Surface Schottky barrier heights

The degree of surface cleanliness or even ordering can be determined by REELS, especially from the intense VEELS signals. The relative intensity of the surface and bulk plasmon peaks is often more sensitive to surface contamination than AES, especially for elements like Al, which have intense plasmon peaks. Semiconductor surfaces often have surface states due to dangling bonds that are unique to each crystal orientation, which have been used in the case of Si and GaAs to follow in situ the formation of metal contacts and to resolve such issues as Fermi-level pinning and its role in Schottky barrier heights. 

The atomic geometry of a surface or interface is, in certain respects, its most fundamental property. Since most surfaces and interfaces are metastable, especially those of technological interest, their composition and structure depends on their process history. Their structures determine, moreover, the "interesting" interfacial properties which are utilized in specific applications, e.g., reactivity and specificity in catalysis or Schottky barrier height in metal-semiconductor contacts. In addition, the interface structure is measurable by one or more of the techniques noted earlier. Therefore the structure of an interface is a measurable link between the process used to prepare it and the electronic and chemical properties which determine its utility. 

Schottky barrier height modulation and stabilization as a "by product" of the original studies. Moreover, since these results are thought to follow from replacement reactions in the vicinity of the interface, they reflect the importance of surface structure as well as composition at semiconductor interfaces. 

The preparation or etching of compound semiconductors is more complex due to the potential of altering the surface stoichiometry. Shiota et al. (36) used AES to show that the final As/Ga at the surface of GaAs was very dependent on the chemical activity of wet chemical etchants. Bertrand was able to follow the changes in the chemical bonding of Ga and As on p-type GaAs etched in HC1 or Br in methanol and relate this to Schottky barrier heights of similarly prepared surfaces with Pb contacts (37). 

Photoelectron spectroscopy is a highly surface sensitive technique because of the inelastic mean free path of the photoelectrons Ae, which depends on the electron kinetic energy Ekin and has typical values of 0.2-3nm [31,37,38]. Determination of Schottky barrier heights b, or valence band discontinuities AEyB, can be performed by following the evolution of the position of the valence band maxima with respect to the Fermi level of substrate and overlayer with increasing thickness of the overlayer. For layer-by-layer growth the attenuation of the substrate intensities is given by the inelastic... 

SiN nanonetwork, the barrier height is 0.76 eV. When the SiN deposition time is increased, the barrier height increases from 0.84 (3 min SiN ) to 1.13 eV (5 min SiN (). At the same time, the ideality factor reduces from 1.3 (no SiN ) to 1.06 (5 min SiN ) which indicates that the SDs are nearly ideal in samples grown with the SiN nanonetwork. Incidentally, this improved value is consistent with the work function of Ni (5.2 eV) and the electron affinity of GaN (4.1 eV). In the literature, a value of 1.099 eV (Ni) barrier height was achieved only after the GaN surface was treated with (NH S [12], which is known to passivate the surface defects albeit temporarily. Our results indicate that the Ni Schottky barrier height is very sensitive to the crystalline quality and the excess current... 

Tredgold R FI and El-Badawy Z I 1985 Increase of Schottky-barrier height at GaAs-surfaces by carboxylic-acid monolayers and multilayers J. Phys. D Appl. Phys. 18 103-9... 

In N-polar GaN Schottky diodes, because of the higher surface reactivity with hydrogen inducing higher polarity, the Schottky barrier heights are reduced much more than those of Ga-polar Schottky diodes. Therefore, the N-polar GaN Schottky diodes have much higher sensitivity than Ga-polar GaN. 

One of the earliest models for the metal/semiconductor contact is due to Schottky. Here the reference level, is the vacuum level vac at the solid s surface. This is a valid approximation if one neglects dipole layers and charged interface states. In this case, the Schottky barrier height for electrons is given by (Figure 19.2a) ... 

Annealed and Alloyed Contacts Annealed contacts are formed by deposition of metal with low Schottky barrier height, such as aluminum on n-type Si. Postdeposition annealing at high temperature, in reducing environment such as forming gas, helps to passivate surface states and lowers the barrier height and contact resistivity. 

In Fig 3 downward band bending at the p-type silicon surface is produced by the choice of a metal whose work function is much less than that of the semiconductor In this case a depletion region and also a strong electric field of opposite sense to that of Fig 2 are produced below the semiconductor surface. The quantity ( )gp which represents the energy required by a hole situated at the metal Fermi level to become part of the hole distribution in the semiconductor is also termed the Schottky barrier height. The subscripts n and p are used to distinguish between the semiconductor material type . 

Figure 3.4 shows some selected examples of preformed polymers. Structure (1) is an octadecene-l-maleic anhydride polymer, which is hydrolyzed on the subphase surface over a period of several hours to produce the maleic acid derivative. By controlling the degree of hydrolysis, the amount of free acid groups, and hence the ionic concentration in the monomer, can be controlled. This material has been used to vary the Schottky barrier height of GaP by using different acid anhydride ratios [14]. 

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