InGaN alloy fluctuations have been exploited in many nitride optoelectronic devices. This work reports on the
application of InGaN alloy fluctuations in a packaged vacuum electronic device utilizing an InGaN photocathode as
the detector element. The resulting image intensifier is the first ever InGaN imaging detector.
Exploitation of the particular InGaN properties of alloy fluctuations has several positive consequences for
photocathodes. One, it is advantages because of the possibility of extending the spectral response to the longer
wavelengths with lower average indium concentrations.
Two, in achieving a longer wavelength response, this lessens the strain at the sapphire-AlN-InGaN
interface because a lower average In percentage can be used. Thirdly, the larger bandgap InGaN matrix material will
have a lower amount of thermionic emission coupled with this longer wavelength photoresponse. Finally, an InGaN
alloy with visible response holds the promise in that it can be grown directly on a sapphire window as opposed to the
compression bonding of GaAs as originally reported by Antypas and Edgecumbe.
Image intensifiers (I2) have many advantages as detectors. They offer single photon sensitivity in an imaging format,
they're light in weight and analog I2 systems can operate for hours on a single AA battery. Their light output is such as
to exploit the peak in color sensitivity of the human eye. Until recent developments in CMOS sensors, they also were
one of the highest resolution sensors available. The closest all solid state solution, the Texas Instruments Impactron chip,
comes in a 1 megapixel format. Depending on the level of integration, an Impactron based system can consume 20 to 40
watts in a system configuration.
In further investing in I2 technology, L-3 EOS determined that increasing I2 resolution merited a high priority. Increased
I2 resolution offers the system user two desirable options: 1) increased detection and identification ranges while
maintaining field-of-view (FOV) or 2) increasing FOV while maintaining the original system resolution.
One of the areas where an investment in resolution is being made is in the microchannel plate (MCP). Incorporation of a
2 micron MCP into an image tube has the potential of increasing the system resolution of currently fielded systems. Both
inverting and non-inverting configurations are being evaluated. Inverting tubes are being characterized in night vision
goggle (NVG) and sights. The non-inverting 2 micron tube is being characterized for high resolution I2CMOS camera
applications. Preliminary measurements show an increase in the MTF over a standard 5 micron pore size, 6 micron pitch
plate. Current results will be presented.
Nitride based photocathodes for image intensifiers are of interest because of the wide span of wavelengths covered by
the bandgap of the AlGaInN alloy system. The potential bandgap range for this alloy system is from 6.2 eV for AlN to
0.7 eV for InN. Coupled with microchannel plate technology, this alloy system potentially offers low noise and high gain
image intensifiers over a wide wavelength range. Results from L-3 EOS work in this area are presented beginning with a
brief summary of unpublished early work carried out from 1992 - 1997 on AlGaN image intensifiers. The early work
wrestled with the dual issues of sealing image intensifiers along with improving the quality of the AlGaN epitaxy layer.
This is followed by our current results on a GaN image intensifier sealed with a photocathode from SVTA. Imagery
using 375nm LED illumination is shown. The quantum efficiency at 300nm was estimated to be 16% measured in
transmission mode. This QE was achieved with a 0.15μm thick Mg doped GaN active layer.
This paper details an image intensifier enhancement program at Litton Electro-Optical Systems (LEOS) and the U.S. Army Night Vision and Electronic Sensors Directorate (NVESD) for the development of an unfilmed bulk conducive glass (BCG) Microchanel Plate (MCP) for use in any image intensifier (I2) to enhance signal-to-noise, reliability, and lifetime. We will discuss the material characterization associated with this new class of MCP glass. Then we will explore the outgassing and ion feedback properties of a BCG MCP in vacuum demountable experiments. Electrical and optical measurements on BCG MCPs with standard Generation III configuration (9-13 micron channel pitch) will be discussed. Test results will be presented for I2 with a start-of- the-art bulk conductive glass MCP in order to provide enhanced imaging capability for 21st century night vision systems.
Current Generation II Gallium Arsenide (GaAs) image intensifier tube technology requires that the tube microchannel plate (MCP) component have a thin dielectric coating on the side facing the tube's photocathode component. This protective coating substantially reduces the release from the MCP of ions and neutral species, particularly when the image intensifier is operated. The prevention of MCP outgassing is necessary in order ot prevent the poisoning of the Cs:O surface on the GaAs photocathode. Many authors have experimented with omitting the MCP coating. Such experiments have consistently led to an intensifier with a significantly reduced lifetime, due to contamination of the Cs:O layer on the photocathode. Unfortunately the MCP film acts as a scattering cneter to electron transport within the intensifier and effectively reduces the photoelectron detection efficiency. Substantial enhancement of the image intensifier operating parameters is the motivation for the removal of the MCP film. Removal of the MCP film promises to simplify MCP fabrication and enhance the intensifier parameters related to Electro-Optical performance and image quality. This paper presents results showing for the first time that it is possible to fabricate a long lifetime image intensifier with a single unfilmed MCP and achieve improved imaging and performance characteristics.
Current GaAs image intensifier technology requires that the microchannel plate (MCP) have a thin dielectric film on the side facing the photocathode. This protective coating substantially reduces the amount of outgassing of ions and neutral species from the microchannels. The prevention of MCP outgassing is necessary in order to prevent the `poisoning' of the Cs:O surface on the GaAs photocathode. Many authors have experimented with omitting the MCP coating. The results of such experiments invariably lead to an intensifier with a reported useful life of less than 100 hours, due to contamination of the Cs:O layer on the photocathode. Unfortunately, the MCP film is also a barrier to electron transport within the intensifier. Substantial enhancement of the image intensifier operating parameters is the motivation for the removal of the MCP film. This paper presents results showing for the first time that it is possible to fabricate a long lifetime image intensifier with a single uncoated MCP.
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