Masahiro Tanaka

Acceptor level related Shockley–Read–Hall centers in p-HgCdTe

Abstract We investigated the minority carrier lifetime in p-type HgCdTe layers grown using liquid-phase epitaxy and found that the lifetime was dominated by the Shockley–Read–Hall (SRH) mechanism whose recombination centers were closely associated with acceptor energy levels. We compared the lifetime and acceptor activation level in two kinds of p-HgCdTe layers having different acceptors. One kind was the conventional Hg-vacancy doped HgCdTe layers and the other kind was the Ag-impurity doped HgCdTe layers using the AgNO3 dipping solution technique. In p-type HgCdTe layers doped with Hg vacancy acceptors, the minority carrier lifetime was very short due to SRH recombination centers existing 20xa0meV above the valence band. This trap energy was slightly larger than that of the acceptor activation energy. When HgCdTe layers were doped with Ag, the above SRH center disappeared and the lifetime increased. In this case, the lifetime was dominated by another SRH center of 5xa0meV, which was again near the acceptor level of the host material. We concluded that SRH centers in Hg-vacancy doped HgCdTe layers originated from the vacancy itself and had no relationship to crystal defects. Ag replacement seems to have brought about the only energy state change for vacancy-related SRH centers where the energy shift corresponded to the acceptor level shift.

Epitaxial growth of HgCdTe on sapphire for photoconductive detectors

Abstract We used a combination of isothermal vapor phase epitaxy (ISOVPE) and liquid phase epitaxy (LPE) to grow HgCdTe on a CdTe/sapphire substrate by metal organic chemical vapor deposition (MOCVD). ISOVPE was used to convert a CdTe layer to Hg 0.8 Cd 0.2 Te. The ISOVPE and LPE processes were consecutive and performed in a closed tube. Using the conversion process, the lattice mismatch between CdTe and HgCdTe decreases. The conversion also reduces the compositional gradient caused by interdiffusion between the CdTe substrate and the epitaxial layer. After annealing the wafer in a Hg atmosphere, performance as a photoconductive detector was used to examine the wafer quality. The results are comparable to the performance of conventional detectors made of LPE-grown HgCdTe on CdZnTe.

Defects in Ion Implanted Hg0.78Cd0.22Te Probed by Monoenergetic Positron Beams

Defects and their annealing properties in ion implanted Hg0.78Cd0.22Te were studied using monoenergetic positron beams. Vacancy-type defects introduced by B+-implantation were identified as open spaces associated with extended defects such as dislocation loops and stacking faults. For an Ar+-implanted specimen, the mean size of the open volume of defects in the damaged region was estimated to be that of divacancies. The observed difference between the species of defects in the B+- and the Ar+-implanted specimens was attributed to the suppression of the recombination between vacancies and interstitials in the damaged region introduced by Ar+-implantation. The annealing temperature of the vacancy-type defects introduced by Ar+-implantation was determined to be 300°C.

Web API Creation for Enterprise Mashup

It is desirable for web applications to be reusable, for example in case a vendor wants to deliver new valuable services by using and combining existing applications quickly. One of the well-known ways of reusing web applications, Mashup, has become popular in the web development community and applied to many open web sites, as we can just combine the data retrieved from Web pages or APIs of the web applications. But in the case of the Mashup of enterprise web applications, or Enterprise Mashup, it is quite difficult since these applications are often not intended to be reusable and have no Web APIs. That means we have to create the Web APIs for the applications, which takes much work. In this paper, we describe a light-weight Web API creation methodology in order to create Web APIs for enterprise web applications much more easily than we can by extending the source code. The created Web API can connect to the web application just as a client who has an account does. So we can create a Web API for Enterprise Mashup without modifying the application at all and we can call the Web API securely using the user account information of the application. We developed the implementation of our methodology and applied it to actual applications to evaluate its effectiveness.

Defects and Their Annealing Properties in B+-Implanted Hg0.78Cd0.22Te Studied by Positron Annihilation

Defects and their annealing properties in B+-implanted Hg0.78Cd0.22Te (p-type) were studied using the positron annihilation technique. For an unimplanted specimen, the major species of defects was identified to be Hg vacancies, VHg, and its concentration was estimated to be 6×1015 cm-3. For the B+-implanted specimen, a damaged region showed n-type character, and vacancy-type defects were found to be present in this region. Below the n-type layer, about 50% VHg was annihilated by the recombination between VHg and Hg atoms. After 150° C annealing, the mean size of open space of the vacancy-type defects in the n-type layer was found to decrease. At the same annealing temperature, the electron concentration in the n-type layer also decreased. Thus, an origin of donors was attributed to interstitial-type defects. The annealing temperature of the vacancy-type defects introduced by ion implantation was determined to be 300° C

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%.