Deng-Sung Lin

Thermal reactions of phosphine with Si(100): a combined photoemission and scanning-tunneling-microscopy study

This study investigates the adsorption and thermal decomposition of phosphine (PH 3 ) on the Si(100)-(2◊1) surface. The adsorption species, dissociation reactions, atomic ordering, and surface morphology of the phosphine/Si(100) surface at temperatures between 300 and 1060 K are examined by scanning tunneling microscopy (STM ) and high-resolution core-level photoemission spectroscopy employing synchrotron radiation. The P 2p core level spectra clearly indicate that phosphine molecularly adsorbs at room temperature and partially dissociates into PH 2 and H on a time scale of minutes at low ( 15 Langmuirs (L, 1 Langmuir=10’6 Torr s’1) of phosphine on the Si(100)-(2◊1) surface at room temperature produces a saturated and disordered surface. The total amount of P on the saturated surface is ca 0.37 ML as calibrated by the P 2p photoemission intensity. Successive annealing of the saturated surface at higher temperatures converts PH 3 into PH 2 , converts PH 2 to P‐P dimers, and causes the desorption of PH 3 . These processes become complete at ~700 K, and the resulting surface is a H/Si(100)-(2◊1) surface interspersed with one-dimensional P‐P islands. Desorption of hydrogen from that surface occurs at ~800 K, and is accompanied by partial displacement of P with Si atoms on the substrate. At 850 K, the Si(100) surface, interspersed with 0.22 ML of two-dimensional islands, is a random alloy of nominal 0.5 ML Si‐P heterodimers and 0.5 ML Si‐Si dimers.

Adsorption and dissociation of Si2H6 on Ge(001)2 × 1

Adsorption and thermally-induced dissociation of disilane (Si2H6) on clean Ge(001)2 × 1 surfaces have been investigated using a combination of Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), reflection high-energy electron diffraction (RHEED), and scanning tunneling microscopy (STM). With initial Si2H6 exposure at room temperature, the Si surface coverage increased monotonically, the EELS surface dangling bond peak intensities continuously decreased, and the intensity of half-order RHEED diffraction rods decreased. The low-coverage Si2H6 sticking probability at 300 K on Ge(001) was found to be ∼ 0.5 while the saturation coverage was ∼ 0.5 ML. A new EELS feature, GSH, involving Si-H and Ge-H bond states was observed at Si2H6 exposures φ ≳ 3.4 × 1013 cm−2. In contrast to Si2H6 -saturated Si(001), the saturated Ge(001) surface significant fraction of dimerized bonds. Adsorbed overlayers were highly disordered with the primary species on saturated surfaces being SiH2, GeH, and undissociated SiH3· Si2H6-saturated Ge(001)2 × 1 substrates were annealed for l min at temperatures Ta between 425 and 825 K. Admolecules were mobile at Ta = 545 K giving rise to significant ordering in one-dimensional chains. By Ta = 605 K, essentially all of the admolecules were captured into coarsened islands. Dangling-bond EELS peaks reappeared by 625 K and the intensities of the half-order RHEED diffraction rods increased. Ge segregation to the surface, which began at Ta ≳ 625 K, occurred rapidly at Ta ⩾ 675 K. All H was desorbed by 725 K.

Surface segregation and growth‐mode transitions during the initial stages of Si growth on Ge(001)2×1 by cyclic gas‐source molecular beam epitaxy from Si2H6

Surface morphological and compositional evolution during the initial stages of Si growth on Ge(001)2×1 by cyclic gas‐source molecular beam epitaxy from Si2H6 has been investigated using in situ reflection high‐energy electron diffraction (RHEED), Auger electron spectroscopy, electron‐energy‐loss spectroscopy, and scanning tunneling microscopy, combined with post‐deposition high‐resolution cross‐sectional transmission electron microscopy. The layers were deposited using repetitive cycles consisting of saturation Si2H6 dosing at room temperature, followed by annealing for 1 min at 550 °C. Film growth was observed to proceed via a mixed Stranski–Krastanov mode. Single‐step‐height two‐dimensional growth was obtained for nominal Si deposition thicknesses tSi up to ≂1.5 monolayers (ML). However, the upper layer remained essentially pure Ge which segregated to the surface through site exchange with deposited Si as H was desorbed. At higher tSi, the Ge coverage decreased slowly, the surface roughened, and two‐dim...

Influence of Sapphire Nitridation on Properties of Indium Nitride Prepared by Metalorganic Vapor Phase Epitaxy

Indium nitride films have been successfully grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) using TMIn and NH3 as source precursors. Experimental results indicated that pregrowth treatments, such as buffer layer growth, nitridation temperature and nitridation duration have dramatic effects on the growth of the InN films. For films nitridated at 1,000°C for 40 min without any buffer layer growth, we obtained an InN film quality with Hall mobility, carrier concentration and line width of Raman E2 mode of 270 cm2/Vs, 5 ×1019 cm-3 and 4.5 cm-1, respectively, which is among the best quality ever reported for such type of film grown by MOVPE.

Atomic burrowing and hole formation for Au growth on Ag(110)

Abstract Scanning tunneling microscopy observations of the initial growth of Au on Ag(110) at room temperature reveal unusual features not reported in previous studies of this system; both islands (positive growth) and holes (negative growth) are observed simultaneously. These results are compared with the growth of Ag on Ag(110) for which no holes are observed. This hole formation is associated with Au adatoms penetrating the surface and moving into atomic sites in the layer below the surface.

Growth and atomic structure of epitaxial Si films on Ge(111)

Abstract Heteroepitaxial growth by molecular beam epitaxy of thin Si films on the Ge(111) surface was studied. The surface morphology and atomic structure were examined by scanning tunneling microscopy and synchrotron-radiation photoemission. For submonolayer Si coverages on the Ge(111) substrate at room temperature, the impinging Si atoms condense to form small islands. The areas surrounding the islands remain c(2×8). Post annealing or growth at high temperatures causes Si indiffusion and Ge segregation to the surface. Multilayer deposition at high temperatures can be described as a mixed two- and three-dimensional growth. Many small three-dimensional islands are observed on a two-dimensional film. The surface structure of the film shows partial disorder, and the film itself contains numerous defects caused by the lattice mismatch between Si and Ge. The role of the segregated Ge as a surfactant in the growth is discussed.

Apparent Topographic Height Variations Measured by Noncontact Atomic Force Microscopy

The topographic height measurement on a sample consisting of domains of different materials in noncontact atomic force microscopy (NC-AFM) is typically incorrect owing to the variation in electrostatic force between a tip and a sample. The tip–sample electrostatic force is owing to the difference in effective contact potential between a tip and a sample. This study demonstrates that the error in height strongly depends on the bias applied between the tip and the sample, the radius of the tip apex, the work function difference, and the frequency shift. Experimental results are well explained by integrated model calculations and by including the van der Waals and electrostatic forces between the tip and the sample in the analysis. When the simultaneous compensation of contact potentials during imaging is not performed, the errors occurring in the height measurement can be estimated from the tip–sample distance vs the bias curves obtained in situ.

Gallium K-edge x-ray absorption study on Mg-doped GaN

Ga K-edge x-ray absorption measurements were employed to investigate Mg-doping effects in GaN samples. Strong polarization-dependent x-ray absorption near-edge structures become less pronounced with increasing doping concentration, indicating the formation of a mixing-phase structure of cubic and hexagonal phases. Analysis of the extended x-ray absorption region of the spectra revealed doping-related defects such as vacancies, substitutions, and interstitial occupations. They were formed anisotropically in the crystal c axis direction and its perpendiculars. Disorderliness arising from phase mix and defects is believed to have lowered the Debye temperature of the doped GaN films and caused the destructive interference of the absorption fine-structure oscillation functions. These effects were taken into account for the observed large coordination number reductions in our samples.

Real-time scanning tunneling microscopy observation of Si(100)−(2 × 1)→(2 × n)→c(4 × 4) structural phase transitions

Abstract We report on the discovery of Si(100)−(2 × 1)→(2 × n)→c(4 × 4) structural phase transitions. Annealing the Si(100)-(2 × 1) surface between 590 and 700°C for some hours causes dimer vacancies to increase and nucleate into chains, ultimately forming the (2 × n) structure. After further annealing, c(4 × 4) areas appear, grow, and finally cover the entire surface. Experimental results raise the possibility not only that c(4 × 4) is a stable low-temperature structure of Si(100), but that (2 × 1) is a high-temperature phase stabilized at room temperature owing to its kinetic limitations.

Scanning tunneling microscopy observation of surface reconstruction of Si(100) during chemical vapor deposition from Si2H6

This study employs real-time high-temperature scanning tunneling microscopy to examine the evolution of the surface atomic structure of Si(100) during homoepitaxy by chemical vapor deposition at 625 C. At the initial stage, a (2 x n) structure is gradually formed, and the growth mode is pure step flow, followed by double step flow after a single-domain surface is obtained due to faster step advance of S B than S A . As growth proceeds, areas with c(4 x 4 ) symmetry appear, grow, and eventually cover the entire surface.