with the Kleinpenning formulation for the diffusion noise in the quasineutral region of the diode, but suggest on the contrary a generation‐recombination origin. © 1995 American Institute of Physics.
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72.70.+m Noise processes and phenomena
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Kk Junction diodes

Slow current transients in metal–oxide–semiconductor capacitors

Ze‐Qiang Yao, Sima Dimitrijev, Philip Tanner, and H. Barry Harrison

Appl. Phys. Lett. 66, 2510 (1995); http://dx.doi.org/10.1063/1.113150 (3 pages) | Cited 2 times

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Glitches of positive current at negative voltages have been observed during current–voltage measurements of metal–oxide semiconductor capacitors. The magnitude of the glitches depends on both stepping rate and duration of holding the metal electrode at the most negative potential before stepping towards positive potentials is initiated. Current versus time measurements show a voltage‐dependent time constant, generally ≳100 ms. Charging/discharging of border traps is suggested as a possible cause for this effect. © 1995 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

Current induced intersubband absorption in GaAs/GaAlAs quantum wells

A. Fenigstein, A. Fraenkel, E. Finkman, G. Bahir, and S. E. Schacham

Appl. Phys. Lett. 66, 2513 (1995); http://dx.doi.org/10.1063/1.113151 (3 pages) | Cited 7 times

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The observation of intersubband (e1–e2) absorption induced by current injection in GaAs/GaAlAs multiquantum wells is reported. The new technique enables sensitive measurement of intersubband transitions in undoped quantum wells. The carrier concentration in the wells is easily controlled by varying the current density. The technique is demonstrated on undoped multiquantum well layers sandwiched in a p‐i‐n laser‐diodelike structure. The lowest confined level was populated by biasing the junction and hence injecting carriers into the quantum wells. The spectra were taken by a Fourier transform infrared (FTIR) spectrometer, modulating the current and using the double modulation method. The dependence of the absorption on current intensity was examined and excess carrier concentration and lifetime were calculated. The induced absorption saturates at current densities higher than 100 mA/cm2. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Band structure engineering and doping of wide gap II–VI superlattices

W. Faschinger, S. Ferreira, and H. Sitter

Appl. Phys. Lett. 66, 2516 (1995); http://dx.doi.org/10.1063/1.113152 (3 pages) | Cited 3 times

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It is shown that the free hole concentration for nitrogen doped ZnSe/ZnTe short period superlattices with a given average Te content of 15% can be increased from 1016 to 1019 cm−3 by just increasing the SL period from 2.5 to 4.5 nm. This behavior can be understood in terms of a model that assumes a pinning of the Fermi level at an energetic position that is fixed with respect to the vacuum level. The model can be applied to other II–VI superlattices, and alternative cladding layers for blue laser diodes are proposed that should exhibit significantly higher p‐doping levels than the currently used ZnMgSSe claddings. © 1995 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.55.Px Semiconductor lasers; laser diodes

Ultrafast‐lifetime quantum wells with sharp exciton spectra

I. Lahiri, D. D. Nolte, E. S. Harmon, M. R. Melloch, and J. M. Woodall

Appl. Phys. Lett. 66, 2519 (1995); http://dx.doi.org/10.1063/1.113153 (3 pages) | Cited 29 times

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Sharp quantum‐confined excitons in semi‐insulating low‐temperature‐growth AlAs/GaAs quantum wells with 15 ps carrier lifetimes are demonstrated. High‐quality well‐barrier interfaces can be grown at low substrate temperatures and annealed up to temperatures of 700 °C, beyond which interface mixing broadens the exciton transitions. Electroabsorption from the quantum‐confined Stark effect in as‐grown modulators approaches 10 000 cm−1, which is comparable to traditional high‐temperature growth quantum wells. The low‐temperature growth quantum well structures eliminate the need for postgrowth processing, such as ion implantation for photorefractive quantum wells, ultrafast saturable absorption, or electro‐optic sampling applications. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
42.79.Hp Optical processors, correlators, and modulators

Si diffusion and intermixing in AlGaAs/GaAs structures using buried impurity sources

K. J. Beernink, R. L. Thornton, G. B. Anderson, and M. A. Emanuel

Appl. Phys. Lett. 66, 2522 (1995); http://dx.doi.org/10.1063/1.113154 (3 pages) | Cited 9 times

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Si diffusion and impurity‐induced layer intermixing from a buried impurity source have been studied by transmission electron microscopy and secondary ion mass spectroscopy of isolated, Si‐doped GaAs layers in an undoped Al0.4Ga0.6As/GaAs superlattice and by photoluminescence measurements on Si‐doped GaAs quantum wells with undoped Al0.4Ga0.6As barriers. In annealed samples, the Si profile suggests a Si diffusion process involving multiply ionized column III vacancies. The width of the resulting Si profile and the spatial extent and completeness of intermixing strongly depend on the initial Si concentration in the doped layer. © 1995 American Institute of Physics.
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66.30.J- Diffusion of impurities
66.30.Ny Chemical interdiffusion; diffusion barriers
68.60.Dv Thermal stability; thermal effects
68.35.Fx Diffusion; interface formation
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