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10 Jun 1996

Volume 68, Issue 24, pp. 3371-3508

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Geometrical anisotropy dependence of thermal diffusivity in lyotropic nematics: Mode mismatched thermal lens measurements

A. C. Bento, A. J. Palangana, L. R. Evangelista, M. L. Baesso, J. R. D. Pereira, E. C. da Silva, and A. M. Mansanares

Appl. Phys. Lett. 68, 3371 (1996); http://dx.doi.org/10.1063/1.116507 (3 pages) | Cited 22 times

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In this work the quantitative theoretical treatment for two beam mode mismatched thermal lens spectrometry is applied to investigate the thermal diffusivity anisotropy of two lyotropic mixtures: (1) potassium laurate, decanol and water and (2) potassium laurate, potassium chloride and water in the nematic calamitic phase. The ratio between the thermal diffusivities parallel and perpendicular to the director has been shown to be smaller than those reported for thermotropic liquid crystal. This observation is explained by using a simple model where this ratio is correlated to the micellar shape anisotropy. © 1996 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
66.10.C- Diffusion and thermal diffusion

Subharmonic‐pumped continuous‐wave parametric oscillator

S. Schiller, G. Breitenbach, R. Paschotta, and J. Mlynek

Appl. Phys. Lett. 68, 3374 (1996); http://dx.doi.org/10.1063/1.116508 (3 pages) | Cited 7 times

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We have operated a doubly resonant optical parametric oscillator (OPO) whose pump wave is generated in the OPO cavity itself by resonant frequency doubling of an injected subharmonic wave. The subharmonic‐pumped oscillator employs a miniature monolithic MgO:LiNbO3 resonator and is pumped by a single‐frequency Nd:YAG laser at 1064 nm. The threshold power was 120 mW at 1064 nm, and an efficiency of 7% for the conversion from 1064 to 1063/1065 nm via the nonresonant 532 nm wave was reached at 300 mW infrared input power. Single‐frequency operation for up to one‐and‐a‐half hours was observed. © 1996 American Institute of Physics.
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42.65.Yj Optical parametric oscillators and amplifiers

Fiber‐optic‐coupled, laser heated thermoluminescence dosimeter for remote radiation sensing

Alan L. Huston, Brian L. Justus, and Tommy L. Johnson

Appl. Phys. Lett. 68, 3377 (1996); http://dx.doi.org/10.1063/1.116509 (3 pages) | Cited 4 times

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We describe an optically transparent, laser heated, thermoluminescent glass dosimeter that is used for fiber‐optic‐coupled remote radiation monitoring. The glass consists of ZnS nanocrystallites embedded in a Vycor glass host, doped with Cu1+ and Nd3+ ions. An 807 nm, 1 W GaAlAs laser is used to rapidly heat microscopic regions, surrounding the Nd3+ ions, in the composite glass to stimulate blue‐green thermoluminescence from metastable traps populated by exposure to ultraviolet or 60Co γ radiation.
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07.60.Vg Fiber-optic instruments
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
78.60.Kn Thermoluminescence

High‐resolution imaging using near‐field scanning optical microscopy and shear force feedback in water

Patrick J. Moyer and Stefan B. Kämmer

Appl. Phys. Lett. 68, 3380 (1996); http://dx.doi.org/10.1063/1.116510 (3 pages) | Cited 21 times

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Near‐field scanning optical microscopy using shear force feedback in water is demonstrated with better than 50 nm lateral spatial resolution. Results also indicate the potential to measure topographic features with higher force sensitivity than contact and noncontact atomic force microscopy (AFM) measurements. Soft surface contaminants are clearly imaged using shear force feedback while the simultaneously obtained optical contrast is due to the higher optical density surface features lying beneath the surface contaminants. AFM measurements do not appear to show the same sensitivity to surface features leading to the conclusion that shear force feedback may be better for imaging soft (i.e., low mechanical compliance) samples, such as biological specimens, in liquid. © 1996 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.Fc Near-field scanning optical microscopes
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics

Influence of aging on the performance of solid source molecular beam epitaxy grown GaInP/AlGaInP quantum well lasers

K. Tappura, J. Aarik, T. Nurmi, and M. Pessa

Appl. Phys. Lett. 68, 3383 (1996); http://dx.doi.org/10.1063/1.116511 (3 pages)

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We have studied the influence of aging on the performance of GaInP/AlGaInP quantum well lasers grown by all solid source molecular beam epitaxy. A remarkable improvement in the laser characteristics was observed during the first 20–30 h of continuous wave operation at a constant current corresponding to the initial output power of 100 mW. After such an aging process the threshold current density was typically decreased 30% from its original value. The comparison of the experimentally and theoretically determined gain‐current curves revealed the improved laser performance to be caused by the reduction of the nonradiative recombination rate. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

In situ infrared spectroscopy as a real time diagnostic for plasma polymer film deposition

Y. Vickie Pan, Ernesto Z. Barrios, and Denice D. Denton

Appl. Phys. Lett. 68, 3386 (1996); http://dx.doi.org/10.1063/1.116512 (3 pages) | Cited 5 times

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In situ Fourier transform infrared spectroscopy (FTIR)/attenuated total reflection (ATR) was used to study the deposition of plasma polymerized methyl methacrylate (PPMMA) film. Real time absorption spectra of PPMMA films were obtained at a time resolution of 20–30 s which is mostly limited by the low optical throughput and low signal‐to‐noise ratio. Postplasma dynamics observed in the system demonstrate the need for an in situ and real time film diagnostic technique. This letter reports the use of this diagnostic on plasma deposited polymers. © 1996 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.30.Jw Organic compounds, polymers

Polarization‐dependent extended x‐ray absorption fine structure measurements of metastable fcc Co on (100) diamond

K. M. Kemner, W. T. Elam, Y. U. Idzerda, J. A. Wolf, and G. A. Prinz

Appl. Phys. Lett. 68, 3389 (1996); http://dx.doi.org/10.1063/1.116513 (3 pages)

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Polarization‐dependent extended x‐ray absorption fine structure (EXAFS) measurements have been made on a single‐crystal 1000 Å thick Co film deposited on (100) diamond. By comparing the EXAFS signals corresponding to the in‐plane and out‐of‐plane structure relative to the film plane, we clearly illustrate that the film exists in the face centered cubic (fcc) phase. An analysis of the first shell Fourier transform peaks for the in‐plane and out‐of‐plane structure surrounding the Co atoms indicates that the majority of the fcc Co crystal lattice is not distorted, demonstrating that the majority of film is relaxed and not pseudomorphic. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Selective solid phase crystallization for control of grain size and location in Ge thin films on silicon dioxide

C. M. Yang and Harry A. Atwater

Appl. Phys. Lett. 68, 3392 (1996); http://dx.doi.org/10.1063/1.116514 (3 pages) | Cited 7 times

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Selective solid phase crystallization for control of grain size and location in polycrystalline thin Ge films on amorphous silicon dioxide substrates is described. The approach consists of solid phase crystal nucleation at predefined nucleation sites, which consist of metal islands deposited on top of the amorphous Ge film, followed by lateral solid phase epitaxial growth. Grain sizes as large as 30 μm have been achieved in 50‐nm‐thick Ge films at temperatures less than 475 °C. © 1996 American Institute of Physics.
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81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)

Real time control of plasma deposited multilayers by multiwavelength ellipsometry

M. Kildemo, P. Bulkin, S. Deniau, and B. Drévillon

Appl. Phys. Lett. 68, 3395 (1996); http://dx.doi.org/10.1063/1.116515 (3 pages) | Cited 11 times

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A robust direct method for real time control, by multiwavelength phase modulated ellipsometry (PME), of the growth of plasma deposited structures is presented here. Transparent multilayers consisting of SiO2 and SiNx alloys are investigated. This feedback control method is based on the comparison between the real time PME measurements and precomputed target trajectories. It can provide the high precision required to deposit high performance optical coatings. In particular an overall accuracy better than 1% is obtained on a fifteen layer quarter‐wave filter, designed at 670 nm. This real time procedure, which is not limited to transparent materials nor plasma processes, appears to be a useful tool for process control. © 1996 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.-w Optical properties of specific thin films

Dosimetric properties of KCl:Eu2+ under α, β, γ, x ray, and ultraviolet irradiation

R. Meléndrez, R. Pérez‐Salas, L. P. Pashchenko, R. Aceves, T. M. Piters, and M. Barboza‐Flores

Appl. Phys. Lett. 68, 3398 (1996); http://dx.doi.org/10.1063/1.116516 (3 pages) | Cited 6 times

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The thermoluminescence (TL) characteristics of KCl:Eu2+ subjected to α, β, γ, x ray, and ultraviolet (UV) radiation (200–300 nm), as well as the dose response was investigated. The TL glow curve structure is very similar for any type of irradiation used with differences only in the peak intensities; it has good reproducibility. Also, the dose response is linear for all types of irradiations. These results allowed us to conclude that the KCl:Eu2+ crystals may be used as a dosimeter for ionizing and nonionizing radiation © 1996 American Institute of Physics.
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78.60.Kn Thermoluminescence
07.77.Ka Charged-particle beam sources and detectors
61.80.-x Physical radiation effects, radiation damage

SrTiO3 buffering effect on Pb1−xLaxTiO3 thin films prepared by pulsed laser deposition

J. P. Wang, Y. C. Ling, M. H. Yeh, K. S. Liu, and I. N. Lin

Appl. Phys. Lett. 68, 3401 (1996); http://dx.doi.org/10.1063/1.116517 (3 pages) | Cited 8 times

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Thin films of phase‐pure perovskite PLT (Pb0.95La0.05Ti0.9875O3) were deposited in situ onto Si, Pt/Ti/SiO2/Si, and SrTiO3/Si substrates by pulsed laser deposition from stoichiometric targets. No Pb loss was observed in the near‐surface region. The blocking of the interdiffusion between inner Si substrate and the outer PLT films by SrTiO3 buffer layer was evidenced using x‐ray diffraction (XRD) and secondary ion mass spectrometry (SIMS) analyses. The formation of TiO2 second phase in PLT/Pt/Ti/SiO2/Si films was indicated by XRD and SIMS spectra to be the outward diffusion of Ti atoms from the underlying Ti layer through the Pt layer, reacting with ambient O2 at the PLT‐to‐Pt interface. © 1996 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology

Effect of hydrostatic pressure in lead indium niobate‐based complex perovskite systems

Naohiko Yasuda, Hidehiro Ohwa, Takuya Mizuno, Makoto Iwata, and Yoshihiro Ishibashi

Appl. Phys. Lett. 68, 3404 (1996); http://dx.doi.org/10.1063/1.115774 (3 pages) | Cited 6 times

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Dielectric properties of (1−x)Pb(In1/2Nb1/2)O3−xPbZrO3(Zr‐PIN) and (1−x)Pb(In1/2Nb1/2) O3−xPb(Yb1/2Nb1/2)O3(Yb‐PIN) mixed crystal systems were investigated under hydrostatic pressures up to 0.7 GPa. There are striking pressure effects in these systems. In Zr‐PIN (x=0.1) the temperature Tm, indicating the maximum of the dielectric constant, ϵrm′, decreases at the rate of dTm/dp∣p=0=−54 °C/GPa, and the ϵrm′ decreases with increasing pressure, while in Zr‐PIN (x=0.34) the Tm decreases at the rate of dTm/dp∣p=0=−100 °C/GPa, and the ϵrm′ decreases and the maximum value of the tan δ, denoted as tan δm, increases with increasing pressure. For Yb‐PIN (x=0.16) the Tm increases at the rate of dTm/dp=155 °C/GPa, both the ϵrm′ and the tan δm decrease with increasing pressure. © 1996 American Institute of Physics.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity

Thickness measurements of Si1−xGex layers on Si mesa structures using Raman spectroscopy

A. Wasserman, D. J. Roth, R. Beserman, A. Hoffman, and K. Dettmer

Appl. Phys. Lett. 68, 3407 (1996); http://dx.doi.org/10.1063/1.115775 (3 pages)

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A Si0.6Ge0.4 layer has been deposited on a patterned Si substrate containing mesas of width ranging from 2 to 200 μm. Raman spectra at various points on the sample were taken, and evaluation of layer thickness has been performed, showing different values in different areas of the mesas. This can be explained as being a consequence of the different growth rates on different crystal planes. The stress was measured from Raman shift, and was found to be constant within the 0.7 μm diameter spot of the laser. Dependence of the thickness on mesa width was not found. © 1996 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors

Characterization of stacked gate oxides by electron holography

W.‐D. Rau, F. H. Baumann, J. A. Rentschler, P. K. Roy, and A. Ourmazd

Appl. Phys. Lett. 68, 3410 (1996); http://dx.doi.org/10.1063/1.115776 (3 pages) | Cited 3 times

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We have used off‐axis electron holography at a resolution of 3 Å to investigate amorphous bilayer gate oxides consisting of thermal and chemically deposited SiO2. The values of the mean inner potential were measured to be: thermal oxide: (10.51±0.35)V (undensified); (10.65±0.32)V (‘‘densified’’); deposited oxide: (11.19±0.38)V (undensified); (10.58±0.69)V (densified). Exploiting the chemical etch rate differences between different oxides, we have delineated stacked gate oxides consisting of closely similar layers. Our results establish that measurement of thickness differences produced by etching can be used to reveal the densification state of the oxide. © 1996 American Institute of Physics.
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61.05.jp Electron holography
85.40.Sz Deposition technology

On the impact of interface energy and vacancy concentration on morphology changes and nucleation of silicon oxide precipitates in silicon

Jan Vanhellemont

Appl. Phys. Lett. 68, 3413 (1996); http://dx.doi.org/10.1063/1.115777 (3 pages) | Cited 12 times

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An expression for the critical radius for growth of spherical precipitates is used to estimate the interface energy between silicon oxide precipitates and the surrounding silicon matrix from observations on precipitate morphology changes. The calculated interface energy is one order of magnitude larger than values commonly accepted but corresponds well with those measured on bonded wafers. The important impact of the vacancy concentration on the critical radius is stressed and allows an understanding of the apparent difference. Implications for balling up of oxide layers embedded in silicon and for oxygen precipitate nucleation during crystal pulling are also addressed. © 1996 American Institute of Physics.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
61.72.J- Point defects and defect clusters

Formation of rare‐earth oxide doped silicon by spark processing

John V. St. John, Jeffery L. Coffer, Young Gyu Rho, and Russell F. Pinizzotto

Appl. Phys. Lett. 68, 3416 (1996); http://dx.doi.org/10.1063/1.115778 (3 pages) | Cited 7 times

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In this work, we report a method for the incorporation of rare‐earth oxides onto silicon surfaces. This process uses a high‐energy dc spark to convert salts of rare‐earth ions such as europium and erbium to the corresponding oxide phase(s) with concomitant formation of a porous layer. Scanning electron micrographs of the silicon substrate show an irregular, pitted surface morphology for those areas exposed to spark processing. Photoluminescence, infrared spectroscopy, and electron microscopy of the spark‐processed regions of the Si substrate are clearly consistent with the formation of the desired luminescent oxide phase. © 1996 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.65.-b Surface treatments

Ultrashort lifetime photocarriers in Ge thin films

N. Sekine, K. Hirakawa, F. Sogawa, Y. Arakawa, N. Usami, Y. Shiraki, and T. Katoda

Appl. Phys. Lett. 68, 3419 (1996); http://dx.doi.org/10.1063/1.115779 (3 pages) | Cited 3 times

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An ultrashort lifetime of photocarriers as short as 600 fs has been obtained in ion‐implanted Ge thin films grown on sapphire substrates. The photocarrier mobility determined by photoconductivity measurements is found to be reasonably high (∼100 cm2/V s). We have observed terahertz (THz) radiation from a photoconductive dipole antenna geometry. © 1996 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
72.40.+w Photoconduction and photovoltaic effects
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Room‐temperature migration and interaction of ion beam generated defects in crystalline silicon

Vittorio Privitera, Salvatore Coffa, Francesco Priolo, Kim Kyllesbech Larsen, and Giovanni Mannino

Appl. Phys. Lett. 68, 3422 (1996); http://dx.doi.org/10.1063/1.115780 (3 pages) | Cited 22 times

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We have investigated the room‐temperature migration properties of ion generated defects in crystalline Si. The defects were injected into the bulk of a pure epitaxial Si layer by a low energy (40 keV) Si implant and monitored using a preexisting defect distribution, produced by a high energy He implant, as a marker. The depth of this defective marker layer was changed by varying the He implant energy in the range 1–3 MeV. Spreading resistance measurements show that the injected defects produce a partial annihilation of the pre‐existing damage. The magnitude of the annihilation process is strongly dependent on the depth of the defective marker, being very large when this marker is confined within 5 μm from the surface and negligible when it lies beyond a depth of ∼10 μm. From these results, detailed information on the nature of ion‐generated defects which are injected and on their migration properties is obtained. It is found that the observed phenomena are due to the annihilation of divacancies and phosphorus‐vacancy defect complexes, generated by the He implant, by Si self‐interstitials injected by the shallow Si implant. © 1996 American Institute of Physics.
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61.72.J- Point defects and defect clusters
66.30.Lw Diffusion of other defects
71.55.Cn Elemental semiconductors
61.72.uf Ge and Si

The temperature dependence of the ion beam induced interfacial amorphization in silicon

T. Henkel, V. Heera, R. Kögler, W. Skorupa, and M. Seibt

Appl. Phys. Lett. 68, 3425 (1996); http://dx.doi.org/10.1063/1.115781 (3 pages) | Cited 3 times

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The temperature dependence of the ion beam induced interfacial amorphization process (IBIIA) in silicon has been investigated at temperatures above 80 K using Rutherford backscattering spectrometry/channeling (RBS/C) and cross‐sectional transmission electron microscopy (XTEM). Three regimes are observed. Above temperatures of about 320 K there is a strong temperature dependence of the IBIIA rate (thermal regime). At lower temperatures the rate moves towards a saturation value (transition regime). Below ∼150 K, IBIIA is nearly temperature independent (ballistic regime). This low‐temperature regime can be explained by an athermal transport of point defects like in ballistic mixing processes. © 1996 American Institute of Physics.
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61.80.Jh Ion radiation effects

Surface migration of ZnSe regrowth using compound source molecular beam epitaxy

Takashi Nishikawa, Minoru Kubo, and Yoichi Sasai

Appl. Phys. Lett. 68, 3428 (1996); http://dx.doi.org/10.1063/1.115782 (3 pages) | Cited 1 time

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We studied ZnSe epitaxial growth on ZnSe and ZnSSe patterned layers with two methods. One was conventional‐type molecular beam epitaxy (MBE) which uses elemental materials as its sources. The other one was compound source molecular beam epitaxy (CSMBE) which uses compound polycrystals. We found that the epilayer is regrown on undercut mesa sidewall by CSMBE, while nothing is grown on the sidewall by conventional MBE. The surface migration length on ZnSSe (221)B plane was estimated from the surface edge profile of the regrown layer by CSMBE. © 1996 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Na‐induced effects on the electronic structure and composition of Cu(In,Ga)Se2 thin‐film surfaces

C. Heske, R. Fink, E. Umbach, W. Riedl, and F. Karg

Appl. Phys. Lett. 68, 3431 (1996); http://dx.doi.org/10.1063/1.115783 (3 pages) | Cited 23 times

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X‐ray and UV photoelectron spectroscopy measurements of Cu(InGa)Se2 thin films grown on Mo coated soda‐lime glass show segregation from the substrate and formation of two different Na species. One of these species is also identified after deliberate deposition of metallic Na. Moreover, the adsorption (or segregation) of this species reduces the native oxide SeO2, while the other, reacted Na species coexists with SeO2. Small amounts of Na (≤0.05 Å) induce a band bending and reduce the surface dipole. These findings reveal a positive influence of segregated Na on the morphology and electrical characteristics of Na‐enriched films, improving the overall performance of the solar cells. © 1996 American Institute of Physics.
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84.60.Jt Photoelectric conversion
68.35.Fx Diffusion; interface formation
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Transport through an array of small ohmic contacts alloyed to the two‐dimensional electron gas of a GaAs/AlGaAs heterostructure

V. Chabasseur‐Molyneux, J. E. F. Frost, M. Y. Simmons, D. A. Ritchie, and M. Pepper

Appl. Phys. Lett. 68, 3434 (1996); http://dx.doi.org/10.1063/1.115784 (3 pages) | Cited 2 times

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We investigate transport through a two‐dimensional electron gas (2DEG) underneath a submicron periodic array of small Ge‐Ag alloyed ohmic contacts and compare the results with the resistance of the small contacts. We find that as the contacts form, the effective mobility of the 2DEG underneath the array decreases and that the carrier concentration between the small contacts is reduced. From the low‐field magnetoresistance we are able to identify ballistic cyclotron orbits commensurate with the period of the array. We find that reducing the diameter of the ohmic metallization to 0.2 μm severely inhibits ohmic contact formation. © 1996 American Institute of Physics.
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73.40.-c Electronic transport in interface structures
73.50.-h Electronic transport phenomena in thin films

High quality Al(Ga)As/GaAs/Al(Ga)As quantum wells grown on (111)A GaAs substrates

Albert Chin and K. Lee

Appl. Phys. Lett. 68, 3437 (1996); http://dx.doi.org/10.1063/1.115785 (3 pages) | Cited 4 times

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We report the growth of high quality molecular beam epitaxy (MBE) AlGaAs, AlGaAs/GaAs/AlGaAs, and AlAs/GaAs/AlAs multiple quantum wells (MQWs) on (111)A GaAs substrates. For (111)A AlGaAs/GaAs/AlGaAs MQWs, there is no detectable photoluminescence (PL) at a growth temperature of 640 °C, and narrow PL linewidth can only be obtained at growth temperatures higher than 680 °C. A PL linewidth of 13.8 meV is measured at the growth temperature of 720 °C. To understand such growth temperature dependence of (111)A MQWs, we have investigated the material quality of (111)A AlGaAs at different growth temperatures. The strong PL integrated intensity of 640 °C grown (111)A AlGaAs indicates good material quality and a low concentration of non‐radiative recombination centers. However, the broad PL linewidth of 640 °C grown (111)A AlGaAs indicates the strong compositional modulation and a rough growth front. We have used AlAs instead of AlGaAs in order to reduce the compositional modulation and smooth the interface. A PL linewidth of 13.4 meV is measured for 640 °C grown (111)A AlAs/GaAs/AlAs MQWs, which is the narrowest value for (111)A MQWs. © 1996 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors

X‐ray crystallographic study of GaN epitaxial films on Al2O3(0001) substrates with GaN buffer layers

Chih‐Hao Lee, G. C. Chi, C. F. Lin, M. S. Feng, and J. D. Guo

Appl. Phys. Lett. 68, 3440 (1996); http://dx.doi.org/10.1063/1.115786 (3 pages) | Cited 16 times

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Samples of GaN(0001) epitaxial films on sapphire Al2O3(0001) with different thicknesses of GaN buffer layers were characterized by x‐ray diffraction method in both in‐plane and plane‐normal directions. The results show that all the epitaxial films are of good quality with the GaN[1010] ∥Al2O3[1120] and GaN[1210]∥Al2O3[1100]. This arrangement of crystal orientation can be attributed to the chemical potential overriding the lattice spacing mismatch. The x‐ray results also indicate that the crystal coherence lengths in the in‐plane direction are smaller than those measured in the plane‐normal direction, i.e., a columnar‐like structure normal to the film is observed. The rocking curve widths in the in‐plane direction are also larger than those measured in the plane‐normal direction. In‐plane measurement of rocking curve and coherence length are essential physical quantities directly related to the electron mobility which was measured predominantly in the in‐plane direction. The best epitaxial structure is the one grown with 10 nm buffer layer. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.05.C- X-ray diffraction and scattering

Naturally formed InxAl1−xAs/InyAl1−yAs vertical superlattices

Sung Won Jun, Tae‐Yeon Seong, J. H. Lee, and Bun Lee

Appl. Phys. Lett. 68, 3443 (1996); http://dx.doi.org/10.1063/1.115787 (3 pages) | Cited 34 times

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InxAl1−xAs/InyAl1−yAs vertical superlattices (VS) were naturally formed by phase separation during the growth of InAlAs/InP layers at temperatures in the range 565–615 °C by metalorganic chemical vapor deposition. The VS lies perpendicular to the (001) growth plane. As the growth temperature increased from 565 to 615 °C, the VS decreased in thickness from ∼15 to ∼6 nm, and became less planar and uniform. Transmission electron diffraction results showed the occurrence of CuPt‐type ordering in some of the layers. Band‐gap reduction of ∼300 meV was observed in the InAlAs layers grown at temperatures ranging from 565 to 615 °C. Such a large reduction in band‐gap energy was attributed to combined effects of the VS and CuPt‐type ordering. © 1996 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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