Air Force

Surface passivation improved IR photodetectors

Reduces or eliminates surface leakage current in infrared detectors

Sensors

Air Force scientists have improved the performance of infrared (IR) detectors by using a passivation layer with dopant to reduce/eliminate leakage currents. The patented technology is available via license agreement to companies that would make, use, or sell it commercially.

Three orders of magnitude reduction in dark current of passivated IR detectors: Top) p-type InAs/InAsSb absorption material. Bulk n-type InAsSb top layer. Bottom) p-type InAs/InAsSb absorption material. Bulk n-type InAsSb top layer. ALD deposition of 20nm ZnO passivation layer. 500 Celsious 1 minute under N2 for diffusion of dopant.

Manufacturing an IR photodetector often exposes the sensor to processes, materials, and techniques that limit their operating range or hinder their performance.

When fabricating such detectors, the processes used can alter the semiconductor absorption material at the surface. This can create a conductive surface layer that bypasses the path through which bulk electrical current should flow.

In such instances, surface leakage current flows through the conductive surface layer instead, significantly hampering reliable operation.

The challenges posed by surface leakage current can be particularly prevalent in devices using p-type absorption materials, where the etching process results in pinning at the surface. This pinning, in turn, leads to an accumulation of electrons near the surface such that the p-type material becomes an n-type material, leading to surface inversion.

Standard passivation layers can act as a protective film but are typically not doped. Also, they must be epitaxially regrown, resulting in a more complicated fabrication process.

The researchers have developed a method to compensate for the effects of the fabrication process on the reliability and operation of photodetectors. More specifically, a uniform passivation layer is deposited on the infrared detector where leakage current is most likely to occur – typically on the sidewalls if the detector is of a mesa construct.

The dopant material in the passivation layer is diffused into the detector material using standard methods. The passivation layer can be retained or later removed by dry or wet etching.

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