摘要:

The effect of placing controlled amounts of oxygen on the clean, cleaved (110) surface of GaAs before exposure to Au has been investigated with ultraviolet photoemission spectroscopy (UPS) and x‐ray photoemission spectroscopy (XPS). We studied: (a) the shape of the Ga‐3d level and changes of Ga (or As) intensity with oxygen and subsequent Au deposition; (b) the position of the Ga‐3d core level, with special regard to the surface or interface Fermi level (Efs), as a function of oxygen and Au coverages; and (c) the valence band structure (where both oxygen and Au provide strong characteristic structure). For chemisorbed oxygen coverages of a small fraction up to 1 monolayer (ML) or above the Au:GaAs intermixing andEfshifts are significantly reduced. For thep‐type sample, after much less than 1 ML of oxygen, the maximum rise ofEfsis suppressed as Au is added; after 107L exposureEfsremains stationary until approximately 1 ML of Au is deposited; for high oxygen coverage (≥108L), the oxygen appears to effectively retard the Au–GaAs interaction up to 10 ML of Au coverage. The width of the Ga‐3d core level increases monotonically with increased oxygen exposure. With 1010L exposure of oxygen, the Au coverage necessary to drop the Ga intensity to 1/eof  its value on the oxidized surface is decreased to 4 ML, instead of 6 ML for the unoxidized surface. Supporting evidence from XPS spectra further demonstrates the intermixing is reduced between Au and GaAs by oxygen. The valence band structure shows the Au is dispersed on the oxidized surface. The results show that, for GaAs surfaces with a few tenths to above 1 ML of oxygen (before Au is deposited and with no annealing), the oxygen–GaAs interaction inhibits Au intermixing with GaAs. It causes a more abrupt interface than the case without oxygen.

ISSN:1071-1023    

DOI:10.1116/1.582605

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

Current–voltage (I–V), capacitance–voltage (C–V), and photovoltage (PV) data are obtained for Ru, Rh, Pd, Os, Ir, and Pt contacts deposited on chemically cleaned 〈100〉n‐GaAs wafers. By explicitly evaluating the relevant equations using realistic values of all parameters, we show that the currents obtained for small voltages are far too large to be explained by thermionic or recombination effects alone but are indicative of barrier height variations as proposed by Freeoufetal. We used the fact that the thermionic emission component is always present to reconcile the difference between apparent barrier heights determined byI–VandC–Vmeasurements to obtain a consistent set of values for all materials. Upon exposure of the Ru and Ir contacts to atmospheric‐pressure hydrogen, the barrier heights are reduced by 160 and 70 mV, respectively, and the ideality factors by 0.3 and 0.3, showing that hydrogen simultaneously lowers the barrier height and makes it more uniform over the contact for these junctions. The introduction of hydrogen into the bulk of these hydrogen‐alloying metals has no effect on the transport properties of the Pt, Rh, and Pd junctions despite a reported work function change of nearly 1 eV for Pt, over 0.5 eV for Rh, and a phase change to a metallic hydride for Pd. The change in optical properties with ambient in the Drude region of Ru shows that the bulk Fermi level does not change by more than 40 meV upon hydrogenation, indicating that hydrogen is affecting primarily the interface dipole. The results, in general, conform to the predictions of Spicer’s unified defect model but the dependence of the detailed behavior on specific transition metals and the evidence for lateral barrier height variations show that some corrections are necessary.

ISSN:1071-1023    

DOI:10.1116/1.582606

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

ISSN:1071-1023    

DOI:10.1116/1.582607

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

We investigated the adatom states for different Al coverages of InP(110) by synchrotron‐radiation photoemission, including ultralow coverages below 0.2 monolayer. The adatom states below 0.1 monolayer and above ∼3 monolayer appear similar to the corresponding Al–adatom states on GaAs(110). In particular, the results for both systems appear consistent with the formation of Al clusters at 0.1–2 monolayer coverage, and the Fermi‐level pinning occurs when the cluster formation starts. However, the similarity between the two systems is limited at intermediate (0.1–2 monolayer) coverages. At those coverages we observe a new bonded state for Al on InP, which is not observed on GaAs. Our results emphasize, in general, the need to extend the experiments to ultralow coverages when studying the Schottky barrier formation process.

ISSN:1071-1023    

DOI:10.1116/1.582608

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

The Al–GaP(110) and Al–InP(110) interfaces are characterized with low energy electron diffraction and Auger electron spectroscopy. Both interfaces are reactive, i.e., the replacement of the cation by Al is thermodynamically favorable. However, Al evaporated on the room temperature substrates has a high surface mobility and forms metallic islands which leave the atomic structure of the uncovered semiconductor areas unperturbed. Limited Al–substrate reaction can be detected at room temperature. Moderate annealing triggers a large scale Al‐cation replacement reaction and leads to the formation of AlP layers. The crystalline quality of the AlP layers is good for Al on GaP (0.01% lattice mismatch between AlP and InP) and poor for Al on InP (7% lattice mismatch between AlP and InP). The atomic geometry of AlP(110) is analyzed with multiple scattering LEED computation. A best fit structure is obtained which is consistent with the correlation recently obtained between atomic structure and atomic size on (110) semiconductor compound surfaces.

ISSN:1071-1023    

DOI:10.1116/1.582609

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

We have used Auger electron spectroscopy (AES) combined with Ar+sputtering to profile the chemical composition of UHV‐cleaved InP(110) interfaces with Au, Al, Cu, Ni, Ti, and Ag films. We observe pronounced anion and cation segregation to the free metal surface which depend sensitively on the metal–InP reactivity. Reactive metal (e.g., Al, Ti, or Ni) interlayers at Au–InP interfaces decrease anion diffusion and surface segregation monotonically with increasing interlayer thickness and AES depth profiles indicate a P accumulation at or just below the intimate metal–InP interface. These and other sputter‐AES studies suggest that the lower (higher) Schottky barriers of reactive (unreactive) metals are associated with cation (anion) depletion within the InP bulk and on anion accumulation at the intimate InP–metal interfaces.

ISSN:1071-1023    

DOI:10.1116/1.582610

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

A room temperature exchange reaction between an Al adsorbate and In atoms from the InP(110) surface has been observed during the early stages (∼0.5 to 5 Å) of interface formation by means of soft x‐ray photoemission spectroscopy of the Al 2pand In 4dcore levels. As much as 8 Å of deposited Al was found to be required to slow down the transport of Al metal to the front of the reaction to the extent that an overlayer of nonreacted Al metal began to be observed on the surface. For all stages of barrier formation a segregation of In atoms, monitored by the chemical shift of the In 4dcore lines, has been observed. A moderate heating (up to 200 °C) of a 12 Å deposition extends the exchange reaction deeper into the bulk. These results are discussed in the context of the widely studied Al–GaAs interface.

ISSN:1071-1023    

DOI:10.1116/1.582611

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

ISSN:1071-1023    

DOI:10.1116/1.582612

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

We have grown GaAs and AlGaAs on (110)‐oriented GaAs substrates by molecular beam epitaxy (MBE). The epitaxial growth was studiedinsituby reflection high energy electron diffraction. Hall measurements, low temperature photoluminescence, and scanning electron microscopy were used to characterize the epitaxial layers. Significant instabilities were found for this orientation under the growth conditions employed. The experimental results are discussed with bonding considerations of the (110) surfaces.

ISSN:1071-1023    

DOI:10.1116/1.582567

出版商:American Vacuum Society    

年代:1983

数据来源: AIP

摘要:

We present here a study on the transport characteristics ofL‐point and Γ‐point derived electrons through abrupt GaAs–Ga1−xAlxAs–GaAs(111) double heterojunctions. The use of complex‐kband structures in the tight‐binding approximation and transfer matrices provide a reasonably accurate description of the wave function at the GaAs–Ga1−xAlxAs interface. A representation of the wave function in terms of bulk complex‐kBloch states is used in the GaAs regions where the potential is bulklike. A representation of the wave function in terms of planar orbitals is used in the central Ga1−xAlxAs region where the potential deviates from its bulk value (i.e., interfacial region). Within this theoretical framework, realistic band structure effects are taken into account and no artificial rules regarding the connection of the wave function across the interface are introduced. The ten‐band tight‐binding model includes admixture in the total wave function of states derived from different extrema of the GaAs conduction band. States derived from the same extremum of the conduction band appear to couple strongly to each other, whereas states derived from different extrema are found to couple weakly. Transport characteristics of incomingL‐point and Γ‐point Bloch states are examined as a function of the energy of the incoming state, thickness of the Ga1−xAlxAs barrier, and alloy compositionx. Transmission through the Ga1−xAlxAs barrier is either tunneling or propagating depending on the nature of the Bloch states available for strong coupling in the alloy. Since Bloch states derived from different extrema of the conduction band appear to couple weakly to each other, it seems possible to reflect the low velocityL‐point component of the current while transmitting the high velocity Γ‐point component.

ISSN:1071-1023    

DOI:10.1116/1.582568

出版商:American Vacuum Society    

年代:1983

数据来源: AIP