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19 Sep 1994

Volume 65, Issue 12, pp. 1477-1596

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Optical waveguides for evanescent field sensing

F. Rehouma, D. Persegol, and A. Kevorkian

Appl. Phys. Lett. 65, 1477 (1994); http://dx.doi.org/10.1063/1.113005 (3 pages) | Cited 7 times

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A new fabrication process of ion‐exchange waveguides well suited for integrated‐sensor applications is presented. The process consists in burying each extremity of the waveguide few microns below the surface while its central region is located at the surface. For a single‐mode waveguide at 785 nm, we measured propagation losses of 0.13 dB/cm for the buried portion, 2.80 dB/cm for the surface portion, and losses of 0.40 dB for the transition region. For this structure, we also observed a deformation of the fundamental mode. The proposed method is easy to implement and permits one to control precisely the topography of the elaborated waveguides.  
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays

Investigation of the bulk laser damage of lithium triborate, LiB3O5, single crystals

Yasunori Furukawa, Steven A. Markgraf, Masayoshi Sato, Hidetsugu Yoshida, Takatomo Sasaki, Hisanori Fujita, Tatsuhiko Yamanaka, and Sadao Nakai

Appl. Phys. Lett. 65, 1480 (1994); http://dx.doi.org/10.1063/1.112018 (3 pages) | Cited 18 times

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The bulk laser damage threshold of lithium triborate (LiB3O5) single crystals were determined to be 45.0 GW/cm2 at 1.064 μm, 1.1 ns pulse width. The damage threshold was dependent on pulse duration and wavelength: at 1.064 μm, 25 ns the damage threshold was 11.2 GW/cm2, at 0.532 μm, 1.0 ns the damage threshold was 26 GW/cm2; and at 0.355 μm, 0.9 ns the damage threshold was 21.9 GW/cm2. To the best of our knowledge this is the highest value reported among inorganic frequency conversion crystals, and approximately 1.8 times higher than that of fused silica.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

High modulation efficiency of intracavity contacted vertical cavity lasers

J. W. Scott, B. J. Thibeault, C. J. Mahon, L. A. Coldren, and F. H. Peters

Appl. Phys. Lett. 65, 1483 (1994); http://dx.doi.org/10.1063/1.112019 (3 pages) | Cited 24 times

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A very high current modulation efficiency of 5.7 GHz/√(mA) has been demonstrated in a low threshold (0.85 mA) InGaAs vertical‐cavity surface‐emitting laser. These top surface emission devices have been fabricated with intracavity contacts on semi‐insulating substrates to realize their high speed potential. Data is presented for various laser diameters. Modulation bandwidths up to 9.3 GHz at a bias of only 4.5 mA have been measured for 7 μm diameter lasers. Derived parameters indicate that considerably higher bandwidths should be possible with better heat dissipation and modified cavity designs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Carrier relaxation in InGaAs heterostructures

G. Sucha, S. R. Bolton, D. S. Chemla, D. L. Sivco, and A. Y. Cho

Appl. Phys. Lett. 65, 1486 (1994); http://dx.doi.org/10.1063/1.112020 (3 pages) | Cited 5 times

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We present time‐resolved measurements of carrier dynamics in bulk and quantum wells InGaAs, using differential absorption spectroscopy. We find that the carrier thermalization time is 200–300 fs regardless of layer width for sample thickness ranging from 100 to 6000 Å. The efficiency of screening relative to phase space filling is larger in the bulk than in the quantum wells.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.47.-p Spectroscopy of solid state dynamics

Thermal control of near‐infrared and visible electroluminescence in alkyl‐phenyl substituted polythiophenes

M. Berggren, G. Gustafsson, O. Inganäs, M. R. Andersson, O. Wennerström, and T. Hjertberg

Appl. Phys. Lett. 65, 1489 (1994); http://dx.doi.org/10.1063/1.112021 (3 pages) | Cited 36 times

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We report electroluminescence from a regioregular alkyl‐phenyl substituted polythiophene. The polymer film exists in two forms, giving widely different optical absorption, as well as photoluminescence and electroluminescence spectra. In the low‐bandgap form, we observe high emission intensity centered at 1.55 eV (800 nm), well into the infrared, while the high‐bandgap form gives a maximum at 1.85 eV (670 nm). The conversion from the high‐bandgap form to the low‐bandgap form can be done by thermal treatment of the polymer light emitting diodes.
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78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
85.60.Jb Light-emitting devices

A nonmechanical laser scanner based on electron‐beam pumped AlGaInP‐GaInP semiconductor structures

Hugo J. Cornelissen, C. J. Savert, M. J. H. Niesten, G. A. H. M. Vrijssen, A. Valster, and C. J. van der Poel

Appl. Phys. Lett. 65, 1492 (1994); http://dx.doi.org/10.1063/1.112022 (3 pages) | Cited 2 times

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An AlGaInP‐GaInP strained‐layer quantum well laser structure emitting at 670 nm is pumped by a 7–20 keV scanning electron beam. At room temperature, a threshold power density as low as 57 W/mm2 is obtained, which is only 3.8× the value for diode laser operation. More than 250 points are resolved on a 5 mm bar. They are scanned at a speed of 1000 m/s at an output level of 20 mW.
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42.79.Ls Scanners, image intensifiers, and image converters
42.55.Px Semiconductor lasers; laser diodes

Optical clarity and waveguide performance of thin film perovskites on MgO

F. J. Walker, R. A. McKee, Huan‐wun Yen, and D. E. Zelmon

Appl. Phys. Lett. 65, 1495 (1994); http://dx.doi.org/10.1063/1.112023 (3 pages) | Cited 34 times

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The optical clarity of a new class of thin film waveguides, epitaxial perovskites on MgO, has been characterized and found to have optical clarity comparable to in‐diffused waveguide structures typically represented by Ti drifted LiNbO3. For the simplest member within this new class, SrTiO3, measurements of the wavelength dependence of optical loss show a monotonic decrease with increasing wavelength between 475 and 705 nm, reaching a value of 1 dB/cm at 705 nm.
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42.82.Et Waveguides, couplers, and arrays

Simultaneous scanning tunneling microscope and collection mode scanning near‐field optical microscope using gold coated optical fiber probes

M. Garcia‐Parajo, E. Cambril, and Y. Chen

Appl. Phys. Lett. 65, 1498 (1994); http://dx.doi.org/10.1063/1.112024 (3 pages) | Cited 18 times

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Simultaneous scanning tunneling microscope (STM) and collection mode scanning near‐field optical microscope (SNOM) images using tunneling regulation are presented. The images were obtained using a gold coated single optical fiber as both a tunneling and near‐field optical probe. The method counts on the reliable STM distance regulation and the short separation between tip and sample (<1 nm). Using optimized fiber probes, both STM and SNOM images show good resolution and image contrast. We describe the STM/SNOM system and present the first images obtained in the collection mode with calibration samples of gratings of period down to 200 nm.
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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
07.60.Pb Conventional optical microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)

Study of diffusion and trapping of a fluorinated hydrocarbon in ion beam irradiated poly(styrene) by nuclear resonance reaction analysis

Kenji Umezawa, Shigemitu Nakanishi, Walter M. Gibson, Harry L. Frisch, and Akira Kitamura

Appl. Phys. Lett. 65, 1501 (1994); http://dx.doi.org/10.1063/1.112025 (3 pages)

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The swelling of a poly(styrene) (PS) glass by sorption of a fluorinated hydrocarbon, 3,5‐bis (trifluoromethyl) aniline (TFMA) is considered in a regime characterized by so called case II diffusion. Attention is focused on diffusion and trapping of vapor into ion beam irradiated glassy PS by using nuclear resonance reaction analysis. The diffusion coefficient for the TFMA is dramatically decreased on irradiation with a 30 keV H+ with 5×1013–1×1014 atoms/cm2 at 22.5 °C. These ion beam irradiation effects are similar to temperature effects on diffusion. As an application of the observed effect, trapping the TFMA was carried out between two different ion beam irradiation regions into PS at room temperature. This feature may allow development of new kinds of devices for applications.
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61.72.up Other materials
61.80.Jh Ion radiation effects
66.30.J- Diffusion of impurities

Diffuse x‐ray scattering from p+ porous silicon by triple axis diffractometry

E. Koppensteiner, A. Schuh, G. Bauer, V. Holy, D. Bellet, and G. Dolino

Appl. Phys. Lett. 65, 1504 (1994); http://dx.doi.org/10.1063/1.112026 (3 pages) | Cited 13 times

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Strain and microstructure of porous silicon on (001) wafers with different porosity were investigated by triple axis x‐ray diffractometry using an instrumental resolution of 12 arcsec. The Bragg diffraction peaks arising from the porous Si contain information both on the mean strain (1.29–2.95×10−3) and on strain gradients (0.70–1.42×10−3) in these samples. In specimens with a porosity of 60% the pores are shown to be elongated over about 200 nm along the [001] direction, and over 50 nm in directions parallel to the growth plane. It is demonstrated that the correlation function for the pores has an extension along the [001] direction which is about a factor of 4 larger than along the [010] direction. From measurements of the intensity distribution of diffuse x‐ray scattering a crystallographical damage in the silicon skeleton can be excluded. Regions of the porous layer near the interface to air are shown to be tensilely strained both along and perpendicular to the substrate normal.
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61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
81.05.Rm Porous materials; granular materials
81.65.-b Surface treatments
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Femtosecond laser excitation of the semiconductor‐metal phase transition in VO2

Michael F. Becker, A. Bruce Buckman, Rodger M. Walser, Thierry Lépine, Patrick Georges, and Alain Brun

Appl. Phys. Lett. 65, 1507 (1994); http://dx.doi.org/10.1063/1.112974 (3 pages) | Cited 50 times

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We have measured the subpicosecond optical response of a solid‐state, semiconductor‐to‐metal phase transition excited by femtosecond laser pulses. We have determined the dynamic response of the complex refractive index of VO2 thin films by making pump‐probe optical transmission and reflection measurements at 780 nm. The phase transition was found to be largely prompt with the optical properties of the high‐temperature metallic state being attained within 5 ps. The ultrafast change in complex refractive index enables ultrafast optical switching devices in VO2.
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78.47.-p Spectroscopy of solid state dynamics
78.66.Li Other semiconductors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
71.30.+h Metal-insulator transitions and other electronic transitions

Novel ablation of fused quartz by preirradiation of vacuum‐ultraviolet laser beams followed by fourth harmonics irradiation of Nd:YAG laser

K. Sugioka, S. Wada, H. Tashiro, K. Toyoda, and A. Nakamura

Appl. Phys. Lett. 65, 1510 (1994); http://dx.doi.org/10.1063/1.112027 (3 pages) | Cited 14 times

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Preirradiation using vacuum‐ultraviolet (VUV) beams of anti‐Stokes stimulated Raman scattering VUV laser, followed by the fundamental beam (266 nm) irradiation, provides a novel scheme for fused quartz ablation. The preirradiation of 5th‐ (171 nm) or 6th‐ (160 nm) order anti‐Stokes beams realizes significant ablation with the succeeding fundamental beam irradiation of a laser fluence less than the ablation threshold. X‐ray photoelectron spectroscopy analysis reveals that SiOx(x < 2) is created in the fused quartz by photolysis using the anti‐Stokes beams. Each effect of the preirradiation and the succeeding fundamental beam irradiation in the ablation process is discussed.
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81.05.Kf Glasses (including metallic glasses)
81.65.-b Surface treatments
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Dense random packing formation of gold cluster‐based film characterized by scanning tunneling microscope

J. X. Ma, M. Han, H. Q. Zhang, Y. C. Gong, and G. H. Wang

Appl. Phys. Lett. 65, 1513 (1994); http://dx.doi.org/10.1063/1.112028 (3 pages) | Cited 2 times

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Gold films prepared by neutral gold cluster deposition on the HF‐treated Si(111) surface in a static argon atmosphere of 50 Pa have been characterized by scanning tunneling microscope in air at room temperature. Our studies demonstrate that the gold film is just the stacking up of clusters formed in the static argon atmosphere and shows dense random packing formation of clusters. The structure of the gold cluster‐based nanophase film is very compact and stable.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
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

Finite‐element modeling of stress distribution and migration in interconnecting studs of a three‐dimensional multilevel device structure

L. T. Shi and K. N. Tu

Appl. Phys. Lett. 65, 1516 (1994); http://dx.doi.org/10.1063/1.112029 (3 pages) | Cited 11 times

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A finite‐element method taking into account plasticity and temperature‐dependent properties of materials was used to calculate the stress distribution in interconnecting studs of a three‐dimensional multilevel device structure. A good correlation between the calculated locations of stress concentration and the experimentally observed failure sites was obtained. On the basis of this, the failure mechanisms associated with different stress components were inferred. In addition, the calculated locations of stress concentration were found to migrate as temperature changed. The phenomenon was also observed experimentally.
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62.20.-x Mechanical properties of solids
66.30.Lw Diffusion of other defects
85.40.Ls Metallization, contacts, interconnects; device isolation

Approach of selective nucleation and epitaxy of diamond films on Si(100)

X. Jiang, E. Boettger, M. Paul, and C.‐P. Klages

Appl. Phys. Lett. 65, 1519 (1994); http://dx.doi.org/10.1063/1.112030 (3 pages) | Cited 25 times

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Heteroepitaxial diamond films were selectively nucleated and grown on mirror‐polished single crystalline (100) silicon by microwave plasma assisted chemical vapor deposition (MWCVD). The silicon substrates were coated by 0.5 μm thick SiO2 films patterned by a standard photolithography process. The selective nucleation was performed under a negative substrate bias condition. Results show that fine patterns of (100) oriented diamond films can be obtained with high deposition selectivity and fine‐line definition. In spite of the relatively large crystal size a structure edge roughness of <0.3 μm was achieved.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Preparation of Pb(Zr,Ti)O3 thin films on electrodes including IrO2

Takashi Nakamura, Yuichi Nakao, Akira Kamisawa, and Hidemi Takasu

Appl. Phys. Lett. 65, 1522 (1994); http://dx.doi.org/10.1063/1.112031 (3 pages) | Cited 153 times

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The development of ferroelectric memory devices requires an improvement of the fatigue properties of ferroelectric thin films. Pb(Zr,Ti)O3(PZT) thin films obtained by the sol‐gel method on Pt/Ti electrodes have reduced residual polarization by continuous polarization reverses about of 108 cycles. The electric characteristics such as fatigue properties have mostly depended on electrode materials. We propose Ir, IrO2, and these layer films as electrode materials and evaluate electric characteristics of PZT thin film capacitors. PZT thin films using Ir/IrO2 and Pt/IrO2 electrodes show no fatigue up to 1012 cycles of ±5 V switching pulses. Moreover, good properties of PZT capacitors, not only on SiO2 but also on polycrystalline silicon, were obtained by using IrO2.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
73.40.Rw Metal-insulator-metal structures
77.80.Fm Switching phenomena

Leakage current behaviors in rapid thermal annealed Bi4Ti3O12 thin films

H.‐J. Cho, W. Jo, and T. W. Noh

Appl. Phys. Lett. 65, 1525 (1994); http://dx.doi.org/10.1063/1.112032 (3 pages) | Cited 31 times

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Bi4Ti3O12 thin films have been grown on indium‐tin‐oxide coated glass by pulsed laser deposition. Films are rapidly thermal annealed at 650 °C in three kinds of atmospheres such as O2, N2, and air. The annealing atmosphere is found to be an important growth parameter which determines the crystallization, microstructures, and the leakage current behaviors. The film annealed in oxygen has a columnar grain structure with an amorphous phase, and its leakage current behavior is in agreement with the prediction of the space‐charge‐limited conduction model. The film annealed in nitrogen has polycrystalline porous structure, and its high field conduction is well explained by the thermoionic emission model, called the Poole–Frenkel emission. On the other hand, the film annealed in air has both the columnar and porous structures, and its electrical behavior shows characteristics of both models.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology

Atomic force microscopy study of uv‐induced anisotropy in hydrogen‐loaded germanosilicate fibers

D. Inniss, Q. Zhong, A. M. Vengsarkar, W. A. Reed, S. G. Kosinski, and P. J. Lemaire

Appl. Phys. Lett. 65, 1528 (1994); http://dx.doi.org/10.1063/1.112033 (3 pages) | Cited 8 times

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Thermally treated and uv‐exposed hydrogen‐loaded germanosilicate fibers are profiled with an atomic force microscope after cleaving the fiber in the exposed region and etching the cleaved endface in hydrofluoric acid. Thermally treated fibers etch symmetrically throughout the core region, but the uv‐exposed fibers etch differently. In the uv‐exposed fibers, both the etch depth and the refractive index are asymmetric. They are highest at the core‐cladding interface on the side exposed to the uv radiation. We propose that a photolytic process increases the refractive index across the entire core, but the asymmetry is the result of transient heating due to uv absorption. Furthermore, we demonstrate that uniform circumferential exposure symmetrizes the etch depth and refractive index change and reduces the induced birefringence.
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42.81.-i Fiber optics
42.70.Ce Glasses, quartz
81.40.Tv Optical and dielectric properties related to treatment conditions

Novel absorption line shape induced by Tamm states in a finite‐length GaAs/AlGaAs superlattice

Roger H. Yu

Appl. Phys. Lett. 65, 1531 (1994); http://dx.doi.org/10.1063/1.112950 (3 pages) | Cited 5 times

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The absorption coefficient of a finite‐length GaAs/AlGaAs superlattice is calculated using the density‐density response function χ(q∥,ω;z,z′). The surface localized Tamm states yield an extra peak in the spectrum. The Coulomb interaction among the electrons shifts the resonant energy upward, changes the line shape, and leaves a weak but well‐defined structure behind.
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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

Femtosecond wave mixing experiments in ZnCdSe/ZnSe quantum wells

D. S. Kim, A. J. Fischer, J. Hays, W. Shan, J. J. Song, D. B. Eason, J. Ren, and J. F. Schetzina

Appl. Phys. Lett. 65, 1534 (1994); http://dx.doi.org/10.1063/1.112034 (3 pages) | Cited 5 times

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Extreme high order nonlinear diffracted signals are found in ZnCdSe/ZnSe quantum wells in two beam, self‐diffraction geometry. Diffracted signals of all observed orders are shown to originate predominantly from excitonic resonances. Using four‐wave mixing, an indication of hole‐longitudinal optical phonon scattering between the heavy and the light hole states is found, and exciton‐phonon interaction is studied.
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78.47.-p Spectroscopy of solid state dynamics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.Hf II-VI semiconductors

Origin of the green/blue luminescence from nanocrystalline silicon

Hideki Tamura, Markus Rückschloss, Thomas Wirschem, and Stan Vepřek

Appl. Phys. Lett. 65, 1537 (1994); http://dx.doi.org/10.1063/1.112035 (3 pages) | Cited 94 times

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It is shown that the green/blue luminescence which is found in oxidized nanocrystalline and ‘‘porous’’ silicon is associated with the presence of OH groups adsorbed on structural defects in the SiO2 network.
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78.55.Hx Other solid inorganic materials
81.65.-b Surface treatments

Field‐induced broadening of optical absorption in InP‐based quantum wells with strong and weak quantum confinement

Takayuki Yamanaka, Koichi Wakita, and Kiyoyuki Yokoyama

Appl. Phys. Lett. 65, 1540 (1994); http://dx.doi.org/10.1063/1.112036 (3 pages) | Cited 22 times

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We have studied in detail the field‐induced broadening of optical absorption in InP‐based quantum well (QW) structures with both strong and weak quantum confinement. Electroabsorption process in the QW structures with the weak confinement is modeled taking both excitonic absorption and subband‐to‐subband absorption into account. It is theoretically shown that the spectral broadening associated with the applied electric fields is largely due to the quantum confinement of the barrier structures. In the InP‐based QW structures absorption spectra, calculated assuming their broadening is due solely to carrier tunneling, successfully explain the measured photocurrent spectra.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Gk Tunneling

Strain relaxation in InAlSb epilayers grown on InSb substrates

P. Maigné, D. J. Lockwood, and J. B. Webb

Appl. Phys. Lett. 65, 1543 (1994); http://dx.doi.org/10.1063/1.112037 (3 pages)

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We report a structural study of partially relaxed, 0.1‐μm‐thick, In1−xAlxSb (0.15<x<0.64) layers grown by magnetron sputter epitaxy on (100) InSb substrates. X‐ray diffraction has been used to measure the extent of strain relief as a function of the Al composition and the results have been compared to the well studied InGaAs/GaAs system. The experimental critical layer thickness is at least five times larger than the critical layer thickness predicted by the mechanical equilibrium model. In addition, a linear relationship was found between the percentage of strain relieved and the normalized thickness of the layers, which suggests that the strain relaxation mechanisms are different for the InAlSb/InSb system. Finally, epitaxial tilting and anisotropy in strain relaxation along 〈011〉 directions, as usually found in III‐V heterostructures, have not been observed in these layers.
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68.55.-a Thin film structure and morphology

Consequences of the silicon donor distribution tail in δ‐doped, pseudomorphic AlxGa1−xAs/In1−yGa1−yAs modulation‐doped heterostructures

A. P. Young, Jianhui Chen, and H. H. Wieder

Appl. Phys. Lett. 65, 1546 (1994); http://dx.doi.org/10.1063/1.112939 (3 pages) | Cited 4 times

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We have investigated the properties of modulation‐doped, pseudomorphic AlxGa1−xAs/ InyGa1−yAs heterostructures containing embedded, Si δ‐doped GaAs wells. From resistivity and Hall effect measurements, and from Shubnikov–de Haas measurements at 1.6 K, we have determined the charge transport parameters before and after optically induced ionization of the DX centers in the structures. We find a DX center diffusion tail associated with the δ‐doped donors extending into the undoped AlxGa1−xAs barrier and spacer layers and conclude that for efficient modulation doping of a quantum well, δ‐doping and embedding of the donors within a GaAs well can reduce but not entirely eliminate the effects of DX centers on the charge transport parameters.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Crystallization at initial stage of low‐temperature polycrystalline silicon growth using ZnS buffer layer with 〈111〉 preferred orientation

T. Matsumoto, Y. Nagahiro, Y. Nasu, K. Oki, and M. Okabe

Appl. Phys. Lett. 65, 1549 (1994); http://dx.doi.org/10.1063/1.112940 (3 pages) | Cited 5 times

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We developed a low‐temperature growth technique for polycrystalline silicon (poly‐Si). When Si is deposited on glass substrates at 450 °C, it crystallizes as thickness increases, but 10‐nm‐thick layers of Si are mainly amorphous. Use of a ZnS buffer layer with 〈111〉 preferred orientation facilities crystallization of Si during the initial growth stages. The preferred orientation of poly‐Si on glass substrates is 〈110〉, while that of poly‐Si on the ZnS buffer layer is 〈111〉. This is probably due to local epitaxial growth on polycrystalline ZnS grains with 〈111〉 preferred orientation. Raman spectroscopy showed that the ZnS buffer layer significantly improved the crystallinity of 25‐nm‐thick Si layers.  
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
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