光发射内量子效率高达60%的a-SiN_x:O薄膜发光机制和瞬态动力学的研究

发布时间：2018-05-05 07:49

  本文选题：a-SiN_x:O薄膜 + N-Si-O发光缺陷态　； 参考：《南京大学》2016年博士论文

【摘要】：在实现Si基单片光电集成的各组成器件研究中,最关键也最困难的任务是实现高效发光的Si基光源。由于Si是间接带隙半导体,导致了其发光效率很低。因此,如何提高荧光量子效率(PL QE),以及相关发光机制和发光动力学的研究,成为了二十多年来人们在该领域内研究上的一项艰巨任务。以前的研究工作大多集中在Si基纳米结构材料上,如多孔硅(PS Si),胶体钝化的Si量子点,以及纳米晶Si (nc-Si)镶嵌Si基薄膜等,而对非晶态Si基化合物的发光机制、量子效率和荧光衰减动力学过程的研究报道得较少。2006年我们小组发现PECVD室温下制备发光效率较低的a-SiN_x薄膜,在经过一段时间的自然氧化后PL光发射强度得到了显著增强。然后我们有意识的将适量的O掺入到固态非晶氮化硅(a-SiN_x)薄膜中,成功实现了以a-SiN_x:O薄膜为发光有源层的黄绿光波段高效电致发光(EL)器件,紧接着报道了a-SiN_x:O薄膜的光增益特性。本文在我们小组a-SiN_x:O薄膜前期研究工作的基础上,深入研究了PECVD制备可见光波段发光可调制的a-SiN_x:O薄膜的PL稳定性和a-SiN_x:O薄膜中来源于发光N-Si-O缺陷态的辐射复合机制；首次研究获得了固态非晶a-SiN_x:O薄膜高达60%的光致发光内量子效率和6.6%的光致发光外量子效率；进而基于温度、时间演化的PL谱,深入研究了光生载流子的瞬态复合动力学过程,并解释了a-SiN_x:O薄膜高荧光量子效率的来源。本论文的主要创新点如下：1、我们首次研究并获得了PECVD低温下制备的固态a-SiN_x:O薄膜高达60%的光致发光内量子效率(PL IQE)和6.6%的光致发光外量子效率(PL EQE)。以往荧光量子效率的研究主要集中在Si基纳米结构材料上,而对非晶态Si基化合物PLQE的研究还未发现有相关报道。为了获得a-SiN_x:O固态薄膜的PL EQE,我们通过校准积分球直接测量了a-SiN_x:O薄膜吸收的激发光子数与出射到薄膜外的发射光子数,从而获得了a-SiN_x:O薄膜6.6%的荧光发射的绝对量子产额(PLAQY,即为PL EQE)。接着我们讨论了如何从a-SiN_x:O固态薄膜的PL EQE去计算相应PL IQE的问题。我们根据平面几何光学原理以及a-SiN_x:O固态薄膜的折射率等光学参数计算得到了a-SiN_x:O薄膜的光萃取因子,同时结合PL EQE结果由光萃取因子的定义计算获得了a-SiN_x:O薄膜的PLIQE。另外,我们通过测量a-SiN_x:O薄膜的漫反射率和吸收系数等光学参数,同时结合积分球中测量得到的激发光子总数与发射光子总数,根据荧光内量子效率的定义直接计算获得了a-SiN_x:O薄膜的PL IQE值。我们进一步通过测试a-SiN_x:O薄膜样品的变温PL谱,深入研究了PL积分强度随着温度变化的依赖关系,得到了不同温度相对于低温下的PL IQE值,来佐证前面两种方法下得到的PL IQE值。我们得至a-SiN_x:O固态薄膜在470 nm发光波长时的PL IQE高达60%以上,这在目前报道的Si基薄膜发光材料的PLQE值中是较高的。以上结果发表在Appl. Phys.Lett.105,011113 (2014)上。2、我们深入研究了a-SiN_x:O薄膜中来源于发光N-Si-O缺陷态的,高量子效率PL的发光机制。首先研究了O的掺入对a-SiN_x薄膜能带结构的影响。通过测试a-SiN_x:O薄膜的Raman谱、FTIR谱、XPS谱和EPR谱,发现了薄膜内部的N-Si-O键合组态和带隙内存在的N-Si-O相关悬挂键缺陷态。随着O的掺入,a-SiN_x:O薄膜较a-SiN_x的结构无序减小,Urbach带尾收缩；同时在能带中产生了N-Si-O键合组态相关的悬挂键缺陷态。我们进一步发现了来源于a-SiN_x:O薄膜中N-Si-O发光缺陷态的,不同于a-SiN_x中带尾态辐射复合过程的两个典型的缺陷态PL特性。一方面,通过改变激发光子能量(Eexc),我们发现a-SiN_x薄膜在EexcEopt时,随着Eexc的增大其发光峰位(EPL)逐渐向高能级位置移动,表现出典型的带尾态载流子跃迁的辐射复合发光机制；而对于a-SiN_x:O薄膜,其EPL并不随Eexc的变化而变化。另一方面,我们发现对于带尾态辐射复合的a-SiN_x薄膜,其PL积分强度(IPL)依赖于Eopt和Eexc之间的相对位置；而对于a-SiN_x:O薄膜,IPL与Eopt的依赖关系并不随Eexc与Eopt之间相对位置的改变而改变。值得注意的是,我们发现a-SiN_x:O薄膜的IPL的变化趋势与薄膜中N-Si-O发光缺陷态Nx的悬挂键浓度保持一致,从而确证其PL主要来源于禁带中由氧引入的N-Si-O发光缺陷态。对于不同R的a-SiN_x:O薄膜,我们发现导带尾到PL峰之间的斯托克斯位移(△Estokes=EU Edge-EPL)并不随Eopt的变化而变化,并且趋于稳定值(～0.75 eV)。最后,我们讨论并提出了发光可调制a-SiN_x:O薄膜的N-Si-O相关缺陷态发光机制。以上结果发表在Appl. Phys. Lett.106,231103 (2015)上。3、基于变温、变探测时间的PL谱,我们深入研究了a-SiN_x:O薄膜中N-Si-O发光缺陷态的瞬态动力学过程,并进一步分析了a-SiN_x:O薄膜高量子效率PL的来源。通过测试变温稳态PL谱(TD-SSPL)和变温时间积分PL谱(TD-TIPL)我们发现a-SiN_x:O薄膜的PL来源于缺陷态发光。瞬态荧光光谱(TR PL)结果表明a-SiN_x:O薄膜的辐射复合过程在纳秒量级；由于俄歇效应发生的时间尺度也可以在纳秒范围,因此我们测试了a-SiN_x:O薄膜变激发功率(WPF)下的TIPL谱和ns-PL衰减曲线进行相应验证,发现TIPL谱的发光主峰位与谱形轮廓,以及不同WPF下的s-PL寿命并不随WPF的变化而变化,从而确证了俄歇复合在a-SiN_x:O薄膜s-PL辐射复合过程中几乎没有贡献。我们进而精确监测了a-SiN_x:O薄膜在亚ns到ns时间范围内的时间演化TR PL谱,发现a-SiN_x:O薄膜TR PL谱的谱线轮廓和PL峰位随着时间演化均未发生改变,这是典型的缺陷态发光的动力学特征,并且明显不同于以往报道a-SiN_x薄膜的带尾态发光动力学特征；从而又一次确证了PL来源于禁带中的N-Si-O发光缺陷态。根据室温下的荧光寿命以及前面得到的60%的PL IQE,我们计算了a-SiN_x:O薄膜的辐射复合寿命并进一步获得了室温下的辐射复合速率kr=1.28×108s-1,如此快的kr可以与直接带隙CdSe纳米晶中的结果相比拟,并且有助于我们理解a-SiN_x:O薄膜高荧光效率的来源。最后我们通过测试a-SiN_x:O薄膜在不同测试温度下的荧光寿命(TD-PL lifetime),结合根据TD-TIPL测量结果得到的PL IQE(T)值,分析了不同测试温度下a-SiN_x:O薄膜的辐射复合过程和非辐射复合过程。以上结果发表在Appl. Phys. Lett.108,111103 (2016)上。
[Abstract]:The most important and most difficult task in the research of Si based monolithic optoelectronic integrated devices is the realization of high efficiency luminescent Si based light sources. Because Si is an indirect band gap semiconductor, its luminous efficiency is very low. Therefore, how to improve the fluorescence quantum efficiency (PL QE), the related luminescence mechanism and the luminescence dynamics have become two. More than 10 years have been a arduous task in this field. Most of the previous work focused on Si based nanostructured materials, such as porous silicon (PS Si), colloidal passivated Si quantum dots, and nanocrystalline Si (nc-Si) embedded Si based films, and the luminescence mechanism, quantum efficiency and fluorescence attenuation power for amorphous Si based compounds. The study process has been reported less.2006 years. Our group found that the a-SiN_x film with low luminescence efficiency at room temperature was found at PECVD room temperature. After a period of natural oxidation, the emission intensity of PL was significantly enhanced. Then we consciously added a proper amount of O into the solid amorphous silicon (a-SiN_x) film and successfully realized the a-S The iN_x:O film is a yellow green light band high efficient electroluminescent (EL) device which is the luminescent active layer. The optical gain characteristics of the a-SiN_x:O thin film are reported. On the basis of the earlier research work of our group a-SiN_x:O film, the PL stability and a-SiN_x:O thinning of the a-SiN_x:O thin films with visible light band are prepared by PECVD. The film is derived from the radiation recombination mechanism of the luminescent N-Si-O defect state; the first study has obtained the internal quantum efficiency of up to 60% of the solid-state amorphous a-SiN_x:O film and the external quantum efficiency of photoluminescence. Then, based on the PL spectrum of temperature and time evolution, the transient dynamic process of the light induced current is studied, and the explanation is explained. The main sources of high fluorescence quantum efficiency of a-SiN_x:O films are as follows: 1, we first studied and obtained 60% photoluminescence internal quantum efficiency (PL IQE) and 6.6% photoluminescence external quantum efficiency (PL EQE) of solid a-SiN_x:O films prepared at low temperature at low temperature. The previous study of fluorescence quantum efficiency was mainly focused on the study of fluorescence quantum efficiency. On the Si based nanostructured materials, the study of the amorphous Si based compound PLQE has not been reported. In order to obtain the PL EQE of the a-SiN_x:O solid film, we directly measured the number of excited photons absorbed by the a-SiN_x:O film and the number of emitted photons out of the film by calibrating the integral sphere, thus obtaining the a-SiN_x:O film 6.6%. The absolute quantum yield of the fluorescence emission (PLAQY, that is, PL EQE). Then we discuss how to calculate the corresponding PL IQE from the PL EQE of the a-SiN_x:O solid film. We calculate the optical extraction factor of the a-SiN_x:O film based on the plane geometric optical principle and the refractive index of the a-SiN_x:O solid film, and combine the optical extraction factor of the a-SiN_x:O film. The PL EQE results obtained the PLIQE. of the a-SiN_x:O film by the definition of the optical extraction factor. By measuring the optical parameters of the diffuse reflectance and absorption coefficient of the a-SiN_x:O film, the total number of excited photons and the total number of emitted photons measured in the integrating sphere are calculated directly and obtained by the definition of the quantum efficiency in the fluorescence. The PL IQE value of a-SiN_x:O film is further studied. We further study the dependence of PL integral strength on the temperature variation by measuring the temperature variation PL spectrum of the a-SiN_x:O film samples, and obtain the PL IQE value at different temperatures relative to the low temperature, to verify the PL IQE value obtained under the two previous methods. We have to get a-SiN_x:O solid-state film in 470 n. The PL IQE of the M luminescence wavelength is up to 60%, which is higher in the PLQE value of the Si based thin film luminescent materials reported now. The above results are published on Appl. Phys.Lett.105011113 (2014).2. We studied the luminescence mechanism of the a-SiN_x:O thin film from the luminescent N-Si-O defect state and high quantum efficiency PL. First, we studied the doping of O. The effect on the band structure of a-SiN_x film is found. By testing the Raman spectrum, FTIR spectrum, XPS spectrum and EPR spectrum of the thin film, the N-Si-O bonding configuration and the N-Si-O related suspension bond state within the band gap are found. With the addition of O, the a-SiN_x:O film is less than the a-SiN_x structure, and the Urbach band is contracted. At the same time, the energy band is in the band. We have produced the suspension bond defect states associated with the N-Si-O bonding configuration. We further discovered that the N-Si-O luminescence defects in the a-SiN_x:O thin films are different from the two typical defect states PL characteristics of the tail state radiation recombination process in a-SiN_x. On the one hand, we find that the a-SiN_x film is in EexcEopt by changing the excitation photon energy (Eexc). With the increase of Eexc, the luminescence peak position (EPL) gradually moves toward the high energy level, showing a typical radiation recombination mechanism with the tail state carrier transition, while for the a-SiN_x:O film, its EPL does not change with the change of Eexc. On the other hand, we find the a-SiN_x film with tail state radiation, its PL integral strength (IPL). Depending on the relative position between Eopt and Eexc, the dependence of IPL and Eopt on the a-SiN_x:O film does not change with the relative position between Eexc and Eopt. It is worth noting that the variation trend of IPL in the a-SiN_x:O thin film is consistent with the Nx suspension bond concentration in the N-Si-O luminescence defect state in the thin film. Its PL mainly comes from the N-Si-O luminescence Defect States introduced by oxygen in the forbidden band. For different R a-SiN_x:O films, we find that the Stokes shift between the tail of the guide band and the PL peak (delta Estokes=EU Edge-EPL) does not change with the change of Eopt, and tends to a stable value (~ 0.75 eV). Finally, we discuss and propose a luminescent modulating a-SiN_x:O. The luminescence mechanism of the N-Si-O related defect states of the thin film. The above results are published on Appl. Phys. Lett.106231103 (2015).3. Based on the PL spectra of temperature variation and variable detection time, we have deeply studied the transient dynamic process of the N-Si-O luminescence defect in the a-SiN_x:O film, and further analyzed the source of the PL of the high quantum efficiency of the a-SiN_x:O thin film. We found that the temperature stable PL spectrum (TD-SSPL) and the temperature variant time integral PL spectrum (TD-TIPL) we found that the PL of the a-SiN_x:O film originated from the defect state luminescence. The transient fluorescence spectra (TR PL) results show that the radiation recombination process of the a-SiN_x:O thin film is at the nanosecond order, and the time scale of the Auger effect can also be in the nanosecond range, so we have tested the a- The TIPL spectrum and the ns-PL attenuation curve under the variable excitation power (WPF) of SiN_x:O film are verified. It is found that the luminescence main peak and spectral profile of the TIPL spectrum and the lifetime of s-PL under the different WPF are not changed with the WPF, which confirms that the auger compound has almost no contribution in the a-SiN_x:O film s-PL radiation recombination process. The time evolution TR PL spectra of the a-SiN_x:O film in the time range of ns to NS have been measured. It is found that the spectral lines and PL peaks of the TR PL spectra of the a-SiN_x:O thin films have not changed with the time evolution. This is the dynamic characteristic of the typical defect state luminescence, and it is obviously different from the tail state luminescence dynamic characteristics of the a-SiN_x film previously reported. It was again confirmed that PL originated from the N-Si-O emission defect in the band gap. According to the fluorescence lifetime at room temperature and the 60% PL IQE obtained at the front, we calculated the radiation recombination life of the a-SiN_x:O film and further obtained the radiation recombination rate at room temperature kr=1.28 * 108s-1, so fast Kr can be with the direct band gap CdSe nanometers. The results in the crystal are similar and help us to understand the source of high fluorescence efficiency of a-SiN_x:O films. Finally, we have analyzed the radiation recovery of the a-SiN_x:O thin films at different test temperatures by testing the fluorescence lifetime (TD-PL lifetime) at different test temperatures (TD-PL lifetime) and the PL IQE (T) values obtained according to the results of the TD-TIPL measurements. The above results are published in Appl. Phys. Lett.108111103 (2016).

【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN304
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