Rectifying junctions

The current-voltage profile of rectifying junctions is strongly asymmetrical. The reason for this can be explained with the aid of a simple band diagram shown in Figure 14-2. 

Figure 14-2. Energy ding rams of a melal-scmi-conduclor (MS) rectifying junction under reverse (a) and forward (b) bias.

Eq. (14.1) is known as the Mott-Schotlky equation. We note llial for a given n-lype semiconductor, the harrier height increases as the work function of the metal increases. It is therefore expected that high work function metals will give a rectifying junction, and low work function metals an ohmic contact (it is the reverse for a p-type semiconductor). 

The optical properties of electrodeposited, polycrystalline CdTe have been found to be similar to those of single-crystal CdTe [257]. In 1982, Fulop et al. [258] reported the development of metal junction solar cells of high efficiency using thin film (4 p,m) n-type CdTe as absorber, electrodeposited from a typical acidic aqueous solution on metallic substrate (Cu, steel, Ni) and annealed in air at 300 °C. The cells were constructed using a Schottky barrier rectifying junction at the front surface (vacuum-deposited Au, Ni) and a (electrodeposited) Cd ohmic contact at the back. Passivation of the top surface (treatment with KOH and hydrazine) was seen to improve the photovoltaic properties of the rectifying junction. The best fabricated cell comprised an efficiency of 8.6% (AMI), open-circuit voltage of 0.723 V, short-circuit current of 18.7 mA cm, and a fill factor of 0.64. 

The rectifier, or diode, is an electronic device that allows current to flow in only one direction. There is low resistance to current flow in one direction, called the forward bias, and a high resistance to current flow in the opposite direction, known as the reverse bias. The operation of a pn rectifying junction is shown in Figure 6.17. If initially there is no electric field across the junction, no net current flows across the junction under thermal equilibrium conditions (Figure 6.17a). Holes are the dominant carriers on the / -side, and electrons predominate on the n-side. This is a dynamic equilibrium Holes and conduction electrons are being formed due to thermal agitation. When a hole and an electron meet at the interface, they recombine with the simultaneous emission of radiation photons. This causes a small flow of holes from the jp-region... 

Figure 6.17 Schematic illustration of electron and hole distribution for a /rw-rectifying junction for (a) no applied electrical potential, (b) forward bias, and (c) reverse bias. Reprinted, by permission, from W. Callister, Materials Science and Engineering An Introduction, 5th ed., p. 631. Copyright 2000 by John Wiley Sons, Inc.

Rectifying junction - [SEMCONDUCTORS - SILICON-BASED SEMICONDUCTORS] (Vol 21)... 

Early solid-state devices relied on observing the ionization in intrinsic semiconductors. Early devices were impractical due to the requirement of extremely pure material. Modem devices are based on semiconductor junction diodes. These diodes have a rectifying junction that only allows the flow of current in one direction. Incident radiation creates ionization inside the bulk of the diode and creates a pulse of current in the opposite direction to the normal current flow through a diode that is straightforward to detect. 

Fig. 2.20 Current-voltage characteristic for a metal-semiconductor rectifying junction.

Russel Ohl of Bell Laboratories discovered and filed patents in 1941 that were granted in 1946 and 1948 " for the p-n junction photovoltaic effect in silicon. The early devices contained rectifying junctions that were accidentally formed by segregation of dopant impurities during cooling. 

Kovtyukhova NI, Martin BR, Mbindyo JKN, Smith PA, Razavi B, Mayer TS, Mallouk TE (2001) Layer-by-layer assembly of rectifying junctions in and on metal nanowires. J Phys Chem B 105 8762-8769... 

The solution has been to adjust the potentials as the deposition takes place. The potentials needed for UPD of the elements on Au, and then on each other, shift as the deposition proceeds. It is suggested here that as the compound semiconductor is formed, a rectifying junction forms between the InAs... 

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 principle of operation of a photoelectrochemical solar cell (PECS) is shown in Figure 2.12 where the absorber is a semiconducting material. The rectifying junction is formed between redox electrolyte and semiconductor, as also shown in... 

In Figure 2.14, it has been assumed that the catalytically active particles form a rectifying junction with the absorber, forming partially overlapping semispherical... 

The results of the development of broadband elliptically polarized anteima arrays and rectifying junctions places the rectenna arrays suitable for tiie AMO spectrum merely on the first rung of development. The real attraction of tiiis technology are the high theoretical efficiencies and the performance of linearly polarized rectennas in ISM bands to date. 

Unlike the systems in the PV-electrolysis category, the photoactive components in the photoelectrode based systems configuration are immersed in solution, and typically include one or more PEC solid/liquid rectifying junctions. 

In PEC photoelectrode systems, the semiconductor/electrolyte interface can form a rectifying jtmction, similar to the solid-state pn junctions or Schottky diode jtmctions used in solar cells. Such rectifying junctions exhibit built-in electric fields... 

The range of available ceramic sensors for measuring humidity in industrial process environments can be classified into four categories (1) ionic, (2) electronic, (3) solid electrolyte, and (4) rectifying-junction types. A solid electrolyte humidity sensor that uses doped strontium cerate has been reported... 

Shimidzu and co-workers prepared two-dimensional polymers from monomers 88 and 89 (Chart 5.28) and the electrical properties of the electrodeposited films were investigated in a sandwich cell [100, 101]. Successive electropolymerizations of the Zn and Pd complexes in a bilayer device provided rectifying junctions where current flows only when the ITO is positively biased. Rectification occurs at the interface... 

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