Document Details

Document Type : Thesis 
Document Title :
FABRICATION AND CHARACTERIZATION OF LIGHT EMITTING DEVICES BASED ON ZERO DIMENSIONAL QUANTUM CONFINED STRUCTURES
تصنيع ودراسة خصائص الانبعاث الضوئي للنبائط المحكمة ذات البعد الصفري
 
Subject : Faculty of Sciences 
Document Language : Arabic 
Abstract : Semiconductor nanocrystals, or quantum dots, have attracted considerable attention in last decades due to their unique properties compared to bulk counterparts as consequence of quantum confinement effect. In this work, cadmium telluride nanoparticles capped with 3-mercaptopropionic acid as stabilizing agent have been prepared via one-pot aqueous colloidal synthetic approach. Sets of samples were synthesized and characterized by different techniques. Then, synthesized nanoparticles were utilized to fabricate light emitting device based on CdTe quantum dots in emissive layer. The device performance was compared to that of another fabricated device based on CdSe nanocrystals. For preparation part, the effect of Cd precursor on the properties of nanoparticles was investigated firstly. The sample prepared by cadmium acetate has dominant cubic crystal structure whereas that synthesized by cadmium chloride has hexagonal one. Emission intensity of cadmium chloride sample was higher than the other. Second, CdTe nanoparticles with different sizes were successfully prepared in the presence of sodium borohydride with different concentrations as reducing agent. EDX analysis showed a significant increase of Te/Cd atomic ratio for the nanoparticles prepared with high percentage of NaBH4. XRD showed that CdTe nanocrystals synthesized with low percentage crystallized in a mixture of zinc blende and hexagonal phases with predominance of cubic one, while the nanoparticles prepared with high percentage crystallized in hexagonal structure. Nanoparticles prepared with low percentage showed high-intensity luminescence with small full width at half maximum. Third, the effect of changing capping agent quantity has been examined for more optimization of prepared samples. All samples exhibited cubic structure as XRD proved which is consistent with above results. The intensity of photoluminescence was increasing by decreasing 3-MPA quantity. The nanostructures obtained with the highest intensity possessed O/Cd atomic percentage ratio higher than other prepared nanostructures. Nanocrystals size was calculated by different formulas. By comparing the results, sizes determined by tight binding approximation from absorption onset agreed well with that attained from emission spectrum using an empirical equation. For the device part, light emitting device based on prepared CdTe quantum dots was fabricated utilizing spin-coating and thermal evaporation techniques. The fabricated device showed electroluminescence peak at 520 nm which was attributed to emission form Alq3 electron transporting layer combined with a little percentage from the interfaces between the conduction band of Alq3 and valance band of CdTe QDs. The reason for such emission is that the energy barrier between QDs and Alq3 layers is not high enough to trap charge carriers at QDs layer which cause excitons formation and recombination within ETL and interfaces instead of nanocrystals layer. Another device based on CdSe NCs was fabricated also for comparison. The device showed electroluminescence spectrum centered at 555 nm which originated from recombination of charge carriers in CdSe nanocrystals layer. The energy bands diagram of device confirmed that result. 
Supervisor : Prof. Wageh Mohammed Helmy Swelm 
Thesis Type : Doctorate Thesis 
Publishing Year : 1439 AH
2018 AD 
Co-Supervisor : Prof. Ahmed Abdullah Al-Ghamdi 
Added Date : Thursday, July 12, 2018 

Researchers

Researcher Name (Arabic)Researcher Name (English)Researcher TypeDr GradeEmail
أحلام محمد القليطيAl-Qulaiti, Ahlam MohammedResearcherDoctorate 

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