Study On Photoelectric Properties Of â…¡-â…¥ Group Semiconductor CdTe Low Dimensional Quantum Structure

Semiconductor quantum dots are widely studied because of their special properties, which are different from bulk materials. In the past decades, it has been a hot topic in scientific researches. Ⅱ-Ⅵ group semiconductor quantum dots have some remarkable advantages, such as simple synthesis route, high flourescent efficiency, narrow light emission band, emission wavelength modulated by its size, etc. They are widely used in optoelectronic device and biological labeling as well as many other fields. In this paper, the microstructure, optical properties of CdTe quantum dots and nanorods as well as the electroluminescence properties of CdTe quantum dots were studied. The main results are as follows:(1) CdTe quantum dots were synthesized by aqueous phase method. In the synthesis of quantum dots, we selected thioglycollic acid as the ligand, so that the surface of the CdTe quantum dots was wrapped by it, which reduced the possible Cd2+ dangling bonds and improved the fluorescence efficiency. We characterized the lattice structure of the quantum dots by means of HRTEM and its estimated diameter was about 5nm. Compared with that of the bulk CdTe, the absorption peak position of the quantum dots had obvious blue shift, its band gap decreased with the growth time passing, and the size of the quantum dots became larger. We had made some modifications in the synthesis of quantum dots by adding cysteine hydrochloride to the Cd2+ precursor and the CdTe nanorods were prepared by this method. It was estimated that the length of the nanorods was about 250nm and the diameter was about 20nm through observation of the formation of CdTe nanorods via TEM. Through the HRTEM, we could observe the connection of the quantum dots along the specific crystal lattice. The obvious red shift of the fluorescence peak of the solution with addition of cysteine hydrochloride was found, which indicated that the CdTe nanorods were formed. Photoluminescence excitation measurements on nanorods whose photoluminescence peaks lie at 550nm,603nm and 610nm showed two peaks in spectra, which indicated that the absorption of the nanorods with one-dimensional structure originated from the direction of length and diameter.(2)We studied two ways of fluorescence enhancement of CdTe quantum dots: surface passivation and surface plasmon resonance enhancement effect of metal nanoparticles. We used CdSe whose lattice structure is similar to CdTe as the shell and encapsulated CdTe quantum dot, so that CdTe/CdSe quantum dots were synthesized. TEM characterization of this structure showed that the size of the quantum dots was uniform and the core shell structure could be observed clearly. The shell of CdSe passivated surface dangling bonds and defects, which would reduce the probability of non-radiative recombination, therefore, fluorescence efficiency of CdTe quantum dots was increased. The luminescence of CdTe quantum dots can also be enhanced by combining the quantum dots with Au nanoparticles. Au nanoparticles were obtained on Si substrate by rapid thermal annealing of Au thin film. The diameter of the Au nanoparticles was estimated to be about 300nm. Au nanoparticles/CdTe quantum dots film composite structure were prepared on samples annealed at the temperature of 400℃,500℃ and 600℃. Measurements of the structure showed that PL of the sample with Au nanoparticles annealed at 600℃ took the most significant fluorescence enhancement, which increased about one times than that without Au nanoparticles.(3) CdTe/CdSe quantum dots were used as the light-emitting layer to fabricate electroluminescence device, and the energy level of each layer, luminescence principle and the eletroluminescence characteristic were studied. According to the device structure ITO/PEDOT:PSS/PVK/QDs/ZnO/Al, the energy level diagram of each layer material was drawn, and the working process of the device was analyzed. The luminescence spectra of the device were measured, and the luminescence intensity increased gradually as the working voltage increasing in the range of 9-16V. The observed electroluminescence peaks had slightly red shift comparing to PL peaks, which was affected by the Stark effect. Ⅰ-Ⅴ characteristic curve of the device was drawn, and the turn-on voltage of the device was 9V, meanwhile the current density was 20mA/cm2. Through the selection rules of hole transport layer and electron transport layer, we analyzed the shortcomings of the device. At the end of this article, some significant advantages of this device were summarized.