Researches On The Luminescence And Carrier Transport Mechanisms Of Silicon Nitride Films Containing Silicon Quantum Dots

Due to their unique quantum confinement effect, silicon quantum dots (Si QDs) hold great potential in light emitting devices, photovoltaic cells and so on. Specifically, silicon nitride films containing Si QDs become one of the most promising candidate materials for Si-based light source, due to their excellent optical properties and complementary metal oxide semiconductor (CMOS)-compatible synthesis. However, up to now, the origin of the luminescence from silicon nitride films containing Si QDs is not completely understood and many factors such as quantum confinement effect (QCE) from Si QDs, band tails and defects inside the silicon nitride and interfacial states can contribute to the luminescence. The behavior of carrier transportation in the light emitting devices based on silicon nitride films containing Si QDs is related with the Si QDs density, the distribution of defects, which needs deeper investigation. In addition, the external efficiency of light emitting devices based on silicon nitride films containing Si QDs is still too low for practical applications, which is also need to be improved. Considering the above, in this paper, we first prepare hydrogenated amorphous silicon nitride (?-SiNx:H) films and subsequently conduct annealing treatment to obtain Si QDs. Then we investigate the growth law of Si QDs, the microstructures and photoluminescence (PL) of silicon nitride films with and without annealing treatment. At last, light emitting devices containing Si QDs were fabricated and their electroluminescence (EL) and carrier transport mechanisms are analyzed. The dissertation's main results are described as follows:a-SiNx:H films with different silicon content are synthesized by changing the flow rate of NH3 with a focused flow rate of SiH4. Optimized parameters are obtained for the synthesis of silicon nitride with crystalline and amorphous Si QDs. The growth law of Si QDs and the microstructures evolutions of silicon nitride are analyzed. We find that, from the FTIR spectra, the post annealing treatment leads to the broken of Si-H and N-H bonds, the escape of H out of the films and the formation of stoichiometric Si3N4. As explored by the Raman spectra, the degree of the excess ratio of Si in the silicon nitride films determines the growth of Si QDs. If the excess ratio of Si is too high, Si QDs tend to aggregate together. While if the excess ratio of Si is too low, no Si QDs can be synthesized even with high-temperature annealing. The effusion of H out from the silicon nitride reduces obviously the optical band gap according to the UV-Vis absorptance spectra. In addition, the size and state of Si QDs in the silicon nitride will also affect the optical band gap.We investigate the PL emission of the as-deposited and annealed silicon nitride films by introducing two lasers with wavelength of 325 nm and 532 nm. Meanwhile, the effect of annealing time and temperature on the PL is analyzed and further the origin of PL is discussed. As for the silicon nitride films in which crystalline Si QDs can be obtained after 1100?-annealing, one PL sub-band at-1.75 eV which comes from the defects is found in all the films with and without annealing under the excitation of 325 nm. The prominent PL of the as-deposited sample originates form the QCE of amorphous Si QDs and the PL of the 1100?-annealed sample is dominated by the QCE of crystalline Si QDs. However, the PL of silicon nitride films from the defects disappears when excited by the 532-nm laser. We find that the PL of films annealed at 800 and 950? can be ascribed to the recombination within the band tails at this time. And the origin of the PL emission of the as-deposited and 1100?-annealed sample is unchanged. We also find the excitation energy-induced QD size selection in the 1100?-annealed samples. As for the silicon nitride film with amorphous Si QDs in its 1100?-annealed sample, all the PL emission for as-deposited and annealed samples under 325-nm laser comes from the defects and the instinct PL centers in the nitride matrix. We further analyze the PL under the excitation of 532-nm laser and find the PL of films annealed at 800 and 950? can be ascribed to the recombination within the band tails. However, the emission from QCE of amorphous Si QDs is found to dominant in the PL of 1100?-annealed sample.We design and fabricate Si QDs based light emitting devices whose structure is ITO/SRN(Si QDs)/p-Si/Al. The origin of EL is investigated by combination of EL and PL spectra, and the carrier transport mechanism is studied by fitting the I-V data with the existing mechanisms. We find some EL spots in some light devices, which can be attributed to the formation of a finite number of preferential conductive paths within the silicon nitride with Si QDs. For those silicon nitride film with crystalline Si QDs, the EL emission is dominated by defects. We only find, for the sample with denser Si QDs, one PL sub-band located at 1.58 eV which comes form the QCE of crystalline Si QDs. The carrier transportation depends on the degree of the excess ratio of Si, and both F-N and TAT tunneling can play a main role. As for the device with the active layer silicon nitride with amorphous Si QDs, we find that its EL emission is originated from the QCE of amorphous Si QDs and that F-N tunneling and the SCLC mechanism dominates in the carrier transportation when the electrical field is 0.55?1.55 MV/cm and larger than 1.55 MV/cm, respectively. Lastly, we fabricated another two light emitting devices based on Si/SiNy and SiNx/SiNy multi-layer structure containing crystalline Si QDs. We find that both the EL and PL, which locates at ?590 nm, can be ascribed to the QCE in crystalline Si QDs. TAT and F-N tunneling mechanisms are found to dominate in the carrier transportation for the Si/SiNy and SiNx/SiNy multilayer structures, respectively.