Schottky barrier contacts

The term photovoltaic effect is further used to denote non-electrochemical photoprocesses in solid-state metal/semiconductor interfaces (Schottky barrier contacts) and semiconductor/semiconductor pin) junctions. Analogously, the term photogalvanic effect is used more generally to denote any photoexcitation of the d.c. current in a material (e.g. in solid ferroelectrics). Although confusion is not usual, electrochemical reactions initiated by light absorption in electrolyte solutions should be termed electrochemical photogalvanic effect , and reactions at photoexcited semiconductor electodes electrochemical photovoltaic effect . 

Finally, surface analysis has been used in the investigation of metal silicides used to form rectifying Schottky barrier contacts to semiconductors. These silicides are formed by thermal or laser sintering of the metal after deposition onto the substrate. Excess unreacted metal is removed by chemical etching. XPS has been used to show that the metal has been oxidized if the excess metal cannot be removed (52). 

Cl. 1 Ohmic contacts to GaN and the III-V nitride semiconductor alloys C1.2 Schottky barrier contacts to GaN Cl.3 Band offsets at interfaces between AIN, GaN and InN... 

Very little work has been performed on Schottky barrier contacts to the other III-N semiconductors, although a strong dependence of the Schottky barrier height of metal contacts to AIN on the electronegativity of the metal was reported in 1969 [35],... 

Figure 23 Ohmic contact (a) and Schottky barrier contact (b) between a metal M and a p-type semiconductor SC. Energies , /, x> and Eg are defined in text. Ef, Fermi level VB valence band, or hole conducting levels CB, conduction band, or electron conducting levels. Dots indicate the acceptors crosses indicate the holes in the SC outside the depletion layer.

Figure 24 Schottky barrier contact with an insulating interfacial layer. In the semiconductor and the insulator, the valence and conduction levels are shown as solid lines at zero bias (barrier heights Vty and < >) and as dashed lines at forward bias (barrier heights VD and ct>ps).

Mark and Gora [24], commenting on the results, considered a model in which initiation is associated with a critical interface field at the Schottky-barrier contact between the metal electrode and the azide. Interface fields depend on properties of the sample and on the work function of the electrode, and are larger than the applied voltage divided by sample thickness. The model predicted an effect for uniform samples which was qualitatively consistent with experiment, but whose magnitude was too small to observe. However, the experimental samples were pressed pellets composed of individual grains which are likely to be separated by potential barriers [25,26]. Taking this into account, the model was consistent with experiment if initiation occurs at a critical interface field of about 2 X 10 V/m. This is a plausible value, in that fields in excess of 10 -10 V/m applied to surfaces of wide band-gap semiconductors commonly result in destructive breakdown due to carrier emission into the bulk from interface states [27-29]. 

The type (1) interface is an ideal Schottky barrier contact in which the barrier height varies directly with the metal work function in accordance with Equation [3.18], The type (2) interface approximates to a Bardeen barrier, provided that the surface states are assumed to be spaced inside the semiconductor so as to allow a potential drop across this region. In the clean contacts of this type, one would expect the barrier height to show a weak dependence on 0 ,.The type (3) interface represents a case of strong chemical bonding between the metal and the semiconductor and, hence, we would expect the barrier height to depend on some quantity related to chemical or metallurgical reactions at the interface. The type (4) contact is the one most frequently encountered in actual metal-semiconductor devices. 

---