Title: Infra-red detector elements

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Abstract: An infra-red radiation detector element and its manufacture. The detector element has a mesa (31) of infra-red sensitive material, e.g. cadmium mercury telluride, with separate metal electrodes (64 and 55, see FIG. 17) formed on side-walls of the mesa (31) from a metal layer 33. This permits a significant proportion of the current flow occurring between the electrodes (64 and 55) in operation of the element to pass across the bulk of the mesa (31) between its side-walls and not adjacent its top surface where the carrier recombination velocity may be higher. The mesa (31) is formed by ion-etching using a masking layer (24) e.g. of photoresist, and this permits reproducible etching over a uniform depth and the obtaining of a topographically rough surface to which the subsequently-deposited metal layer (33) can have good adhesion. The electrodes are formed from this layer (33) by a lift-off technique using the same masking layer (24). The ion-etch definition of the mesa (31) can also be used to etch unmasked parts of a passivating layer (14) on the element surface without any significant undercutting.


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