掺施主和受主的GaP:N发光的热猝灭

对GaP:N(Te,Zn)中束缚激子发光热猝灭的测量和分析表明,中性Te原子以“俄歇阻断”作用,在NN对发光猝灭温度相对于不掺施主和受主的GaP:N有所降低方面起了关键的影响。掺Te后孤立N发光峰的猝灭温度提高,则是由于增加了N原子上电子分布的几率。这支持了N束缚激子的Hopfield-Thomas-Lyneh模型。受主Zn的作用是使自由激子发光随温度升高而缓慢增强,对A峰猝灭的减缓可能也有贡献。     

高激发功率对GaP∶N发光谱的影响

讨论了掺氮磷化镓（GaP∶N）荧光光谱的峰值强度（孤立氮等电子中心束缚激子发光峰A、最邻近N-N对束缚激子发光峰NN1和次邻近N-N对束缚激子发光峰NN3）随激发强度的变化规律,并在发光跃迁动力学方程中计入了由于高激发密度引起的样品温度升高,而导致孤立氮A的能级NA和最邻近N-N对NN1的能级的热激发的增强,得到了R（即最近邻N-N对(NN1)束缚激子发光峰与孤立N等电子中心束缚激子发光峰的强度比INN1/IA）与掺N浓度和激发光强的变化关系。利用实验数据进行拟合,得到了更好的拟合结果,并讨论了用此法计算GaP∶N样品中氮浓度时应注意的一些问题。     

高激发功率GaP：N发光谱的影响

讨论了掺氮磷化镓（GaP:N）荧光光谱的峰值强度（孤立氮等电子中心束缚激子发光峰A、最邻近N－N对束缚激子发光峰NH1和次邻近N－N对束缚激子发光峰NN3）随激发强度的变化规律,并在发光跃迁动力学方程中计入了由于高激发密度引起的样品温度升高,而导致孤立氮A的能级NA和最邻近N－N对NH1的能级的热激发的增强,得到了R（即最近N-N对（NH1）束缚激子发光峰与孤立N等电子中心束缚激子发光峰的强度比INN1／IA）与掺N浓度和激光发光强的变化关系。利用实验数据进行拟合,得到了更好的拟合结果,并讨论了用此法计算GaP:N样品中氮浓度时应注意的一些问题。     

金属有机物化学气相沉积GaAs／Si外延层中1.13eV发光带特性研究

用不同温度和激发强度下的近红外光致发光研究了金属有机物化学气相沉积方法在Ｓｉ衬底上生长的ＧａＡｓ外延层中的１．１３ｅＶ发光带的发光特性，表明此发光带为施主－受主对复合发光．根据１．１３ｅＶ发光带的峰值能量和发光强度随温度和激发强度的变化关系，确定施主和受主的束缚能分别为５和２９５ｍｅＶ，并证实ＧａＡｓ／Ｓｉ外延层中的１．１３ｅＶ发光为硅施主－镓空位受主对的复合发光．     

Ar等离子体处理对GaAs纳米线发光特性的影响

采用Ar等离子体处理GaAs纳米线,通过光致发光测试研究了等离子体偏压功率对GaAs纳米线发光性能的影响。在不同测试温度和不同激发功率密度下,研究了发光光谱各个发光峰的来源和机制。研究结果表明:随着功率增加,GaAs自由激子发光逐渐消失,束缚激子发光强度先减小后增大;当功率增加到200 W时,出现施主-受主对(DAP)发光。通过对比不同样品在283℃下的发光光谱,得到了等离子体处理过程中GaAs纳米线的结构变化:当处理功率较小时,Ar等离子体在消除表面态的同时将空位缺陷引入GaAs中;当处理功率较大时,GaAs的晶体结构遭到破坏,形成施主类型的缺陷,出现DAP发光。     

非掺杂n型氮化镓外延层的光致发光

研究了热处理对非掺杂n型氮化镓外延层光致发光谱的影响和光谱中各发光带强度与温度之间的关系．热处理后,光谱中的带边峰和黄光峰的强度较热处理前都有明显降低．黄光峰强度随温度升高的衰减速度要比带边峰慢得多．由这些实验结果得出结论：光谱中的带边峰是由自由激子和束缚在一浅施主能级的束缚激子的谱线重合而成,这个浅施主能级很有可能是由氮空位产生;黄色荧光的机制应为自由电子或施主能级向深受主能级的跃迁,并且黄色荧光肯定和氮化镓中的一内部缺陷产生的深受主能级有关,该内部缺陷很有可能是镓空位．     

非掺杂n型氮化镓外延层的光致发光

研究了热处理对非掺杂 n型氮化镓外延层光致发光谱的影响和光谱中各发光带强度与温度之间的关系 .热处理后 ,光谱中的带边峰和黄光峰的强度较热处理前都有明显降低 .黄光峰强度随温度升高的衰减速度要比带边峰慢得多 .由这些实验结果得出结论 :光谱中的带边峰是由自由激子和束缚在一浅施主能级的束缚激子的谱线重合而成 ,这个浅施主能级很有可能是由氮空位产生 ;黄色荧光的机制应为自由电子或施主能级向深受主能级的跃迁 ,并且黄色荧光肯定和氮化镓中的一内部缺陷产生的深受主能级有关 ,该内部缺陷很有可能是镓空位 .     

ZnSe薄膜的激子光谱

采用分子束外延 (MBE)技术 ,在 Ga As(1 0 0 )衬底上生长了厚度从 0 .0 4 5到 1 .4μm的 Zn Se薄膜 .X射线衍射谱证实 ,随着薄膜厚度的增加 ,应变逐步弛豫 .测量了低温下样品的反射谱和光致发光谱 ,观察到轻重空穴的能级在不同应变下的分裂、移动和反转 ,以及激子极化激元 (Po-lariton)对反射谱的影响 .也观察到束缚激子发光随着薄膜厚度的变化规律 :束缚在中性受主杂质上的束缚激子发光 (I1峰 )随着薄膜厚度的增加逐渐变弱直至消失 ,而束缚在中性施主杂质上的束缚激子发光 (I2 峰 )则随着厚度增加逐渐增强 .     

ZnSe薄膜的激子光谱

采用分子束外延(MBE)技术,在GaAs(100)衬底上生长了厚度从O.045到1.4μm的ZnSe薄膜.X射线衍射谱证实,随着薄膜厚度的增加,应变逐步弛豫.测量了低温下样品的反射谱和光致发光谱,观察到轻重空穴的能级在不同应变下的分裂、移动和反转,以及激子极化激元(Polariton)对反射谱的影响.也观察到束缚激子发光随着薄膜厚度的变化规律:束缚在中性受主杂质上的束缚激子发光(I1峰)随着薄膜厚度的增加逐渐变弱直至消失,而束缚在中性施主杂质上的束缚激子发光(I2峰)则随着厚度增加逐渐增强.     

非掺杂InP的低温光致发光研究

研究了2K低温下非有意掺杂InP单晶的光致发光谱,对近带边的辐射跃迁进行了仔细分析,报道了InP单晶在大功率光激发时束缚于中性施主的激子跃迁发光相对减弱、而束缚于中性受主的激子跃迁发光相对增强的现象,并探讨了其机制,确认了材料中存在Mg、Zn等残余受主杂质,并计算得到Mg受主的离化能为41.5meV.     

Irregular shifts of excitonic states in reflectivity and PL spectra of ZnSe crystals under uniaxial stress

Splittings and shifts of excitonic states in ZnSe crystals under uniaxial stress along [100], [111] and [110] directions were studied by spatially resolved spectroscopy of both the reflectivity and the photoluminescence (PL) at 5 K. These methods enabled us to check the local strains in different surface microareas of deformed crystals and as a result to reveal the irregular free and bound exciton state shifts related to the influence of the strain nonuniformity and to the presence of structural imperfections (twins) in the crystals. It is shown that elastic deformation of twinned crystals along directions not exactly [111] gives rise to a doublet structure for all the bound exciton lines in the PL spectra. New values of deformation potentials for ZnSe crystals were deduced. The anisotropic influence of the uniaxial stress on the free and bound exciton state splittings was determined.     

Synthesis and photoluminescence properties of the 4H-SiC/SiO2 nanowires

4H-SiC/SiO2 nanowires are synthesized and the temperature-dependent photoluminescence （PL） properties of the nanowires are studied. Their structure and chemical composition are studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD）, and Raman spectra. At room temperature, an ul- traviolet PL peak and a green PL band are observed. From the PL spectrum measured in the temperature range from 80 K to 300 K, the free excition emission, donor bound excition emission and their multiple-phonon replicas have been observed in ultraviolet region, and their origins have been identified. Moreover, it has been found that the temperature dependence of the free exciton peak position can be described by standard expression, and the thermal activation en- ergy values extracted from the temperature dependence of the free exciton and bound exciton peak integral intensity are about 40 meV and 181 meV, respectively.     

Annealing effects of a high-quality ZnTe substrate

The sharp photoluminescence (PL) and optical-reflection spectra in the bandedge region of the high-quality nondoped ZnTe substrate (100) were observed at 4.2 K. Free exciton, associated with lower and upper polaritons (EX^L and EX^U) at 2.382 eV and 2.381 eV, respectively, were clearly observed. This meant that this substrate was high quality. The intensity of a bound exciton peak (2.375 eV), which is caused by a Zn vacancy, of a neutral acceptor decreased with an increase of the Zn vapor pressures.     

等电子施、受主杂质共掺的磷化镓发光特性和能量转移

本文研究了液相外延生长的不同掺Bi,N浓度GaP∶(Bi_7N)材料的低温光致荧光光谱,观察到了N谱线“猝灭”和Bi束缚激子发光增强的现象.这可以解释为束缚激子由等电子受主N向等电子施主Bi隧穿能量转移的结果.变激发密度下各中心发光强度的变化关系以及与GaP∶(Bi)材料的实验结果比较,为这一能量转移过程提供了进一步的论据.     

Growth and photoluminescence study of ZnSe quantum dots

We report detailed photoluminescence (PL) studies of ZnSe quantum dots grown by controlling the flow duration of the precursors in a metal-organic chemical vapor deposition system. The growth time of the quantum dots determines the amount of blue shift observed in the PL measurements. Blue shift as large as 320 meV was observed, and the emission was found to persist up to room temperature. It is found that changing the flow rate and the total number of quantum dot layers also affect the peak PL energy. The temperature dependence of the peak PL energy follows the Varshni relation. From analyzing the temperature-dependent integrated intensity of the photoluminescence spectra, it is found that the activation energy for the quenching of photoluminescence increases with decreasing quantum dot size, and is identified as the binding energy of the exciton in ZnSe quantum dot.     

Low-Temperature Photoluminescence Study of CdTe:In Crystals Annealed in Molten Bismuth

We used a low-temperature photoluminescence (PL) technique to investigate CdTe:In crystals after annealing in molten bismuth (Bi). The two annealed samples showed different resistivities after the treatment. For both samples, we observed very strong emissions in the excitonic spectral region and revealed fine structures of exciton emissions in the PL spectrum. In the sample with high resistivity, we found one ionized donor-bound exciton peak, (D⁺,X), that we ascribed to incorporated Bi atoms occupying Cd sites in the CdTe. The temperature dependence of the (D⁺,X) peak emission had an associated activation energy of 3.59 meV for the exciton bound to this ionized donor. Meanwhile, a donor–acceptor pair peak at 1.5315 eV, which was absent from the PL of the low-resistivity sample, suggested the likelihood of some Bi atoms occupying Te sites in the high-resistivity sample. Our findings highlight the need for detailed investigation of annealing conditions to ensure precise control of the electrical properties of the material during annealing in molten Bi.     

Over 17.4% Efficiency of Layer-by-Layer All-Polymer Solar Cells by Improving Exciton Utilization in Acceptor Layer

Layer-by-layer all-polymer solar cells (LbL all-PSCs) are prepared with PM6 and PY-IT by using sequential spin coating method. The exciton dissociation efficiency in acceptor layer near electrode is rather low due to the limited exciton diffuse distance and impossible energy transfer from narrow bandgap acceptor to wide bandgap donor. In this study, less PM6 is incorporated into PY-IT layer to enhance exciton dissociation in PY-IT layer near electrode. A power conversion efficiency (PCE) of 17.45% is achieved in the LbL all-PSCs incorporating 10 wt% PM6 into PY-IT layer, which is much larger than 16.04% PCE of PM6/PY-IT-based LbL all-PSCs. Over 8% PCE enhancement can be realized by incorporating 10 wt% PM6 into PY-IT layer, which is attributed to the enhanced exciton utilization efficiency in PY-IT layers near electrode. The enhanced exciton utilization efficiency in PY-IT layer can be confirmed from the quenched photoluminescence (PL) emission in PY-IT:PM6 films. Meanwhile, charge transport in acceptor layers can be optimized by incorporating less PM6, as confirmed from the optimized molecular arrangement. This study indicates that the strategy of incorporating less donor into acceptor layer has great potential in fabricating efficient LbL all-PSCs by improving exciton utilization efficiency in acceptor layer near electrode.     

Spontaneous and stimulated UV luminescence of ZnO:N at 77 K

The spontaneous and stimulated UV luminescence spectra of ZnO:N samples possessing different nitrogen contents are measured at a temperature of 77 K. Luminescence peaks resulting from bound and free excitons, biexcitons, and electron recombination via the nitrogen acceptor level are identified. The optical depth (123 meV) of the N_O impurity acceptor level is determined. It is established that stimulated UV luminescence originating from inelastic exciton interaction sets in as the optical pump power increases.     

Shallow donor generation in ZnO by remote hydrogen plasma

We investigate the effects of a remote hydrogen-plasma treatment on Hall parameters as well as on the bound exciton (BEx) photoluminescence (PL) for a variety of ZnO single crystals: bulk air-annealed, Li-doped, and epitaxially grown on sapphire. We present transport and spectroscopic evidence in favor of the hypothesis that hydrogen behaves as a shallow donor rather than a compensating center in ZnO. Specifically, we show that H-plasma-induced increases in I₄ luminescence (photon energy: ∼3.363 eV at 4 K) correlate with increases in free-carrier concentrations from Hall-effect measurements.