A recently developed gallium nitride-based linear array of ultraviolet detectors is blind to most of the visible spectrum, with a cutoff wavelength of 370 nm. This device is a prototype of GaN detector arrays for ultraviolet-light imaging in the presence of significant visible radiation, without need for extensive baffling to suppress stray light or for costly filters to block visible light. The volume, weight, and power consumption of this GaN detector array is an order of magnitude below those of comparable photomultiplier tubes and microchannel plates now used to detect ultraviolet light. This GaN detector array also operates at lower voltage. Moreover, GaN is rugged, and the fabrication of detectors from GaN is relatively easy.

The prototype device - a 1 × 16 array - was fabricated by a conventional lift-off technique. Each detector element comprises a metal/semiconductor/metal interdigitated structure (see Figure 1). The overall area of the array is 4 mm2. Semi-insulating GaN was used to obtain low dark current. The metal digits and connecting lines were formed in a Ti/Al/Au multilayer, which was used to ensure good ohmic contact.

Figure 1. The Array Contains 16 Elements, each having an interdigitated metal/semiconductor structure with 20 fingers coming in from each end. The fingers are spaced at intervals of 4 µm. Each finger is 2 µm wide and 500 µm long.

Figure 2 shows the measured responsivity of one detector element. This detector element was found to have a responsivity of 3.1 ± 0.3 A/W at a wavelength of 365 nm, a response time of 0.5 ± 0.2 ms, and a dark current of 5 ×10 - 11 A; as of the time of submission of the information for this article, these performance figures were the best yet reported for GaN ultraviolet detectors.

Figure 2. The Responsivity of One Detector Element was measured during operation at a potential under 10 V. Note the sharp cutoff at the wavelength of 370 nm.

There are numerous potential industrial, medical, and scientific-research applications for GaN detector arrays like this one. For example, because of their solar-blind nature, such arrays would be well suited for geophysical observation. They could also be used to detect ultraviolet light in hot environments and to detect ultraviolet emissions from flames and rocket exhausts.

This work was done by Zhenchun Huang, David Brent Mott, and Peter K. Shu of Goddard Space Flight Center. No further documentation is available. GSC-13828

NASA Tech Briefs Magazine

This article first appeared in the October, 1999 issue of NASA Tech Briefs Magazine.

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