摘要:

We report results of tight binding calculation for ordered half monolayer coverages of Al on GaAs(110) in a variety of chemisorption configurations. We find that differences between the chemisorption geometries and relaxations of these configurations lead to a variety of electrical characteristics of the surfaces. The relation of this result to the barrier formed at higher coverages is discussed.

ISSN:0022-5355    

DOI:10.1116/1.570180

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Valence‐band photoemission spectra taken as a function of overlayer coverage during the formation of Ga–GaAs(110) and Al–GaAs(110) interfaces are analyzed. Possible chemisorption site geometries of Ga on GaAs(110) are studied through total energy calculations and the surface electronic structure for Ga (or Al) in an optimal twofold configuration as well as for the ideal onefold coordinated position is obtained. The calculations show that the interface formation results in a change in the relaxation of the GaAs surface from its vacuum interface configuration. Thisinterfacialrelaxationat the initial stage of metal–semiconductor interface formation pulls unoccupied surface states into the gap and pins the Fermi level.

ISSN:0022-5355    

DOI:10.1116/1.570181

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Angular‐resolved photoemission and low energy electron loss spectroscopy (LELS) measurements are reported on GaAs(110) surfaces with adsorbed In, N, P, and As. It is shown that the photoemission from the ’’As dangling bond’’ surface state vanished after In adsorption, whereas the surface photoemission is unaffected by deposition of N, P, or As. This result is confirmed by tight‐binding‐type surface band structure calculations for models with a relaxed GaAs surface on which adsorbed In is assumed to be bound to the surface As atoms and N, P, or As to the Ga. However, some other observations like the surface Fermi level position and the behavior of the Ga 3dexciton peak in the LELS spectrum cannot be understood from this model.

ISSN:0022-5355    

DOI:10.1116/1.570182

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

We show that Raman scattering by LO phonons and their coupled modes can be used to obtain quantitative information on the band bending at surfaces or interfaces of doped III–V semiconductors. We have studied Schottky barrier formation and effects related to surface photovoltage at etched<111≳Bsurfaces of InP. These experiments yield information similar to that obtained from photoemission and photovoltage measurements, but they can also be carried out on surfaces which are contaminated or even covered with partially transparent layers such as metallic films.

ISSN:0022-5355    

DOI:10.1116/1.570183

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

It is shown by using Auger depth profiling andI–Vmeasurements that Schottky barriers of Pb on Pb0.8Sn0.2Te form only when the semiconductor surface is exposed to oxygen prior to the deposition of the Pb. In those cases where the Pb is deposited on a clean semiconductor surface the Sn migrates through the interface and no Schottky barrier is formed. The presence of oxygen at the interface acts as a barrier to the migration of Sn and so plays an important role in barrier formation.

ISSN:0022-5355    

DOI:10.1116/1.570184

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

The effects of localized electron irradiation of the (111) surface of PbTe are described. These studies show that fast surface diffusion processes considerably extend the lateral range of electron induced effects. The modifications that occurred over a relatively large surface area were compositional, in doping levels in the underlying material and in oxygen sorption mechanisms. The irradiated surface effectively passivated the underlying material against much of its normally strong interactions with oxygen which involve conduction and valence band electrons. A model is set up to account for these observations.

ISSN:0022-5355    

DOI:10.1116/1.570185

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Usingabinitiomethods (generalized valence bond with small clusters to represent the surface), we have studied reconstruction of the GaAs (110) surface and the initial steps of oxidation. The relaxation of the surface atoms (26° twist angle) is found to be in good agreement with the results of recent LEED experiments (27°±2° twist angle). The results indicate that the reconstruction is dominated by hybridization effects of orbitals localized at the surface. The calculations of chemisorbed O2and O support the following picture: (i) Molecular O2can bond only weakly (physisorb) to the perfect GaAs(110) surface. Chemisorption of the O2requires a defect site which may then catalyze decomposition of the O2. (ii) There is an intermediate oxidized state at low coverages (before O is inserted in the GaAs bonds) in which O atom is chemisorbed to a surface As (donor–acceptor bond). For this intermediate oxide we calculate chemical shifts of 2.6 eV (deeper) in the 3dlevels of the surface As and 0.8 eV (deeper) in the 3dlevels of the surface Ga, which are in agreement with recent experiments. We propose several experiments to test various aspects of the initial stages in the oxidation process.

ISSN:0022-5355    

DOI:10.1116/1.570186

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

The interaction of unexcited oxygen with vacuum‐cleaved GaAs(110) surfaces has been studied by XPS (hν=1253 eV) and UPS (hν=21.2, 40.8, and 48.4 eV) over the exposure range 105to 1014L. The corresponding coverage range is estimated as ϑ∠0.2 to ϑ∠0.8 monolayers (where ϑ=1 corresponds to an oxygen atom for each surface atom). From the UPS and O 1sXPS results it is concluded that the adsorption is dissociative over this entire range. From a study of the Ga and As 3dcore levels; and the Ga and AsL3MMx‐ray‐induced Auger lines it is shown that chemical shifts associated withbothAs and Ga levels occur over the entire adsorption range. These shifts are appropriate to those for Ga2O3and As2O3, as is the stoichiometry of the reacted layer. There is no direct evidence for a stable chemisorption state preceeding oxidation in the 105to 1015L exposure regime. It is suggested that reaction with molecular oxygen takes place by dissociation at defect sites leading to growth of Ga and As oxides.

ISSN:0022-5355    

DOI:10.1116/1.570187

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

The adsorption of nonexcited molecular oxygen on ordered and disordered(110) surfaces of GaAs was studied using photoemission techniques. On the ordered surface, only one chemically shifted level was observed for the As3dcore level up to 1013exposure. The Ga3dcore level exhibits an asymmetrical broadening towards higher binding energy for the same exposure, indicating the presence of a shifted component. The percentages of shifted Ga and shifted As appear to be about equal. However, when a sputtered (disordered) surface was exposed to oxygen, there was preferential adsorption on the Ga. Implications of these data are discussed.

ISSN:0022-5355    

DOI:10.1116/1.570188

出版商:American Vacuum Society    

年代:1979

数据来源: AIP

摘要:

Surface extended x‐ray absorption fine structure measurements (EXAFS) are reported for the initial oxidation stage of the GaAs(110) surface which is characterized by a +2.9 eV binding energy shift of the As 3dphotoemission peak. The surface EXAFS measurements employed a variation of the previously used secondary‐electron‐collection technique which significantly increased the surface sensitivity. We find oxygen to be chemisorbed in atomic form. The importance of using phaseshifts derived from model systems rather than using theoretically calculated phaseshifts for distance determinations from low Z atoms is pointed out.

ISSN:0022-5355    

DOI:10.1116/1.570189

出版商:American Vacuum Society    

年代:1979

数据来源: AIP