摘要:

Treating the GaAs surface with Na2S⋅9H2O or (NH4)2S has previously been shown to form a thin layer (∼1 ML) of sulfur bonded to the GaAs surface. The exact nature of this bond is not clear since a number of different bonding energies have been reported. This paper reports the results of an investigation of the formation of S–GaAs bonds using H2S gas as the source of sulfur. The angle resolved x‐ray photoelectron spectra show that as the substrate temperature is increased, three different S–GaAs bonding states appear: As–S bonding peaks in the As3dspectra exhibit core level shifts of 1.0 and 1.6 eV, Ga–S bonding causes a core level shift of 0.6 eV. These binding energy shifts (ΔBEs) are approximately the same as those observed for GaAs treated with (NH4)2S or Na2S⋅9H2O although the H2S treated samples yield a much larger amount of S bonding.

ISSN:0734-211X    

DOI:10.1116/1.584975

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The interaction of NH3with cleaved InP(110) surfaces was investigated by using a Kelvin probe, photoemission spectroscopy with monochromatic ultraviolet radiation (UPS), and low‐energy electron energy‐loss spectroscopy (LEELS). An NH3‐induced buildup of a depletion layer was found on samples dopedptype. For exposures larger than 1×1020NH3molecules per cm2, the Fermi level becomes pinned 1.3 eV above the top of the valence band at the surface, while the bands remain flat for samples dopedntype. The NH3‐induced surface states thus are of donor type. In the same exposure range the ionization energy was found to decrease by up to (0.5±0.05) eV, indicating the presence of NH3‐induced surface dipoles. In UPS the In(4d) core lines excited with 40.8 eV are insensitive to the NH3uptake within the limits of experimental error while the energy loss at 17.9 eV observed with LEELS, which is attributed to transitions from In(4d) core levels into empty dangling bonds, decreases as a function of NH3exposure. Therefore, the initially empty dangling bonds at surface In atoms have to become occupied with increasing uptake of NH3. By using temperature programmed desorption spectroscopy, NH3was established to adsorb as molecules on InP(110) and GaAs(110) surfaces at room temperature. It is concluded that NH3molecules are forming surface bonds via their lone electron pairs with empty dangling bonds of surface In atoms. In a surface molecule picture, these bonds will act as surface donors. The decrease in ionization energy is consistent with this model because NH3molecules are polar with the nitrogen atoms being negatively charged.

ISSN:0734-211X    

DOI:10.1116/1.584976

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

The changes in chemical composition and Fermi level position ofn‐ andp‐InP surfaces induced by reactions with sodium sulfide and ammonium sulfide solutions and with vapor from ammonium sulfide solution have been characterized by x‐ray photoelectron spectroscopy (XPS). Further,insituXPS analysis was used to study interfaces formed on sulfide passivated surfaces by remote plasma enhanced chemical vapor deposition of silicon nitride. We found that both indium and phosphorus sulfide phases were formed as a result of exposing InP to sulfide vapor at room temperature. However, most of the surface native sulfides dissolved in water and the resultant surface was then covered with about one monolayer of indium sulfide. Further, reduction in donor states in the upper band gap was evident by these sulfide treatments. However, heating the sulfide passivated sample caused an increase in surface states. Sulfur doping effect was also observed upon heating InP covered with the air oxidation products of the sulfide vapor. In the study of silicon nitride deposition, we found that the formation of native nitride could be avoided by optimizing the processing parameters. In addition, we also found that the surface native sulfide on InP reacted with the deposited silicon nitride. Capitance–voltage (C–V) data collected at 1 MHz indicate that a low interface state density could be obtained on silicon nitride/sulfide passivated InP. However, measurements of surface band bending of InP as a function of charging potential on a 10 nm silicon nitride on InP by XPS indicate that slow surface states were present which restricted changes in band bending to less than 0.3 eV when the applied voltage on the thin dielectric was −2 V.

ISSN:0734-211X    

DOI:10.1116/1.584977

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We report on the thermal and chemical stability of (100) GaAs interfaces passivated with aqueous, selenium‐based reagents. Photoluminescence from the Se treated surfaces shows that they remain passivated after extended water rinses. The surfaces were studied under ultrahigh vacuum by reflection high‐energy electron diffraction (RHEED) from room temperature to 620 °C. A streaky (1×1) RHEED pattern at low temperature gives way at 580 °C to a stable (4×1) reconstruction, suggesting strong bonding between Se and the GaAs surface. X‐ray photoelectron spectroscopy confirms the presence of Se at the surface at high temperature, possibly in the form of gallium selenate. The stability of these Se‐treated interfaces suggests that chemical treatments could be used in conjunction with molecular beam epitaxy to obtain high‐quality regrown interfaces.

ISSN:0734-211X    

DOI:10.1116/1.584978

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We have studied the properties of metal–oxide–semiconductor structures fabricated by plasma enhanced chemical vapor deposition of SiO2upon GaAs substrates. We have characterized the dependence of these properties upon the presence of a silicon interlayer, the type and the degree of misorientation of the substrate, and the type of plasma enhancement. We conclude that the presence of a silicon interlayer is beneficial forn‐type GaAs if the oxide is deposited by a remote plasma technique. For such oxides onn‐type GaAs coated with silicon, integration of the quasi‐static capacitance curve suggests a band‐bending range of 0.6–0.9 V. Also for these samples, we observe a hysteresis of order 0.6 V, and shifts of only 0.2 V in the midpoint of the rise from minimum to maximum capacitance upon changing frequency from 10 to 200 kHz. The benefits of using a silicon interlayer with a direct plasma deposited SiO2film are less evident. It is assumed that much of the improvement of these results arises not from a large reduction of the interface density but rather from a shift of the spectrum towards the conduction band edge. This appears evident from the improvement onn‐type samples coincident with a degradation onp‐type samples. The total band bending change derived from the integral from the quasi‐static capcitance–voltage curves is less sensitive to this interlayer than is the frequency dispersion.

ISSN:0734-211X    

DOI:10.1116/1.584979

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

A recently proposed passivation structure of In0.53Ga0.47As surface is characterized by x‐ray photoelectron spectroscopy (XPS), capacitance–voltage, and deep‐level transient spectroscopy measurements. It uses an ultrathin molecular beam epitaxy Si interface control layer (ICL) and a photochemical vapor deposition (CVD) SiO2outer insulator. XPS study indicates that growth of Si ICL is coherent and two‐dimensional up to about 10 Å beyond which clustering is initiated, and that it is effective in preventing the InGaAs layer from selective oxidation of Ga during photo‐CVD SiO2deposition.C–Vand deep level transient spectroscopy (DLTS) measurements giveNssdistributions of very different shapes, the latter exhibiting two distinct peaks, which may be erroneously interpreted as defect levels. Suppression of selective oxidation of InGaAs does not alter the shapes of these distributions, although it reduces the magnitude. The results are explained by the disorder‐induced gap state model rather than the defect model or the effective work function model.

ISSN:0734-211X    

DOI:10.1116/1.584980

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Changes in the structure of the steps on vicinal Si(100) and Si(111) due to arsenic adsorption have been characterized using low‐energy electron diffraction. Under equilibrium conditions all the surfaces studies show reversible step rearrangements as a function of arsenic coverage. On vicinal Si(111) double layer steps form at approximately 0.2 ML of As. On vicinal Si(100) arsenic adsorption causes the steps to group to form facets. If the surfaces are not equilibrated, the step structures formed depend sensitively on preparation procedure. Prior observations on the growth of GaAs on stepped Si(100) are discussed in terms of our observations of step rearrangements.

ISSN:0734-211X    

DOI:10.1116/1.584981

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

We have investigated the structure and composition of the ZnSe(100)c(2×2)–Zn surface. Contrary to prior assumptions, this surface is not terminated with Zn dimers, but, rather with a half monolayer of Zn atoms. This new structure markedly changes our understanding of the growth interface and should lead to better heteroepitaxial growth on this and similar surfaces.

ISSN:0734-211X    

DOI:10.1116/1.584982

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Two new minimum‐energy surface structures have been identified forp(1×1) overlayers of Sb on the (110) surface of III–V compound semiconductors using a tight‐binding total‐energy formalism previously developed for these systems. The first is the ‘‘epitaxical on top structure’’ (EOTS) in which Sb zig–zag chains are commensurate with, and on top of, the Ga–As unreconstructed surface zig–zag chains. This structure differs from the previously found ‘‘epitaxical continued layer structure’’ (ECLS) by virtue of the registry of the Sb chains ‘‘on top of ’’ rather than ‘‘in between’’ the substrate Ga–As chains. Like the ECLS, the EOTS is compatible with both scanning tunneling microscopy (STM) and photoemission data. The second new structure is the ‘‘epitaxical overlapping chain structure’’ (EOCS) in which the Sb chains are 180° out‐of‐phase with, and on top of, the Ga–As substrate chains. This structure is, however, incompatible with both low‐energy electron diffraction and STM data for GaAs(110)–p(1×1)‐Sb. Computations for GaP(110)–p(1×1)‐Sb and InSb(110)–p(1×1)‐Sb reveal that the energy difference between the EOTS and ECLS is approximately constant over this range of overlayer/substrate lattice mismatch.

ISSN:0734-211X    

DOI:10.1116/1.584983

出版商:American Vacuum Society    

年代:1990

数据来源: AIP

摘要:

Theoretical calculations of the surface dielectric function of (001) GaAs with As‐ and Ga‐terminated (2×1) reconstructions are presented. An empirical nearest‐neighbor tight‐binding model with six orbitals (s,x,y,x2−y2,3z2−r2) per atom is used. The calculated dielectric functions anisotropies for GaAs (2×1) surfaces are analyzed with reference to the electronic structures. The theoretical results are in qualitative agreement with present data, and allow structures observed at 1.8, 2.6, and 4.1 eV in the surface dielectric anisotropy to be related to transitions from Ga bonding dimer to Ga dangling bond, As lone pair to As antibonding dimer, and As bonding dimer to As antibonding dimer transitions, respectively.

ISSN:0734-211X    

DOI:10.1116/1.584984

出版商:American Vacuum Society    

年代:1990

数据来源: AIP