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In this paper we present studies of the I-V characteristics of CdZnTe detectors with Pt contacts fabricated from highresistivity single crystals grown by the high-pressure Brigman process. We have analyzed the experimental I-V curves using a model that approximates the CZT detector as a system consisting of a reversed Schottky contact in series with the bulk resistance. Least square fits to the experimental data yield 0.78-0.79 eV for the Pt-CZT Schottky barrier height, and <20 V for the voltage required to deplete a 2 mm thick CZT detector. We demonstrate that at high bias the thermionic current over the Schottky barrier, the height of which is reduced due to an interfacial layer between the contact and CZT material, controls the leakage current of the detectors. In many cases the dark current is not determined by the resistivity of the bulk material, but rather the properties of the contacts; namely by the interfacial layer between the contact and CZT material.

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or DECnet { UAZHEP::MCGUIRE A dark matter (DM) search experiment was own on the IMAX balloon payload, which tested the hypothesis that a minor component of the dark matter in the Galactic halo is composed of ionizing massive particles (IMPs) (with dE=dx > 1 MeV/g/cm 2 or > 2 10 ?20 cm 2 ; m x 2 10 4 ; 10 12 ] GeV/c 2) that cannot penetrate the atmosphere due to their low-velocities (2 0:0003; 0:0025]). The DM search experiment consisted of a delayed coincidence between four 2400 cm 2 plastic scintillation detectors arranged in a vertical 2.5 m stack, with a total acceptance of 100 cm 2 sr. In order to search for ultra-slow particles which do not slow down in the IMAX telescope, the experiment contained TDCs which measured the time-delays T i;i+1 2 0:3; 14:0] s between hits in successive counters to 2% precision. Using the rst 5 hours of data at oat altitude (5 g/cm 2 residual atmosphere), we observed 5 candidate non-slowing and 16 candidate slowing dark matter particle events, consistent with the background expected from accidental coincidences of 4:0 non-slowing and 18:3 slowing events. This implies that the DM ux is less than 6:5 10 ?6 cm ?2 s ?1 sr ?1 (95% C.L.) for non-slowing IMPs (=m x < 2:31 10 ?26 cm 2 =GeV); and the DM ux is less than 7:9 10 ?6 cm ?2 s ?1 sr ?1 (95% C.L.) for slowing IMPs (=m x < 2:1 10 ?25 cm 2 =GeV). This experiment e ectively closes much of a previously unconstrained`window' in the mass/cross-section joint parameter space for massive particles as the dominant halo DM, and implies that for certain regions of this parameter space, massive particles cannot be more than one part in 10 5 by mass of all the DM. These results can also directly constrain`light' magnetic monopoles, neutral hadrons and neutraCHAMPs in a previously unconstrained mass region m x 2 10 6 ; 10 8 ] GeV.

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