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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Issue 5 • Date Sep 1997

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Displaying Results 1 - 25 of 49
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Nanoscale etching of GaAs surfaces in electrolytic solutions by hole injection from a scanning tunneling microscope tip

    Page(s): 1595 - 1598
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    Controllable etching of GaAs(100) has been electrochemically achieved on a nanometer scale by using a scanning tunneling microscope (STM) in acidic solutions (pH=2–3). The realized features on n-GaAs(100) surface were as small as 10 nm. We studied the dependence of the etching rate on the potentials applied to the STM tip as well as the GaAs substrate. These results indicate that the hole injection from the tip is responsible for the local etching of GaAs surfaces in electrolytes rather than local charges induced by an electric field. © 1997 American Vacuum Society. View full abstract»

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  • Effect of etch holes on the mechanical properties of polysilicon

    Page(s): 1599 - 1603
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    For large movable parts in the microelectromechanical systems, etch holes are needed to facilitate the releasing process. These etch holes obviously weaken the structure and affect its mechanical properties. New techniques and structures have been developed to measure the mechanical properties of very thin microelectromechanical systems (MEMS) materials. A dog-bone shaped tensile specimen is imposed with a uniaxial stress field and strain is directly measured on the specimen with the interferometric strain/displacement gage. This testing approach has been used to study the effect of etch holes on the mechanical properties of polysilicon thin film. The material is phosphorus doped, low pressure chemical vapor deposited polysilicon deposited at MCNC the multi-user MEMS processes. The specimen is 3.5 μm thick and 0.6 mm wide at its narrowest point. The etch holes are about 5 μm in diameter and 30 μm apart. Compared with the mechanical properties of the specimens without etch holes, the tensile strength has dropped by 50% and the Young’s modulus decreases only about 18% due to the existence of the etch holes. Finite element modeling is applied to the specimens with etch holes and in agreement with the test results. © 1997 American Vacuum Society. View full abstract»

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  • Modification of surface morphology and optoelectronic response in porous Si films by electrochemical methods

    Page(s): 1604 - 1606
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    The effect of varied H+concentration on surface morphology of porous silicon (PS) is observed by atomic force microscopy technique. A new mechanism of PS formation concerning H+ effect is proposed. The photoluminescence (PL) spectra of two typical PS samples have different responses in the short-wavelength region. Surface photovoltage spectra results imply that the short-wavelength PL band of the PS sample prepared in high H+ concentration may be related to direct band-gap transition. © 1997 American Vacuum Society. View full abstract»

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  • Visible photoluminescence of Ge nanocrystallites embedded in SiO2 thin films

    Page(s): 1607 - 1609
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    A strong photoluminescence (PL) with a peak position of ∼420 nm (2.95 eV) under exciting radiation of λ=300 nm, and two new luminescence peaks at ∼420 and 470 nm, under λ=633 nm excitation at room temperature are observed, evidently for Ge nanocrystallites embedded in SiO2 thin films (Ge–SiO2) prepared by the ion-beam sputtering technique. The studies reveal that the nanometer-size crystalline Ge have a type of face-centered-cubic structure and characteristics of direct optical transition. It is suggested that the visible PL of Ge–SiO2 thin films is not only related to the quantum size effect due to three-dimensional confinement of electrons and holes, but also closely associated with the particular microstructure of the Ge nanocrystallites. © 1997 American Vacuum Society. View full abstract»

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  • Structure and phonon density of states in nanoclusters: Molecular dynamics study for Al

    Page(s): 1610 - 1612
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    The generalized phonon density of states for Al nanoclusters was studied theoretically using molecular dynamics. By doing this anharmonic effects could be fully considered. In order to investigate the structure of the clusters we have also calculated the structure factor S(q)(Fourier transform of the pair correlation function). The calculations were done for systems consisting of 500 atoms and at several temperatures. Stable and metastable cluster states are observed: The clusters in the metastable state show a well defined peak in the structure factor S(q) which we interpret as superstructure. The appearance of the superstructure in the metastable state is accompanied by substantial change in the phonon density of states. © 1997 American Vacuum Society. View full abstract»

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  • Thermal desorption of Si clusters from Si and Si-deposited Ta surfaces

    Page(s): 1613 - 1617
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    We performed quadrupole mass spectrometry (QMS) of Si clusters that thermally desorbed from various surfaces in ultrahigh vacuum. To investigate the effect of substrate on cluster formation, different kinds of substrates were prepared: Si(100) wafers, Si(111) wafers, and Si-deposited Ta polycrystalline sheets. When Si wafers were heated at 900–1300 °C, QMS spectra showed that clusters up to Si6 sublimed from the surfaces. Both of (100) and (111) had the same activation energy for desorption of the clusters. On the contrary, QMS spectra from Si-deposited Ta at 1500 °C showed monomeric Si only. These results agree with the thermodynamic consideration that the desorption rate of each cluster is determined by its formation energy. The relation of cluster formation with the surface structure is also discussed. © 1997 American Vacuum Society. View full abstract»

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  • Nanoscale organized assembly of nanoparticulate TiO2-stearate monolayers through the Langmuir–Blodgett method

    Page(s): 1618 - 1622
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    Nanoparticulate titanium dioxide-stearate (TiO2-St) monolayer was directly obtained using TiO2 hydrosol as the subphase. The atomic force microscopy images of monolayer, show that the higher coverage were obtained through deposition on the hydrophilic Si(100) surface rather than the hydrophobic Si(100) surface. From the surface photovoltage spectra of TiO2-St monolayer, it can be followed that the photovoltage response of the n-type silicones increased by a factor of 25, and 5 times after a monolayer of TiO2-St Langmuir–Blodgett (LB) films was transferred onto hydrophobic and hydrophilic Si surface, respectively. On the contrary, the photovoltage response value is reduced by ∼40 and 5 times by the deposition of the LB monolayer in the case of the hydrophobic and hydrophilic p-type Si surface, respectively. It is considered that the enhancement of the photovoltage response may be due to the ordered electrostatic potential orientation of the Si(100)/TiO2-St/ITO heterostructures.© 1997 American Vacuum Society. View full abstract»

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  • Tensor low energy electron diffraction study for the structure of a Cr(001)-p-(1×1)-N surface

    Page(s): 1623 - 1627
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    The structure of the Cr(001)-p-(1×1)-N surface was studied by use of the tensor low energy electron diffraction (LEED) current-voltage (I–V) analysis. From the LEED diffraction pattern observed in the process of cleaning of the Cr(001) surface, N was found to form a (1×1) structure on the Cr(001) surface. Experimental I–V characteristic curves for the Cr(001)-p-(1×1)-N structure were generated by Video LEED System and these experimental results were compared with that obtained through theoretical calculations via the TLEED program to analyze surface structure. As a result, we found that N is adsorbed in the hollow site on the Cr(001) surface. The interlayer distances of dN1, d12, and d23 are found to be 0.251, 1.814, and 1.410 Å, respectively. © 1997 American Vacuum Society. View full abstract»

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  • Extraordinary growth of C60 on a GaAs(001) As-rich 2×4 surface

    Page(s): 1628 - 1632
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    We have systematically investigated, by using scanning tunneling microscopy, the adsorption and film growth of C60 on the various GaAs(001) surface phases prepared by molecular-beam epitaxy. For most phases, the C60 overlayer exhibits the usual close-packed fcc(111) configuration with its lattice constant close to that of the bulk C60 crystal. However, in the case of C60 on the As-rich 2×4 substrate, the epitaxial growth is found to be quite different and unique; C60 film takes its (110) crystalline axis; the C60 overlayer is highly strained with a lattice expansion of ∼13%, and this structure is very stable at least up to 10 ML. We will address the underlying formation mechanism of this new structure in terms of a charge transfer from the As-dangling bonds to C60s and a site-specific C60-substrate interaction, as confirmed by molecular dynamic simulations. The present system provides a unique opportunity to study fullerene and/or noble-gas related two-dimensional phenomena, and demonstrates a potential for fabrication of novel fullerene-based devices, such as strained superlattice structures. © 1997 American Vacuum Society. View full abstract»

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  • Precise force curves in air and liquid by magnetic force feedback

    Page(s): 1633 - 1636
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    We developed an atomic force microscopy with the tip position was accurately controlled through the magnetic interaction between a coil and the magnet fixed behind the cantilever. By incorporating a feedback system, we could control the motion of a soft cantilever (0.68 N/m) in air and liquid, and obtain force curves without instabilities originating from the strong attractive and adhesive forces between the tip and the sample. © 1997 American Vacuum Society. View full abstract»

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  • Possible multistranded DNA induced by acid denaturation–renaturation

    Page(s): 1637 - 1640
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    λ-DNA Hind III was denatured by HCl, renatured by NaOH, and completely digested by DNase I sequentially. The produced mixture was separated by gel filtration, and one component was obtained which showed resistance to the digestion of DNase 1. The results of atomic force microscopy (AFM) studies on this component indicated that an unusual form of DNA was presented, with the height 13 times that of double-stranded DNA. The renatured and partially digested λ-DNA Hind III was also studied by AFM, and the images revealed both the duplex DNA and the unusual DNA. By comparison with known results, it is suggested that the unusual DNA is a multistranded DNA rather than a simple supercoil. © 1997 American Vacuum Society. View full abstract»

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  • Scanning tunneling microscopy and low energy electron diffraction study of the formation of a ×R30° reconstruction on the hydrogen etched Si(111) 1×1 surface

    Page(s): 1641 - 1646
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    The Si(111) 7×7 surface is exposed at room temperature to atomic hydrogen and studied with scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) in ultrahigh vacuum. For increasing exposures, the LEED pattern of the surface changes in well defined steps to a 1×1 pattern. The STM images of the 1×1 surface appear rough and disordered. The 1×1 pattern and rough surface are consistent with an etching of several surface layers by the atomic hydrogen. Heating the 1×1 surface to 560 °C and cooling to room temperature produces a surface with a ×R30° LEED pattern. The STM images of this surface are consistent with a distribution of adatoms on an ideal Si(111) surface. Further heating results in a 7×7 surface. © 1997 American Vacuum Society. View full abstract»

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  • Frequency modulation detection high vacuum scanning force microscope with a self-oscillating piezoelectric cantilever

    Page(s): 1647 - 1651
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    This article attempts to describe a novel high vacuum scanning force microscope (HV-SFM) using a self-oscillating piezoelectric cantilever in frequency modulation (FM) mode. Since no external deflection sensor or external vibrator is needed, the new HV-SFM is very simple and easy to handle in vacuum conditions in comparison with conventional systems using optical sensors. FM detection is used to detect the force gradient acting on the end of the piezoelectric cantilever because it gives higher response speed in vacuum conditions compared to the commonly used slope detection. The unimorph cantilever consists of a 1.0 μm thick Pb(Ti,Zr)O3 (PZT) layer on a SiO2 elastic base, which becomes self-oscillating when an ac voltage is applied to the piezoelectric layer. The 160 μm long piezoelectric cantilever has successfully been oscillated at its natural resonance frequency of 117 kHz by connecting its piezoelectric layer directly into the FM loop, which applies positive feedback to the piezoelectric charge current caused by cantilever vibration. The shift in oscillation frequency of the FM loop, or the shift of cantilever resonance frequency due to force gradient acting on the cantilever end, is measured as a SFM feedback signal. At a frequency shift of 80 Hz, the force gradient and the force acting on the cantilever tip were calculated as 0.012 N/m and 0.02 nN, respectively, from an obtained force curve. At that set point, high-resolution images of a gold film have been obtained. The constructed FM detection noncontact SFM with a self-oscillating PZT cantilever has proven to be stable and easy to handle in vacuum conditions. © 1997 American Vacuum Society. View full abstract»

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  • Atomic force microscopy studies of Hg1-xCdxTe thin films grown by isothermal vapor phase epitaxy

    Page(s): 1652 - 1656
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    Atomic force microscopy measurements have been performed in order to study mercury cadmium telluride thin films grown on hybrid substrates by means of a new method based on an isothermal vapor phase epitaxy process (iso-VPE). The morphology of the samples, grown both on sapphire and on silicon 2 in. substrates, was observed at the different steps of the iso-VPE process. In the case of the silicon substrate the absence of interdiffusion with the deposited film was detected by means of a cross sectional atomic force microscopy analysis of the sample. Moreover, the surface quality of the iso-VPE grown thin films has been found to be comparable with that of samples grown on hybrid substrates by means of conventional techniques like liquid phase epitaxy. Fourier-transform infrared measurements were also performed in order to prove the high optical goodness of the samples. © 1997 American Vacuum Society. View full abstract»

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  • Ga focused-ion-beam shallow-implanted quantum wires

    Page(s): 1657 - 1660
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    Quantum wires were fabricated by shallow implantation of Ga ions from a focused-ion-beam source into a modulation-doped AlxGa1-xAs/GaAs heterostructure. This type of implantation reduces crystal damage and keeps the implanted ions away from the two-dimensional electron gas. An electron mobility as high as 5.04×105cm2/V s was obtained for 10-μm-long wires with an effective width of 0.152 μm, which is much higher than any previously reported values. The electron ballistic lengths in the wires were determined from measurements of the bend and transfer resistance and agreed well with the calculated elastic mean free paths. The transfer resistance versus magnetic field profiles exhibited electron focusing peaks associated with good specularity at the boundary. © 1997 American Vacuum Society. View full abstract»

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  • Improved cold electron emission characteristics of electroluminescent porous silicon diodes

    Page(s): 1661 - 1665
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    The property of electroluminescent porous silicon (PS) diodes as surface-emitting cold cathodes were investigated. The experimental PS diodes consist of thin Au films, PS, n+-type Si substrates, and ohmic back contacts. When a positive bias voltage VPS is applied to the Au electrode with respect to the substrate, electrons are uniformly emitted through the Au contact as well as photons. The cold electron emission characteristics are presented here in terms of the PS layer thickness dependence, effects of rapid thermal oxidation (RTO), and electroluminescence (EL) characteristics. It was demonstrated that both the decrease in the PS layer thickness (dPS) and the introduction of RTO treatment are useful for a significant improvement in the emission characteristics, and that the emission current and efficiency for a RTO-treated diode with dPS=3 μm reach 450 μA/cm2 and 0.2%, respectively, at VPS=27 V. It is also shown that in every case, the Fowler–Nordheim scheme holds in the bias voltage dependence of the emission current. The emission mechanism based on the high-field effect near the outer surface of PS layer, is discussed in relation to the visible EL emission. © 1997 American Vacuum Society. View full abstract»

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  • Nanoprotrusion model for field emission from integrated microtips

    Page(s): 1666 - 1677
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    A study of the field emission from Spindt-type metallic integrated single microtips and arrays of microtips has been carried out. Measurements of field emission patterns, I/V curves, current stability, energy distributions against both applied voltage and angle of emission, and high frequency noise were made throughout the seasoning process. These measurements show that the emitters are not conventional metal emitters but undergo an evolution that depends on their past history such as operating time and exposure to ambient gases. In particular, the energy distributions showed three distinct behaviors; (1) a large and even dominating part of the total emission current could come from low-energy secondary electrons generated by collisions of the emitted electrons with the grid, particularly in the beginning of the seasoning process. After seasoning, the electrons were predominantly emitted from either, (2) multiple discrete bands nearer to the Fermi level that displace with applied voltage, or, (3) from the standard conduction band at the Fermi level. This invalidates the strict use of simple Fowler–Nordheim theory for analyzing the field emission from these emitters. A model based essentially on the field emission from nanoprotrusions all along the surface of the conical shank of the deposited tip is proposed which is consistent with all the experimental results. The spatial distribution of the noncontrolled nanoprotrusions evolves from the shanks to the microtip apex regions during the seasoning process. © 1997 American Vacuum Society. View full abstract»

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  • Electron emission from the pyramidal-shaped diamond after hydrogen and oxygen surface treatments

    Page(s): 1678 - 1681
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    The emission properties of the pyramidal-shaped diamond after hydrogen and oxygen surface treatments were discussed. There was a shift in C1s binding energy peak in the x-ray photoelectron spectrum due to the surface treatments. The lowest turn-on voltage in the emission current versus anode voltage characteristics is observed after the hydrogen treatment. The emission barrier height ratios against the as-prepared surface are found to be 0.68 for hydrogen treated and 2.1 for oxygen treated surfaces, respectively, from the slopes of the Fowler–Nordheim characteristics. The change in the barrier height is speculated to be explained by the dipole formed at the diamond surface. The emission stability is also confirmed, and this remarkable feature was obtained for a hydrogen-treated surface. © 1997 American Vacuum Society. View full abstract»

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  • Technique for fabricating self-aligned gates onto silicon field emitter arrays

    Page(s): 1682 - 1684
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    A technique for fabricating self-aligned gate structures onto pre-existing silicon field emitter arrays is introduced in detail in this article. The gate-controlled field emission characteristics of the resulting devices are also described. © 1997 American Vacuum Society. View full abstract»

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  • Growth mechanism of planar-type GaAs nanowhiskers

    Page(s): 1685 - 1687
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    The mechanism for the lateral growth of ultrathin GaAs whiskers is discussed in connection with the vapor–liquid–solid growth model. The observed growth rate shows that the migration of the source material plays an essential role in such whisker growth. © 1997 American Vacuum Society. View full abstract»

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  • Fabrication of one-dimensional nanowire structures utilizing crystallographic orientation in silicon and their conductance characteristics

    Page(s): 1688 - 1696
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    We propose a process for fabricating one-dimensional Si nanowires with a point contact. The nanowire structure can be easily obtained through two steps: KOH etching of a {110} Si layer of a silicon on insulator substrate and sufficient oxidation of the Si patterns formed by etching. In the etching process, vertical sidewalls comprised of {111} planes are formed into a wire. In addition, other {111} planes, projecting obliquely along the vertical sidewalls, spontaneously appear in the etched substrate. This is due to the fact that the etching proceeds as {111} planes appear because the etch rate of the {111} plane is the lowest of all planes. The bottom-corner region of two inclined {111} planes becomes a point-contact structure by making the distance between two inclined planes appropriate. The oxidation process converts the two-dimensional wire into one-dimensional nanowire by the stress-dependent oxidation phenomena of the Si wire. Consequently, a Si nanowire with a point contact can be formed in the bottom region. The Si nanowires fabricated through this process show clear conductance steps with little fluctuation on plateaus at 45 K. In addition, we discuss the conductance step characteristics in connection with a calculated energy level for a nanowire in (110) Si. © 1997 American Vacuum Society. View full abstract»

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  • Cyclotron resonance in asymmetric modulation-doped field-effect transistor heterostructures using InxGa1-xAs quantum well and InAs–GaAs superlattice channels

    Page(s): 1697 - 1702
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    Cyclotron resonance and photoluminescence measurements were carried out on two types of modulation-doped field-effect transistor heterostructures whose channels were made of an InAs–GaAs short-period superlattice and of an InxGa1-xAs quantum well, respectively. From cyclotron resonance data a linear dependence of the channel electron effective mass on indium content was obtained for both series of samples. For a given mean value of the indium content in the channel, the effective mass is found to be systematically higher in samples where the channel is based on a short-period superlattice rather than on an alloy-based channel. This can be attributed to larger nonparabolic effects in the former. Calculations of nonparabolicity corrections are in agreement with these results. In our theoretical model, the energy of the electron and heavy hole levels were determined self-consistently. © 1997 American Vacuum Society. View full abstract»

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  • High quality interfaces in GaAs–AlAs quantum wells determined from high resolution photoluminescence

    Page(s): 1703 - 1706
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    High resolution photoluminescence (PL) measurements performed on several GaAs–AlAs quantum well structures revealed sharp excitonic transitions separated in energies corresponding to roughly half-monolayer fluctuations in well size. The narrow linewidths correlate with interface island structure whose lateral extent is either much larger or much smaller than the exciton diameter. The half-monolayer separation results from a sharply peaked PL intensity response occurring around those areas of the laterally nonuniform interface which have roughly 50% island coverage, with the average island size much smaller than the exciton diameter, about 225 Å. © 1997 American Vacuum Society. View full abstract»

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  • Role of atomic hydrogen in argon plasma-assisted epitaxy of InGaAsP/InP

    Page(s): 1707 - 1714
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    Epitaxial layers of InP and InGaAsP have been grown on (100) InP substrates by gas source molecular beam epitaxy over the temperature range 400–480 °C while simultaneously exposed to an Ar plasma stream produced by electron cyclotron resonance (ECR). Transmission electron microscopy, x-ray diffraction, and photoluminescence studies indicate improved structural and optical properties of the InGaAsP layers as compared to layers grown by conventional epitaxy without plasma. This improvement is attributed to a reduction in lateral composition modulation (LCM), which develops at the surface during growth due to the existence of a miscibility gap. Comparison of these results with that achieved by an independent thermal hydrogen cracker suggests that the reduced LCM results from molecular hydrogen, produced from the cracking of the group V hydride sources, backflowing into the ECR chamber and resulting in a flux of atomic hydrogen toward the growth front. Atomic hydrogen exposure of the growing surface may then result in surfactant-mediated epitaxy, thereby, reducing the adatom surface diffusion length and, hence, the LCM. Atomic hydrogen, therefore, appears to be the sole actor in reducing the LCM, while the effects of the plasma itself are negligible. © 1997 American Vacuum Society. View full abstract»

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Aims & Scope

The Journal of Vacuum Science and Technology B is devoted to reports of original research, review articles, and Critical Review articles.

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Editor
Gary E. McGuire
International Technology Center