本文選題：a-SiN_x:O薄膜 + N-Si-O發(fā)光缺陷態(tài)��； 參考：《南京大學(xué)》2016年博士論文

【摘要】：在實現(xiàn)Si基單片光電集成的各組成器件研究中,最關(guān)鍵也最困難的任務(wù)是實現(xiàn)高效發(fā)光的Si基光源。由于Si是間接帶隙半導(dǎo)體,導(dǎo)致了其發(fā)光效率很低。因此,如何提高熒光量子效率(PL QE),以及相關(guān)發(fā)光機制和發(fā)光動力學(xué)的研究,成為了二十多年來人們在該領(lǐng)域內(nèi)研究上的一項艱巨任務(wù)。以前的研究工作大多集中在Si基納米結(jié)構(gòu)材料上,如多孔硅(PS Si),膠體鈍化的Si量子點,以及納米晶Si (nc-Si)鑲嵌Si基薄膜等,而對非晶態(tài)Si基化合物的發(fā)光機制、量子效率和熒光衰減動力學(xué)過程的研究報道得較少。2006年我們小組發(fā)現(xiàn)PECVD室溫下制備發(fā)光效率較低的a-SiN_x薄膜,在經(jīng)過一段時間的自然氧化后PL光發(fā)射強度得到了顯著增強。然后我們有意識的將適量的O摻入到固態(tài)非晶氮化硅(a-SiN_x)薄膜中,成功實現(xiàn)了以a-SiN_x:O薄膜為發(fā)光有源層的黃綠光波段高效電致發(fā)光(EL)器件,緊接著報道了a-SiN_x:O薄膜的光增益特性。本文在我們小組a-SiN_x:O薄膜前期研究工作的基礎(chǔ)上,深入研究了PECVD制備可見光波段發(fā)光可調(diào)制的a-SiN_x:O薄膜的PL穩(wěn)定性和a-SiN_x:O薄膜中來源于發(fā)光N-Si-O缺陷態(tài)的輻射復(fù)合機制；首次研究獲得了固態(tài)非晶a-SiN_x:O薄膜高達60%的光致發(fā)光內(nèi)量子效率和6.6%的光致發(fā)光外量子效率；進而基于溫度、時間演化的PL譜,深入研究了光生載流子的瞬態(tài)復(fù)合動力學(xué)過程,并解釋了a-SiN_x:O薄膜高熒光量子效率的來源。本論文的主要創(chuàng)新點如下：1、我們首次研究并獲得了PECVD低溫下制備的固態(tài)a-SiN_x:O薄膜高達60%的光致發(fā)光內(nèi)量子效率(PL IQE)和6.6%的光致發(fā)光外量子效率(PL EQE)。以往熒光量子效率的研究主要集中在Si基納米結(jié)構(gòu)材料上,而對非晶態(tài)Si基化合物PLQE的研究還未發(fā)現(xiàn)有相關(guān)報道。為了獲得a-SiN_x:O固態(tài)薄膜的PL EQE,我們通過校準(zhǔn)積分球直接測量了a-SiN_x:O薄膜吸收的激發(fā)光子數(shù)與出射到薄膜外的發(fā)射光子數(shù),從而獲得了a-SiN_x:O薄膜6.6%的熒光發(fā)射的絕對量子產(chǎn)額(PLAQY,即為PL EQE)。接著我們討論了如何從a-SiN_x:O固態(tài)薄膜的PL EQE去計算相應(yīng)PL IQE的問題。我們根據(jù)平面幾何光學(xué)原理以及a-SiN_x:O固態(tài)薄膜的折射率等光學(xué)參數(shù)計算得到了a-SiN_x:O薄膜的光萃取因子,同時結(jié)合PL EQE結(jié)果由光萃取因子的定義計算獲得了a-SiN_x:O薄膜的PLIQE。另外,我們通過測量a-SiN_x:O薄膜的漫反射率和吸收系數(shù)等光學(xué)參數(shù),同時結(jié)合積分球中測量得到的激發(fā)光子總數(shù)與發(fā)射光子總數(shù),根據(jù)熒光內(nèi)量子效率的定義直接計算獲得了a-SiN_x:O薄膜的PL IQE值。我們進一步通過測試a-SiN_x:O薄膜樣品的變溫PL譜,深入研究了PL積分強度隨著溫度變化的依賴關(guān)系,得到了不同溫度相對于低溫下的PL IQE值,來佐證前面兩種方法下得到的PL IQE值。我們得至a-SiN_x:O固態(tài)薄膜在470 nm發(fā)光波長時的PL IQE高達60%以上,這在目前報道的Si基薄膜發(fā)光材料的PLQE值中是較高的。以上結(jié)果發(fā)表在Appl. Phys.Lett.105,011113 (2014)上。2、我們深入研究了a-SiN_x:O薄膜中來源于發(fā)光N-Si-O缺陷態(tài)的,高量子效率PL的發(fā)光機制。首先研究了O的摻入對a-SiN_x薄膜能帶結(jié)構(gòu)的影響。通過測試a-SiN_x:O薄膜的Raman譜、FTIR譜、XPS譜和EPR譜,發(fā)現(xiàn)了薄膜內(nèi)部的N-Si-O鍵合組態(tài)和帶隙內(nèi)存在的N-Si-O相關(guān)懸掛鍵缺陷態(tài)。隨著O的摻入,a-SiN_x:O薄膜較a-SiN_x的結(jié)構(gòu)無序減小,Urbach帶尾收縮；同時在能帶中產(chǎn)生了N-Si-O鍵合組態(tài)相關(guān)的懸掛鍵缺陷態(tài)。我們進一步發(fā)現(xiàn)了來源于a-SiN_x:O薄膜中N-Si-O發(fā)光缺陷態(tài)的,不同于a-SiN_x中帶尾態(tài)輻射復(fù)合過程的兩個典型的缺陷態(tài)PL特性。一方面,通過改變激發(fā)光子能量(Eexc),我們發(fā)現(xiàn)a-SiN_x薄膜在EexcEopt時,隨著Eexc的增大其發(fā)光峰位(EPL)逐漸向高能級位置移動,表現(xiàn)出典型的帶尾態(tài)載流子躍遷的輻射復(fù)合發(fā)光機制；而對于a-SiN_x:O薄膜,其EPL并不隨Eexc的變化而變化。另一方面,我們發(fā)現(xiàn)對于帶尾態(tài)輻射復(fù)合的a-SiN_x薄膜,其PL積分強度(IPL)依賴于Eopt和Eexc之間的相對位置；而對于a-SiN_x:O薄膜,IPL與Eopt的依賴關(guān)系并不隨Eexc與Eopt之間相對位置的改變而改變。值得注意的是,我們發(fā)現(xiàn)a-SiN_x:O薄膜的IPL的變化趨勢與薄膜中N-Si-O發(fā)光缺陷態(tài)Nx的懸掛鍵濃度保持一致,從而確證其PL主要來源于禁帶中由氧引入的N-Si-O發(fā)光缺陷態(tài)。對于不同R的a-SiN_x:O薄膜,我們發(fā)現(xiàn)導(dǎo)帶尾到PL峰之間的斯托克斯位移(△Estokes=EU Edge-EPL)并不隨Eopt的變化而變化,并且趨于穩(wěn)定值(～0.75 eV)。最后,我們討論并提出了發(fā)光可調(diào)制a-SiN_x:O薄膜的N-Si-O相關(guān)缺陷態(tài)發(fā)光機制。以上結(jié)果發(fā)表在Appl. Phys. Lett.106,231103 (2015)上。3、基于變溫、變探測時間的PL譜,我們深入研究了a-SiN_x:O薄膜中N-Si-O發(fā)光缺陷態(tài)的瞬態(tài)動力學(xué)過程,并進一步分析了a-SiN_x:O薄膜高量子效率PL的來源。通過測試變溫穩(wěn)態(tài)PL譜(TD-SSPL)和變溫時間積分PL譜(TD-TIPL)我們發(fā)現(xiàn)a-SiN_x:O薄膜的PL來源于缺陷態(tài)發(fā)光。瞬態(tài)熒光光譜(TR PL)結(jié)果表明a-SiN_x:O薄膜的輻射復(fù)合過程在納秒量級；由于俄歇效應(yīng)發(fā)生的時間尺度也可以在納秒范圍,因此我們測試了a-SiN_x:O薄膜變激發(fā)功率(WPF)下的TIPL譜和ns-PL衰減曲線進行相應(yīng)驗證,發(fā)現(xiàn)TIPL譜的發(fā)光主峰位與譜形輪廓,以及不同WPF下的s-PL壽命并不隨WPF的變化而變化,從而確證了俄歇復(fù)合在a-SiN_x:O薄膜s-PL輻射復(fù)合過程中幾乎沒有貢獻。我們進而精確監(jiān)測了a-SiN_x:O薄膜在亞ns到ns時間范圍內(nèi)的時間演化TR PL譜,發(fā)現(xiàn)a-SiN_x:O薄膜TR PL譜的譜線輪廓和PL峰位隨著時間演化均未發(fā)生改變,這是典型的缺陷態(tài)發(fā)光的動力學(xué)特征,并且明顯不同于以往報道a-SiN_x薄膜的帶尾態(tài)發(fā)光動力學(xué)特征；從而又一次確證了PL來源于禁帶中的N-Si-O發(fā)光缺陷態(tài)。根據(jù)室溫下的熒光壽命以及前面得到的60%的PL IQE,我們計算了a-SiN_x:O薄膜的輻射復(fù)合壽命并進一步獲得了室溫下的輻射復(fù)合速率kr=1.28×108s-1,如此快的kr可以與直接帶隙CdSe納米晶中的結(jié)果相比擬,并且有助于我們理解a-SiN_x:O薄膜高熒光效率的來源。最后我們通過測試a-SiN_x:O薄膜在不同測試溫度下的熒光壽命(TD-PL lifetime),結(jié)合根據(jù)TD-TIPL測量結(jié)果得到的PL IQE(T)值,分析了不同測試溫度下a-SiN_x:O薄膜的輻射復(fù)合過程和非輻射復(fù)合過程。以上結(jié)果發(fā)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).

【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TN304
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本文編號：1846829