摘要:

The unpinning of the etched GaAs(100) surface has recently been reported by both photowashing and by Na2S⋅9H2O treatments. Both techniques hold promise of elucidating the mechanism by which GaAs passivation is achieved. We have identified as part of the photowashing process a separate photoactivation step. The activation step did not become apparent until we modified the photowash process in order to minimize light exposure when flowing water was not applied to the substrate. The degree of unpinning produced by this process has been found to be related to the thickness of this oxide, the presence of oxygen and water vapor and the integrated light flux incident on the sample. Photoluminescence experiments clearly show that a photoactivation step involving water vapor is required to achieve the flat‐band condition. This process is relatively insensitive to the surface treatment prior to the photowash. We have observed similar photoactivation and insensitivity to surface treatment on GaAs coated with Na2S⋅9H2O. This suggests the possibility of a common passivation process.

ISSN:0734-211X    

DOI:10.1116/1.584275

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The effects of photochemical oxidation in water, Na2S deposition and exposure to NH3and HCl gas ambients on the Fermi level pinning, and the surface recombination process at GaAs surfaces were studied by measuring the band edge photoluminescence (PL) intensity, x‐ray photoelectron spectroscopy spectra, and surface current transport(SCT). Computer simulation of the surface recombination process was also made on the basis of the disorder‐induced gap state model. Marked increase of PL intensity was observed after both photochemical oxidation and deposition of Na2S as previously reported. However, SCT measurements onn‐type materials detected increase of surface band bending in the dark. Exposure to NH3resulted in a slight reduction in the band bending with little change in the PL intensity. Exposure to HCl, on the other hand, resulted in marked reduction of the band bending with marked increase of the PL intensity. The computer simulation shows that the contradictory behavior of the PL intensity and band bending, as observed after photochemical oxidation and Na2S deposition, is explicable by a shift of the Fermi level pinning position towards the valence band edge due to a fixed negative interface charge which reduces the effective recombination velocity. On the other hand, exposure to HCl reduces the surface‐state density and weakens the pinning remarkably.

ISSN:0734-211X    

DOI:10.1116/1.584276

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We report studies of the chemical bonding of Cd and Te atoms to O atoms in air grown native oxides of CdTe. We find that the oxide grown in laboratory air on CdTe{100} surfaces: (i) always contains both Te–O and Cd–O bonds which we have detected, respectively, by x‐ray photoelectron spectroscopy and x‐ray Auger electron spectroscopy, and (ii) is soluble in deionized water. Based on these two observations and comparisons with the results of previous studies of native oxide formation of both CdTe and (Cd,Hg)Te, we conclude that the CdTe air grown native oxide is a compound oxide of the form CdxTeyOx, probably CdTeO3, and not a mixture of the elemental oxides, CdO and TeO2.

ISSN:0734-211X    

DOI:10.1116/1.584278

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Hg1−xCdxTe (111)B surfaces have been studied with x‐ray photoelectron spectroscopy (XPS). A surface shift is deduced from a careful analysis of Te 4dcore‐level spectra. The presence of small Hg clusters on these surfaces is observed, and the size is estimated from the XPS data (R=5–20 Å). The positive binding energy shift for these clusters agrees very well with the calculated Coulomb energy due to the positive charge which appears on the clusters during the photoemission process. The origin of these clusters is briefly discussed.

ISSN:0734-211X    

DOI:10.1116/1.584279

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The effect of the lateral dimension of interface islands on the subband eigenvalue spectrum of quantum well heterostructures is investigated by direct numerical solution of the two‐dimensional Schrödinger equation. We find a decrease in the lowest subband energy equivalent to a half‐monolayer change in well width for an island size of two to three times the nominal well thickness. Changes in the lowest subband eigenvalue equivalent to a monolayer change in well width are not anticipated for island sizes<∼1000 Å for quantum well widths of ∼100 Å.

ISSN:0734-211X    

DOI:10.1116/1.584280

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We report on a photoemission study of the ZnTe/GaSb(110) heterojunction prepared under ultrahigh vacuum conditions. Upon deposition of ZnTe on a cleaved GaSb(110) surface by molecular‐beam epitaxy, a reacted layer is formed, which is characterized by the liberation of Sb atoms from the substrate, and the reaction between Ga and Te. The thickness of this layer is dependent on the temperature of the substrate, and is on the order of one monolayer under optimum conditions. The ZnTe overlayers show good crystalline order as evidenced by low‐energy electron diffraction and valence level photoemission. Taking into account band bending upon interface formation, we derive a valence‐band offset of −0.34 eV. This result is compared with theoretical predictions as well as experimental data based on band offset transitivity. The determination of ionization energies for both substrate and overlayer demonstrates the failure of the electron affinity rule in predicting heterojunction valence‐band offsets.

ISSN:0734-211X    

DOI:10.1116/1.584281

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Angular‐resolved synchrotron radiation photoemission spectroscopy and reflection high‐energy electron diffraction (RHEED) are used to study the molecular‐beam epitaxy of CdTe/ α‐Sn(110) interfaces and superlattices. Core level photoemission spectra indicate that both sides of the interface are stable, nonreactive, and abrupt for growth temperatures up to 100 °C. At the α‐Sn/CdTe interface, the valence band maximum at Γ is atEV=1.1 eV below the Fermi level. This gives a valence band offset of ΔEV=1.1 eV, assuming zero band gap for the Sn. Stable superlattices of α‐Sn/CdTe(110) have been grown at 100 °C. The surface quality of the superstructure degrades after the growth of several α‐Sn/CdTe periods. After the growth of ten periods each 50‐Å thick, the RHEED pattern shows mainly three‐dimensional bulk diffraction, indicating increased surface, and interface roughness.

ISSN:0734-211X    

DOI:10.1116/1.584282

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

InP/Ga0.47In0.53As/InP single quantum wells, which are grown by the organometallic vapor phase epitaxy technique, exhibit multiple peaks in thermally modulated photoluminescence (TMPL) spectra. In two samples with nominal well widths at 10 Å, at least four well‐resolved negative and at least two positive TMPL peaks are observed. The number of peaks is related to the growth conditions, and the relative intensities of the peaks depend on the sample temperature and the PL excitation intensity. In the thinnest quantum wells at least some of these discrete peaks may be associated with regions where the well widths differ in thickness by single monolayer steps.

ISSN:0734-211X    

DOI:10.1116/1.584283

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The progress in understanding heterojunction band lineups has increasingly become dependent upon the availability of accurate and reliable measurements. The reported values of the band offset for the Si/GaAs system measured by photoemission range from 0.05 to 0.70 eV. Such a large scatter in experimentally determined discontinuities is common for other systems as well and not only makes the evaluation of different theories difficult, but raises the question as to whether such variations are real and representative of technological variations in the offset. Clearly the understanding and control of these variations is essential before any device applications can be realized. We attempted to study the source of these variations in the Si/GaAs(110) heterojunction. We altered the growth conditions to effect modifications in the overlayer crystalline order, strain, and chemical reactivity. While some of these studies have been previously reported, their collective consideration gives us a much more coherent overview of the problems involved in discontinuity measurements. In our studies we found the offset to be 0.23±0.05 eV for both amorphous and crystalline overlayers, either strained or unstrained. We did, however, observe discontinuities as large as 0.7 eV for room temperature growths. We show that such large discontinuities are due to dangling bond type states which extend into the band gap and change the apparent valence band maximum energy. These states can be removed by annealing the sample without crystallization. Offsets as small as 0.05 eV may be inferred from our data if we fail to account for the contributions of rather subtle chemical effects at the interface. Overall, we found the discontinuity to be more dependent on the interpretation of the data than on technological variations. If we discern and properly account for extrinsic effects and unambiguously define the discontinuity, photoemission can yield accurate and single valued measurements of the valence band discontinuity.

ISSN:0734-211X    

DOI:10.1116/1.584284

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Angle‐resolved photoemission spectroscopy has been used to study strained InxGa1−xAs(001) layers in pseudomorphic heterostructures grown by molecular‐beam epitaxy. It is found that the Δ3+Δ4 bands and the Δ1 band respond differently to the strain perturbation. For strained GaAs(001), the Δ3+Δ4 bands (Px+Py‐ like) are shifted upward in energy by a maximum amount of 0.3 eV, while in contrast, the Δ1 band (Pz‐ like) is shifted downward by about 0.5 eV. For both strained In0.2Ga0.8As(001) and In0.9Ga0.1As(001), the band shifts are in the opposite direction to that in the GaAs case, consistent with the opposite strain conditions. The strain‐induced effects due to cation (Ga or In) alloying are also discussed.

ISSN:0734-211X    

DOI:10.1116/1.584242

出版商:American Vacuum Society    

年代:1988

数据来源: AIP