dc.description.abstract | The recent developments in high Al-content AlxGa1−xN material growth
technology made it possible to fabricate high performance solar-blind
photodetectors operating in the ultraviolet (UV) spectral region with improved
receiver sensitivity, low noise, low dark current density, and high speed.
AlGaN-based Schottky, p-i-n, and metal-semiconductor-metal photodetectors
(MSM) with very high performances have already been demonstrated. The UVfiltering
nature of the atmospheric ozone molecules blocks the solar radiation to
reach the earth’s surface for wavelengths shorter than 280 nm. In this case, UV
photodetectors with cutoff wavelengths around 280 nm, which are also called
solarblind detectors, can detect very weak UV signals under intense background
radiation. These devices have important applications including missile plume
detection, chemical/biological agent sensing, flame alarms, covert space-tospace
and submarine communications, ozone-layer monitoring, and gas
detection. Due to their high responsivity (600 A/W), high speed, high cathode
gain (on the order of a million), and low dark current properties, photomultiplier
tubes (PMTs) are frequently used in such applications. However, PMTs are very
expensive and bulky. Besides, they require a cooling system, and they have high
operation voltages in excess of 1000 V. To achieve solar-blind detection, PMTs
should also be integrated with complex and expensive filters. In order to avoid
these disadvantages, high performance solid-state UV photodetectors with high internal gain are needed. Wide band-gap semiconductor photodetectors, such as
AlxGa1−xN with x=0.4, are ideal candidates for this purpose. These devices are
intrinsically solar blind, in which no additional filters are needed, they have low
noise, and fast response times. The lack of high internal gain has been the major
limitation for the usage of AlGaN photodetectors for applications that require
high sensitivity detectors. There have been several theoretical research works
that examined the avalanche effect in GaN and AlGaN-based structures.
However, reproducible high gain in AlGaN-based APDs is still a major
limitation. We have designed, fabricated, GaN/AlGaN based photodetectors, and
according to characterization measurements, the Schottky, p-i-n, and avalanche
detectors have high performance in terms of quantum efficiency, dark current,
detectivity, high speed response, and high reproducible avalanche gain. | en_US |