PbTe Flash Evaporation on Si <100> Substrates for Heterojunction Infrared Detectors
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PbTe Flash Evaporation on Si Substrates for Heterojunction Infrared Detectors Sonia Guimarães, Sabrina de C. F. F. da Silva1 and João M. K. de Assis Instituto de Aeronáutica e Espaço, Divisão de Materiais, São José dos Campos, SP, Brazil. 1 Faculdade de Engenharia Química de Lorena, Lorena, SP, Brazil. ABSTRACT This work is to present results of flash evaporation of PbTe directly over single crystals p-type Si substrates, in order to produce heterojunction infrared detectors (HIRD), working at 4.3µm IR wavelength. The evaporation was performed on modified JEOL vacuum equipment, model JEE4B(a), working with vacuum pressure around 10-5 torr, using diffusion pump. The HIRDs produced with this method presented the same detectivity (D*) values of HIRDs made with Hot Wall Epitaxial System (HWE)(b), in which PbTe epitaxial layers were grown directly over the same Si substrates, where an ionic pump reached about 10-7 torr as vacuum pressure. The best results, were obtained with PbTe layers grown with Molecular Beam Epitaxial (MBE) method(c) directly over Si substrates, where the vacuum pressure is around 10-9 torr, also using an ionic pump. The advantage of growing PbTe directly over Si wafers is that the HIRDs perform at room temperature. The detectivity values of HIRDs obtained with methods (a) and (b), were D*≈4,8 x 105 cm.Hz1/2 W-1 and with method (c), D* ≈ 6,7 x 106 cm.Hz1/2 W-1. Different technologies: (a) very low costs, (c) high technology; not very different results. INTRODUCTION Single crystal semiconductor thin layers can be processed through several growth techniques. However, when it is grown for devices application, epitaxial techniques are the most used. Among the epitaxial growth methods: Hot Wall Epitaxy (HWE) [1,2], Molecular Beam Epitaxy (MBE) [3] and Flash Evaporation (FE) [4,5], are some of them. Flash evaporation used in this work consisted of a modified vacuum equipment with three basic steps: a) solid phase source transition to gas phase, using the heat of a resistor, which contains the material to be evaporated; b) vapor transportation to the substrate surface, c) vapor condensation on the substrate surface. The modification performed in the evaporator was to provide a sample heater system, which enable us to heat, and control the Si substrates temperature till about 230 °C. Besides PbTe, cadmium telluride (CdTe) flash evaporated layers are also attractive materials for fabrication of semiconductor devices, such as solar cells, γ and IR detectors and field effect transistors [5,6]. Rusu and Rusu [6] studied the electrical conductivity of CdTe thin films evaporated onto unheated glass substrates, and obtained and amorphous structures. Domadara Das and Selvaraj [7] studied the time dependent electrical resistance of Bi2(Te0.4Se0.6)3 flash evaporated thin films, related with the effects of oxygen adsorption. These thin films find many applications such as in small thermoelectric power generators, thermoelectric refrigerators, thermopile detectors, etc. Boustani et al. [8] studied the influence of the s
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