L. Pekarek

High Detection Performance of Particle Detectors Based on SI InP Doped With Ti and Zn

In this work, we present results of measurements of spectra of alpha-particles carried out on semi-insulating (SI) InP detectors. The detectors were fabricated from Ti and Zn co-doped SI InP crystals grown by Czochralski technique. Tests of detectors performance with alpha-particles emitted from 241Am (5.48 MeV) radioactive source are reported. Excellent detectors performance has been evaluated by values of charge collection efficiency 99% and energy resolution ~ 1% obtained from the spectra measured at 230 K. Such high performance can be explained by InP doping with suitable Ti atoms and co-doping with low concentration of Zn acceptors sufficient for the full compensation of shallow donors, to reach SI properties. The electron mobility of reported SI InP detectors co-doped with Ti and Zn has been found to be equal to 2510 cm2 V-1 s-1 at room temperature. This value is much higher than that obtained previously with our SI InP co-doped with Ti and Mn or with InP crystals converted to SI state by temperature annealing. Excellent detector performance and high electron mobility makes the reported InP material promising to be used for the detection of X-rays and gamma-radiation.

Evaluation of Semiinsulating Annealed InP:Ta for Radiation Detectors

InP crystals were grown by the Czochralski technique. They were purified by inclusion of Ta into the growth melt and then converted to the semiinsulating state by annealing. Various annealing regimes were examined to find the optimum material for radiation detectors. Temperature dependent Hall measurements were carried over the range from 300 to 430 K and the activation energy of the impurity responsible for the semiinsulating state was determined from the slope of a straight line plot to be 0.75 eV from the conduction band edge. This energy is different from the activation energy, 0.65 eV, of Fe2+ in InP which was observed for annealed InP grown with an admixture of Fe. An InP wafer selected for fabrication of prototype particle detectors was lapped and chemomechanically polished on the both sides to a final thickness of 0.25 mm. The detectors themselves were fabricated by deposition of circular metal electrodes of 1 mm diameter on both sides of the wafer, using vacuum evaporation of Ni/Ge/Au. The performance of these particle detectors was characterised by pulse-height spectra obtained with alpha particles emitted from 241Am. The maximum of the spectral line measured at 300 K corresponded to an 85% charge collection efficiency when 100 V voltage was applied

Temperature change of Hall and Seebeck coefficient sign in InP doped with transition metals

Semi-insulating InP samples doped with transition metals were grown by the Czochralski technique. Both Hall and Seebeck effect measurements show the change of Hall and Seebeck coefficient sign at low temperatures. Electron hopping between iron or titanium ions in the nearest sites is assumed to cause the change. The theoretical calculations based on the mixed conductivity model are in good agreement with experimental values. Different temperatures for the change of sign of Seebeck or Hall coefficients for different samples are related to the activation energy of deep Ti donor and Fe acceptor energy levels, and also to the acceptor-to-donor compensation ratio.

Evaluation of InP:Ti and InP:Mn and its use for particle detectors

Semi-insulating and semiconducting InP single crystals without intentional doping and doped with Fe, co-doped with Zn and Ti and doped with Mn were grown by Czochralski technique. Samples cut from these crystals were characterized by Hall effect measurements and DLTS. Two electron traps were found in undoped InP which concentration was suppressed in Mn doped InP. Binding energies of Fe, Ti and Mn deep level impurities were determined from the temperature dependent Hall effect measurements. The curves of Hall coefficient vs. reciprocal temperature decline from straight lines at low temperatures for InP:Fe and for InP:Ti samples due to electron and hole mixed conductance. The value of resistivity reaches about 10/sup 6/ /spl Omega/m at 230 K and 100 K for InP:Ti and InP:Mn, respectively, the value suitable for using these materials for designing particle detectors operating at the low temperatures.

Hydrogen photoevolution on InGaP polycrystalline and tandem-type electrodes

We report on preparation of p-In1−xGaxP polycrystalline, p-In0.5 Ga0.5P/p-GaAs, and p-In0.5 Ga0.5P/n-GaAs/n-InP tandem-type cathodes. The photovoltaic efficiency of InGaP tandem type epitaxial electrodes is two times higher than that of polycrystalline photocathodes. The most significant advantage of epitaxial electrodes is in their markedly better corrosion resistance in comparison with polycrystalline photocatodes.

Growth of InP crystals with rare-earth elements

We report on the influence of rare earth (RE) elements (Pr, Er, and Dy) addition during vertical Bridgman low pressure synthesis on the properties of InP crystals. The temperature dependent Hall measurement and low-temperature photoluminescence (PL) spectroscopy were employed to study the changes in electrical and optical properties of the crystals. The observed changes are attributed to the gettering effect of REs caused by the high affinity of REs towards shallow impurities in InP.

Detectors of Gamma Rays and Alpha Particles Based on Ta-Doped InP Converted to the Semi-Insulating State by Annealing

InP crystals were synthesized with a Ta admixture grown by the Czochralski technique, and wafers cut from the grown crystals were converted to the SI state by high-temperature annealing. The good detection performance of such material-based detectors has been tested with alpha-particles from a 241Am source (5.48 MeV). The charge collection efficiency (CCE) of 84% and relative energy resolution at full width at half maximum (FWHM) of 5% were obtained at room temperature 295 K (RT). Low-energy gamma-photons of 122 keV from a 57Co source and gamma-photons from a 137Cs source were detected at 242 K, 272 K, and 295 K, respectively. The values of CCE 88% and FWHM 16 keV of 122 keV photons and CCE 87% and FWHM 48 keV of gamma-photons of 662 keV were obtained at reduced temperatures. A pulse-height spectrum of 662 keV gamma-photons registered at room temperature is also shown in this work.

Semi-insulating InP detectors with guard ring electrode

Particle detectors made with a guard-ring electrode (GR) on a semi-insulating Ti and Zn co-doped InP crystal grown by Czochralski technique are reported. Cathode electrode consisted of an active circular electrode and an encircling GR. Detection performance of particle detectors was measured by pulse-height spectra with alpha particles emitted from the 241Am source. An improved energy resolution of the detector with the GR compared to detectors without GR was observed. Applied bias voltage on the GR reduced the leakage current of the detector and improved spectral characteristics at room temperature (RT). The best values of charge collection efficiency 99 % and of energy resolution 0.9 % at 230 K or respectively 17 % and 16 % at RT for the detector with the GR is presented. These results deserve further investigation of InP co-doped with Ti and Zn as suitable material for X- and gamma-ray detectors operating at RT.

Growth of indium phosphide bulk crystals for radiation detectors

Bulk indium phosphide single crystals were grown by the liquid encapsulation Czochralski method using vertical Bridgman low pressure synthesis of poly-crystalline InP. The semi-insulating state necessary for radiation detection was created by the iron doping or iron-zinc and titanium-zinc co-doping. High temperature annealing of very pure or tantalum doped InP were also done. For characterization of InP crystals the Hall measurements and mass spectroscopy analysis were used. Crystal structure defects were studied by the etching and X-ray methods. Samples of X-ray detectors of this material were constructed and the efficiency of detection was measured.

Room-temperature particle detectors based on purified InP single-crystals converted to semi-insulating state by annealing

InP were grown by Czochralski technique. They were purified by admixture of Ta into the growth melt and then converted to semi-insulating state by annealing. Temperature dependent Hall measurements were carried out in the range from 300 K to 430 K and the activation energy of the impurity responsible for the semi-insulating state was determined from the slope of the straight line as 0.75 eV from the conduction band edge. This energy is much different from the activation energy of Fe2+ in InP, 0.65 eV, which was observed in the annealed InP grown with Fe admixture. InP wafer selected for fabrication of prototype particle detectors was lapped and chemo-mechanically polished on the both sides to final thickness of 0.25 mm. The detectors were fabricated by metal deposition of circular electrodes of 1 mm diameter overlaying on both sides of the wafer, using vacuum evaporation of Ni/Ge/Au. Detection performance of particle detectors was measured at room temperature by pulse-height spectra with alpha particles emitted from 241Am. Maximum of the spectral line corresponded to 85% of charge collection efficiency when 100 V voltage was applied