Rectifying contacts

Stability, and can provide both ohmic low resistance contacts and rectifying contacts. Typically, siUcide layers are formed in situ by sputteriag a thin platiaum layer onto the siUcon surface, followed by sintering. Infrared detection is another appHcation of platiaum siUcide technology. 

Metals for Schottl Contacts. Good Schottky contacts on semiconductor surfaces should not have any interaction with the semiconductor as is common in ohmic contacts. Schottky contacts have clean, abmpt metal—semiconductor interfaces that present rectifying contacts to electron or hole conduction. Schottky contacts are usuaHy not intentionaHy annealed, although in some circumstances the contacts need to be able to withstand high temperature processing and maintain good Schottky behavior. 

In a light-emitting MSM structure the two metal electrodes selected such that the work functions of the electrodes are near the edge of the valence band (VB) and the conducting band (CB) of the semiconductor, respectively, so that oppositely charge carriers are injected from the opposite electrodes. An ohmic and a rectifying contact is therefore formed in the MSM structure (see Fig. 9-22). 

The LED structures consist of an aluminum rectifying contact on the blend polymers which have been spin-cast onto ITO glass as a hole-injecting contact. The film thickness ranged from 60 to 80 nm. The electron-injecting aluminum contacts are deposited by vacuum evaporation at pressure below 10 6 torr, giving active area of 0.195 cm2. 

Rectifiers without moving parts are aluminium or tantalum rectifiers, vacuum tube rectifiers, contact rectifiers and mercury-arc rectifiers. The first two types of rectifiers, the function of which has already been described in the theoretical section of this book are suitable for laboratory purposes only. Likewise vacuum tube rectifiers can also be used where a medium output is required these tubes act as valves allowing the alternating current to pass through in one direction only they are built for both low (up to 100 V) and high voltage (up to 10 000 V). 

Figure 7 Current-voltage characteristic of a rectifying contact.

Silicide formation has been reviewedand the interaction between thin metal films and Si substrates is of interest for the use of silicides as ohmic or rectifying contacts and as interconnects in Si semiconductor device technology. Information about metal-silicon (M-Si) phase diagrams is also available . 

Carachteristographers are d.c. instruments made up by a current (voltage) power supply and a voltage (current) meter. They give a two quadrant V-I relation for the resistive device. The information supplied by such instruments is more exhaustive than that supplied by a.c. bridges, but the measurement is time consuming, and an inversion of polarity is necessary to detect the possible presence of partially rectifying contacts. In Fig. 9.8, an example of a V-I relation in the first quadrant for a Ge-NTD 12 resistor (see Section 15.2.1.1) is shown. Note that the power used in the measurements can be as low as 10-14W. 

The charge carrier depletion width, W, at the rectifying contact, which forms a Schottky barrier, can be calculated using the following Eq. (99) [47] ... 

The rectification properties of semiconductor interfaces are the most important electrical characteristic of semiconductor contacts. Certain types of devices, such as transistors, require both ohmic and rectifying contacts on a given semiconductor surface, whereas other devices, such as Schottky barriers, are based on the inherent rectification properties of semiconductor/metal Junctions. Numerous photonic devices, such as photon detectors and photovoltaic cells, require rectification at a semiconductor Junction, and light-emitting diodes require both ohmic contacts and rectifying Junctions in a well-defined geometry. Thus, successful fabrication of a desired device structure depends entirely on the electrical properties of the specific semiconductor contacts that are formed in the process. The principles described above allow the rational fabrication of contacts with the desired properties, and also describe the operation of the resulting devices within a simple, chemically intuitive, kinetic framework. 

The strong interaction of Ag is in line with earlier findings by Fichou et al. [234,262] in which Ag forms rectifying contacts for n- and p-type a6T. 

IJ/r (n-type), or V(II)/(III) and S2 /Sj (p-type) can be used. For photoelectrocata-lytic devices, a first approach is to use noble metal catalysts as nanoemitters such as Pt, Ir, and Rh (H2 generation, CO2 reduction) on p-type samples or Ru, Ruir, RUO2, and mixed oxides on n-type samples (O2 generation). It should be noted that the rectifying contact behavior is dominated in electrochemistry by the redox energy of the respective redox couple in solution, whereas for solid-state devices the work function of the nanoemitter with respect to the semiconductor Fermi level defines the barrier. 

Dhar S, Chakrabarti S (1996) Electroless Ni plating on n- and p-type porous Si for ohmic and rectifying contacts. Semicond Sci Technol 11 1231... 

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