Ge/SiO_2 film optical properties and applied research
|Keywords||nc-Ge/ SiO2 film RF magnetron reaction sputtering photoluminescence Third-order nonlinear optical dSaturable absorption|
Ge and Si are indirect-gap semiconductors, because of their light absorption and light emission are far from the direct band gap materials, which affect their application in the optoelectronics. To overcome the limitations in their optical properties, people have fabricated semiconductor quantum dots on silicon substrates. These nano-semiconductor materials demonstrate excellent characteristics in the light emission, light absorption and the third-order nonlinear, which make up for the lack of material and make great progress in realizing Si-based photonic devices. Thus the nc-Ge/ SiO2 compound films have broad applications prospects in optical emission, display, information storage, transmission, processing, photoelectric detection, high-speed optical switches and so on.The Ge-rich SiO2 compound films are prepared by RF magnetron reaction and the nc-Ge/ SiO2 compound films are obtained through post-annealing treatment. The structure, bonding state, composition, optical band gap of thin films are tested by XRD、FTIR、SEM and UV-VIS technologies. The experiments show that the absorption property of thin films is enhanced with the deposition thickness increasing, but the characteristic of near-infrared absorption area have changed. The higher the annealing temperature is, the larger of their average size, the more of their number and the narrower their optical band. The photoluminescence spectra （PL） of films are measured at room temperature. The result shows hat the samples can not only give off ultraviolet, but also violet and orange luminescence, when excited by 265nm ultra-violet of the xenon lamp. The photoluminescence spectra of samples which are prepared under different parameters and annealing conditions are compared. We analyzed the factors that affect the luminescence efficiency through the results of their characterization. The nano-Ge and defects relative to oxygen have a great impact on the intensity of its luminescence. The efficiency of their photoluminescence is great improved at 320nm and 420nm through optimizing the parameters reasonably.The third-order nonlinear optical properties of the nc-Ge/ SiO2 compound films are investigated by using single beam Z-scan technique with a picoseconds laser pulse atλ=532nm andλ=1064nm. The measured third-order refractive index coefficient and nonlinear absorption coefficient are estimated to be the order of 10-8esu and 10-7m/W respectively. The improved third-order nonlinear susceptibility is mainly attributed to the enhancement of quantum confinement、the absorption of surface state and defect state. It is fist reported that the nc-Ge/ SiO2 compound films are inserted as saturable absorber into the resonator of LD pumped Nd:YVO4 laser. The passive Q-switched operation of 1.064μm and 1.34μm laser are achieved and their laser pulses are 25ns and 40ns respectively. Through the experiment phenomenon and the nonlinear optical properties of the films, the form mechanism of the Q-switched pulse is discussed.