J. H. Neave

Imperial College London, London, ENG, United Kingdom

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Publications (120)184.15 Total impact

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    ABSTRACT: We have utilised the technique of reflectance anisotropy (RA) to study the growth of GaAs, AlAs, and InAs on (001) GaAs substrates by molecular beam epitaxy and simultaneously recorded both the RA response and the surface electron diffraction pattern obtained using (RHEED). For macroscopic coverage variations the change in the RA response in all cases appears to correlate exactly with the appearance of a new RHEED pattern. In this respect RA growth "oscillations" are observed which correlate exactly in period with the usual RHEED oscillations observed during growth and can be made to be in-phase with the RHEED oscillations by varying the RHEED collection system. In the case of InAs growth, much more subtle (ca. 0.1 monolayers) coverage variations are easily detectable by RA while the macroscopic (2×4) to (4×2) phase transition which occurs for this system at InAs coverages of ca. one monolayer produces a marked change in both the RA and RHEED response. Since all three systems were studied using the same optical excitation energy (ca. 1.92 eV) and since in all cases the change in the RA response occurred concurrently with the change in the RHEED pattern we question the currently popular theory regarding the nature of the RA response in relation to a supposed local surface dimer state resonant absorption and suggest that geometric factors or longer range surface state resonances may be of equal if not more importance.
    Surface Review and Letters 01/2012; 01(04). · 0.28 Impact Factor
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    ABSTRACT: One-dimensional disorder in a reconstructed surface can give rise to sheetlike structures in reciprocal space. For disorder caused by one-dimensional domain boundaries such as those that occur on the GaAs{100}(2 × 4) surface, sheetlike structures are only present at fractional order diffraction features. The absence of these sheets at integral diffraction features is explained using kinematic theory of diffraction and "selection rules" for these sheetlike structures are established. Applications of these rules are demonstrated using optical transmission diffraction.
    Surface Review and Letters 01/2012; 08(05). · 0.28 Impact Factor
  • D.W. Pashley, J.H. Neave, B.A. Joyce
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    ABSTRACT: In this letter we report on the formation of long-range surface disorder features during the growth by molecular beam epitaxy (MBE) of homoepitaxial GaAs (0 0 1) films having the β2(2 × 4) reconstruction. Observations were made in real-time at the growth temperature using reflection high energy electron diffraction (RHEED) and analyzed kinematically. We show that kinks (cooperative shifts of whole columns of 2 × 4 units along the [1 1 0] direction) form rapidly as growth commences and that the antiphase domain structure present on the substrate prior to growth as a result of the arrangement of As–As dimers persists. This produces a surface with two types of long-range disorder. We speculate on the role of incident Ga atoms on this process.
    Surface Science 01/2009; 603(1). · 1.87 Impact Factor
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    ABSTRACT: AlAs growth by molecular-beam epitaxy has been successfully achieved on 〈100〉-aligned mesas on GaAs (001) patterned substrates. The final ridge morphology was found to be radically different from that observed from the homoepitaxial growth of GaAs on similar substrates. The significant modification to the final ridge profile is related to the reduction of the adatom diffusion length when using Al as the group-III species. These results provide direct evidence of a growth mode modification with alteration of the group-III element from Ga to Al and have significant implications for controlling the ridge formation process and for fabrication of more complex structures.
    Journal of Applied Physics 01/2005; 97(4):044905-044905-5. · 2.21 Impact Factor
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    ABSTRACT: Gas source molecular beam epitaxy is used for the growth of SiGeC layers from disilane, germane and methylsilane precursors at low substrate temperatures. A systematic method of carbon concentration determination based on a combination of X-ray diffraction and X-ray reflectivity is examined. The grown layers were annealed using rapid thermal annealing and analysed with X-ray diffraction, X-ray reflectivity and secondary ion mass spectrometry. The recovery of compressive strain in the SiGeC layer is correlated to the loss of carbon through diffusion and indicates that the carbon atoms are incorporated substitutionally in the as-grown layers.
    Journal of Crystal Growth. 01/2005;
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    ABSTRACT: The availability of compliant substrates has opened new avenues to exploit SiGe materials for optoelectronic applications. In this paper, relevant issues including fabrication of compliant substrates through compositionally graded buffer layers, strain (stress) balance in active layer design and X-ray characterisation are discussed. Quantum cascade structures designed for light emitting devices at THz range are grown using a combination of low pressure chemical vapour deposition and gas source molecular beam epitaxy in a single growth system. The results of structural characterisation by X-ray diffraction and transmission electron microscopy show that by following stringent design criteria, active layer structures more than 4 μm thick with low threading dislocation density can be achieved. Electroluminance in the THz frequency range have been observed from these structures.
    Optical Materials 01/2005; · 1.92 Impact Factor
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    ABSTRACT: The realisation of III–V quantum cascade lasers has initiated a strong interest in developing a Si/SiGe-based quantum cascade laser over the last 3 years. Most efforts were focused on the growth of strain-balanced Si/SiGe superlattices on strain-relaxed SiGe virtual substrates. This paper discusses the progress so far and addresses some of the material issues related to the epitaxy of Si/SiGe quantum cascade structures, including strain–stress balance and production of strain-relaxed SiGe virtual substrates.
    Journal of Crystal Growth 01/2005; 278:488-494. · 1.55 Impact Factor
  • D. W. Pashley, J. H. Neave, B. A. Joyce
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    ABSTRACT: We first summarise previous work on long-range disorder effects occurring on the GaAs(001) β2(2×4) surface, as determined by reflection high energy electron diffraction (RHEED), grazing incidence X-ray diffraction and scanning tunnelling microscopy (STM). Models which have been deduced are related to the assembly of β2(2×4) and c(2×8) unit cells and involve the presence of antiphase domains and one-dimensional disorder boundaries. We ignore kinks produced by cooperative shifts of whole (2×4) units in the [110] direction, since they are only present in significant numbers on surfaces formed in the presence of a large excess of arsenic. We show from a combination of multi-azimuthal RHEED data and structure factor calculations that none of the existing models is consistent with all of the diffraction information. In particular, STM images show that the surface has a non-ideal c(2×8) structure made up of a distribution of β2(2×4) cells having equal but irregular occupancy of the two possible phase positions. The equal occupancy means that certain reflections should be forbidden, but in practice some of these appear strongly. We have suggested possible structural effects which might produce these results, such as a change in atom positions in the boundary region where two cells conjoin, so that they are no longer identical entities. We have been unable to obtain confirmation, however, since the precise atom locations are not known.
    Surface Science 01/2005; 582(1):189-201. · 1.87 Impact Factor
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    ABSTRACT: The evolution of InAs nanostructures grown by solid source molecular beam epitaxy on InP(0 0 1) substrates has been studied by atomic force microscopy (AFM), with specific emphasis on the effects of the incident V:III flux ratio. Wire structures oriented along are generally formed at moderate V:III flux ratios (˜10:1). AFM images show that the wires are generally kinked with small three-dimensional (3D) islands appearing at the kinks. Higher V:III ratios (>100:1) lead to an increase in the number of kinks and the formation of much larger 3D features. By contrast, low V:III ratios (˜2:1) favour the formation of small 3D islands (quantum dots) with densities of ˜5×1010 cm-2. The results indicate that it is possible to produce arrays of InAs/InP quantum wires or quantum dots through careful control of the growth conditions.
    Journal of Crystal Growth - J CRYST GROWTH. 01/2005; 278:131-135.
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    ABSTRACT: The growth of GaAs, AlAs and AlAs/GaAs multilayers on GaAs (001) patterned substrates has been used as a probe of the group III adatom kinetics during molecular beam epitaxy. The deposition of GaAs and AlAs films on patterned substrates is significantly different due to modification of the inter-planar adatom migration and surface diffusion. This behaviour results in contrasting growth modes and different final ridge morphologies for the alternative deposition series. It also provides a route to either tune the final ridge profile or to produce alternative ridge structure geometries for novel device applications, from the deposition of AlAs, GaAs or multilayer structures.
    Journal of Crystal Growth - J CRYST GROWTH. 01/2005; 278(1):458-463.
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    ABSTRACT: The formation of ridge structures on 〈100〉 aligned mesa stripes defined on GaAs (001) substrates has been investigated as a function of the substrate temperature, V/III flux ratio, and GaAs deposition quantity. Across the entire range of deposition conditions employed, the ridge structures were observed to form with {110} facets, indicating a similar growth mechanism in all cases. The {110} facet lengths on the ridge structures were accurately reproduced using a simple one-dimensional geometric model that included the effects of Ga adatom migration from the {110} facets to the upper ridge surface and resulting in an additional Ga flux. The results have important implications for the controlled growth of micron-scale ridge structures on patterned substrates. © 2004 American Institute of Physics.
    Journal of Applied Physics 05/2004; 95(11):6112-6118. · 2.21 Impact Factor
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    ABSTRACT: The incorporation behaviour of phosphorus (P2) during growth by molecular beam epitaxy of InP thin films on InP(0 0 1) substrates has been studied in situ by reflection high energy electron diffraction. The incorporation coefficient of P2 decreases from 0.94 at 360 °C to 0.54 at 470 °C. This behaviour is attributed to the increasing fraction of the incident P2 flux that desorbs from the surface at higher temperatures and does not contribute to layer growth. The low- and temperature-dependent incorporation coefficients imply the need for high P2:In flux ratios and low substrate temperatures for the preparation of smooth InP epitaxial layers.
    Surface Science 01/2003; 531(3). · 1.87 Impact Factor
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    ABSTRACT: The self-assembled growth of GaAs on mesa stripes with a sidewall angle of ∼65° formed on pre-patterned GaAs(001) substrates has been studied by secondary electron microscopy (SEM) and atomic force microscopy (AFM). Specific emphasis is placed on the morphological evolution and interplay of different growing facets with increasing GaAs deposition. Three facets form during the initial stages of growth (
    Semiconductor Science and Technology 01/2003; 18(11):950-954. · 1.92 Impact Factor
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    ABSTRACT: InP thin films grown by solid source molecular beam epitaxy on InP(001) substrates have been studied by atomic force microscopy (AFM). The morphology of the films is highly dependent on growth temperature and the P2:In incident flux ratio. High substrate temperatures and low flux ratios result in a large density of micron-sized, three-dimensional islands and a poor overall surface morphology. By contrast, relatively low substrate temperatures and high flux ratios lead to very smooth surfaces with a negligible defect density. The results indicate that a high incident P2 flux is required to generate a sufficient phosphorus supply for the growth of morphologically smooth InP thin films.
    Semiconductor Science and Technology 10/2002; 17(12):1209. · 1.92 Impact Factor
  • E.S Tok, J.H Neave, J Zhang
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    ABSTRACT: Examination of experimental basis of a new mechanism for “re-entrant” bahaviour in reflection high energy electron diffraction intensity oscillations during homoepitaxial growth of GaAs on the (1 1 1)A surface has shown that surface morphology continue to change periodically under all the growth conditions. The observed re-entrant behaviour under specific diffraction conditions can be explained in terms of diffraction related mechanisms without invoking change of growth mode between 2D and 3D or 2D nucleation and step propogation as suggested in the original papers. This diffraction related mechanism is based on competition between coherent and incoherent diffraction processes as a result of a change on the average island size (length scale) in comparison to the coherence length of the electron beam.
    Surface Science 08/2002; 515(1):263-265. · 1.87 Impact Factor
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    ABSTRACT: The incorporation of cube-corner mirrors into semiconductor microcavity device structures is one way of mitigating the problems of accurately growing two distributed Bragg stack reflectors involving multiple layers of different semiconductor materials. These mirrors can be achieved in-situ through growth on pre-patterned substrates, which makes use of the differences in growth mode between different crystallographic planes. Manipulation of these growth modes by altering the exposed planes on the pre-etched substrates and controlling the growth conditions leads to different sets of planes being formed by self-assembled growth. In this work, we demonstrate that the facets produced during growth by solid source MBE on pre-patterned GaAs [001] substrates formed, by standard photolithography and wet chemical etching, can be manipulated by the initial facets present.
    01/2002;
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    ABSTRACT: Reflection high-energy electron diffraction and scanning tunnelling microscopy (STM) have been used to study InAs/GaAs quantum dot (QD) formation in bilayer QD structures grown by molecular beam epitaxy on GaAs(0 0 1) substrates. For GaAs spacer layers thicknesses <200 Å, there is a reduction in the critical coverage (θcrit) required to form the second layer QDs, the change in θcrit compared with first layer growth depending on the size of the QDs in the initial layer. STM measurements of the uncapped QDs show that second layer dots grown on thick GaAs spacer layers (>200 Å) are identical to those grown in the first layer. By contrast, QD formation on a thin spacer layer (<200 Å) results in a lower density of larger QDs that nucleate preferentially on top of the mounds that dominate the morphology of the relatively thin GaAs capping layer. The introduction of an annealing step before second layer QD growth smooths the spacer layer surface morphology but has no effect on θcrit. The implication is that strain is the dominant cause of the observed variation in second layer θcrit.
    Journal of Crystal Growth 01/2002; 244(1):39-48. · 1.55 Impact Factor
  • E. S Tok, J. H Neave, J Zhang
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    ABSTRACT: Examination of experimental basis of a new mechanism for “re-entrant” bahaviour in reflection high energy electron diffraction intensity oscillations during homoepitaxial growth of GaAs on the (111)A surface has shown that surface morphology continue to change periodically under all the growth conditions. The observed re-entrant behaviour under specific diffraction conditions can be explained in terms of diffraction related mechanisms without invoking change of growth mode between 2D and 3D or 2D nucleation and step propogation as suggested in the original papers. This diffraction related mechanism is based on competition between coherent and incoherent diffraction processes as a result of a change on the average island size (length scale) in comparison to the coherence length of the electron beam.
    Surface Science - SURFACE SCI. 01/2002; 515(1):263-265.
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    ABSTRACT: Arrays of GaAs pyramids with square (001) bases of length 1–5 μm have been fabricated by molecular beam epitaxy regrowth on pre-patterned GaAs (001) substrates. The optical properties of the pyramid faces have been studied by microreflection and microtransmission imaging measurements with light (λ=900–1000 nm) incident through the pyramid base. Digitized charge coupled device images indicate that total internal reflection occurs at the {110} pyramid facets and that their reflectivities are greater than 80%, provided overgrowth of the facets does not occur. These properties suggest that such structures may be suitable as the top mirror in novel micron-scale vertical microcavity devices. © 2001 American Institute of Physics.
    Journal of Applied Physics 06/2001; 90(1):475-480. · 2.21 Impact Factor
  • P K Larsen, J H Neave, B A Joyce
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    ABSTRACT: Two prominent surface states have been observed in angular resolved photoemission measurements on reconstructed (2*4) and (4*2) GaAs (100) surfaces, which were grown in situ by molecular beam epitaxy. Changes brought about by adsorption of H2 and O2, and also by annealing, indicate the presence on each type of surface of both an As-associated and a Ga-associated surface state. It is also shown that the symmetry of the repeated surface Brillouin zone of the As-stable (2*4) reconstructed surface is observed for the As-associated surface state.
    Journal of Physics C Solid State Physics 01/2001; 12(22):L869.

Publication Stats

2k Citations
184.15 Total Impact Points

Institutions

  • 1986–2009
    • Imperial College London
      • • Department of Physics
      • • Department of Chemistry
      London, ENG, United Kingdom
  • 1996
    • Imperial Valley College
      Imperial, California, United States
  • 1990
    • University of London
      Londinium, England, United Kingdom