Person:

Golovchenko, Jene

We have imaged with the tunneling microscope the microscopic surface topography of germanium layers grown by molecular-beam epitaxy on Si(111)-7×7. The surface structures corresponding to Ge(111)-c2×8 and Ge(111)-7×7 are resolved. The Ge-c2×8 structure is shown to consist of a coherent combination of two simpler units both of which exist independently on the surface. The associated phase boundaries are illustrated. The Ge 7×7 structure is shown to be similar to that obtained for Si(111). Defects in the cell are also imaged.

The time‐resolved reflectivity at 0.63 μm from arsenic‐implanted silicon crystals has been measured during annealing by a 1.06‐μm laser pulse of 50‐ns duration. The reflectivity was observed to change abruptly to the value consistent with liquidsilicon and to remain at that value for a period of time which ranged from a few tens of nanoseconds to several hundreds of nanoseconds, depending on the annealing pulse intensity. Concurrently, the transmission of the primary annealing beam dropped abruptly. These observations confirm the formation of a metallic liquid phase at the crystal surface during the annealing process.

An x-ray standing-wave-field apparatus has been constructed that demonstrates an impurity atomic position resolution of ∼0.02 Å. The method is applied to the measurement of ion-implantation-induced lattice relaxation. It is pointed out that the method is also suited to determine surface impurity locations perpendicular to crystal surfaces.

We have investigated the incorporation of boron into the Si(111) (√3×√3)R30° surface from low boron concentration up to (1/3 monolayer, using tunneling microscopy and spectroscopy and first-principles total-energy calculations. Surprisingly, we find that a (√3×√3)R30° structure composed almost entirely of Si adatoms on a Si double layer can be stabilized by boron doping in near surface layers. Moreover, when boron atoms are in the surface layers, the adatom site is unfavorable compared with the site underneath the adatom, unlike other group-III elements adsorbed on the Si(111) surface.

We have observed surface states indigenous to the Si(111) 7×7 superlattice with the tunneling microscope. The data show the states' energies and strengths to be strongly dependent on position in the unit mesh. Implications of this for structural models of the 7×7 superlattice are discussed.

Tunneling images of single atomic steps on Si(111) have been obtained with a tunneling microscope. The 7×7 reconstruction is observed to persist essentially undistorted right up to the steps. The position of each step coincides with a 7×7 unit-mesh edge in both the upper and lower terraces adjacent to it. Asymmetry within the 7×7 unit mesh is observed and correlated with faulting of terraces adjacent to the step. The results are described by an extension of the dimer adatom stacking-fault model of Takayanagi et al.

Standing waves of x rays have been used to determine the positions of bromine atoms in submonolayer coverages on a (111) silicon surface. In addition to the bromine position normal to the crystal surface its components relative to a plane inclined to the surface are also measured. This information suffices to establish the registration of the surface atoms relative to the crystal below.

The charge state dependence of channeled ion energy loss has been determined for a series of ions ranging from fluorine to chlorine along the ⟨110⟩ direction in a silicon crystal. Energy losses for both bare ions and ions partially clothed with bound electrons at EA≅3 MeV/amu have been measured. The energy-loss rate for bare ions follows a strict Z21 scaling and agrees reasonably well with quantal perturbation calculations without the need for polarization or Bloch corrections. An explanation for this result is discussed. The clothed-ion energy losses appear to demonstrate screening effects that agree qualitatively with simple estimates. The angular dependence of the observed energy-loss effects is also presented.

With use of bromine atoms, deposited on the surface of a silicon single crystal, the presence of x-ray standing waves above the crystal surface has been detected under conditions of strong Bragg diffraction.

A simple and efficient method of annealing ion‐implantation damage in semiconductors is demonstrated which utilizes a relatively weak optical pulse in the visible to initiate surface melting in combination with a more energetic infrared pulse to drive in the melt front to the crystalline substrate. The efficacy of this approach is illustrated by an example in which an arsenic‐implanted silicon crystal is simultaneously exposed to 530‐ and 1060‐nm pulses. The results are discussed in relation to theoretical estimates of the melting thresholds at the two wavelengths.