We present a new analytical potential fluctuations model for the interpretation of current/voltage and capacitance/voltage measurements on spatially inhomogeneous Schottky contacts. A new evaluation schema of current and capacitance barriers permits a quantitative analysis of spatially distributed Schottky barriers. In addition, our analysis shows also that the ideality coefficient n of abrupt Schottky contacts reflects the deformation of the barrier distribution under applied bias; a general temperature dependence for the ideality n is predicted. Our model offers a solution for the so‐called T0 problem. Not only our own measurements on PtSi/Si diodes, but also previously published ideality data for Schottky diodes on Si, GaAs, and InP agree with our theory.

Barrier inhomogeneities at Schottky contacts

Theoretical models of Schottky-barrier height formation are reviewed. A particular emphasis is placed on the examination of how these models agree with general physical principles. New concepts on the relationship between interface dipole and chemical bond formation are analyzed, and shown to offer a coherent explanation of a wide range of experimental data.

Recent advances in Schottky barrier concepts

The formation of the Schottky barrier height (SBH) is a complex problem because of the dependence of the SBH on the atomic structure of the metal-semiconductor (MS) interface. Existing models of the SBH are too simple to realistically treat the chemistry exhibited at MS interfaces. This article points out, through examination of available experimental and theoretical results, that a comprehensive, quantum-mechanics-based picture of SBH formation can already be constructed, although no simple equations can emerge, which are applicable for all MS interfaces. Important concepts and principles in physics and chemistry that govern the formation of the SBH are described in detail, from which the experimental and theoretical results for individual MS interfaces can be understood. Strategies used and results obtained from recent investigations to systematically modify the SBH are also examined from the perspective of the physical and chemical principles of the MS interface.

The physics and chemistry of the Schottky barrier height

Introductory Fourier transform spectroscopy

NEXAFS investigations of transition metal oxides, nitrides, carbides, sulfides and other interstitial compounds

The nature of n‐CdTe surfaces prepared by various chemical treatments has been studied by x‐ray photoelectron spectroscopy. In parallel experiments Schottky barrier heights have been measured for Sb and Au contacts deposited on surfaces prepared in an identical manner. Reducing etches are found to leave the surface rich in Cd, and for these surfaces Sb and Au always produce barrier heights of 0.93±0.02 eV. Bromine in methanol solutions leaves the surface rich in Te and gives rise to two valued barrier heights of 0.93 and 0.72 eV. It is found that the probability of generating contacts with the higher value of barrier height increases as the surface becomes richer in Cd.

Effects of surface treatments on Schottky barrier formation at metal/n‐type CdTe contacts

The formation of a thin interfacial layer of indium telluride in InSb‐CdTe heterostructures has been previously suggested by soft x‐ray photoemission (SXPS) results. However, the detailed nature of this layer was difficult to interpret by SXPS. Therefore, samples being previously investigated by SXPS were studied by Raman spectroscopy. Spectra were taken of heterostructures grown by deposition of CdTe on (100) InSb substrates at room and elevated temperatures. For the room‐temperature sample the vibrational modes of CdTe and crystalline Te were detected. In the case of elevated substrate temperatures it was possible to identify the interfacial layer rich in indium and tellurium as consisting largely of In2Te3 using the Raman spectrum of In2Te3 as a fingerprint. Furthermore, the segregation of antimony was confirmed by the detection of the vibrational modes of antimony at the interface.

Formation of interfacial layers in InSb‐CdTe heterostructures studied by Raman scattering

We have performed photoluminescence (PL) measurements on chemically etched single‐crystal p‐CdTe. In addition, x‐ray photoemission measurements have been used as a guide to surface stoichiometry for each chemical treatment. The relative intensities of the 0.875±0.005 eV and 1.125±0.005 eV PL bands are seen to be linked to the preferential depletion of either Cd or Te from the CdTe surface. Furthermore, the energies of these deep level transitions measured at T=4 K show remarkable agreement with the two values of Schottky barrier, Φb=0.72±0.02 eV and Φb=0.93±0.02 eV, normally obtained at room temperature for Au and Sb contacts to n‐CdTe.

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Correlation of photoluminescence measurements with the composition and electronic properties of chemically etched CdTe surfaces

The molecular‐beam epitaxial growth of InAs on GaAs(100) was investigated in situ using reflection anisotropy spectroscopy (RAS) and simultaneously reflection high‐energy electron diffraction. The RAS spectra of the GaAs c(4×4) and (2×4) and the InAs (4×2) and (2×4) reconstructions are reported. During InAs deposition, the RAS signal shows significant changes for InAs coverages as low as 1/6 of a monolayer. At this coverage surface reconstructions are responsible for the signal variation. For InAs coverages larger than four monolayers, the RAS signal is essentially determined by the anisotropic roughness of the three‐dimensional growing surface. This is verified using a three‐layer model which gives an excellent description of the experimental spectra at large coverages.

Analysis of molecular-beam epitaxial growth of InAs on GaAs(100) by reflection anisotropy spectroscopy

The transport properties of over 400 Schottky diodes, fabricated on cleaved, atomically clean and on cleaved, air-exposed GaAs (110) surfaces, have been examined for a diverse range of metallisations using the conventional current-voltage and capacitance-voltage techniques. The resulting body of experimental data provides a reliable base for studying the correlation between the Schottky barrier height and fundamental quantities. In particular, the range of barrier heights obtained from the diodes fabricated on the clean surfaces are compared with the metal work function and the metal electronegativity. It is demonstrated that central transition metals, from groups Va-VIII of the periodic table, produce mid-gap Fermi-level pinning on GaAs. In contrast, the barrier heights extracted from simple- and noble-metal contacts, and from transition metals situated towards the beginning and end of a transition series, exhibit a near-linear dependence on electro-negativity.

https://iopscience.iop.org/article/10.1088/0022-3719/21/4/016/pdf

R. H. Williams

Papers

Effects of surface treatments on Schottky barrier formation at metal/n‐type CdTe contacts

Formation of interfacial layers in InSb‐CdTe heterostructures studied by Raman scattering

Correlation of photoluminescence measurements with the composition and electronic properties of chemically etched CdTe surfaces

Analysis of molecular-beam epitaxial growth of InAs on GaAs(100) by reflection anisotropy spectroscopy

Schottky contacts to cleaved GaAs (110) surfaces. I. Electrical properties and microscopic theories