Gallium metal-oxide-semiconductor

Gallium arsenide s native oxide is found to be a mixture of nonstoichiometric galhum and arsenic oxides and elemental arsenic. Thus, the electronic band structure is found to be severely disrupted, causing a breakdown in normal semiconductor behavior on the GaAs surface. As a consequence, the GaAs MISFET (metal insulator semiconductor field-effect transistor) equivalent to the technologically important Si-based MOSFET (metal-oxide semiconductor field-effect transistor) is, therefore, presently unavailable. 

Thermal oxidation of OaAs for example produces a gallium rich oxide. In a number of studies, it has been shown that the oxide on GaAs contains Ga O and GajOg (see figure 6) and As is peaked at the interface. By preferential oxidation of one component of the compound semiconductor, defects are produced at the interface. Again this produces a barrier height equal to that observed for most of the metals evaporated on the GaAs surface (10). This accounts for the unsuccessful attempts to make metal oxide semiconductor structures by intrinsic III-V oxidation. 

Nakano and Jimbo investigated the interface electronic properties of thermally oxidized n-type GaN metal-oxide-semiconductor (MOS) capacitors [230]. The formation of an intermediate gallium oxide nitride layer vith a graded composition could provide the origin of a small capacitance transient observed experimentally. 

Because of the potential importance for industrial-scale catalysis, we decided to check (i) whether an influence of a semiconductor support on a metal catalyst was present also if the metal is not spread as a thin layer on the semiconductor surface but rather exists in form of small particles mixed intimately with a powder of the semiconductor, and (ii) whether a doping effect was present even then. To this end the nitrates of nickel, zinc (zinc oxide is a well-characterized n-type semiconductor) and of the doping element gallium (for increased n-type doping) or lithium (for decreased n-type character) were dissolved in water, mixed, heated to dryness, and decomposed at 250°-300°C. The oxide mixtures were then pelleted and sintered 4 hr at 800° in order to establish the disorder equilibrium of the doped zinc oxide. The ratio Ni/ZnO was 1 8 and the eventual doping amounted to 0.2 at % (75). 

If the pH value in the PAR reagent is lowered to 8.8 by adding a phosphate buffer, gallium(III), vanadium(IV)/(V), and mercury (II) can be detected and may be separated from the other heavy metals with PDCA as the eluent [151]. Fig. 3-157 shows the separation of vanadium(V) that was applied as ammonium(meta)vanadate, NH4V03. Under these conditions, vanadium(IV) elutes after about 17 minutes the two most important oxidation states of vanadium being easily distinguished. Gallium(III), of particular importance for the semiconductor industry, elutes near the void volume. 

As silicon nitride has a higher density than amorphous silicon oxide, it will serve as a better barrier to metal atom diffusion, and consequently it is used in VLSI production to prevent the cross-penetration of dopant atoms from one region of the device to another. During the manufacture of devices based on gallium arsenide, silicon nitride coatings will prevent the evaporation of (toxic) arsenic. Further information on the use of silicon nitride in semiconductor processing is available elsewhere (Belyi et al., 1988). 

Arsenic is a metalloid on the borderline between metals and nonmetals. Certain arsenic compounds, such as gallium arsenide (GaAs), are used as semiconductors. The white oxide As O is the assassin s poison arsenic. Two- or three-tenths of a gram is a lethal dose. On the other hand, some persons have built up a tolerance for it, so that they can ingest each day an amount that would normally be fatal. 

---