Competição elétron-buraco induzida por pré-iluminação em cristais de óxido de titânio bismuto

Abstract

The electron-hole competition produced in photorefractive crystals of the type Titanium Oxide Bismuth (Bi12TiO20) doped and undoped can exist intrinsically inside the material or can be induced by some physical process of prior preparation of the material medium. In our research we used pre-illumination (using coherent light) of Bi12TiO20 (BTO) samples as an excitation mechanism for the electron-hole competition. In these samples, the pre-illumination process excites charge carriers inside the material, producing concentrations of electron donor centers and holes that compete with each other and that can allow a series of studies ranging from the characterization of the material to the technique used for to investigate the competition and even the quantum nature of competition between carriers of opposite sign charges. BTO-type crystals are known in the literature for their photorefractive properties, that is, they are simultaneously photoconductive and electro-optical materials. This combination of properties allows holographic diffraction gratings (also called phase holograms) to be recorded by means of non-uniform illumination of the material which imposes a modulation of the refractive index of the crystal. Thus, our goal is to use photorefractive holographic engraving on Bi12TiO20 crystals after they have been pre-illuminated with light at 532 nm (green) to study the competition induced electron-hole inside the material. The study Electron-hole competition through holographic recording can be done by analyzing diffraction efficiency measures of the signals diffracted by the hologram etched into the material. The etched and erased holograms used an interferometric experimental arrangement in a two-beam coherent (LASER) coupling configuration. The measured diffracted signals are expected to have a characteristic signature of electron-hole competition including a phase difference due to opposite carrier signals and which is theoretically predicted.