Formation And Photoluminesence Properties Of Semiconductor Nanocrystals Embedded In High-K Dielectric Materials

Crystal Ge, Si are indirect bandgap semiconductor materials with a smaller optical bandgap and very low optical radiation efficiency. And also, the emission peak located nearby infrared region, which in some extent limited the application of Ge, Si materials as optical devices. With the development of thin film growth technology, we can assemble or fabricate nanomaterials and thin film in the atomic scale. The nano-semiconductor thin film exhibit peculiar properties in the optics and microelectronics, ect, which is especially useful in applications. Especially, in recent years, Ge nanocrystals embedded in dielectric matrix material show various optical properties, and attract many researchers attention. However, recently research work still mainly focused on Ge nanocrystals embedded in dielectric matrix materials. Our understanding on the origin of Photoluminescence in this system is also incomplete to date.In this work, we used Pulsed Laser Deposition (PLD) to prepare Ge/Lu₂O₃, Ge/SiO₂ High-K dielectric nanocomposite thin film. Surface morphology, microstructure and optical properties of the as-deposited and annealed sample were characterized and analyzed by means of X-ray diffraction, transmission electron microscopy (TEM) and photoluminescence (PL), ect. At the same time, we used the software of Fullprof to fit the XRD spectra of the samples. From the simulation results of Ge/Lu₂O₃, Ge/SiO₂ thin film, we found that the crystal structure of Ge nanocrystal is still cubic structure even it embedded in a host matrix. In comparison with that of bulk Ge crystals, the bend lengths of Ge nanocrystals embedded in Lu₂O₃ and SiO₂ matrix decrease. Furthermore, the bond length of Ge decreases much more in the annealed sample. It can be concluded that Ge core was wrapped by the oxidation layer GeOx after annealing in air and suffered the compressive strain from the GeO_x shell. The photoluminescence band of both samples central at 454nm and 458nm are observed in both samples, which can be attributed to the Ge/O related defect existing in the core-shell structure. This core–shell structure Ge nanocrystals would induce much more defects in the interface between the core and the shell, and thus enhanced the photoluminescence.