Army

Polarization enhanced avalanche photodetector

Separate absorption and multiplication avalanche layers in a photodiode for novel high-performance that combines the high quantum efficiency of a direct band gap material with a material having superior avalanche multiplication properties

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Scientists at the Army Research Laboratory has recently invented an APD which does not require a charge layer and thus reduces the voltage penalty of previous designs. The patented technology is available via patent license agreement to companies that would make, use, or sell it commercially.

In APDs, incoming light is used to generate carriers (free electrons or holes). Once the avalanche breakdown begins, the carriers are accelerated by the electric field to very high speeds striking other atoms and knocking carriers free from another atom, and ionizing them. As this process continues the number of free carriers moving through the material increases exponentially; often in just picoseconds. The avalanche multiplication process takes place in the multiplication portion of the photodetector. The carriers are absorbed for conversion to electrical current in the absorption portion of the photodetector.

Typical applications for APDs include laser rangefinders and long-range fiber optic telecommunications. Parameters for judging the usefulness of APDs for a particular application include quantum efficiency, or the efficiency related to the absorption of incident optical photons and subsequent generation of primary charge carriers; total dark current, noise equivalent power, spectral sensitivity range, and operating voltage.

Advancing APD technology, ARL researchers have created polarization enhanced, separate absorption and multiplication avalanche layers in a photodiode (PE-SAM-APD). The approach combines the high quantum efficiency of a direct bandgap material with a material having superior avalanche multiplication properties similar to what is widely employed for InGaAs/InP telecommunications APDs. However, in contrast to a traditional SAM region system, the PE-SAM-APD employs an absorption region and an adjacent multiplication region composed of semiconductors having different magnitudes or directions of polarization (both spontaneous and/or piezoelectric) that result in the formation of beneficial polarization interface charge at their hetero-interface.

The formation of this beneficial polarization interface charge at the hetero-interface for a PE-SAM-APD enables the sharp transition from a desirable large electric field in the multiplication region to a low or zero electric field on nearly the atomic scale, thereby eliminating the need for the charge layer, and the concomitant higher operating voltage penalty associated with it.

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$3,000
$4,000
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4%
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$1,000
$1,000
$1,000
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40%
40%

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