摘要:

Passivating AsxSyphases that form on GaAs after reactions with aqueous sulfides [Na2S⋅9H2O and (NH4)2S] decompose in the presence of oxygen and light, producing a surface composed primarily of As2O3. X‐ray photoelectron spectroscopy (XPS) shows that (NH4)2S‐treated surfaces degrade in two steps with the initial AsxSy(present as a disulfide) degrading by S–S bond cleavage to yield As2O3and an As2S3phase like the one that forms on GaAs after Na2S⋅9H2O reactions. XPS reveals little decomposition of surface sulfides in the presence of light or oxygen alone, showing that GaAs passivation could be made long‐lived if either is rigorously excluded.

ISSN:0734-211X    

DOI:10.1116/1.584611

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

X‐ray photoelectron spectroscopy (XPS) and reflection high‐energy electron diffraction (RHEED) results are presented for ammonium sulfide treated (100)GaAs surfaces. XPS shows that the sulfur coverage is independent of the ammonium sulfide concentration, although the relative amount of arsenic decreases as the sulfide concentration increases. RHEED patterns show that higher temperatures are required for the surface to restructure following treatment with higher sulfide concentration. In addition to the order of magnitude changes in the diode saturation current densities following ammonium sulfide treatment, we observe that the characteristics of gold and aluminum Schottky barriers on sulfide‐treated GaAs surfaces also vary with the substrate temperature during metal deposition.

ISSN:0734-211X    

DOI:10.1116/1.584612

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Sulfur treatments have previously been shown to improve the electrical characteristics of InP and GaAs devices. This paper reports the results of an Auger/x‐ray photoelectron spectroscopy investigation of the InP surface after sulfur treatment. It is shown that the sulfur remains on the surface bonded to indium. There is no indication of elemental sulfur or sulfur bonded to phosphorus. This suggests that the sulfur has replaced phosphorus on the surface and has filled the phosphorus vacancies.

ISSN:0734-211X    

DOI:10.1116/1.584613

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Recent studies of plasma‐enhanced chemical vapor deposition of SiO2upon Si epitaxial layers growninsituupon epitaxial GaAs layers, with the deposited interfacial Si of order 10 Å, strongly suggest that greatly reduced state densities at SiO2/GaAs interfaces have been attained with this approach. We report spectroscopic ellipsometry results for molecular‐beam epitaxy (MBE) Si/GaAs samples both before and after SiO2deposition, as well as before and after annealing. The ellipsometric results indicate that the SiO2/GaAs interface is<9 Å thick. The amount of unreacted silicon ranged from 3±3 to 0.4±0.2 Å equivalent thickness for the best fit cases. Ellipsometric results for samples without the deposited SiO2suggest of order 0.4‐Å unoxidized silicon at the interface. Results of x‐ray photoelectron spectroscopy (XPS) studies of the samples (without deposited SiO2) suggest that all silicon is being oxidized prior to SiO2deposition for at least some of the ‘‘unpinned’’ samples. Raman studies find no Si–Si bonds for some of the unpinned samples. Our data strongly suggest that the reduced interface state density is not dependent upon the presence of unoxidized silicon, at least in the amount required to form the Si/GaAs heterojunction previously assumed in explaining this improved interface. We further report preliminary electrical data for a sample prepared with no silicon deposition; indentical heat treatments on this sample gave similar results, i.e., reduced interface states forn‐GaAs metal–oxide semiconductor capacitors.

ISSN:0734-211X    

DOI:10.1116/1.584614

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We have observed that in the low‐temperature deposition of thin films of SiO2onto semiconductor surfaces by remote plasma enhanced chemical vapor deposition, oxidation occurs at the semiconductor–SiO2interface. Thissubcutaneousprocess generates a thin film ofnativeoxide, which can then play a significant role in determining the electrical properties of the semiconductor/oxide interface. The native oxide formed on Si is SiO2, and we have determined that the growth of this oxide does not interfere with the formation of device quality interfaces provided that the thickness of the deposited oxide layer is less than ∼250 Å. For an oxide thickness greater than ∼250–300 Å, trapping states associated with defects produced along with the subcutaneous oxidation degrade the properties of the Si/SiO2interface. The native oxide that forms on Ge surfaces during SiO2depositions is the water‐soluble, rutile‐structured form of GeO2, and the presence of this oxide significantly degrades the electrical quality of the Ge/dielectric interface. In the case of the compound semiconductor interfaces with deposited SiO2, native oxide formation also generally degrades the electrical characteristics. For example, the oxide that forms on GaAs is predominantly Ga2O3, whereas the oxide on CdTe displays both Cd–O and Te–O bonding. Interposing a thin layer of epitaxial, and pseudomorphic Si between a Ge, GaAs, or CdTe semiconductor surface and the deposited SiO2film, can provide a viable approach to the formation of good metal–oxide‐semiconductor (MOS) devices, provided that the subcutaneous oxidation of the Si layer that occurs during oxide deposition does not ‘‘punchthrough’’ that layer and thereby allow for the oxidation of the underlying Ge, GaAs, or CdTe substrate as well.

ISSN:0734-211X    

DOI:10.1116/1.584615

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We have chosen CaF2/Si(111) as a prototype to study the two‐dimensional band structure of an ordered interface using angle‐resolved photoemission and optical second harmonic generation. A pair of interface state bands is found, one occupied, the other empty. The former disperses fromEF−0.8 eV at Γ toEF−1.4 eV (−1.6 eV) atM(K). An interface band gap of 2.4 eV is determined via resonant second harmonic generation using a truly buried interface with 500 Å of CaF2on top of Si. Therefore, the interfacial gap is twice as large as the gap in Si and five times smaller than the gap in CaF2. The pair of interface bands can be understood as bonding/antibonding combinations of the Si dangling bond orbital and the Ca 4sorbital, with Ca in the 1+oxidation state.

ISSN:0734-211X    

DOI:10.1116/1.584617

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

Various aspects of the physics of the interaction of GaAs surfaces with H2discharges are shown in this paper. Ultraviolet photoemission measurements have been done on (110) cleaved surfaces. Comparison of the core‐level spectra with electronic structure calculations (molecular orbital model) shows that some of the Ga atoms on the hydrogenated surface have two dangling bonds, instead of one on the clean relaxed surface. This indicates that Ga–As bonds on the (110) surface have been broken by exposure to the hydrogen in our discharge conditions. In parallel, some new surface states in the valence‐band region are detected which we have tentatively attributed to the formation of As–H bonds. Onp‐type (110) cleaved surfaces, the Fermi level is pinned near valence‐band maximum (VBM) +0.4 eV after hydrogenation. In a second part of the paper, we describe x‐ray photoemission spectroscopy results on the plasma treatments of GaAs(100) wafers in H2/AsH3(deoxidation, Fermi level position as a function of the surface stoichiometry, etc.).

ISSN:0734-211X    

DOI:10.1116/1.584618

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The interaction of Cl2and of O2molecules with cleaved InAs(110) surfaces was investigated at room temperature. Ultraviolet photoemission spectroscopy, a Kelvin probe, and electric‐field‐induced Raman spectroscopy were used to determine both the changes of surface band bending and of the ionization energy as a function of exposure to the molecules mentioned. Chlorine as well as oxygen are inducing depletion (inversion) and accumulation layers on samples dopedp‐ andn‐type, respectively. The Fermi level becomes finally pinned at 0.52 eV above the valence‐band top for both adsorbates. This behavior indicates the presence of adsorbate‐induced surface states of donor type at this energy position. With chlorine, an intermediate pinning position at 0.48 eV above the valence‐band maximum, which is below the branch point of the virtual gap states of the complex InAs band structure, is observed. This result suggests that chlorine induces surface states of acceptor character on InAs(110) surfaces as is observed with GaAs(110) as well as InP(110) surfaces. Electric‐field‐induced Raman scattering has proven to be a very valuable tool for studies of accumulation layers.

ISSN:0734-211X    

DOI:10.1116/1.584619

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

The x‐ray standing‐wave method is a powerful technique for accurately locating the position of impurity atoms at surfaces, interfaces, and in bulk crystals. Using UHV to prepare crystal surfaces andinsitux‐ray experiments, we have addressed a number of problems in surface physics. Specifically the location of As atoms on Si(111) has been accurately established and has allowed for the first time a direct test of theoretical, density functional, total energy minimization, calculation of atom positions. For As, with only nearest neighbor relaxations, there is excellent agreement between theory and experiment. For Ga on silicon (111) the situation is much more complex. At low coverages (∼1/3 monolayer) the adatomT4site for Ga has been accurately measured. X‐ray standing waves were used to establish the vertical position and the in‐plane registration site of Ga to the substrate silicon atoms was established both by standing waves and tunneling microscopy. At higher coverages, Ga occupies substitutional sites in the top half of the Si(111) double plane, but contracted inwards by about one‐half of the distance between the Si(111) double planes. The consequences of the large surface strain generated by this contraction is discussed in the context of the standing wave and tunneling microscopy results. In addition, the atom positions that prevail when both Ga and As atoms are deposited on Si(111) are described.

ISSN:0734-211X    

DOI:10.1116/1.584576

出版商:American Vacuum Society    

年代:1989

数据来源: AIP

摘要:

We determine the temporal evolution of the real and imaginary parts of the anisotropic components of the surface dielectric responses Δ(εd) of singular and vicinal GaAs surfaces on interruption of the As flux during otherwise normal growth by molecular‐beam epitaxy (MBE). The measurement of dielectric, rather than simply reflectance, anisotropies is made possible by a new, essentially strain‐free quartz window that not only extends our spectral range but also allows relative phases as well as amplitudes to be measured for near‐normal incidence reflectances along [110] and [1̄10]. Data are obtained in 0.1‐eV increments from 1.5 to 5.5 eV for a singular (001) surface and for vicinal surfaces 6° off (001) toward (111)A and (111)B, respectively. The observed temporal evolutions are approximately piecewise linear or exponential, indicating that each surface passes through several distinct phases before arriving at its final Ga‐stabilized condition. Nearly exponential initial transients with time constants of<1 s are interpreted as evaporation of excess As present during growth. A supersaturation phase transition is observed for the vicinal surface 6° off (001) toward (111)A. Spectra constructed from these transients show optical structures at 1.8–1.9. 2.5, and 4.1 eV that, because they are already well developed at 1 s, can be related to the initial As excess. The change in Δ(εd) that occurs between 2 and 5 s for the singular surface is similar to the Δ(εd) spectrum of Ga–Ga dimers, which is calculated here in a tight‐binding approximation.

ISSN:0734-211X    

DOI:10.1116/1.584577

出版商:American Vacuum Society    

年代:1989

数据来源: AIP