含硅量子点氮化硅薄膜的发光特性及载流子输运机理研究
发布时间：2018-09-07 10:01
【摘要】：硅量子点由于其独特的量子限域效应特性在发光二极管和太阳能电池等领域具备巨大潜力。特别地,含硅量子点氮化硅薄膜由于其良好的光学特性,且制备方式与现行成熟的互补金属氧化物半导体(CMOS)工艺相兼容等优势成为极具潜力的硅基光源候选材料之一。然而,截至目前,对于含硅量子点氮化硅薄膜发光机制的探讨还未有定论,量子限域效应(QCE)发光,带尾态发光和界面态发光等多种机制被提出；硅量子点发光器件的载流子输运与硅量子点密度、缺陷态分布等密切相关,也需进行深入分析；此外,当前硅量子点器件的发光效率依然很低,有待提高。基于此,本文采用等离子体增强化学气相沉积(PECVD)方式沉积氢化非晶氮化硅(a-SiNx:H)薄膜,经退火工艺凝析出硅量子点；研究了硅量子点生长规律以及氮化硅薄膜的微结构及光致发光(PL)性能；制备了硅量子点发光器件并探索了其电致发光(EL)来源及其载流子输运机理。本文主要的研究结果如下：通过调控NH3/SiH4流量比制备了富硅程度不同的a-SiNx:H薄膜,获得了优化的晶硅量子点和非晶硅量子点制备工艺；分析了退火过程中氮化硅薄膜的微结构演变及硅量子点的生长机理。研究发现,退火处理导致薄膜内Si-H和N-H键断裂,H将逃逸出薄膜,且薄膜内趋向于形成化学剂量比的氮化硅。依据Raman谱,薄膜的富硅程度决定了硅量子点的生长状况。富硅含量过高时,将导致硅量子点接连生长；而当薄膜富硅程度太低时,将无法生长硅量子点。UV-Vis吸收谱研究发现,H的逃逸显著地降低了薄膜的光学带隙；硅量子点的长大与晶化也影响着其光学带隙。引入325 nm和532 nm两波长激光研究了薄膜退火前后的PL特性；探索了退火温度、时间对于薄膜PL的影响；结合UV-Vis吸收谱阐明了氮化硅薄膜PL来源。对于1100℃退火后有晶硅量子点析出薄膜,在325 nm波长激发下,退火前后PL谱中均有～1.75 eV源于缺陷态的发光峰；未退火样品主峰来源于非晶硅量子点QCE发光；经1100℃退火后薄膜PL由晶硅量子点的QCE发光占据主导。然而,在532 nm波长激发下,缺陷态发光被掩盖；800℃和950℃退火薄膜的PL来源于带尾态发光；而未退火和1100℃退火样品,其PL来源并未改变,且1100℃退火样品展现激发波长尺寸选择激发。对于1100℃退火后析出有非晶硅量子点氮化硅,其在325 nm波长激发下退火前后的PL来源于缺陷态发光和氮化硅本身固有的发光。在532 nm波长激发下,未退火及800℃和950℃退火样品的PL均源自带尾态发光；而1100℃处理后薄膜的PL由非晶硅量子点的QCE发光占据主导。设计制备了ITO/SRN (Si QDs)/p-Si/Al结构发光器件,对EL谱高斯分峰并对比PL谱分析了EL来源；依据I-V数据进行各可能传导机制拟合,获得了发光器件在各工作区域的载流子输运机理。研究发现载流子遂穿过程中出现择优路径选择,导致分散发光亮点的出现。对于含晶硅量子点氮化硅发光器件,其EL主要来源于缺陷态,仅在含硅量子点密度较大器件EL谱中发现～1.58 eV的子峰,其来源于晶硅量子点的QCE发光。载流子输运依赖于薄膜中富硅含量,F-N和TAT隧穿在载流子传输中均可能占据主导。而对于含非晶硅量子点氮化硅发光器件,其EL来源于非晶硅量子点的QCE发光；此外,基于F-N和SCLC隧穿机制的载流子输运在场强为0.55～1.55MV/cm和场强大于1.55 MV/cm区域分别占据主导。制备了Si/SiNy和SiNx/SiNy两种含硅量子点多层结构发光器件,发现其EL和PL均位于～590 nm,来源于晶硅量子点的QCE发光,而载流子输运分别由TAT遂穿和F-N遂穿占据主导。
[Abstract]:Silicon quantum dots (QDs) have great potential in the fields of photodiodes and solar cells due to their unique quantum confinement effects. In particular, silicon-containing QDs-based silicon nitride thin films have great potential due to their excellent optical properties and compatibility with the current mature complementary metal oxide semiconductor (CMOS) processes. However, up to now, there is no final conclusion about the mechanism of luminescence of silicon nitride thin films containing silicon quantum dots. Many mechanisms have been proposed, such as quantum confinement effect (QCE), tail state luminescence and interface state luminescence. In addition, the luminous efficiency of silicon quantum dot devices is still very low and needs to be improved. Silicon quantum dot luminescent devices were fabricated and their electroluminescent (EL) sources and carrier transport mechanisms were explored. The main results are as follows: A-SiNx:H thin films with different Si-rich degree were prepared by adjusting the NH3/SiH4 flow ratio, and the optimized silicon content was obtained. The microstructure evolution of silicon nitride films and the growth mechanism of silicon quantum dots during annealing were analyzed. It was found that the Si-H and N-H bonds in the films were broken by annealing treatment, and H would escape from the films and tend to form chemical dose ratio silicon nitride in the films. The growth of silicon quantum dots depends on the degree of silicon. When the content of silicon is too high, it will lead to the growth of silicon quantum dots. When the degree of silicon-rich film is too low, it will be unable to grow silicon quantum dots. The PL properties of the films before and after annealing were studied by introducing 325 nm and 532 nm laser. The influence of annealing temperature and time on the PL properties of the films was explored. The PL source of the silicon nitride films was elucidated by UV-Vis absorption spectra. For the films annealed at 1100 C, the PL spectra before and after annealing were ~1.75 eV excited at 325 nm. The main peak of the unannealed sample comes from the QCE luminescence of the amorphous silicon quantum dots, and the QCE luminescence of the silicon quantum dots dominates the PL film annealed at 1100 C. However, the defect luminescence is masked under 532 nm excitation, the PL of the films annealed at 800 C and 950 C comes from the band tail luminescence, while the PL film annealed at 1100 The PL source of the samples annealed at 1100 C has not changed, and the samples annealed at 1100 The PL of samples annealed at 0 C and 950 C originated from tail state luminescence, while the PL of films annealed at 1100 C was dominated by QCE luminescence of amorphous silicon quantum dots. Carrier transport mechanism in various working regions of light emitting devices is obtained. It is found that the selective path selection occurs during carrier tunneling, resulting in the appearance of dispersed luminescent spots. Carrier transport depends on the silicon-rich content in the film, and F-N and TAT tunneling may dominate the carrier transport. For silicon nitride light-emitting devices containing amorphous silicon quantum dots, the EL originates from the QCE luminescence of amorphous silicon quantum dots; furthermore, carrier transport based on the F-N and SCLC tunneling mechanism may be dominant. Transport dominates in the region of 0.55-1.55 MV/cm and 1.55 MV/cm, respectively. Si/SiNy and SiNx/SiNy multilayer luminescent devices are fabricated. The EL and PL of these devices are located in the range of 590 nm, which originate from QCE luminescence of crystal silicon quantum dots. Carrier transport is dominated by TAT tunneling and F-N tunneling, respectively.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304.2
，
本文编号：2227930
[Abstract]:Silicon quantum dots (QDs) have great potential in the fields of photodiodes and solar cells due to their unique quantum confinement effects. In particular, silicon-containing QDs-based silicon nitride thin films have great potential due to their excellent optical properties and compatibility with the current mature complementary metal oxide semiconductor (CMOS) processes. However, up to now, there is no final conclusion about the mechanism of luminescence of silicon nitride thin films containing silicon quantum dots. Many mechanisms have been proposed, such as quantum confinement effect (QCE), tail state luminescence and interface state luminescence. In addition, the luminous efficiency of silicon quantum dot devices is still very low and needs to be improved. Silicon quantum dot luminescent devices were fabricated and their electroluminescent (EL) sources and carrier transport mechanisms were explored. The main results are as follows: A-SiNx:H thin films with different Si-rich degree were prepared by adjusting the NH3/SiH4 flow ratio, and the optimized silicon content was obtained. The microstructure evolution of silicon nitride films and the growth mechanism of silicon quantum dots during annealing were analyzed. It was found that the Si-H and N-H bonds in the films were broken by annealing treatment, and H would escape from the films and tend to form chemical dose ratio silicon nitride in the films. The growth of silicon quantum dots depends on the degree of silicon. When the content of silicon is too high, it will lead to the growth of silicon quantum dots. When the degree of silicon-rich film is too low, it will be unable to grow silicon quantum dots. The PL properties of the films before and after annealing were studied by introducing 325 nm and 532 nm laser. The influence of annealing temperature and time on the PL properties of the films was explored. The PL source of the silicon nitride films was elucidated by UV-Vis absorption spectra. For the films annealed at 1100 C, the PL spectra before and after annealing were ~1.75 eV excited at 325 nm. The main peak of the unannealed sample comes from the QCE luminescence of the amorphous silicon quantum dots, and the QCE luminescence of the silicon quantum dots dominates the PL film annealed at 1100 C. However, the defect luminescence is masked under 532 nm excitation, the PL of the films annealed at 800 C and 950 C comes from the band tail luminescence, while the PL film annealed at 1100 The PL source of the samples annealed at 1100 C has not changed, and the samples annealed at 1100 The PL of samples annealed at 0 C and 950 C originated from tail state luminescence, while the PL of films annealed at 1100 C was dominated by QCE luminescence of amorphous silicon quantum dots. Carrier transport mechanism in various working regions of light emitting devices is obtained. It is found that the selective path selection occurs during carrier tunneling, resulting in the appearance of dispersed luminescent spots. Carrier transport depends on the silicon-rich content in the film, and F-N and TAT tunneling may dominate the carrier transport. For silicon nitride light-emitting devices containing amorphous silicon quantum dots, the EL originates from the QCE luminescence of amorphous silicon quantum dots; furthermore, carrier transport based on the F-N and SCLC tunneling mechanism may be dominant. Transport dominates in the region of 0.55-1.55 MV/cm and 1.55 MV/cm, respectively. Si/SiNy and SiNx/SiNy multilayer luminescent devices are fabricated. The EL and PL of these devices are located in the range of 590 nm, which originate from QCE luminescence of crystal silicon quantum dots. Carrier transport is dominated by TAT tunneling and F-N tunneling, respectively.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304.2
，
本文编号：2227930
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