Kunihiro Tanikawa

Minority carrier lifetime in the region close to the interface between the anodic oxide and CdHgTe

This paper describes minority carrier lifetime in n-type CdHgTe surface layers, especially the relationship between minority carrier lifetime and dislocations. A new method has been developed to evaluate lifetime in the surface layer of semiconductors. This method measures the concentration of minority carriers remaining after injection by utilizing surface potential measurement of an MIS diode. Computer simulation reveals how dislocations affect minority carrier lifetime and confirms the validity of this method. Experimental results indicate the dislocation-induced recombination is dominant for dislocation densities over 5×105 cm-2 and that minority carrier lifetime is inversely proportional to dislocation density. These results are similar to the results of the R0A product as a function of dislocation densities that have been reported by Colombo and Syllaios. The conjugate pairs r (radius of dislocation pipe) and s (recombination velocity at the dislocation site) are 0.3 to 0.5 cm2 s-1. The lifetimes become almost constant - scatter 3 to 4 μs - for dislocation densities less than 2×105 cm-2. Lifetime is not dominated by dislocations in this dislocation density range.

Evaluation of dark‐current nonuniformity in a charge‐coupled device

This letter investigates the relationship between stacking faults (SF’s) and dark‐current nonuniformity in a charge‐coupled device (CCD) through the measurements of cell‐to‐cell dark‐current distribution, leakage current, C‐t characteristics, and the Sirtl etching of the device. It is revealed that stacking faults are strongly connected with the nonuniformity in the dark current and are the dominant origin of the dark‐current spikes.

CCD with Meander Channel

The basic concept, structure and some experimental results of a new type of CCD are reported. The CCD has only two straight gate electrodes over a meander channel and no bus lines for clocking. The structure gives some advantages over conventional CCDs in applications such as transversal filters, line addressable memories and area sensors. The signal can be picked up at any point along the channel without a crossover. The simple electrode configuration promisses high packing density.

Diffractive lens in 8- to 10-μm forward-looking infrared system

We realize for the first time a forward-looking IR (FLIR) sys- tem using a diffractive optical element (DOE) in its optics made of ger- manium in the 8- to 10-mm IR wavelength. We describe the design and the performance of the DOE optics. The IR diffractive lens made of ger- manium is proposed to correct the axial chromatic aberration in optics of the FLIR system. Compared with conventional optics of an FLIR system the optics using a DOE singlet instead of ZnSe achromat, we have a DOE system modulation transfer function (MTF) that is almost equal to the conventional one. The DOE singlet instead of ZnSe achromat ap- pears to be enough to compensate for the chromatic aberration of the optical system. Using the DOE system, the numbers of lens elements, the mass, and the cost are reduced.

A PtSi Schottky-barrier area imager with meander-channel CCD readout registers

This paper describes improvement of the fill factor of Schottky-barrier infrared CCD arrays by using a meander-channel CCD (MCCD) as both the vertical and the horizontal readout registers. A 64 × 64 element monolithic Schottky-barrier infrared meander channel CCD(SB-IRMCCD) with 23 percent fill factor has been fabricated with negligible element to element cross talk. This letter also describes how a fill factor of 57 percent is possible by decreasing the area of the vertical MCCD register to 30 percent of that in the present device.

The design consideration on a meander-channel CCD

This paper describes some of the design consideration on a meander-channel CCD (MCCD). The design concept of the MCCD is different from that of conventional CCDs. Mask misalignment in fabrication process and narrow-channel effect must be taken into consideration. Mask misalignment induces the potential bump and dip near the boundary between the two electrodes. The narrow-channel effect induces the potential decrease at the bottleneck between the interdigitated channel stops. These problems are investigated by means of the analyses of potential in the buried MCCD. The model is based on a numerical solution of the two-dimensional Poissons equation with the ideal electrode structure.

Reduction of Hg1−xCdxTe native oxide during the SiNx deposition process

Electron cyclotron resonance plasma chemical vapor deposition enables low‐temperature SiNx deposition on Hg1−xCdxTe (MCT). The SiNx film has an excellent interface on MCT with a low surface state density of 1.0×1011 cm−2 eV−1 and a low fixed charge of −1.4×1011 cm−2. A detailed analysis by x‐ray photoelectron spectroscopy and Auger electron spectroscopy spectra of Te, Cd, and Si at the SiNx/MCT interface indicated that the SiNx deposition reduces the naturally grown MCT native oxide. The oxygen taken from Te oxidizes SiH4 and produces silicon oxides which remain in the SiNx film. Since a chemical shift caused by oxidized Cd at the fresh surface of MCT is very slight, intentionally oxidized samples were used to confirm the above reaction. The analysis of the shape of the Si(2p) peak at the interface indicated that the silicon oxides are composed of SiO and SiO2. Thermodynamic considerations support such a mechanism.

480 × 8 hybrid HgCdTe infrared focal plane arrays for high-definition television format

We explain the technologies used for high-performance long linear arrays based on HgCdTe/CMOS hybrid multiplexers with bidirectional time delay and integration (TDI) functions and describe the development of the first high-resolution IR imaging system with a superextended graphics array (SXGA) format. Long-wavelength IR photodiode arrays are fabricated using liquid-phase epitaxially grown HgCdTe on a CdZnTe substrate. Each photodiode array consists of 480x8 element n+/n-on-p diodes formed by B+ implantation. Diodes with a 10.3-μm cutoff wavelength have a typical zero-bias resistance of 10 MΩ and a shunt resistance of 1 GΩ. Four CMOS readout integrated circuits (ROICs) are used for bidirectional TDI and multiplex operations, where each ROIC sums up and multiplexes eight signals from 120 channels. The ROIC also includes pixel deselection and gain control circuits along with the corresponding memory and writing means. The IR focal plane arrays (IRFPAs) have a typical noise equivalent temperature difference (NETD) of 18 mK after TDI with F/1.55 optics and 10-μs integration. The IR imaging system adopts an interlace scan using the 480x8 element IRFPA to demonstrate a high spatial resolution of 1280 horizontal lines by 960 vertical lines (SXGA format) and an NETD of less than 30 mK. The unique algorithm for image enhancement is successfully confirmed to be efficient.

Six band multispectral sensor using off-axis three-mirror reflective optics

This paper describes design and experimental results for the future airborne multispectral sensor with six bands between visible and infrared regions. The multispectral sensor features single optics using off-axis three-mirror reflective optics to provide same field of views for all six bands and dichroic mirrors to separate the spectral range into six bands. The off-axis three-mirror optics provides an obstruction free FOV with a wide spectral range and high spatial resolution over a wide FOV. The six bands consist of three visible bands, a near infrared band, an MWIR band and an LWIR band. The 10,000 element CCD sensors are used for the three visible bands and the near infrared band. The 960 element HgCdTe linear arrays are used for the MWIR and the LWIR bands. The results of experiments reveal that the ground-base multispectral sensor has a wide spectral range from 0.4 ^m to 10 xm, the wide FOV over 5.7° and the high spatial resolutions of less than 10 xrad for visible and near infrared bands and of less than 104 xrad for the MWIR and the LWIR bands. The overall MTF at the center of the FOV is more than 0.3 at Nyquist frequency for all bands.

Designing and testing of off-axis three-mirror optical system for multispectral sensor

Future airborne surveillance systems require high performance optics to provide high spatial resolution over wide field of view. The system for 10 km altitude needs to resolve a ground target of 10 cm over 6 degree FOV. The spectral range covers from 0.4 to 10.0 micrometer. The spectral bands of interest include the visible, near infrared, MWIR (middle wavelength infrared), and LWIR (long wavelength infrared). This paper describes the design and the experimental results of the off- axis three mirror optical system which fulfills these requirements. The three mirror anastigmat consists of two aspherical concave mirrors and a spherical convex mirror. The design is configured for a telecentric flat focal plane.