Akira Sawada

Tilt growth of CdTe epilayers on sapphire substrates by MOCVD

Abstract We studied model lattice matching in the growth direction by tilt growth and found that the ratio of the tilt angle of the epilayer (α) to the offset angle of the substrate (θ) had a maximum at α / θ = 0.73, independent of the offset angle. Experimental plots of the ratio versus the full width at half maximum (FWHM) of (333) CdTe rocking curves in double-crystal X-ray diffraction show that the ratio ranges from 0.05 to 0.6 while the FWHM varies from 1100 to 400 arc sec. This result suggests that the lattice inclination orients the lattice structure perpendicular to the CdTe-sapphire heterointerface and that the tilt angle reduces defects such as dislocations and stacking faults. Most epilayers grown on sapphire substrates with offset angles above 3° were confirmed to have a α / θ ratio below 0.2. This suggests that crystal defects may be generated by shearing stress due to large offset angles. Greater defect density lowers the ratio and degrades crystallinity.

480 x 2 hybrid HgCdTe infrared focal plane arrays

To meet the sensitivity and resolution requirements of high-performance long-wavelength infrared (LWIR) imaging systems, we developed hybrid HgCdTe 480 X 2 infrared focal plane arrays (IRFPAs) for the 8 - 10 micrometers band. We connected the hybrids using indium bumps and a sapphire wiring substrate to reduce the thermal expansion mismatch between the silicon readout circuits and the photodiode arrays. Using the mature liquid phase epitaxy (LPE) technology and a CdZnTe substrate, we fabricated LWIR photodiode arrays. Each photodiode array consists of 240 X 2-element n+/n/p diodes formed by boron implantation. The arrays have an average zero-bias resistance of 3.8 M(Omega) and a shunt resistance of more than 100 M(Omega) for a 10.5 micrometers cutoff wavelength. For the readout devices, we used n-channel charge coupled devices (CCDs) with charge capacities greater than 4 X 107 electrons, and 4 signal outputs capable of 6 MHz data rates. The input stages of the CCD include skimming and partitioning functions. Operating at 80 K, the arrays had a mean laboratory D*(lambda p) of 6.4 X 1010 cmHz0.5/W with f/1.2 optics. The detectivity variation ((sigma) /m) was 14%, and the operable pixel yield exceeded 99%.

A Highly Sensitive And Compact SO2 Gas Sensor Using A Pbsnte Laser

We have developed a highly sensitive, compact SO2 gas sensor that uses a PbSnTe laser. To increase its sensitivity, we used wedge-shaped windows that decrease etalon fringes and a SO2 absorption line that is little influenced by water vapor and that has a strong coefficient. The etalon-fringe intensity of the optical system was reduced to 1 x 10-4 and the SO2 absorption line selected is 1380.9 cm-1. To make the sensor compact, we developed single-mode lasers to eliminate the need for a monochromator, used a 30-cm multipath cell with an optical path of 10 m and a liquid-nitrogen-cooled, small metal dewar to cool the laser. The sensor performs stably at 30 ppb over a range of 10°C to 35°C, has a sensitivity of 7 ppb RMS at a fixed temperature, and is 32 cm x 50 cm x 20 cm.