We report current-voltage data for back-illuminated mesa photodiode test structures fabricated by arsenic-diffusion
into n-type LPE HgCdTe films. Arsenic diffusion was carried out in a sealed quartz ampoule containing a source of
both Hg and As. The arsenic-diffused p-on-n photodiodes were characterized at 70 K and 80 K. The cutoff
wavelength was about 11 μm at 80 K. The data for 400 μm diameter photodiodes fabricated by the arsenic diffusion
process are very similar to those from a conventional two-layer LPE
P-on-n process for material with approximately
the same cutoff wavelength. We outline process and doping level changes that should improve detector
performance.
This paper reviews and assesses progress in back-illuminated P-on-n photovoltaic HgCdTe detector technology, grown by two-layer Liquid Phase Epitaxy on CdZnTe substrates, for applications at wavelengths beyond 15 μm in a new generation of spaceborne multispectral instruments for remote sensing. We review data that demonstrate the feasibility of useful cutoff wavelengths as long as 17.5 μm. We recommend that LPE photovoltaic HgCdTe technology be extended to the 20-25 μm wavelength region for single elements and arrays for NASA remote-sensing applications.
This paper reviews and assesses back-illuminated P-on-n photovoltaic HgCdTe detector technology, based on two-layer growth by Liquid Phase Epitaxy on CdZnTe substrates, for application at wavelengths beyond 15 μm in a new generation of spaceborne multispectral instruments for remote sensing. We review data that show feasibility of useful cutoff wavelengths as long as 18-19 μm. We recommend that that LPE photovoltaic HgCdTe technology be extended to the 20-25 μm wavelength region for single elements and small arrays for NASA remote-sensing applications.
Hg1-XCdXTe photodiode arrays have assumed a critical importance for systems requiring sensitivity in any one of the infrared bands of interest extending from the SWIR 1-3 micrometer band to the VLWIR >14 micrometer band. As arrays have become larger, system requirements more stringent and cutoff wavelengths longer, more pressure has been placed on improving the Liquid Phase Epitaxial (LPE) Hg1-XCdXTe growth technique at BAE Systems. In this paper we will report on improvements made in each critical aspect of LPE growth, covering the entire range of Hg1-XCdXTe compositions required for photodiodes with cut-off wavelengths ranging from 3 to greater than 14 micrometers. Data presented will demonstrate that continual advances in LPE Hg1-XCdXTe growth techniques at BAE Systems promise high infrared system performance meeting SWIR to VLWIR needs.
High Performance LWIR Focal Plane Arrays are critical for many space applications. Reliable LWIR focal plane arrays are needed for these applications that can operate in space environment without any degradation.
In this paper, we present various LWIR detector array architectures currently being evaluated for LWIR applications. These include backside-illuminated configurations for HgCdTe fabricated on CdZnTe and Silicon substrates. To optimize the LWIR device performance, minimize the anti-reflection losses, and significant reduction in the effects of solarization in space, innovative Anti-reflection coatings are needed, that will enhance the performance of the LWIR detector / focal plane arrays.
We also present AR Coating models and experimental results on several promising multi-layer AR coatings that includes CdTe, Si3N4 and diamond like Carbon, that have the necessary spectral response in the 8-14 microns and are hard materials with excellent bond strength. A combination of these materials offers the potential of developing anti-reflection coatings with high optical quality with controlled physical properties.
Focal plane arrays fabricated in Hg1-xCdxTe have matured to the point where they are entering pilot production for military and civilian applications. Loral chose the p-on-n heterostructure photodiode architecture produced by a two step LPE process for production scale-up because of its demonstrated high performance over a broad range of cut-off wavelengths from approximately equals 4 micrometers to > 15 micrometers . To meet the manufacturing requirements of high throughput and flexibility, Loral has successfully scaled and transferred into production, both tellurium rich horizontal slider (for growth of the active n-type base layer) and mercury rich vertical dipping (for growth of the p-type cap layer) technologies. This approach capitalizes on the advantages of each process to maximize the producibility of LPE films in a manufacturing environment. This paper discusses the advantages of horizontal Te-rich growth. Production reactors have demonstrated excellent compositional uniformity (+/- 0.005 in x) over 24 cm2. Issues related to the scale-up of the equipment are discussed.
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