Si and si(1-x)ge(x) nanocrystals: synthesis, structural characterization, and simultaneous observation of quantum confined and interface related photoluminescence


Thesis Type: Doctorate

Institution Of The Thesis: Middle East Technical University, Faculty of Arts and Sciences, Department of Physics, Turkey

Approval Date: 2010

Thesis Language: English

Student: Nader Asghar Pour Moghaddam

Supervisor: RAŞİT TURAN

Abstract:

In this work we have prepared Si and SI(1-X)GE(X) nanocrystals by rf magnetron cosputtering method. The e ect of annealing parameters and Ge content of x on the structural and optical properties sandwiched SiO2/SiO2: Si: Ge/SiO2 nanostructures have been investigated. For characterization we have used cross-sectional high resolution electron microscope (HREM), X-ray di raction (XRD), Raman spectroscopy (RS), Fourier transform infrared (FTIR), photoluminescence (PL), and temperature dependent PL (TDPL) techniques. It was shown that Ge content of x, annealing temperature, and annealing time are important parameters a ecting the structural and optical properties of the nanocrystals. We have observed a uniform SI(1-X)GE(X) nanocrystal formation upon annealing at relatively low temperatures and short annealing time. However, Ge-rich SI(1-X)GE(X) nanocrystals do not hold their compositional uniformity when annealed at high temperatures for enough long time. A segregation process leads to the separation of Ge and Si atoms from each other and formation of Si-rich core covered by a Ge-rich shell. Related to the optical properties of Si and SI(1-X)GE(X) nanocrystals, influence of annealing treatments and Ge content of x on the simultaneous observation and relative contribution of quantum confined and interface related radiative emission to PL spectra are investigated. On the other hand, temperature dependent photoluminescence (TDPL) measurements have been applied to investigate in detail the involving PL mechanisms and the competing thermally activated emission process and the thermally activated escape process of carriers into nonradiative recombination centers and/or tunneling of the excitons into the interface or to larger nanocrystals.