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30 Nov 1992

Volume 61, Issue 22, pp. 2633-2728

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Laminated polarization splitter with a large split angle

T. Sato, K. Shiraishi, K. Tsuchida, and S. Kawakami

Appl. Phys. Lett. 61, 2633 (1992); http://dx.doi.org/10.1063/1.108484 (2 pages) | Cited 11 times

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A new spatial walk‐off polarizer with a large polarization‐splitting angle is fabricated. The polarizer, which utilizes artificial anisotropic dielectrics, is composed of layers of periodically laminated a‐Si:H/SiO2 thin films. The thickness of each layer is 67 nm, while the total number of the layers amounts to 1440. The measured polarization‐splitting angle is 15.5° at λ=1.55 μm, which is 2.7 times larger than that of existing polarizers.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Fm Reflectors, beam splitters, and deflectors

Visible to UV up‐conversion in Er3+ doped cadmium chloride and zinc chloride glasses

Ali Gharavi and Gary L. McPherson

Appl. Phys. Lett. 61, 2635 (1992); http://dx.doi.org/10.1063/1.108118 (3 pages) | Cited 23 times

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Up‐conversion luminescence in the UV has been observed in Er3+ doped cadmium chloride and zinc chloride glasses (Cd0.5Ba0.3K0.2Cl1.8 and Zn0.5K0.5Cl1.5) when the 4S3/2(E) excited state is pumped by pulsed laser between 545 and 555 nm. The principal up‐conversion emissions arise from the 4G9/2(T), 4G11/2(L), and 2H9/2(K) excited states at 36 200, 26 000, and 24 300 cm−1, respectively. The main up‐conversion process is the sequential two‐photon absorption at a single Er3+ ion to populate the 4G9/2(T) state. At excitation intensities of roughly 1018 photons/cm2 the UV emissions from the cadmium chloride glass are remarkably strong, approaching 5% of the intensity of the visible emission from the directly pumped state. The up‐conversion luminescence from the zinc chloride glass is detectable but very weak. The emission from the 4G9/2(T) state decays nonexponentially over roughly 200 μs in the cadmium chloride glass. The 4G9/2(T) emission decays in less than 1 μs in the zinc chloride glass.
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78.55.Hx Other solid inorganic materials
78.66.Jg Amorphous semiconductors; glasses
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Ce Glasses, quartz

High power monolithically integrated diode laser, preamplifier, and coherent beam expander

S. O’Brien, D. Mehuys, D. F. Welch, R. Parke, and D. Scifres

Appl. Phys. Lett. 61, 2638 (1992); http://dx.doi.org/10.1063/1.108119 (3 pages)

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An integrated coherent beam expander utilizing a transverse leaky mode waveguide has been integrated with a single mode distributed Bragg reflector laser and a preamplifier producing powers in excess of 70 mW cw in a single spectral and spatial mode across an aperture over 100 μm wide. The far‐field pattern in the direction parallel to the plane of the p‐n junction, consists of one main lobe 0.45° wide, indicating that the beam is coherent over the full emitting aperture. The expanded beam is suitable as an injection source for an integrated broad area amplifier.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Bq Design and performance testing of integrated-optical systems

Novel electro‐optical phase modulator based on GaInAs/InP modulation‐doped quantum‐well structures

C. Thirstrup

Appl. Phys. Lett. 61, 2641 (1992); http://dx.doi.org/10.1063/1.108120 (3 pages) | Cited 2 times

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A novel electro‐optical phase modulator working at 1.55 μm is analyzed and proposed. It is shown by a numerical model that in a GaInAs/InP pn‐nin‐pn multiple‐quantum‐well waveguide structure, large optical phase modulation can be obtained at small intensity modulation and with improved performance compared to what is achieved in quantum confined Stark effect modulators of the same material system. The device proposed is based on a modulation of the quasi‐Fermi energies of the electrons in the GaInAs quantum wells. This operational principle allows GHz modulation frequencies.  
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42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

Fragmentation process induced by nanosecond laser pulses

K. Rink, G. Delacrétaz, and R. P. Salathé

Appl. Phys. Lett. 61, 2644 (1992); http://dx.doi.org/10.1063/1.108095 (3 pages) | Cited 16 times

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A fiber‐optic stress sensing technique is applied to evaluate the fragmentation mechanism induced by nanosecond laser pulses. We demonstrate that fragmentation is achieved in response to the shock induced by the laser initiated plasma expansion. This shock is followed by a second shock of similar magnitude observed some hundreds of microseconds later, which originates from the collapse of the induced cavitation bubble. The strength of this second shock is able to induce further fragmentation of the target. This is in contrast to the fragmentation process observed with microsecond pulses where the shock induced by the cavitation bubble collapse is the governing phenomenon.
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62.50.-p High-pressure effects in solids and liquids
42.62.Be Biological and medical applications
87.85.Ox Biomedical instrumentation and transducers, including micro-electro-mechanical systems (MEMS)

Long‐pulse electron‐beam generation from the back‐lighted thyratron

Rong Lin Liou, Tseng‐Yang Hsu, and Martin A. Gundersen

Appl. Phys. Lett. 61, 2647 (1992); http://dx.doi.org/10.1063/1.108096 (3 pages) | Cited 4 times

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A variable pulse‐length electron‐beam source capable of 100’s μs pulse is reported. Long‐pulse electron‐beam generation was based on the hollow cathode discharge mode of operation of the back‐lighted thyratron and achieved by the modification of circuit parameters that control the discharge. With 75 mTorr Ar and 20 kV applied voltage, the electron beam went through a transient phase before reaching a steady‐state long‐pulse generation. During the transient phase, a fast‐decaying voltage (20–2 kV) and a pulse of 2.5 A and 130 ns FWHM electron beam were observed. The self‐extracted long‐pulse electron beam has a duration ∼100 μs, energy ∼2 keV, and current density ∼10 A/cm2. The results demonstrate the feasibility of controlling the electron‐beam pulse length. The device is simple, robust, and compatible with a plasma environment.
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52.80.Hc Glow; corona
41.75.Fr Electron and positron beams
52.80.-s Electric discharges

High energy carbon ions implantation: An attempt to grow diamond inside copper

Z. H. Zhang, L. Chow, K. Paschke, N. Yu, Y. K. Tao, K. Matsuishi, R. L. Meng, P. Hor, and W. K. Chu

Appl. Phys. Lett. 61, 2650 (1992); http://dx.doi.org/10.1063/1.108097 (3 pages) | Cited 6 times

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1 MeV carbon ions were implanted into single‐crystal copper which was then annealed in argon at temperatures ranging from 350 to 750 °C. Regrowth of the radiation‐damaged copper was examined by RBS‐channeling measurements. Carbon segregation occurred on annealing at 750 °C. Prolonged annealing at 750 °C caused blistering of the copper layer over the buried carbon. After removal of the blistered copper overlayer, the previously buried carbon layer was examined by Raman scattering, showing that graphite is the dominant phase.
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61.72.up Other materials
81.15.Np Solid phase epitaxy; growth from solid phases
64.75.-g Phase equilibria

Paramagnetic centers of amorphous carbon thin films: Influence of hydrogen content and O2 permeation

M. Hoinkis, E. D. Tober, R. L. White, and M. S. Crowder

Appl. Phys. Lett. 61, 2653 (1992); http://dx.doi.org/10.1063/1.108098 (3 pages) | Cited 25 times

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Electron paramagnetic resonance (EPR) studies of sputtered amorphous hydrogenated carbon (a‐C:H) films have been conducted in several gaseous ambients, at three microwave frequencies, and as a function of film H content. Unpaired electron concentrations are found to decrease with increasing H content while EPR linewidths are shown to be a function of H content; unresolved proton hyperfine interaction is the linewidth determining factor for H content greater than 24% while conductivity is suggested to be the most significant linewidth determining factor for H content less than 24%. Furthermore, the EPR linewidth of a‐C:H films broadens in the presence of gaseous O2 and demonstrates that these films are permeable to O2 and other gases.
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76.30.Pk Conduction electrons
61.05.Qr Magnetic resonance techniques; Mössbauer spectroscopy (for structure determination only)

Elastic misfit stress relaxation in heteroepitaxial SiGe/Si mesa structures

A. Fischer and H. Richter

Appl. Phys. Lett. 61, 2656 (1992); http://dx.doi.org/10.1063/1.108099 (3 pages) | Cited 29 times

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We present a two‐dimensional analysis of the in‐plane misfit stress and its elastic relaxation in rectangular patterned heteroepitaxial SiGe structures on the Si substrate. Based on the generally acknowledged model of relaxing film stress we calculate the distribution of the misfit stress versus distance from the free surface of a mesa edge. By superposition of the isolated stress fields of the mesa edges, we obtain the biaxial misfit stress distribution in a finite heteroepitaxial SiGe mesa on silicon substrate. The formalism developed permits the determination of the variation of stress values as a function of material and size characteristics of the patterned layer‐substrate system. A main result of this letter is that the elastic misfit stress is relaxed appreciably in small square SiGe/Si mesa structures, but not in a narrow/long pattern. Furthermore, the theoretical analysis can be applied to most of the pseudomorphic and heteroepitaxial material systems of current interest.
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68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.60.Bs Mechanical and acoustical properties
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Atomic force microscopy on homoepitaxial SrTiO3 films grown under monitoring of intensity oscillation in reflection high energy electron diffraction

M. Yoshimoto, H. Ohkubo, N. Kanda, H. Koinuma, K. Horiguchi, M. Kumagai, and K. Hirai

Appl. Phys. Lett. 61, 2659 (1992); http://dx.doi.org/10.1063/1.108100 (3 pages) | Cited 22 times

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Homoepitaxial SrTiO3 film growth by laser molecular beam epitaxy (MBE) was tuned up to a level as to give not only fine streak in the reflection high energy electron diffraction (RHEED) pattern but also the intensity oscillation persisting more than 70 unit cell lengths. The films thus produced were verified to have atomically flat surfaces (root‐mean‐square roughness of 0.12 nm) and very high crystal quality (χmin of 2%) by the analyses of atomic force microscopy and the Rutherford backscattering, respectively.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Control of selectivity during chemical vapor deposition of copper from copper (I) compounds via silicon dioxide surface modification

A. Jain, J. Farkas, T. T. Kodas, K.‐M. Chi, and M. J. Hampden‐Smith

Appl. Phys. Lett. 61, 2662 (1992); http://dx.doi.org/10.1063/1.108101 (3 pages) | Cited 23 times

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The selective chemical vapor deposition of the compounds, (hfac)CuL, where hfac=1,1,1,5,5,5‐hexafluoroacetylacetonate and L=trimethylphosphine (PMe3); 1,5‐cyclooctadiene (1,5‐COD); vinyltrimethysilane (VTMS), and 2‐butyne onto W in the presence of SiO2 has been studied as a function of surface pretreatment. Cleaning the substrates with hot aqueous H2O2, followed by washing and drying resulted in blanket copper deposition (except for L=PMe3). In contrast, the nucleation of copper onto SiO2 can be controlled by reacting the SiO2 surface with chlorotrimethylsilane regardless of the nature of L. Transmission FTIR studies of (hfac) Cu(VTMS) adsorbed on a model (Cab‐O‐Sil) SiO2 surface in the presence and absence of chlorotrimethylsilane suggested that the chlorotrimethylsilane interacted with the surface hydroxl groups to reduce the number of sites at which (hfac) Cu(VTMS) can adsorb and react, therefore providing selectivity.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.40.Ls Metallization, contacts, interconnects; device isolation

Direct evidence of Er atoms occupying an interstitial site in metalorganic chemical vapor deposition‐grown GaAs:Er

Jyoji Nakata, Moriyuki Taniguchi, and Kenichiro Takahei

Appl. Phys. Lett. 61, 2665 (1992); http://dx.doi.org/10.1063/1.108102 (3 pages) | Cited 26 times

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Er doped GaAs grown by metalorganic chemical vapor deposition is studied by the Rutherford backscattering channeling method. We directly confirmed, for the first time, that Er ions occupy a somewhat displaced tetrahedral interstitial site, rather than a substitutional site, in the GaAs host. This is concluded from the observation of a remarkable peak of the doped Er ions caused by the flux peaking effect in the 〈110〉 channeling direction. Also leading to this conclusion is the fact that the ratios of the 〈111〉 and 〈100〉 channeling yields to the random yields for Er ions were larger than those for the GaAs host. Moreover, we observe peak shifts towards the higher energy region in the 〈110〉 spectra compared to the random spectra. This is due to the lower stopping power of He ions in the GaAs host in the channeling direction than in the random direction. We deduce the strikingly small stopping power ratio of the 〈110〉 to the random incidence is also discussed.
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61.72.U- Doping and impurity implantation
71.55.Eq III-V semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

New technique to dope GaAs crystals with the 111In→111Cd probe for perturbed‐angular‐correlation spectroscopy

James M. Adams, Jianming Fu, Gary L. Catchen, and D. L. Miller

Appl. Phys. Lett. 61, 2668 (1992); http://dx.doi.org/10.1063/1.108103 (3 pages) | Cited 2 times

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Perturbed‐angular‐correlation (PAC) spectroscopy is an important technique for measuring defect and dopant interactions in group IV and III‐V semiconductors. The probe of choice for most of the successful PAC experiments on semiconductors has been 111In→111Cd introduced by ion implantation. To expand the gamut of PAC experiments that can be performed on III‐V semiconductors, we have developed a simple closed‐tube, vapor‐phase‐epitaxy (VPE) technique to produce 111In‐doped GaAs single‐crystal epitaxial materials. PAC measurements on these crystals yielded nearly nonperturbed correlations that indicate that the 111In probe was incorporated substitutionally into the GaAs crystals. These correlations differ significantly from the previously reported weakly perturbed correlations that were measured on GaAs crystals implanted with 111In ions. An exploratory experiment using this VPE technique also showed that Sn can be incorporated along with 111In.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.U- Doping and impurity implantation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Electrical properties of p‐type ZnSe:N thin films

Z. Yang, K. A. Bowers, J. Ren, Y. Lansari, J. W. Cook, and J. F. Schetzina

Appl. Phys. Lett. 61, 2671 (1992); http://dx.doi.org/10.1063/1.108104 (3 pages) | Cited 17 times

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The van der Pauw Hall effect measurements from 77–350 K are reported for a series of p‐type nitrogen‐doped ZnSe thin films. Epitaxial HgSe electrodes were used as ohmic contacts in these experiments.
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73.61.Ga II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.U- Doping and impurity implantation

Low‐temperature Si/Si1−xGex/Si heterostructure growth at high Ge fractions by low‐pressure chemical vapor deposition

Reiner Schütz, Junichi Murota, Takahiro Maeda, Roland Kircher, Kuniyoshi Yokoo, and Shoichi Ono

Appl. Phys. Lett. 61, 2674 (1992); http://dx.doi.org/10.1063/1.108105 (3 pages) | Cited 4 times

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The growth of a Si/Si1−xGex/Si heterostructure at high Ge fractions was investigated by an ultraclean low‐pressure chemical vapor deposition using SiH4 and GeH4 gases in the temperature range of 450–650 °C. It was found that a lowering of the deposition temperatures of the Si1−xGex and Si capping layers is necessary with the increasing Ge fraction in order to prevent island growth of the layer during deposition. For a Ge fraction around 0.2, atomically flat surfaces and interfaces can be obtained by depositing Si1−xGex and Si capping layers at 550 °C. For higher Ge fractions, even much lower deposition temperatures are suitable, namely 450 °C for a Si0.3Ge0.7 layer and 500 °C for a Si0.5Ge0.5 layer, respectively, with a Si capping layer deposited at temperatures of 550 °C or less. Nevertheless, the degradation of the Si0.3Ge0.7 layer with the capping layer was not observed even after a wet oxidation at 700 °C.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Anomalous intense ultraviolet emission bands in the radio‐frequency glow discharges of GeH4‐fluorocarbon‐H2 mixtures

Shigeru Yagi and Noriyoshi Takahashi

Appl. Phys. Lett. 61, 2677 (1992); http://dx.doi.org/10.1063/1.108106 (3 pages) | Cited 3 times

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Anomalous intense ultraviolet emission bands in the region 320–370 nm with a maximum at 340 nm were observed in radio frequency glow discharges of CF4‐H2 mixtures containing 0.3%–1% of GeH4. The system of emission bands is prominent also in the discharges of GeH4‐C2F6‐H2 mixtures but the corresponding emission system was not observed in the discharge spectra of GeH4‐CH4‐H2 and SiH4‐CF4‐H2 mixtures. From the vibrational analysis of the bands, it was found that the emission bands almost agree with the weak emission system of GeF2, which has been tentatively assigned in earlier work as the 3B1–1A1 transition.
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52.80.Hc Glow; corona
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Residual strain analysis of InxGa1−xAs/GaAs heteroepitaxial layers

V. Krishnamoorthy, Y. W. Lin, L. Calhoun, H. L. Liu, and R. M. Park

Appl. Phys. Lett. 61, 2680 (1992); http://dx.doi.org/10.1063/1.108107 (3 pages) | Cited 33 times

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InxGa1−xAs/GaAs heteroepitaxial layers, having various compositions and thicknesses, have been analyzed using the high resolution x‐ray diffraction technique which has revealed that the residual strain in the epilayers is strongly dependent on both the epilayer composition as well as thickness. However, published theoretical models concerning residual strain in InxGa1−xAs/GaAs epilayers suggest that the extent of relaxation is independent of epilayer composition. In this letter, we present an empirical model based on our findings which can be used to accurately predict the extent of lattice relaxation in InxGa1−xAs/GaAs epilayers which includes the influence of epilayer composition.
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68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Minority hole mobility in n+GaAs

M. L. Lovejoy, M. R. Melloch, M. S. Lundstrom, and R. K. Ahrenkiel

Appl. Phys. Lett. 61, 2683 (1992); http://dx.doi.org/10.1063/1.108108 (2 pages) | Cited 10 times

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The minority hole diffusivity, or equivalently the hole mobility, was measured in n+GaAs with the zero‐field time‐of‐flight technique. The minority hole mobility was measured for the donor doping range of 1.3×1017 cm−3 to 1.8×1018 cm−3 and was found to vary from 235 to 295 cm2/V s. At the lower doping level, the minority hole mobility is comparable to the corresponding majority hole mobility, but at 1.8×1018 cm−3 the minority hole mobility was 30% higher than the majority carrier hole mobility. These results have important implications for the design of devices such as solar cells and pnp‐heterojunction bipolar transistors.
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73.61.Ey III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Effect of photoexcitation on the surface band bending in δ‐doped GaAs:Si/Al0.33Ga0.67As double heterostructures

D. Richards, J. Wagner, A. Fischer, and K. Ploog

Appl. Phys. Lett. 61, 2685 (1992); http://dx.doi.org/10.1063/1.108109 (3 pages) | Cited 6 times

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Photoluminescence spectroscopy in combination with electric‐field‐induced Raman scattering have been used to study the effect of photoexcitation on the surface electric field due to surface trap states in δ‐doped GaAs:Si/Al0.33Ga0.67As double heterostructures. Upon variation of the optical power density over four orders of magnitude a continuous reduction of the surface electric field is found for increasing cw illumination. This is evident from a decrease of the electric‐field‐induced Raman signal and from a high‐energy shift of the photoluminescence due to recombination of electrons at the δ‐doping layer with photogenerated holes localized at the topmost heterointerface. For the highest power densities of ≂103 W/cm2 the electric field at that interface becomes almost zero indicating that band bending due to surface trap states is essentially removed.  
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73.20.At Surface states, band structure, electron density of states
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.25.+i Surface conductivity and carrier phenomena
78.55.Cr III-V semiconductors

Hydride vapor phase epitaxial growth of a high quality GaN film using a ZnO buffer layer

T. Detchprohm, K. Hiramatsu, H. Amano, and I. Akasaki

Appl. Phys. Lett. 61, 2688 (1992); http://dx.doi.org/10.1063/1.108110 (3 pages) | Cited 120 times

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In hydride vapor phase epitaxial (HVPE) growth of GaN, the sputtered ZnO layer has been found to be one of the best buffer layers because of the fact that physical properties of ZnO are nearly analogous with those of GaN. With a ZnO buffer layer, the reproducibility of growing GaN single crystal by HVPE has been greatly improved. The GaN films grown by this method show excellent crystalline, electrical, and optical properties. In particular, the Hall mobility of 1920 cm2 V−1 s−1 at 120 K is the highest value that has ever been reported by HVPE.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
78.55.Hx Other solid inorganic materials

Interstitial carbon‐oxygen complex in near threshold electron irradiated silicon

K. Shinoda and E. Ohta

Appl. Phys. Lett. 61, 2691 (1992); http://dx.doi.org/10.1063/1.108111 (3 pages) | Cited 2 times

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A new electron trap at Ec‐0.06 eV is detected in n‐type silicon irradiated with 200 keV electrons at room temperature using deep‐level transient spectroscopy. The annealing behavior of this defect level shows that the level arises from an interstitial carbon‐interstitial oxygen complex that is a configurational precursor of the EPR G15 center. We propose a simple model of defect formation that is consistent with the dependence of the defect level concentration on the electron fluence.
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71.55.Ht Other nonmetals
61.80.Fe Electron and positron radiation effects
61.72.Bb Theories and models of crystal defects

Growth orientation dependence of normal incidence absorption in ellipsoidal‐valley quantum wells

H. Xie, J. Katz, and W. I. Wang

Appl. Phys. Lett. 61, 2694 (1992); http://dx.doi.org/10.1063/1.108112 (3 pages) | Cited 12 times

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We have investigated theoretically the dependence of normal incidence absorption from interconduction subband transitions on the growth direction in ellipsoidal‐valley quantum wells. Due to the effective‐mass anisotropy of electrons in the ellipsoidal valleys, normal incidence absorption is allowed in these structures when the growth direction is not collinear with the principal axes of the ellipsoidal valley which is associated with the ground state. We found that in the AlAs X‐valley system the absorption is near optimal for such low‐index orientated structures as [210] and [113] quantum wells, while in the Ga0.7Al0.3Sb L‐valley system the absorption reaches a maximum for the [110] growth direction.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors

A uniformity degradation mechanism in rapid thermal chemical vapor deposition

Mehmet C. Öztürk, Mahesh K. Sanganeria, and F. Yates Sorrell

Appl. Phys. Lett. 61, 2697 (1992); http://dx.doi.org/10.1063/1.108113 (3 pages) | Cited 6 times

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In this letter, a new physical mechanism that can significantly degrade the thickness uniformity in rapid thermal chemical vapor deposition (RTCVD) has been identified and experimentally verified using polycrystalline silicon (polysilicon) deposition on silicon dioxide. The mechanism is initiated by small temperature variations across the wafer typically caused by edge cooling or large area patterns. The amount of light absorbed in a silicon wafer is determined by the wafer absorptivity weighted by the emission spectrum of the heat lamp. The absorptivity is a strong function of the thickness and optical properties of the layers on the wafer surface. Consequently, during RTCVD, once a nonuniform deposition pattern is established, the absorptivity and hence, the temperature uniformity become strongly dependent upon the thickness uniformity. This causes the nonuniformity to increase with process time and the thickness of the deposited layer.
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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

Nondestructive detection of titanium disilicide phase transformation by picosecond ultrasonics

H.‐N. Lin, R. J. Stoner, H. J. Maris, J. M. E. Harper, C. Cabral, J.‐M. Halbout, and G. W. Rubloff

Appl. Phys. Lett. 61, 2700 (1992); http://dx.doi.org/10.1063/1.108114 (3 pages) | Cited 10 times

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We demonstrate that picosecond ultrasonics is a sensitive nondestructive probe of the formation of TiSi2 from the reaction of titanium films on silicon annealed at temperatures of 300–800 °C. From the measured change in optical reflectivity, the responses due to electronic excitation, acoustic echoes, and thermal coupling to the underlying Si are resolved. The results show significant differences in the electronic response and the ultrasonic echo pattern before and after the structural phases C49 and C54 TiSi2 are formed. The longitudinal sound velocity is measured to be (8.3±0.2)×105 cm/s for C49 TiSi2, and about 5% lower for the C54 phase.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Noise gain and operating temperature of quantum well infrared photodetectors

H. C. Liu

Appl. Phys. Lett. 61, 2703 (1992); http://dx.doi.org/10.1063/1.108115 (3 pages) | Cited 50 times

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The difference between the noise gain associated with dark current and the photoconductive gain in quantum well infrared photodetectors is discussed in light of recent experiments. The theoretical model is based on a single key parameter: the electron trapping probability. An empirical expression for the trapping probability or, alternatively, the electron escape probability is proposed. Using the dark current, the gain, the trapping probability expressions, and the device operating temperature for achieving background limited infrared performance is discussed.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.De Semiconductor-device characterization, design, and modeling
73.50.Pz Photoconduction and photovoltaic effects
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