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

The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS2) and tungsten diselenide (WSe2), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides.

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Electrical contacts to two-dimensional semiconductors

http://antonirogalski.com/wp-content/uploads/2011/12/Infrared-detectors-Status-and-trends.pdf

Infrared detectors: status and trends

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

We investigate the temperature dependence of Schottky barrier heights on silicon. The analysis of a large variety of polycrystalline diodes shows that the temperature coefficient of the barrier height depends on the chemical nature of the metal. This observation is in contradiction with models suggesting Fermi‐level pinning at the center of the semiconductor’s indirect band gap. From the analysis of epitaxial NiSi2/Si Schottky contacts, we conclude that there is a direct influence of interface crystallography on both the barrier height and its temperature dependence. Finally, we present some new results on the pressure coefficient of barrier heights. Pressure and temperature coefficients of polycrystalline Schottky contacts are correlated similarly to the pressure and temperature coefficients of the band gap.

Temperature dependence of Schottky barrier heights on silicon

Electronic properties of Schottky diodes depend sensitively on spatial inhomogeneities of the metal/semiconductor interface. We find that, contrary to previous theories for low‐frequency noise, the electronic properties of Schottky contacts cannot be understood if one neglects spatial fluctuations of the Schottky barrier height. Our systematic investigation of several silicide/silicon diodes yields as an empirical law that excess noise increases drastically when the standard deviation σs of the spatial distribution of Schottky barrier heights exceeds the critical threshold value of 2kT.

Influence of barrier inhomogeneities on noise at Schottky contacts

We review an analytical model for the interpretation of transport measurements on spatially inhomogeneous Schottky contacts. The comparison of barriers from current/voltage- as well as from capacitance/voltage-curves permits a quantitative analysis of spatially distributed Schottky barriers. We reveal 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 and observed. An extension of our model includes the so-called flat band barrier of current/voltage curves. Here we demonstrate the interdependence of flat band Schottky barrier, ideality n and the homogenization of the barrier distribution under the application of a bias voltage. Effective photoresponse barriers and electrical noise at inhomogeneous Schottky diodes are also discussed.

https://iopscience.iop.org/article/10.1088/0031-8949/1991/T39/039/pdf

Transport Properties of Inhomogeneous Schottky Contacts

Evaluating either curved Richardson plots or temperature-dependent ideality data allows for a quantitative characterization of spatial inhomogeneities at Schottky contacts. Applying the two independent methods to PtSi/Si diodes we obtain a standard deviation around 70mV for the barrier fluctuations. These results agree with those from the comparison of temperature-dependent current and capacitance barriers. We discuss also flat band barrier heights which should be used if one investigates the temperature dependence of fundamental Schottky barrier heights. Their temperature coefficients depend on metallization. For epitaxial NiSi2/Si contacts on (100) oriented Si we find a strong influence of interface crystallography on the temperature coefficients.

Herbert H. Güttler

Papers

Barrier inhomogeneities at Schottky contacts

Temperature dependence of Schottky barrier heights on silicon

Influence of barrier inhomogeneities on noise at Schottky contacts

Transport Properties of Inhomogeneous Schottky Contacts

Barrier Inhomogeneities at Schottky Contacts: Curved Richardson Plots, Idealities, and Flat Band Barriers