S. B. Visbeck

Structure-sensitive oxidation of the indium phosphide (001) surface

The oxidation of anion- and cation-rich indium phosphide (001) has been investigated by exposure to unexcited molecular oxygen. Indium phosphide oxidation is an activated process and strongly structure sensitive. The In-rich δ(2×4) surface reacts with oxygen at 300 K and above. Core level x-ray photoemission spectra have revealed that the O2 dissociatively chemisorbs onto the δ(2×4), inserting into the In–In dimer and In–P back bonds. By contrast, the P-rich (2×1) reconstruction does not absorb oxygen up to 5×105 Langmuir at 300 K, as judged by the unperturbed reflectance difference spectrum and low energy electron diffraction pattern. Above 455 K, oxygen reacts with the (2×1) inserting preferentially into the In–P back bonds and to a lesser extent into the phosphorus dimer bonds.The oxidation of anion- and cation-rich indium phosphide (001) has been investigated by exposure to unexcited molecular oxygen. Indium phosphide oxidation is an activated process and strongly structure sensitive. The In-rich δ(2×4) surface reacts with oxygen at 300 K and above. Core level x-ray photoemission spectra have revealed that the O2 dissociatively chemisorbs onto the δ(2×4), inserting into the In–In dimer and In–P back bonds. By contrast, the P-rich (2×1) reconstruction does not absorb oxygen up to 5×105 Langmuir at 300 K, as judged by the unperturbed reflectance difference spectrum and low energy electron diffraction pattern. Above 455 K, oxygen reacts with the (2×1) inserting preferentially into the In–P back bonds and to a lesser extent into the phosphorus dimer bonds.

Reflectance difference spectroscopy of mixed phases of indium phosphide (001)

Reflectance difference spectra of mixed (2×1) and (2×4) phases of indium phosphide (001) have been recorded and benchmarked against scanning tunneling micrographs of the surface. The line shapes are found to be linear combinations of the spectra of the pure (2×1) and (2×4) structures, Δr/rmixed=xΔr/r(2×4)+(1−x)Δr/r(2×1), where x is the weighting factor. Thus, in the absence of adsorbates, the reflectance difference spectra can be used to estimate the surface composition, i.e., the fractional coverage of phosphorous is ΘP=1−0.81x±0.06x.

Kinetics of tertiarybutylphosphine adsorption and phosphorus desorption from indium phosphide (001)

Abstract The kinetics of tertiarybutylphosphine adsorption and phosphorus desorption from indium phosphide ( 0 0 1 ) have been determined using reflectance difference spectroscopy for real-time monitoring of the phosphorus coverage. The precursor adsorption rate depends linearly on the coverage, and the initial sticking coefficient varies from 0.007 to 0.001 as the temperature increases from 420 to 520 °C. The phosphorus desorption rate is first order in the coverage and exhibits an activation energy and pre-exponential factor of 2.4 ± 0.2 eV and 10 14.7 ± 1.5 s −1 . These reaction kinetics play an important role in the growth of phosphide-based alloys by metalorganic vapor-phase epitaxy.

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.

Reflectance difference spectroscopy of an ultrathin indium arsenide layer on indium phosphide (001)

A model system has been created which allows the surface and bulk contributions to the reflectance difference spectrum to be distinguished. In particular, an indium arsenide film, less than 10 A thick, has been grown on indium phosphide (001). Reflectance difference spectra of the InAs/InP surfaces were collected and compared to those of InP and InAs. It was found that the InAs/InP heterostructures exhibited electronic transitions between surface states characteristic of InAs (001), while retaining the surface-perturbed bulk transitions characteristic of InP (001). Furthermore, the optical anisotropy arising from the arsenic dimer bonds was shifted 0.2 eV higher for InAs/InP compared to that for InAs. This shift is proportional to 1/a2, where a is the bulk lattice constant.

Atomically resolved investigation of InGaAs/InP heterojunction formation during metalorganic vapor-phase epitaxy

We have studied the formation of indium gallium arsenide/indium phosphide heterojunctions during metalorganic vapor-phase epitaxy (MOVPE). The films are characterized using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS). Exposing an InP [001] film to 10 mTorr of tertiarybutylarsine below 500/spl deg/C results in the deposition of a thin InAs layer from 1.5 to 5.0 atomic layers thick (2.3 to 7.5 /spl Aring/). The surface of this epilayer remains atomically smooth independent of arsenic exposure time. However, in an overpressure of tertiarybutylarsine at or above 500/spl deg/C, the arsenic atoms diffuse into the bulk, creating strained InAsP films. These films form three-dimensional island structures to relieve the built-up strain.