Observation of the atomic surface structure of GaAs(001) films grown by metalorganic vapor-phase epitaxy (original) (raw)
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GaAs(001) Surface under Conditions of Low As Pressure: Evidence for a Novel Surface Geometry
Physical Review Letters, 2000
Using density-functional theory we identify a new low-energy structure for GaAs(001) in an As-poor environment. The discovered geometry is qualitatively different from the usual surface-dimer based reconstructions of III-V semiconductor (001) surfaces. The stability of the new structure, which has a c͑8 3 2͒ periodicity, is explained in terms of bond saturation and favorable electrostatic interactions between surface atoms. Simulated scanning tunneling microscopy images are in good agreement with experimental data, and a low-energy electron diffraction analysis supports the theoretical prediction. PACS numbers: 68.35.Bs, 61.14.Hg, 68.35.Md, 73.20.At III-V semiconductors play an increasing role in microelectronics, such as light-emitting diodes and high frequency, low noise devices for mobile phones, and are important candidates for the development of devices in the emerging field of spin electronics. The knowledge of the surface atomic structure is a prerequisite to achieve understanding and controlling of the surface or interface electronic properties. As we will show below, however, up to date analyses of surface structures of III-V semiconductors are hindered by some prejudice on the type of structures considered. For an example of the GaAs(001) surface, we show the existence of a new type of surface reconstruction.
Surface structure of GaAs(2 5 11)
Physical Review B, 2002
GaAs samples with orientations vicinal to ͑2 5 11͒ within 1°were prepared by molecular beam epitaxy and analyzed in situ by scanning tunneling microscopy, low-energy electron diffraction, and reflection high-energy electron diffraction. In addition, first-principles electronic structure calculations were carried out. GaAs͑2 5 11͒ is a stable surface whose orientation is located within the stereographic triangle. For a wide range of As-rich conditions a (1ϫ1) reconstruction forms that is characterized by an inclined series of three As dimers and that fulfills the electron counting rule. The terrace size is limited only by the macroscopic off-orientation of the samples. The surface is perturbed by thin stripes of the nearby orientation ͑3 7 15͒. While the dangling bond densities of GaAs͑2 5 11͒ and GaAs͑3 7 15͒ are almost equal, GaAs͑3 7 15͒ violates the electron counting rule. The analysis of this perturbation suggests that, in general, on semiconductor surfaces the gain in stability arising from the minimization of the number of dangling bonds is significantly greater than the gain arising from reaching a semiconducting ground state. Upon annealing of the samples in ultrahigh vacuum, a fairly rough surface structure develops whose mean orientation is different from ͑2 5 11͒.
Surface geometry of MBE-grown GaAs(001) surface phases
Thin Solid Films, 1996
The MBE-grown GaAs(OOI) surface exhibits various surface phases depending on the surface temperature and As/Ga flux ratio during the growth. Using scanning tunneling microscopy, reflection high energy electron diffraction and theoretical simulations, we have carried out a systematic study of various phases from As-rich c(4 X 4), 2 X 4 to Ga-rich 4 X 2 and 4 X 6, utilizing migration-enhanced epitaxy. Based on our thorough investigation, we were able to propose a simple and unified structural model for the evolution of surface phases. The As-rich 2 X4 phase consists of two Asdimerson the top layer andanother Asdimer on thethird layer (Chadi's two-dimeI' model), while there isstill a small window where a slightly As-poor phase may exist consisting oftwo As dimers onthetop layer and second layerrelaxation (Northrup-Froyen model). AsfortheGa-rich 4 X2, we determined that theBcigclsen's two-Ga-dimer model fits best toourexperimental and theoretical results, which consists of two On dimcrs on thetop layer and an additional Ga dimcr on thethird layer, a mirror image of Chadi's two-dimcr model for the As-rich 2 X4 phase. Ourdirect observations reveal that there arctwo distinct 4 x 6 phases.
A UNION OF THE REAL-SPACE AND RECIPROCAL-SPACE VIEW OF THE GaAs(001) SURFACE
International Journal of Modern Physics B, 2001
A union of the real-space and reciprocal space view of the GaAs(001) surface is presented. An optical transmission temperature measurement system allowed fast and accurate temperature determinations of the GaAs(001) substrate. The atomic features of the Ga A s (001)-(2×4) reconstructed surface are resolved with scanning tunneling microscopy and first principles density functional theory. In addition, the 2D lattice-gas Ising model within the grand canonical ensemble can be applied to this surface to understand the thermodynamics. An algorithm for using electron diffraction on the GaAs(001) surface to determine the substrate temperature and tune the nanoscale surface roughness is presented.
Atomic and electronic structures of GaAs (001) surface
Russian Physics Journal, 2006
The atomic and electronic structures of α, β, β2, and ζ reconstructions for the Ga-terminated GaAs (001)-(4 × 2) surface are investigated in the framework of the pseudopotential approach. Total, surface, and local densities of electron states, electron-energy spectra, and relative surface energies of the structures under consideration are calculated.
2002
Ga-rich GaAs (001) surfaces are successfully observed during high-temperature annealing by scanning tunneling microscopy (STM). With a substrate temperature of 550 C, reflection high-energy diffraction patterns and reflectance anisotropy spectra confirm a (4x2) Ga-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that detaching and attaching of Ga adatoms may be the cause
Surface phase diagram of (2×4) and (4×2) reconstructions of GaAs(001)
Physical Review B, 2000
Total-energy calculations for a series of (2ϫ4) and (4ϫ2) reconstructed GaAs͑001͒ surfaces not included in previous theoretical studies are presented. A (2ϫ4) surface model containing single anion dimers in the first and third atomic layers is predicted for a balanced surface stoichiometry. It is more stable than the two-Asdimer ␣ structure assumed previously, due to its lower electrostatic energy. Our results for the (4ϫ2) reconstructed surface confirm the two-Ga-dimer 2 structure suggested by Biegelsen and co-workers. Nearly degenerate in energy, however, are mixed Ga-As dimers adsorbed on a Ga-terminated substrate.
Ga-rich GaAs(001) surfaces observed by STM during high-temperature annealing in MBE
Journal of Crystal Growth, 2003
Ga-rich GaAs (0 0 1) surfaces are successfully observed by scanning tunneling microscopy (STM) during hightemperature annealing in molecular beam epitaxy. With a substrate temperature of 5501C, reflection high-energy diffraction patterns and reflectance anisotropy spectra confirm a (4 Â 2) Ga-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that detaching and attaching of Ga adatoms may be the cause of this surface dynamics. For these conditions it is determined that z(4 Â 4), z2(4 Â 4) and z(4 Â 6) reconstructions co-exist on the surface. The z2(4 Â 4) reconstruction contains a Ga tetramer cluster. r
As-rich GaAs(001) surfaces observed during As4-irradition by scanning tunneling microscopy
2002
As-rich GaAs (001) surfaces are successfully observed during As4-irradition by a system in which scanning tunneling microscopy (STM) and molecular beam epitaxy can be performed simultaneously. With a substrate temperature of 440 C and an As4 partial pressure of 2x10-6 torr, reflection high energy electron diffraction patterns and reflectance anisotropy spectra confirm a c(4x4) As-stabilized surface. STM images clearly show