This thesis is concerning the plasma synthesis of semiconductor nanocrystals (NCs). Two systems of nanocrystals were studied, indium phosphide and doped silicon. A new method of synthesis of InP NCs is presented. It represents a new route for the synthesis of high quality compound semiconductor NCs. Additionally the electronic properties of doped silicon NCs were studied as a function of the doping concentration.
Indium phosphide nanocrystals (InP NCs) were synthesized using a nonthermal plasma. The NCs were synthesized using a simple capacitively coupled plasma where the precursors are flowed through a 3/8” quartz tube with two outer ring electrodes. The size of the NCs was primarily controlled through the residence time of the NCs in the plasma. Residence times of 2-10 ms lead to particles with mean sizes between ~2.5-4 nm with size distributions less than 25% of the mean particle size. The mass yield for this system was found to be up to 40 mg/hr. When a ZnS shell was grown around the InP NCs, size-tunable emission from the blue-green to the red was observed. Quantum yields as high as 15% were observed with this synthesis route. This route allows for synthesis of free-standing NCs that can be easily manipulated with colloidal based techniques or included in devices without stabilizing ligands.
The electrical conductivity of phosphorus doped Si NCs was studied as a function of the doping concentration. Doped Si NCs with mean sizes of 8-13 nm were spun cast onto a substrate with pre-deposited aluminum electrodes. The spin cast process produces films with zero to several monolayers of NCs. The conductivity of the films varies continuously from 10-11 S/cm for intrinsic NCs to 10-1 S/cm for highly doped NCs. These results indicate that the dopants are electrically active. The interpretation of these results means that the electronic properties of NCs can be tuned in a similar fashion as bulk semiconductors by introducing dopants. The ability to successfully dope NCs can have broad impact on the ability to form semiconductor devices.
University of Minnesota M.S. thesis. February 2010. Major: Mechanical Engineering. Advisor: Professor Uwe Kortshagen. 1 computer file (PDF); vi, 56 pages, appendices A-B.
Gresback, Ryan Gerard.
Nonthemal plasma synthesis of indium phosphide nanocrystals and electrical properties of doped silicon nanocrystal films..
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