Silicon nanocrystals/SiO2 superlattices based optoelectronic devices

• Main Authors: Sheng-WenFu, 傅聖文
• Other Authors: Chuan-Feng Shih
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/54p548

博士 === 國立成功大學 === 電機工程學系 === 105 === This thesis focus on the progress of Si NCs embedded in Si-rich oxide (SRO) in SRO/SiO2 superlattices application for LED and memory device by employing ion-beam assisted sputtering (IBAS) system. The chapters are organized as follows: In chapter 2, this study exploits the material and optical properties of silicon nanocrystals (Si NCs) embedded SRO films prepared by IBAS. Transmission electron microscopy and grazing-angle X-ray diffraction revealed that the IBAS improved the formation of the Si NCs in the SRO films. The size and density of Si NCs were dominated by IBAS with varying anode voltage. The photoluminescence for the SRO films was enhanced, which was associated with the quantum confinement effect of the Si NCs. The impact of Ar ion beam on the SRO films were discussed. The results exhibited the promising for development of highly efficient Si-based optoelectronic devices. In chapter 3, this study investigated the electroluminescence (EL) properties of Si-rich oxide (SRO)/SiO2 superlattices light emitting devices (LEDs). Each SiO2 layer of the superlattices was prepared by using argon ion beam assisted sputtering (IBAS). Transmission electron microscopy revealed that the treatment of Ar ion beams on the SiO2 layers did not affect the size or distribution of the Si NCs in the SRO layers, but enhanced the thin-film quality of the SiO2 and formed a clear SiO2/SRO interface. The refractive index of SiO2 was increased by IBAS because of an increase in the density of SiO2. The EL efficiency was doubled for the IBAS device compared with that of a reference device. According to the retention property, the enhanced EL intensity of the IBAS device was ascribed to lower the charge loss rate through enhancing injection barrier of SiO2. The mechanism of the EL enhancement of the IBAS LED was discussed. In chapter 4, this paper presents a novel method for enhancing the electroluminescence (EL) efficiency of ten-period silicon-rich oxide (SRO)/SiO2 superlattice–based light-emitting diodes (LEDs). A hydrogen ion beam (HIB) was used to irradiate on each SRO layer of the superlattices to increase the interfacial roughness in nanoscale and density of the Si nanocrystals (Si NCs). Fowler–Nordheim (F–N) tunneling was the major mechanism for injecting the carriers into the Si NCs. The barrier height of the F–N tunneling was lowered by forming the nano-roughened interface and nonradiative Pb centers were passivated through the HIB treatment. Additionally, the reflectance of the LEDs was lowered because of the nano-roughened interface. These factors considerably increased the slope efficiency of EL and maximum output power of the LEDs. The lighting efficiency increased by an order of magnitude, and the turn-on voltage decreased considerably. This study established an efficient approach for obtaining bright Si NCs/SiO2 superlattice-based LEDs. In chapter 5, This study examined the material and optical properties of Si nanocrystals (NCs) embedded in Si-rich oxide (SRO) films prepared through ion beam-assisted sputtering (IBAS). Transmission electron microscopy and grazing-incidence X-ray diffraction revealed that IBAS improved the formation of the Si NCs in the SRO films. The size and density of Si NCs were predominantly controlled by IBAS with varying anode voltage. The photoluminescence levels of the SRO films were enhanced, which was associated with the quantum confinement effect of the Si NCs. The benefits of an Ar ion beam used on the SRO films are discussed in this paper. The results indicate that IBAS is a promising approach for the development of highly efficient Si-based optoelectronic devices. In chapter 6, the Al-doped ZnO (AZO) films, which is an important transparent and conducting electrode in optoelectronic devices, are prepared using ion-beam assisted sputtering (IBAS) with substrate heating. Further reduction of the resistivity and an increase in the transmittance of AZO are required for optimized optoelectronic devices. A low-energy Ar ion-beam with a kinetic energy between 0-50 eV is used. The electrical and optical properties of IBAS AZO films are studied in terms of the substrate temperature (RT-300 ℃). The results show that the resistivity of AZO films decreases as the amount of chemisorbed oxygen and O-Zn bonds decrease, which increases the number of oxygen vacancies. The transmittance in the visible region is increased because of the high crystallinity of AZO films. The resistivity of IBAS AZO deposited at 300 ℃ with an anode voltage of 30 V is reduced to 5.6 × 10-3 Ω-cm because of the high carrier concentration and mobility. This shows that ion-beam treatment changes the surface/adatom reaction during the growth of AZO films, which is similar to the effect of substrate heating. The electrical and optical properties of the AZO films that depend on the ion-beam energy and substrate temperature are discussed.