- Patent JPS4731680

Document Type and Number:

Japanese Patent JPS4731680

Kind Code:

A

Abstract:

1365804 Photoconductive detectors HONEYWELL Inc 14 Jan 1972 [19 Feb 1971] 1974/72 Heading H1K A photoconductive ultraviolet radiation detector, e.g. for flame detection comprises (Fig. 4) a body of potassium tantalate 13 with two metal contacts 10, 11 deposited on an as-grown surface 12, which is the smooth external surface of a crystal unmodified by chemical or mechanical polishing; so as to form two surface barrier metal-semi-conductor junctions at the interface, a bias battery and ammeter measuring the current flow as a function of radiation incident on surface 12. Contacts 10, 11 are of identical metals establishing identical barrier potentials and may be, e.g. Cu, Ag, Ga, Au, In, Cr, Pt, Mg, Al evaporated or silk screened on the surface as closely spaced dots or an interdigital pattern (Fig. 4a). The potassium tantalate crystal is undoped and grown at constant temperature of approximately 1285-1340 C. to give low dark current and high photosensitivity. Figs. 5, 6 show photocurrent for Ga contacts at different D.C. biases, and for Cu, Ag, Au, Mg, Al contacts; all peaking at 2600-2800. It is shown that barrier potentials are established at the electrode-semi-conductor interface and that photoconductive gain peaks at a value greatly exceeding unity, while the photoresponse at the front side of the detector peaks at a higher value and shorter wavelength than that at the rear side thereof, and the response with both contacts on one surface exceeds that with a contact on each surface. It is shown also that the photocurrent response is greatly increased by the as-grown surface layer over that obtained after erosion, or cleavage to the interior material. For photovoltaic operation without external bias (i.e. operation in a fail-safe mode) it is shown that the two contacts on the as-grown surface may be of different metals to establish differing surface barrier potentials in opposition (Figs. 13-15, not shown). These contacts may, e.g. comprise Ag dots and ultrasonically soldered In rich alloy ohmic contacts, which may contain Sb and Ga. Physical theory is expounded in detail.

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