Experimental study of negative photoconductivity in n-PbTe(Ga) epitaxial films

We report on low-temperature photoconductivity (PC) in n-PbTe(Ga) epitaxial films prepared by the hot-wall technique on -BaF_2 substrates. Variation of the substrate temperature allowed us to change the resistivity of the films from 10^8 down to 10_{-2} Ohm x cm at 4.2 K. The resistivity reduction is associated with a slight excess of Ga concentration, disturbing the Fermi level pinning within the energy gap of n-PbTe(Ga). PC has been measured under continuous and pulse illumination in the temperature range 4.2-300 K. For films of low resistivity, the photoresponse is composed of negative and positive parts. Recombination processes for both effects are characterized by nonexponential kinetics depending on the illumination pulse duration and intensity. Analysis of the PC transient proves that the negative photoconductivity cannot be explained in terms of nonequilibrium charge carriers spatial separation of due to band modulation. Experimental results are interpreted assuming the mixed valence of Ga in lead telluride and the formation of centers with a negative correlation energy. Specifics of the PC process is determined by the energy levels attributed to donor Ga III, acceptor Ga I, and neutral Ga II states with respect to the crystal surrounding. The energy level corresponding to the metastable state Ga II is supposed to occur above the conduction band bottom, providing fast recombination rates for the negative PC. The superposition of negative and positive PC is considered to be dependent on the ratio of the densities of states corresponding to the donor and acceptor impurity centers.Comment: 7 pages, 4 figure

Conhecimentos sobre prevenção da SIDA entre profissionais e acadêmicos da área de saúde

Este estudo exploratório foi realizado pelas alunas e alunos da Disciplina de Enfermagem nas Doenças Transmissíveis. Foram analisadas as respostas de 52 questionários distribuídos entre acadêmicos de enfermagem, de medicina, médicos, dentistas, enfermeiros e auxiliares de enfermagem que assistem pacientes com SIDA e enfermeiros que não assistem pacientes com SIDA. Estes questionários versaram sobre medidas de prevenção da transmissão sexual, normal de biossegurança, testes diagnósticos, direitos do paciente e do trabalhador e alterações no atendimento aos portadores desta patologia.This work is a exploratory research based on the analysis of the answers to the questionaires of 52 students and health care professionals knowledge about AIDS sexual prevention, biossecurity, diagnosis tests, patients and workers rights and the modifications of nursing and medica/ care to this kind of diseaseTrata se de un estudio exploratório acerca del conocimiento de la prevención de la SIDA, normas de seguridad biológica, pruebas diagnósticas, derechos de /os enfermos y trabajadores con SIDA y de esa mfermedad. Fueron analizados las respuestas de 52 cuestionários de estudientes de enfermería, nédicos, odontólogos, enfermeras y ajudantes de enfermería