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Reducing the Resistance of Ohmic Contacts Using Resonant Tunneling

IP.com Disclosure Number: IPCOM000039718D
Original Publication Date: 1987-Jul-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Gueret, P: AUTHOR

Abstract

The resistance of ohmic contacts on semiconductors is attributed to the tunneling resistance of a depleted Schottky layer at the metal-semiconductor interface. Conduction takes place through tunneling across the Schottky depletion layer. The contact resistance is made small by using a highly-doped semiconductor permitting a very thin Schottky layer ls . A typical conduction-band diagram of a metal-semiconductor ohmic contact is shown in Fig. 1. Dopant concentrations cannot be increased indefinitely because with increasing dopant concentration and with the ensuing decrease of the depletion layer thickness, doping fluctuations become more and more important.

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Reducing the Resistance of Ohmic Contacts Using Resonant Tunneling

The resistance of ohmic contacts on semiconductors is attributed to the tunneling resistance of a depleted Schottky layer at the metal-semiconductor interface. Conduction takes place through tunneling across the Schottky depletion layer. The contact resistance is made small by using a highly-doped semiconductor permitting a very thin Schottky layer ls . A typical conduction- band diagram of a metal-semiconductor ohmic contact is shown in Fig. 1. Dopant concentrations cannot be increased indefinitely because with increasing dopant concentration and with the ensuing decrease of the depletion layer thickness, doping fluctuations become more and more important. The resistance of ohmic contacts can be reduced by placing an additional tunneling barrier in series with the Schottky layer, so as to form a quantum well which is resonant at the Fermi energy. Fig. 2 shows the anticipated conduction band diagram for the particular case of GaAs-based technology. The left-hand part of Fig. 2 is contributed by the standard ohmic contact, as in Fig. 1. The right-hand part characterizes the additional barrier using AlxGa1-xAs with a suitably chosen value for x which determines the barrier height. The value for x and the barrier thickness lB should be chosen such that the barrier transmissivity is equal to that of the Schottky barrier. The thickness lw of the quantum well between the two barriers must be designed so...