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DLTS, ODLTS and DLOS have been used to characterise the main deep level trapping centres in some II-VI semiconductors; these were single crystal CdS, (ZnCd)S, CdSe, CdTe and ZnS, and polycrystalline CdS films. Undoped, single crystal CdS contained four electron traps as detected by DLTS, at 0.29eV, 0.41eV, 0.61eV and 0.74eV below the conduction band (CB). The first two were observed in all samples and were due to native defects. The two states of highest energy were found only in material that had been annealed in S or Cd vapours. The 0.61ev level could be photoinduced by illumination at photon energies greater than about 1eV. It decayed in the dark with an activation energy of 0.25eV. The 0.61eV and 0.74eV centres were associated with electrically active extended defects (subgrain boundaries Such samples had dislocation densities of about 10(^10) cm(^-2). Copper was found to be a residual impurity in CdS. It produced two deep hole traps resulting from a crystal field splitting of the Cu d(^9) state. They were detected by ODLTS and DLOS and were found at 0.35eV and 1.lev above the valence band (VB).Introduction of the isoelectronic impurity tellurium into CdS induced a hole repulsive centre at 0.21eV above the VB. This is thought to be an inportant radiative recombination centre. The main electron trap in CdS at 0.41eV was found to shift to higher energy with incorporation of Zn. Replacement of 20% of the Cd with Zn shifted the energy to 0.63eV. The level appeared fixed to the VB and had a similar functional dependence on composition as the band gap. The activation energies of the copper centres observed in CdS remained unchanged with incorporation of Zn up to the composition (^Zn)0.45 (^cd)0.55(^s) showed that the crystal field splitting was constant and that these levels were also pinned to the VB. During the fabrication process of the (ZnCd)S/Cu(_2)S solar cell, a deep level was induced at about 1.2eV below the CB. This is thought to be a recombination centre and one of the contributory factors to the reduction observed in the current collection efficiency of these devices. Polycrystalline CdS films were prepared by silk screen printing (SP) and evaporation. The SP films were annealed at various times and temperatures to improve the crystallinity of the layers. At 640C for 1hr, deep states at 0.16eV and 0.48eV were detected. The levels disappeared when annealed at 670C-700C and a new level was observed at 0.13eV. CdS/Cu(_2)S heterojunctions were prepared on the material sintered at 670C; this induced a further trapping level at 1.1eV and one that was poorly resolved. Copper diffused into the CdS during the fabrication of the device so the states associated with copper were detected at 0.35eV and 1.1eV, The evaporated CdS layers showed that the defect signature was sensitive to the type of substrate. Using Ag instead of the usual SnO(_x), deep states were induced at 0.48eV and 0.98eV below the CB. These Ag-associated impurity centres prevent the indiffusion of Cu during the optimising heat treatment of the CdS/Cu(_2)S heterojunction. This maintains the stoichicmetry of the Cu(_2)S layer, thereby, preventing degradation of the devices. CdSe and copper doped CdSe were found to contain several important defect centres: a native sensitising centre (0.64eV from the VB), a class I recombination centre (0.9eV from the CB), a copper impurity centre (0.2eV from the CB) and two native defects (0.16eVand 0.45eV from the CB). n-type CdTe grown by the Piper-Polich technique contained6 electron traps at 0.15eV, 0.21eV, 0.40eV, 0.47eV, 0.53eV and 0.63eV. Their presence was shown to be dependent upon the method of growth of the crystal by comparing with material grown by other techniques. One or more of these states were thought to be due to extended defects or Te precipitates. Low resistivity ZnS contained two deep electron traps at 0.25eV and O.50eV as detected by DLTS. In addition DLOS showed the presence of four further states at 1.25eV, 1.37eV, 1.89eV and 2.19eV below the CB. The first two are thought to be the strong luminescence centres observed by other workers.

The objective of this work was to investigate the distribution of donor-like centres produced by boron implantation into p-type, Bridgeman grown Hg[0.8]Cd[0.2]Te and fabricate photodiodes from implanted substrates. Low carrier concentration substrates, 4-5x10[16]cm[-3], were implanted at room temperature with dose rates (&phis;) of 4x10[-2] or 6x10[-3]muAcm[-2], to a total dose of 1 x 10[15]B[+] cm[-2] (50,100keV) or 1x10[14]B[+]cm[-2] (150keV), respectively. Encapsulated specimens were annealed at 200&deg;C or 235&deg;C to activate the dopant or redistribute electrically active radiation damage centres to produce p-n junctions. The effects of materials processing on Hg[l-x]Cd[x]Te was investigated by x-ray photoelectron spectroscopy. Concentration profiles of electrically active centres were obtained from differential measurements of the Hall effect and resistivity at 77K. Through a comparison of distributions in as-implanted and annealed samples, the nature of donor-like centres forming the distributions were established. The quality of photodiodes produced from identical samples was assessed through current-voltage, capacitance-voltage and optoelectronic measurements. The nature and distribution of donor-like centres are dependent upon the dose rate of boron ions. An immobile defect is contained within the implanted region. Mercury interstitials (Hg[int]) are complexed within the implanted region for &phis; > 4x10[-2] muAcm[-2]. Irradiation enhanced diffusion of Hg[int] occurs if &phis; < 6x10[-3] muAcm[-2]. Thermal annealing redistributes bound and unbound accompanied by recombination with mercury vacancies and the formation of electrically neutral complexes. Annealing at 235&deg;C for 10 mins completely removes the donor-like activity ascribed to Hg's [int] and reduces the concentration of electrically active immobile defects. P-N junctions are formed between the mercury vacancy distribution and unbound Hg's[int] or the immobile damage centres in annealed substrates. Junction formation is inhibited by the formation of the bound Hg[int] complex. Optimum R[o]A[j] products may be obtained from junctions formed from the immobile defect centre, although degradation of the implanted region occurs after annealing at 235&deg;C. Anodic oxides grow by the differential electromigration of ions, which can produce a passivating layer to further anodization. The native oxide on Hg[0.8] Cd[0.2] Te is an ill-defined chemical mixture of the primary elements (Cd, Hg, Te). Native oxides degrade the R[o]A product of p-n junctions.

Neste trabalho, os cristais de TlBr foram crescidos pelo método de Bridgman, a partir de materiais purificados pela técnica de fusão zonal. A eficiência da purificação e avaliação da superfície cristalina em relação ao desempenho como detectores de radiação foi observada. Bons resultados foram obtidos com os aprimoramentos realizados nos processos de purificação, crescimento de cristais e na fabricação dos detectores. A resposta à radiação foi verificada excitando os detectores com fontes de raios gama: 241Am (59 keV), 133Ba (80 e 355 keV), 57Co (122 keV), 22Na (511 keV) e 137Cs (662 keV) à temperatura ambiente. Os valores de resolução em energia mais satisfatórios encontrados nesse trabalho foram a partir de detectores mais puros. Os melhores valores de resolução em energia obtidos foram de 10keV (16%), 12keV (15%), 12keV (10%), 28 keV (8%), 31keV (6%) e 36keV (5%) para as energias de 59, 80, 122, 355, 511 e 662 keV, respectivamente. Também foi realizado um estudo da resposta à detecção a uma temperatura de -20ºC e da estabilidade desses detectores. Nos detectores desenvolvidos não houve diferença significativa na resolução tanto em temperatura ambiente quanto na reduzida. Em relação à estabilidade foi observada uma degradação das características espectrométricas sob operação contínua do detector a temperatura ambiente e esta instabilidade variou para cada detector. Ambas características também foram observadas por outros autores. A viabilidade de utilização do cristal de TlBr como fotodetector para acoplamento em cintiladores também foi estudada neste trabalho. TlBr é um material promissor para ser utilizado como fotodetector devido a sua adequada eficiência quântica na região de 350 a aproximadamente 500 nm. Como uma aplicação para este trabalho foram iniciados estudos para fabricação de sondas cirúrgicas utilizando cristais de TlBr como o meio detector. / In this work, TlBr crystals were grown by the Bridgman method from zone melted materials. The influence of the purification efficiency and the crystalline surface quality on the crystal were studied, evaluating its performance as a radiation detector. Due to significant improvement in the purification and crystals growth, good results have been obtained for the developed detectors. The spectrometric performance of the TlBr detector was evaluated by 241Am (59 keV), 133Ba (80 e 355 keV), 57Co (122 keV), 22Na (511 keV) and 137Cs (662 keV) at room temperature. The best energy resolution results were obtained from purer detectors. Energy resolutions of 10keV (16%), 12keV (15%), 12keV (10%), 28keV (8%), 31keV (6%) and 36keV (5%) to 59, 80, 122, 355, 511 and 662 keV energies, respectively, were obtained. A study on the detection response at -20ºC was also carried out, as well as the detector stability in function of the time. No significant difference was observed in the energy resolution between measurements at both temperatures. It was observed that the detector instability causes degradation of the spectroscopic characteristics during measurements at room temperature and the instability varies for each detector. This behavior was also verified by other authors. The viability to use the developed TlBr crystal as a photodetector coupled to scintillators crystals was also studied in this work. Due to its quantum efficiency in the region from 350 to 500 nm, TlBr shows to be a promising material to be used as a photodetector. As a possible application of this work, the development of a surgical probe has been initiated using the developed TlBr crystal as the radiation detector of the probe.

Neste trabalho, os cristais de TlBr foram crescidos pelo método de Bridgman, a partir de materiais purificados pela técnica de fusão zonal. A eficiência da purificação e avaliação da superfície cristalina em relação ao desempenho como detectores de radiação foi observada. Bons resultados foram obtidos com os aprimoramentos realizados nos processos de purificação, crescimento de cristais e na fabricação dos detectores. A resposta à radiação foi verificada excitando os detectores com fontes de raios gama: 241Am (59 keV), 133Ba (80 e 355 keV), 57Co (122 keV), 22Na (511 keV) e 137Cs (662 keV) à temperatura ambiente. Os valores de resolução em energia mais satisfatórios encontrados nesse trabalho foram a partir de detectores mais puros. Os melhores valores de resolução em energia obtidos foram de 10keV (16%), 12keV (15%), 12keV (10%), 28 keV (8%), 31keV (6%) e 36keV (5%) para as energias de 59, 80, 122, 355, 511 e 662 keV, respectivamente. Também foi realizado um estudo da resposta à detecção a uma temperatura de -20ºC e da estabilidade desses detectores. Nos detectores desenvolvidos não houve diferença significativa na resolução tanto em temperatura ambiente quanto na reduzida. Em relação à estabilidade foi observada uma degradação das características espectrométricas sob operação contínua do detector a temperatura ambiente e esta instabilidade variou para cada detector. Ambas características também foram observadas por outros autores. A viabilidade de utilização do cristal de TlBr como fotodetector para acoplamento em cintiladores também foi estudada neste trabalho. TlBr é um material promissor para ser utilizado como fotodetector devido a sua adequada eficiência quântica na região de 350 a aproximadamente 500 nm. Como uma aplicação para este trabalho foram iniciados estudos para fabricação de sondas cirúrgicas utilizando cristais de TlBr como o meio detector. / In this work, TlBr crystals were grown by the Bridgman method from zone melted materials. The influence of the purification efficiency and the crystalline surface quality on the crystal were studied, evaluating its performance as a radiation detector. Due to significant improvement in the purification and crystals growth, good results have been obtained for the developed detectors. The spectrometric performance of the TlBr detector was evaluated by 241Am (59 keV), 133Ba (80 e 355 keV), 57Co (122 keV), 22Na (511 keV) and 137Cs (662 keV) at room temperature. The best energy resolution results were obtained from purer detectors. Energy resolutions of 10keV (16%), 12keV (15%), 12keV (10%), 28keV (8%), 31keV (6%) and 36keV (5%) to 59, 80, 122, 355, 511 and 662 keV energies, respectively, were obtained. A study on the detection response at -20ºC was also carried out, as well as the detector stability in function of the time. No significant difference was observed in the energy resolution between measurements at both temperatures. It was observed that the detector instability causes degradation of the spectroscopic characteristics during measurements at room temperature and the instability varies for each detector. This behavior was also verified by other authors. The viability to use the developed TlBr crystal as a photodetector coupled to scintillators crystals was also studied in this work. Due to its quantum efficiency in the region from 350 to 500 nm, TlBr shows to be a promising material to be used as a photodetector. As a possible application of this work, the development of a surgical probe has been initiated using the developed TlBr crystal as the radiation detector of the probe.