Study On Carrier Controlling And Pn Junctions Of Lithium Niobate Crystals

Compared with electronic integrated circuits, photonic integrated circuits (PICs) exhibit higher speed, larger capacity, lower propagation loss, etc. From the point of view of material structure, monolithic PICs are more expected. Monolithic PICs are often smaller than hybrid PICs to achieve the same function and furthermore fabrication of monolithic PICs is much easier, various devices in monolithic PICs are much more harmonious and steady. In order to obtain monolithic PICs, a multifunctional optical material is essential. Fortunately, lithium niobate (LiNbO3) is such a material.LiNbO3has excellent optical and electrical properties, such as electro-optic effect, acousto-optic effect, pyroelectric effect, piezoelectric effect, photorefractive effect, nonlinear effect, etc. Most devices used in PICs can be prepared by LiNbO3crystal, such as optical waveguide, optical switch, electro-optical modulator, acousto-optic modulator, pyroelectric sensor, piezoelectric sensor, optical parametric oscillator, wavelength division multiplexer, coupler, etc. To fabricate monolithic PICs, the main obstacle is a lack of laser diode (LD) based on LiNbO3wafer.As we known that pn junction is the main structure of a semiconductor diode, so the main purpose of this thesis is to fabricate LiNbO3pn junction. Because of its wide energy gap, LiNbO3pn junction will emit an ultraviolet light. This is helpful for LD luminescence.The main work of this dissertation can be decided to LiNbO3monolithic PICs and quasi-monolithic PICs. For the monolithic PICs, we try to fabricate p type LiNbO3by various dopants and oxidation, then grow the pn junctions by magnetron sputtering method, liquid phase epitaxial method and laser molecular beam epitaxial method. The pn junction shows good rectifying properties by measuring the current-voltage curve. Considering of the poor conductivity of LiNbO3crystal, we consider the quasi-monolithic PICs. Highly iron doped LiNbO3crystals show excellent conductive properties. Compared to the undoped congruent LiNbO3crystals, the conductivity can be improved by6orders of magnitude. We grow n-type high iron doped LiNbO3films on p-type silicon by laser molecular beam epitaxial method to form pn junctions. The pn junctions also show good rectifying properties.The content of this dissertation is arranged as follows:Chapter1introduces the development of LiNbO3, crystal structure, defect types and site occupation, energy band structure, carrier type, the development of integrated optics and integrated optical devices; we also give the main purpose of this thesis and experimental arrangement.Chapter2introduces the detection methods of conductive type. We find the holographic method is most suitable for LiNbO3crystal. Then we investigate p-type LiNbO3and finally find that3mol%zirconium doped LiNbO3crystal and iron doped LiNbO3crystals treated by thermo-electric oxidization are p-type ones.Chapter3, LiNbO3pn homojunctions are prepared by liquid phase epitaxy, magnetron sputtering and laser molecular beam epitaxy. Then the basic characteristics of these pn junctions are measured.Chapter4, we search for LiNbO3crystals with high conductivity. We grow highly iron doped LiNbO3crystals, its conductivity is6orders of magnitude than that of nominally pure one. Then we fabricate LiNbO3/Si heterojunction by laser molecular beam epitaxy. Properties of the pn junctions are investigated.Chapter5, summary and prospect, we summarize the work of this dissertation and prospect the futher work.