Transport properties of semiconductor nanostructures

Slunjski, Robert (2014) Transport properties of semiconductor nanostructures. Doctoral thesis, Sveučilište u Zagrebu, Prirodoslovno-matematički fakultet.

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Abstract

In the scientific community semiconductor nano structures are very active field of research because of the possibility to design materials with specifc electrical properties. Such structures have a great potential for the use as new semiconductor devices, sensors, photovoltaics etc. Despite many years of active research and many published papers it is still a big challenge to produce nano structures in a reliable and economical manner with exact size and small number of defects. In this doctoral thesis we applied magnetron sputtering technique to produce semiconductor nano structures of Si and Ge in different environments of SiO2, Si3N4 and SiC. It was found that the temperature annealing process at 1050°C for Si and 700°C for Ge during 1h in the atmosphere of N2 is ideal for creating the nano crystalline Si and Ge. X-ray diffraction reveals the crystallinity of produced nano material and with the luminescence in the visible range the capture of photons in nano crystals is demostrated. The electrical transport properties are studied using MOS structures in which the oxide layer is made with the semiconductor nano material of Si and Ge. The interface defect density of MOS structures shows, a quality of samples with D_it ~ 10^12cm^-2eV^-1. The charge capture in nano crystals is shown with capacitive techniques and is most pronounced for a samples with nano crystals of Ge size of 2.5 nm embedded in multilayer oxide structure. The most dominant way of current transfer through matrix with nano crystals when MOS structure is forward polarised is the space charge limited current (SCLC) for high voltages and the ohmic current for low voltages. For thicker samples the ohmic current is dominant way of charge transfer and for thinner samples the SCLC current is the dominant way of charge transfer in any voltage regime. Measurement under light excitation showed us that the current is getting bigger and the type of conductivity didn't change except for some samples in which the change of density of defect states was noticed. The samples with nano-structure of Si in SiO2 showed the photovoltaic effect after excitation by light source which is interesting for using nano-structures for photovoltaic applications.

Item Type:

Thesis (Doctoral thesis)

Uncontrolled Keywords:

quantum dots; nanocrystalline Si i Ge; MOS structure SCLC current; magnetron sputtering; Raman

Subjects:

NATURAL SCIENCES > Physics

Divisions:

Division of Materials Physics

Projects: