Q. Fu

A phosphorous-rich structure of InP (001) produced by metalorganic vapor-phase epitaxy

A phosphorous-rich structure is generated on the InP (001) surface during metalorganic vapor-phase epitaxy. It consists of phosphorous dimers, alkyl groups, and hydrogen atoms adsorbed onto a layer of phosphorous atoms. The adsorbed dimers produce c(2×2) and p(2×2) domains, with total phosphorous coverages of 2.0 and 1.5 ML. The alkyl groups and hydrogen atoms adsorb onto half of the exposed phosphorous atoms in the first layer. These atoms dimerize producing a (2×1) structure. It is proposed that the first layer of phosphorous atoms is the active site for the deposition reaction, and that the organometallic precursors compete with phosphorous dimers, alkyl radicals, and hydrogen for these sites during growth.

Structure and composition of the c(4×4) reconstruction formed during gallium arsenide metalorganic vapor-phase epitaxy

Surfaces of GaAs (001) were prepared by metalorganic vapor-phase epitaxy and characterized by scanning tunneling microscopy, x-ray photoelectron spectroscopy, infrared spectroscopy, and low-energy electron diffraction. Upon removal from the reactor, the gallium arsenide surface exhibits a (1×2) reconstruction, which is a disordered variant of the c(4×4). The disorder arises from the presence of adsorbed alkyl groups. Heating the sample to 350 °C desorbs the hydrocarbons and produces a well-ordered c(4×4) structure. A model is proposed for the alkyl-terminated (1×2) reconstruction.

Hydrogen atoms as a probe of the optical anisotropy of indium phosphide (001)

The reflectance difference spectra of the InP(0 0 1) (2×1) and δ(2×4) reconstructions have been characterized using hydrogen as a probe of the surface bonds. Bands observed at 1.9, 3.1, 4.1, and 4.6 eV on the (2×1) and at 2.8, 3.7, and 4.6 eV on the δ(2×4) decrease in direct proportion to the hydrogen coverage. By comparing the changes in the reflectance difference spectra to the changes in the atomic structure of the surfaces, it is possible to relate the peaks to transitions involving specific valence bond states.

Stress-induced anisotropy of phosphorous islands on gallium arsenide

The initial growth of (2×4) phosphorous islands on (4×2) terraces of gallium arsenide (001) has been studied. The islands grow anisotropically in the [110] direction with an aspect ratio of approximately 8 to 1 at moderate coverages. The distribution of island widths in the [110] direction follows a Gaussian function. The mean width increases from 24±6 to 47±11 A as the phosphorous coverage increases from 0.10 to 0.85 monolayers. Evidently, the island anisotropy is caused by stress imposed on the underlying gallium layer by the smaller, more tightly bound phosphorous dimers.

Hydrogen adsorption on GaAs (001) reconstructions

Hydrogen adsorption on the c(4×4), (2×4), (2×6), and (4×2) reconstructions of GaAs (001) have been characterized by internal-reflection infrared spectroscopy. The infrared spectra contain up to 15 bands due to the stretching vibrations of arsenic hydrides (2150–1950 cm−1), terminal gallium hydrides (1950–1800 cm−1), and bridging gallium hydrides (1800–950 cm−1). These features arise from hydrogen adsorption on arsenic and gallium dimers, and second-layer arsenic and gallium atoms. The large number of peaks observed indicates that the surface atoms exist in a variety of different chemical environments.