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Low Resistance Contacts for Amorphous Chalcogenide Semiconductors

IP.com Disclosure Number: IPCOM000077374D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Abstract

A typical structure of an electronic device which comprises an amorphous semiconductor, is one that consists of a thin film of an amorphous chalcogenide semiconductor having two or more metal contacting electrodes. The problem confronted in the use of these devices is the formation of blocking contacts between the metal electrodes and the amorphous semiconductors in thin-film devices. Such effect has to be avoided in order to obtain optimum device characteristics.

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Low Resistance Contacts for Amorphous Chalcogenide Semiconductors

A typical structure of an electronic device which comprises an amorphous semiconductor, is one that consists of a thin film of an amorphous chalcogenide semiconductor having two or more metal contacting electrodes. The problem confronted in the use of these devices is the formation of blocking contacts between the metal electrodes and the amorphous semiconductors in thin-film devices. Such effect has to be avoided in order to obtain optimum device characteristics.

In this connection it has been found from a study of high-field effects in amorphous As(2)Te(3) sandwich devices that when aluminum contacts are utilized as the metal contacts, such contacts are always blocking. Thus, for example, Al-As(2)Te(3)-Al devices which should have had a resistance of 10/3/ ohms if there was no contact resistance, showed values, typically, of 10/7/ ohms. It is believed that such variation between the theoretically calculated resistance and the actual resistance is caused by a reaction which takes place between the aluminum electrodes and the amorphous semiconductor thin film, As(2)Te(3), thereby creating a thin barrier layer of a large band-gap, high-resistance material, e.g., AlAs or Al(2)Te(3), between the As(2)Te(3) and the Al. From these findings, it is clear that a suitable metal electrode material for the thin film amorphous chalcogenide semiconductor has to have the following characteristics:

(1) It must not diffuse rapidly in the amorphous semiconductor (thereby eliminating as possible metals for this use the coinage metals and the platinum group metals which diffuse rapidly);

(2) It must have a sufficiently high conductivity such that the stripe resistance in the thin-film electrode is negligible compared to the device resistance (thus making graphite unattractive as an electrode material);

(3) It must not form any high band-gap reaction products with the amorphous chalcogenide (thereby eliminating Al as an electrode metal).

In consideration of the fore going conclusions, it is realized that the refractory metals are those which are most suitable as metal contacting electrodes for thin- film devices comprising a thin film of an amorphous chalcogenide semiconductor. Thus, for example, titanium reacts readily with As and Te to form only low band- gap or metallic reaction products.

However, the use of the refractory metals, e.g., such as titanium, for example, present the disadvantages that films tend to be highly strained and often nonadherent when deposited at room temperatures. Concomitantly, the tendency of the chalcogenide films to devitrify at elevated temperatures precludes the heating of the substrate in order to overcome the latter disadvantages.

There is accordingly described herein a technique which eliminates the foregoing disadvantages and also eliminates other difficulties, i.e., the possible shorting of electrodes by the reaction products produced by their reac...