Narrow-bandgap oxides

A problem with the monolithic arrays is that the techniques for building metal-oxide-semiconductor (MOS) devices in silicon cannot be transferred intact to narrow bandgap materials such as mercury cadmium telluride, mainly due to tunneling and avalanche breakdown occuring at very low voltages. A monolithic array, in which read-out electronics is integrated in the same mercury cadmium telluride chip as the infrared detectors, is therefore difficult to achieve. 

If Ki Kg, which holds for oxides that have narrow bandgaps, the oxide is a semiconductor at all oxygen pressures. At low oxygen pressures (in the left part) it is n-type, at high oxygen pressure it is p-type, and in the middle it is an intrinsic semiconductor. 

In order to obtain a narrower bandgap of these oxides, the substitutional doping of N might be effective since its p states contribute to the bandgap narrowing by mixing with O 2p states [70]. The density functional theory calculations show that the valence band is composed mainly of the anion 2p orbitals hybridized with metal d states. In case of TaON, the upper energy level of the valence band is dominated by N 2p states [71]. 

Since most "surface-sensitive" techniques sample at least a few atomic planes into the sample, it is difficult to experimentally separate the electronic structure of the outermost plane of atoms from that of the planes below. Theoretical calculations are able to clearly separate surface from bulk electronic structure, of course it is common to calculate a separate electronic density-of-states for each plane in the crystal structure ("layer density-of-states"). Significant changes from the bulk electronic structure are sometimes found for the surface planes in calculations. However, it is difficult to confirm those results experimentally [1]. In some oxides, the bandgap at the surface has been observed to narrow compared to that of the bulk. The measured core-level binding energies of partially coordinated surface atoms are often shifted, by as much as an eV, from their bulk values [32] these are referred to as "surface core-level shifts". However, the experimental separation of surface from bulk electronic structure is at present far from satisfactory. 

Mercury cadmium teiluride (HgCdTe) is a direct bandgap semiconductor widely used as a material for infrared detectors due to his narrow variable band gap. The achievement of high-performance detectors depends critically on a low surface recombination velocity of the minority carriers. The chemical growth of a passivation oxidized superficial layer in an aqueous Fe(CN)g3- basic solution is studied in this work. The depth profiles of the different elements in the oxidized layer superficial layer and its thickness are studied by X-ray photoelectron spectroscopy. The electrical properties of the interface are evaluated from MIS devices. The conditions of oxidation have been optimized. 

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