Ohmic contacts backside

Reagent grade chemicals were utilized. Electrodeposition was carried out in a conventional three-electrode cell under potentiostatic control with a mercury sulfate electrode as reference (in the following, all potentials are quoted versus this reference) and a platinum wire as counter electrode. Solutions were stirred and deoxygenated by bubbling nitrogen. Backside ohmic contacts of Si samples were achieved with an InGa eutectic. The i-U characteristics of the solid state junctions were measured in air. 

A reliability concern with semiconductor devices, such as chip transistors in which one of the connections is made through the backside metallization by attaching with either eutectic alloy or conductive epoxy, is the loss of backside ohmic contact. Loss of ohmic contact may be due either to mechanical/physical or chemical mechanisms. Mechanical failures occur from partial or complete delamination of the adhesive interface. The smooth surface of the die metallization contributes to the problem whereas roughening the surface improves results. Loss of contact is evident from increases in resistance during initial electrical testing, but may better be detected... 

In principle, electrochemical photovoltaic cells (also known as regenerative solar cells) can be constructed very simply. They consist of a semiconductor electrode, an electrolyte containing a redox system and a counter electrode, as illustrated in the lower part of Fig. 2.30. The energy scheme for a cell with an -type semiconductor and a redox system with a standard potential close to the valence band is shown in the upper part of Fig. 2.30. On illumination of such a cell, holes are created and transferred to the reduced species of the redox couple. The electrons reach the ohmic contact on the backside of the semiconductor, traverse the external circuit, do useful work, and reach the counter electrode, at which they reduce the oxidised component... 

Nickel Schottky contacts with a diameter of 300 am and a thickness of 1500 A were deposited on the porous SiC by magnetron deposition followed by photolithography patterning. A blanket ohmic contact was formed by Ni deposition on the backside and rapid thermal annealing at 1000 °C was done prior to anodization. The schematic cross-section of the formed structure is shown in Figure 2.21. Note, nickel contacts were deposited on a porous substrate with the skin layer which is characterized by low porosity and pore diameters of <20 nm. Thus, the effect of contact... 

A heavily doped wafer (p , ean be readily anodized in a variety of HF-based electrolytes to form mesoporous silicon. A lightly doped wafer (p , n , and majority carrier concentration <10 cm ) generally requires an ohmic contact to be made on the backside, either by ion implantation or by depositing a thin metal layer such as A1 (for p-type wafers) and Au-Sb (for n-type wafers) mechanical abrasion of the backside of the wafer, before metal deposition, can often improve the ohmic contact. 

In the first method, a second ohmic contact has to be produced at the backside of the semiconductor species. In order to measure conductivity changes, a voltage has to be applied across the two ohmic contacts. When varying the potential across the interface, the conductivity may change. This happens only if a change of... 

After the cleaning procedure, deposit an A1 layer with a thickness of about 300 nm by, e.g., an electron-beam evaporation process anneal the contact at 420°C for 15 min to create an Ohmic backside contact. 

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