We report our simulations on the profile of the electric field in semi insulating CdTe and CdZnTe with Au contacts under
radiation flux. The type of the space charge and electric field distribution in the Au/CdTe/Au structure is at high fluxes
result of a combined influence of charge formed due to band bending at the electrodes and from photo generated carriers,
which are trapped at deep levels. Simultaneous solution of drift-diffusion and Poisson equations is used for the
calculation. We show, that he space charge originating from trapped photo-carriers starts to dominate at fluxes
1015-1016cm-2s-1, when the influence of contacts starts to be negligible.
Thermodynamic conditions for a post growth annealing to prepare near stoichiometric semi-insulating (SI) of CdTe with a minimized concentration of point defects are looked for in undoped and Sn-doped single crystals. The high temperature (200-1000°C) in-situ conductivity σ and Hall effect measurements are used to control the native defect density and to find out the Cd pressure PCd at which shallow defects are compensated. We show, that contrary to the undoped samples, where the change of the type of conductivity by variations of PCd is easy, the Sn-doped samples exhibit due to the Sn self-compensation much more stable behavior. The temperature near 500°C is reported to be optimum for the real-time annealing of bulk samples. The chemical diffusion is sufficiently fast at this temperature, simultaneously the lower temperature is preferred because the native defect density can be tuned gently by changing PCd. The measurement of temperature dependencies of σ in annealed samples below 500°C is used to establish the position of Fermi level and to characterize the structure of both shallow and deep levels detected in the sample. The quasichemical formalism is used for evaluation of defect density and for analysis of nature of deep levels.
Experimental conditions for a growth of near stoichiometric high resistive CdTe single crystals with a minimized concentration of point defects have to be defined. The position of the stoichiometric line in the pressure-temperature (P-T) phase diagram was evaluated from high-temperature in situ galvanomagntic measurements. Calculations based on a model of two major native defects (Cd vacancy and Cd interstitial) show, that a very small variation of Cd pressure P_{Cd} results in a strong generation of uncompensated native defects. Modelling of room temperature carrier density in dependence of the deep defect density NDD, PCd, and annealing temperature T shows, that the range of optimal PCd, at which the high resistivity can be reached, broadens with increasing NDD or decreasing T. It is shown, that at low T<450 degree(s)C the deep defect density <1015cm-3 is sufficient to grow the high resistive CdTe. CdTe doped with Vanadium is used as a model example.
Measurements of the Hall coefficient and conductivity of not intentionally doped p-Hg1-xCdxTe samples at temperatures 4.2-300K are reported. A theoretical approximation of experimental data based on a solution of the electronic Boltzmann transport equation and subsequent fitting procedure is done giving a very good agreement between the experiment and calculation. The measurements are analyzed in the full temperature interval simultaneously using the same relevant model parameters in the doping, intrinsic and intermediate region as well. The three- acceptor-level model for one divalent acceptor and one monovalent residual acceptor is discussed. The precision of model parameters determined by this way is analyzed. A novel method to check the sample homogeneity is suggested.
Diffusion length (L) of minority carriers was determined in not intentionally doped Cd0.93Zn0.07Te single crystals by the EBIC method at temperatures 80-300K using an evaporated Au Schottky barrier for a separation of electron- hole pairs. The L values in P-(CdZn)Te were longer, than those of the binary CdTe and some showed a steep increase with decreasing temperature. The correlation of the diffusion length measurements with photoluminescence for the (CdZn)Te was observed. Temperature dependence of L for holes in N-(CdZn)Te fabricated by In diffusion were measured as well.
Diffusion lengths of minority electrons and holes in Hg1-xCdxTe single crystals produced by the diffusion controlled Bridgman growth from melt of constant composition were studied. Bulk p-HgCdTe samples were etched by low energy Ar ions in the VEECO ion etching system or in Ar plasma in a plasma etching reactor. As a result of this treatment a deep p-n junction was created in the samples. Secondary-electron and electron beam induced current images were used to determine the position of the p-n junction. The obtained EBIC data were then sued for evaluation of a set of minority carrier diffusion lengths at temperatures 140-270 K.
High resistivity Ge-doped crystals with exact defined by radiometric analysis Ge contain were characterized by IR microscopy, dislocation etch techniques, scanning electron microscopy followed by detector performance features examination. the influence of several defect structure types on detector parameters were shown.
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