摘要:

The nucleation and growth of Si onto Si(100) has been studied during deposition in ultrahigh vacuum (UHV) by spot profile analysis of low‐energy electron diffraction (SPA‐LEED). The growth mode and surface atom arrangement have been determined not only by the intensity oscillation of the 00 beam during deposition but also after interruption and cooling by a detailed measurement of the energy dependence of the spot profile. We present two different new evaluation procedures to determine out of the structure factorG(0,K⊥) the layer distributions, i.e., the roughness of the surface, and deposited layers. During deposition a rough surface is always observed with a root mean square value (rms) of Δ=0.75 Å for the fist layer up to Δ=0.9 Å for the 50th layer. In contrast to Si(111), which starts growing islands with double step height (d=6.27 Å), for Si(100) it is found the minimum possible step height ofa0/4=1.36 Å for neighboring terraces, i.e., a monoatomic growth mode. The resulting terrace width distribution of the islands on the surface is a geometric distribution with an average terrace length of 16 atoms and an island density of about 6×1011per cm2at 415 °C substrate temperature.

ISSN:0734-211X    

DOI:10.1116/1.584358

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

ISSN:0734-211X    

DOI:10.1116/1.584359

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We propose a mechanism for molecular‐beam epitaxial growth on GaAs(100) and other III–V(100) surfaces which includes a detailed description of the changes in surface reconstructions throughout the growth cycle. We have previously used the electronic stability criterion which requires all arsenic dangling bonds to be filled and all gallium dangling bonds to be empty to successfully predict static surface reconstructions of III–V surfaces. In the work presented here, we use these same criteria to predict electronically stable intermediates during the growth cycle which are characterized by surface dimers and dimer vacancies. The resulting model proposes specific reconstructed electronically stable intermediates during the complete growth cycle. The model explains the retention of the (2×4) overall reconstruction throughout the cycle, provides at least one mechanism for the cyclical roughness variations observed via reflection high‐energy electron diffraction oscillations, and pinpoints certain rate limiting configurations in the process which should lead to further fruitful experimental investigations.

ISSN:0734-211X    

DOI:10.1116/1.584360

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The use of reflection high‐energy electron diffraction (RHEED) intensity oscillations to calibrate molecular‐beam epitaxy (MBE) growth rates is an accurate and widely used technique. In order to actually monitor the accumulation of layers during growth, however, the orientation of the substrate must remain fixed. This typically results in much less uniform growth than is obtained with a rotating substrate. As an alternative we have studied near‐threshold photoemission of electrons from a growing surface. Light from an ultraviolet lamp was focused through a sapphire window onto a wafer in a Varian Gen‐II MBE system. A simple biased collector plate monitored the resulting photoemission current. Small oscillations were observed in the collected current after growth of GaAs was initiated. The photoemission oscillations occurred at the same frequency at which RHEED oscillations were subsequently observed. Since no azimuthal orientation is in principle required between the wafer, light source, and collector, with further optimization, this technique may allow for layer accumulation to be monitored during growth on a rotating substrate.

ISSN:0734-211X    

DOI:10.1116/1.584361

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We report measurements of the reflectance difference (RD) of light polarized along the [110] and [1̄10]directions of a growing (001) GaAs crystal in a molecular‐beam epitaxy (MBE) chamber. Observations of RD transients occurring due to changes in surface stabilization resulting from interruption of the As beam are compared with simultaneous observations of reflection high‐energy electron diffraction intensities and are shown to give both chemical and structural information about the growing surface. Spectral dependencies of the RD data show distinct responses for Ga and Al surface coverages, suggesting optimal wavelengths and polarizations for selective modification of surface dimer bonding during growth.

ISSN:0734-211X    

DOI:10.1116/1.584362

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

ISSN:0734-211X    

DOI:10.1116/1.584363

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Reflection high‐energy electron diffraction intensity oscillations have been used to measure group III and group V controlled incorporation rates. The growth condition for measuring the incorporation rates under control of the group III flux is to have an excess of the group V flux. Conversely, the condition for measuring the incorporation rates under control of the group V arrival rate is to have an excess of the group III flux. At normal growth temperatures the group III controlled incorporation rates are not substrate temperature dependent, while the group V controlled incorporation rates exhibit a growth temperature dependence. The use of incorporation rate ratios is of greater value for growth characterization than the traditional beam equivalent flux ratios, which does not reflect the substrate temperature dependence. Furthermore, group V controlled incorporation rates can be used to set accurate reproducible growth conditions.

ISSN:0734-211X    

DOI:10.1116/1.584364

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The principal streak of reflection high‐energy electron diffraction (RHEED) patterns of (100) GaAs grown by molecular‐beam epitaxy (MBE) has been studied with an advanced imaging system which uses a charge‐coupled device (CCD) camera and an array processor. Calculations by Fernandez suggest that the profile of the principal streak from MBE GaAs should be very sensitive to the relative coverage of Ga and As, as well as the degree of roughness of the GaAs surface. Observations of the principal streak profile under static and dynamic conditions confirm qualitatively the theoretical calculations of Fernandez. The principal streak profile changes dramatically as the relative coverage of Ga and As is changed. At approximately equal Ga and As coverage, the intensity at the specular position is relatively low, and increases as the degree of Ga or As coverage increases. Significant changes in principal streak intensity and shape are produced by changes in adatom coverage as small as 0.1 monolayer (ML), and these changes saturate as the surface reaches full Ga or As coverage. The streak profile is noticeably different for Ga‐ and As‐stabilized surfaces, indicating that the (2×4) and (4×2) reconstructions are tetragonally distorted. Furthermore, the relative coverage of Ga and As adatoms during growth is strongly dependent on the ratio of the Ga and As fluxes. The lack of strong damping of oscillations in the specular spot intensity under optimized growth conditions is probably the result of relatively high Ga coverage and therefore higher Ga mobility on partially completed monolayers.

ISSN:0734-211X    

DOI:10.1116/1.584365

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Monte Carlo simulation results are presented for the growth by molecular‐beam epitaxy (MBE) of diamond‐structure semiconductors on both specular (001) surfaces and surfaces misoriented by up to 2° from (001) toward (110). The simulation includes calculation of the topography and reconstruction of the surface. Based on the resulting surface structures the streak profile and peak intensity of specularly reflected electron beams are calculated using a kinematic scattering approximation. The results confirm models proposed to explain oscillations observed in the intensity of beams of electrons specularly reflected from terraced surfaces parallel to the terrace edges during MBE. Small clusters of atoms are shown to nucleate on the surface of the terraces and gradually become incorporated into the terrace edges as growth proceeds. On specular surfaces, nucleation occurs randomly followed by growth and coalescence of islands. Stable, statistically random, surface structures are shown to develop leading to an increase in the root‐mean‐squared roughness of the surface with increasing time. These structures result in a gradual damping of oscillations in the specularly reflected electron beam intensities. The damping rate decreases with increasing surface diffusion and decreasing surface roughness. The strongly bound atomic dimers present on (2×1)‐reconstructed diamond‐lattice (001) surfaces are shown to influence surface diffusion and hence the critical size for nucleation of new surface layers.

ISSN:0734-211X    

DOI:10.1116/1.584368

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

ISSN:0734-211X    

DOI:10.1116/1.584369

出版商:American Vacuum Society    

年代:1988

数据来源: AIP