Schottky barrier formation

Parenthetically, no clear indication of the presence of MnAs clusters has been observed in the transport results, even in the cases where direct magnetization measurements detect their presence. One of possibilities is that the Schottky barrier formation around the MnAs clusters prevents their interaction with the carriers. 

The issue of Schottky barrier formation to ZnO is not treated in this chapter as such contacts are not of big importance in thin-film solar cells. This is related to the fact that in thin film solar cells metals are only used to contact highly-doped films. For degenerately doped semiconductors, the barrier heights become very small because of the large space charge associated with depletion layers in such materials. 

In case of metal junction with a p-type semiconductor, charge flow through the interface also occurs, depending on both, and Xsc, with a consequent Schottky barrier formation, in a situation analogous to that of the Figure. 

However, the assumption of the Schottky barrier formation raises some complex questions regarding both the size of particles on the surface of which (in principle, in a region of less than 0.5 nm) a significant change of electron density may be expected, and the nature of the space charge layer on the oxide side of the barrier. 

The properties of metals on doped a-Si H are sure to be an important area of research. Conflicting models have already been di ussed. Sorting this problem out will be important for both research applications and technology. Lastly, the actual details of Schottky-barrier formation remain a mystery, The previous studies seem to indicate a strong similarity in many aspects of Schottky barriers on a-Si H and crystalline Si. 

The model suggests that charge transfer is a primary mechanism of Schottky barrier formation, and a good agreement with the experimental results is found for polycrystalline inorganic semiconductors. It should be emphasized that the model is based on the thermod)mamic equilibrium of electrons across the interface between the metal and the semiconductor, and is facilitated by the interface bonds. Therefore, it does not depend on the details of the interface reactions, so long as the physical properties of the semiconductor, such as IP and Eg, remain intact at the interface. The model does not apply to interfaces where strong chemical reactions result in the domination of the interface by new reacted species. 

Table 3.2 Enumeration of the layer-by-layer stages of Schottky barrier formation...

Bachrach,R., Interface chemistry and structure of Schottky barrier formation in Sharma, B., Metal-semiconductor Schottky barrier junctions and their application, New York, Plenum, 1984,61-112. 

The adsorption of K on H Si(lll)lxl has been investigated as a way to interpret the K/Si(lll)7x7 core levels and analyze the Schottky barrier formation mechanisms [98Gru]. 

Results of PES studies of the interface between aluminum and poly(p-phenylenevinylene) have been reported for XPS studies [82,87,88] and UPS studies [87]. In general it is found that oxygen may be present in various degrees, either as contamination at the surface of the as-prepared PPV films or in the metal source itself. The pre.sence of oxygen will, of course, affect the characteristics of the interface [82.88]. The XPS results obtained by Ettedgui et al.(88 were interpreted in terms of a delay of Schottky barrier formation due to formation of a buffer layer, induced by the surface impurities, which prevents the PPV substrate from interacting with the deposited aluminum layer. 

However, the process of Schottky barrier formation using the above-described way of cleaning, showed strong dependence of electrophysical properties on the time interval between the last operation of chemical treatment and the vacuum processing of the... 

Mosbacker, H.L., Strzhemechny, Y.M., White, B.D., Smith, P.E., Look, D.C., Reynolds, D.C., Litton, C.W. and Brdlson, L.J. (2005) Role of near-surface states in ohmic-schottky barrier formation of gold contacts to ZnO. Applied Physics Letters, 87, 012102. 

Junctions formed with indium and with chromium also showed reasonable Schottky barrier formation, though we find in general that the ideality factors for these devices were poorer than for the aluminium structures, with values of 2 found in both cases. There is some variation in the barrier height deduced from the value of Jq fitting to the diffusion model using the same parameters as used above we find lower values for < )b, of 0.34 eV for chromium and 0.42 eV for indium. 

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