高密度激发下CdS单晶的自由激子发光

本文首次在77K温度的电致发光光谱上,观测到了自由激子和自由激子(Ex-Ex)散射的发射带P。根据半经典理论,得到CdS单晶在高激发密度下的激子有效温度高于晶格温度。并且在77K温度下,通过氮分子激光器3371Å谱线的激发,观察到了Ex-Ex散射的P带的受激发射现象。     

Ⅲ-Ⅴ族化合物中氮束缚激子发光的动力学研究

用发光动力学的分析方法,研究了Ⅲ—Ⅴ族化合物中N束缚激子的发光强度与温度的关系,得到的理论公式与实验结果符合得较好。我们的分析指出,由于无辐射能量传递的存在,束缚激子的△J=2跃迁的发光效率低于△J=1跃迁的发光效率,致使低温(T<50K)下束缚激子的发光强度可能随温度的下降而变弱。另外,N杂质对自由激子再俘获的可能性的大小直接影响束缚激子发光的热猝灭过程:束缚激子可能因热离解成自由激子或自由的电子和空穴。我们找到了区分这两类情况的条件。     

镓铝砷双异质结红光二极管中红外辐射起因的研究

本文研究了镓铝砷双异质结红光二极管发射光谱中的红外谱带随工作电流及温度的变化规律,并看到器件的发光效率与红外带的强度有明显的联系.通过红外带峰值位置,半值宽度、峰值位置随温度的移动及发光区深能级的测定,认为该谱带来源于衬底.由于有源区厚度的不均匀及限制作用不充分,使注入到有源区中的一部分电子能穿过限制层进入P型GaAs衬底,从而产生红外谱带.指出改善有源区厚度均匀性,增大限制层的势垒高度是降低红外辐射,提高器件发光效率的有效途径.     

量子限制受主远红外电致发光器件的制备与测量

采用分子束外延技术生长GaAs/AlAs三量子阱,并在中间的GaAs阱中δ-掺杂浅受主杂质Be原子,制作出量子限制受主远红外Teraherz原型电致发光器件.实验上测量得到4.5 K时器件的电致发光谱（EL）和电传输特性（I-V曲线）.在EL发射谱中清楚地观察到222 cm^-1处宽的尖峰,这来源于Be受主奇宇称激发态到其基态的辐射跃迁,而非辐射弛豫过程则使发射谱的信号很弱.另外在I-V曲线中072和186 V的位置出现两个共振隧道贯穿现象,分别对应于中间δ-掺杂量子阱受主能级1s_3/2(Γ₆+Γ₇)到左边非掺GaAs量子阱中HH带,及右边非掺杂GaAs量子阱中HH重空穴带到中间掺杂GaAs量子阱中Be受主杂质原子奇宇称激发态2p_5/2(Γ₆+Γ₇)能级的共振隧穿.     

不同激发密度下CdS晶体的光致发光和受激发射

本文主要研究在77-111K温度范围内、不同激发密度的N2激光器的337.1nm谱线激发下,激子-激子(Ex-Ex)、激子-载流子(Ex-e)的相互作用和发射一个LO声子(Ex-1LO)、两个LO声子(Ex-2LO)的自由激子的辐射复合行为.并在77K温度下观测到由Ex-Ex发射产生的受激发射.     

磁控溅射制备ZnO薄膜的受激发射特性的研究

用射频磁控反应溅射法在二氧化硅衬底上制备ZnO薄膜。得到了在不同温度下ZnO薄膜的吸收与光致发光。观测到了纵光学波 (LO)声子吸收峰与自由激子吸收峰 ;室温 (30 0K)下 ,PL谱中仅有自由激子发光峰。这些结果证实了ZnO薄膜具有较高的质量。探讨了变温ZnO薄膜的发光特性。研究了ZnO薄膜的受激发射特性。     

非对称方势阱中的激子及其与声子的相互作用

采用类LLP(Lee-Low-Pines)变换和分数维变分法,在讨论有限深非对称方势阱Ga_1－xAl_xAs/ GaAs/Ga_0.7Al_0.3As的分数维基础上,计算了其中激子的基态能量以及声子对其影响,随着势阱宽度增加,激子能量先减小后增大,出现一个最小值.讨论了一侧势垒高度变化对分数维、激子基态能量的影响,并发现声子作用使得激子能量明显增大.另外,非对称方势阱中的激子结合能随阱宽的减小而增     

γ-LiAlO2上a面ZnO薄膜的光谱特性研究

利用激光脉冲沉积(PLD)技术在(302)γ-LiAlO₂衬底上成功生长了非极性的a面(1120)ZnO薄膜，光致发光谱(PL)带边发射峰半峰宽仅为115meV.研究了非极性ZnO薄膜光谱特性的面内各向异性，发现随着入射光偏振方向改变，在偏振透射光谱上，吸收边移动了20meV，这与A、B激子和C激子的能量差一致；而在拉曼光谱上，激发光偏振方向的改变导致E₂模式的强度发生明显改变.     

磁场作用下的有机电致发光

分别制备了荧光器件ITO/NPB/Alq₃/LiF/Al和磷光器件ITO/NPB /CBP: Ir（ppy）₃/BCP/Alq₃/LiF/Al, 测试了50 mT磁场作用下器件的I-V和L-V特性. 与零磁场相比荧光器件和磷光器件的效率分别增加了44%和7%. 从有机电致发光的机制出发对该现象进行了解释, 认为外加磁场可以使三重态激子发生塞曼分裂, 进而在荧光器件中引起了三重态激子T     

Zn离子注入和退火对ZnO薄膜光学性能的影响

 利用溶胶凝胶方法在石英玻璃衬底上制备了ZnO薄膜，将能量56 keV、剂量1×10¹⁷ cm^-2的Zn离子注入到薄膜中。离子注入后，薄膜在500~900 ℃的氩气中退火，利用X射线衍射谱、光致发光谱和光吸收谱研究了离子注入和退火对ZnO薄膜结构和光学性质的影响。结果显示：衍射峰在约700 ℃退火后得到恢复；当退火温度小于600 ℃时，吸收边随着退火温度的提高发生蓝移，超过600 ℃时，吸收边随着退火温度的提高发生红移；近带边激子发光和深能级缺陷发光都随退火温度的提高而增强。     

ZnCdse-ZnSe多量子阱中的激子发光

在77-300K温度下研究了Zn_1-xCd_xSe-ZnSe多量子阱(MQWs)的光致发光特性.首次在77K,Ar离子激光器的457.9nm激发下,在Zn_0.68Cd_0.32Se-ZnseMQWs中观测到5个发光带,其中三个发光带被归因于不同的激子发射:即n=1重空穴(HH)激子;n=l轻-重空穴(LH)激子和n=IHH激子同时发射两个纵光学声子的复合发光,并且n=1HH激子发光可延续至室温.     

Resonant exciton trapping at impurity states in silver bromide

Excitation spectra near the indirect exciton edge of AgBr at 1.8K are reported for several luminescence lines from weakly localized excitons. Excitation below the exciton absorption threshold reveals several excited bound exciton states the energetic positions of which are determined. For excitation above the threshold, strong energy dependent structure is observed. It is interpreted in terms of resonant trapping of free excitons in both ground and excited bound exciton states associated with emission of LO(Γ), long wavelength acoustic and intervalley TA(X) and LA(X) phonons as well as combinations and overtones of these. From measurements in doped crystals two bound exciton systems are found to be correlated with Cd²⁺ and Ca²⁺, respectively.     

Exciton recombination in silver bromide

The recombination luminescence of the free indirect exciton is studied in pure AgBr single crystals at low temperature. The participation of two phonons with wavenumbers of 96 and 64 cm^?1, respectively, is discussed in view of the unusual behaviour of the transverse phonon branches near L. Weak coupling of the exciton to the LO (Γ) phonon and recombination via a shallow trap are observed.     

Pressure dependence of the near-band-edge photoluminescence from ZnO microrods at low temperature

The temperature and pressure dependences of band-edge photoluminescence from ZnO microrods have been investigated. The energy separation between the free exciton (FX) and its first order phonon replica (FX-1LO) decreases at a rate of k_BT with increasing temperature. The intensity ratio of the FX-1LO to the bound exciton (BX) emission is found to decrease slightly with increasing pressure. All of the exciton emission peaks show a blue shift with increasing pressure. The pressure coefficient of the FX transition, longitudinal optical (LO) phonon energy, and binding energy of BX are estimated to be 21.4, 0.5, and 0.9 meV/GPa, respectively.     

ZnCdse－ZnSe多量子阱中的激子发光

在７７－３００Ｋ温度下研究了Ｚｎ（１－ｘ）ＣｄｘＳｅ－ＺｎＳｅ多量子阱（ＭＱＷｓ）的光致发光特性．首次在７７Ｋ，Ａｒ离子激光器的４５７．９ｎｍ激发下，在Ｚｎ（０．６８）Ｃｄ（０．３２）Ｓｅ－ＺｎｓｅＭＱＷｓ中观测到５个发光带，其中三个发光带被归因于不同的激子发射：即ｎ＝１重空穴（ＨＨ）激子；ｎ＝ｌ轻－重空穴（ＬＨ）激子和ｎ＝ＩＨＨ激子同时发射两个纵光学声子的复合发光，并且，；ｎ＝１ＨＨ激子发光可延续至室温．     

Studies of relaxation times of secondary radiations in ZnTe by circular polarization correlation

Population and spin relaxation rates concerned with exciton luminescence and multiple LO-phonon emission lines are studied in ZnTe at 77 K by means of optical circular polarization correlation between the exciting and emitted lights. The decay times of the LO lines are determined to be much less than 10^-11sec, which are definitely shorter than the obtained exciton lifetime of 10^-10-10^-9sec. It is concluded that the LO lines are not due to hot luminescence but due to resonance Raman scattering.     

Resonant Raman effect in TlBr: Forbidden one-phonon and intervalley scattering at the direct exciton

Resonant Raman scattering at the direct exciton in TlBr at 1.8K is reported. The cross-section for forbidden 1LO (Γ) scattering shows resonances at both the 1s and 2s exciton. For the first time strongly resonant forbidden 1TO (Γ) scattering is observed for which possible mechanisms are discussed. Several two-phonon Raman processes involving M-point phonons confirm by direct observation the phonon intervalley scattering between non-equivalent X-points.     

Photoluminescence and multiphonon resonant Raman scattering in Ni-and Co-doped Zn1−x MnxTe crystals

Low-temperature photoluminescence, exciton reflection, and multiphonon resonant Raman scattering spectra of Ni-and Co-doped Zn_1−x Mn_xTe crystals were investigated. Intense emission occurs in a broad spectral region (1100–17 000 cm⁻¹) in the crystals containing Ni atoms. It is caused by intracenter transitions involving Mn²⁺ ions and transitions between the conduction band and a level of the doubly charged acceptor. The features of the exciton photoluminescence and multiphonon resonant Raman scattering involving longitudinal-optical (LO) phonons at various temperatures are investigated. The insignificant efficiency of the localization of excitons on potential fluctuations in the Zn_1−x Mn_xTe:Co crystals is established. A temperature-induced increase in the intensity of the 5LO multiphonon resonant Raman scattering line due to the approach of the conditions for resonance between this line and the ground exciton state is observed in these crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 616–621 (April 1998)     

Formation of excitons from free electron–hole pairs due to acoustic phonon interactions in quantum wells

A study of the process of exciton formation due to acoustic phonon interaction in quantum wells (QWs) is presented. Considering that excitons are formed from photoexcited free electron–hole pairs, we have derived the rate of such formation as a function of density and temperature of charge carriers and wavevectorK_|| of the center-of-mass motion of exciton, and finally applied our theory to GaAs/AlGaAs QWs. We have found that the formation of an exciton due to acoustic phonon emission is more efficient at relatively large values ofK_|| (hot excitons) whereas that due to longitudinal optical (LO) phonon emission is more efficient at relatively small values of K_||.     

Exciton-phonon interaction in mixed silver halides: Resonant Raman scattering vs photoluminescence

An investigation of resonant Raman scattering in mixed crystals of AgBr:Cl at 1.8 K shows that the zero-phonon and LO phonon-assisted exciton luminescence excited in the free indirect exciton absorption, exhibits an anomalous dependence on the exciton photon energy E_L. Close to the exciton gap, the bands show a Raman-like behaviour with their peaks at constant energetic distance from E_L. As E_L is tuned further into the absorption, the bands gradually develop into normal photoluminescence. The effect is explained by taking into account exciton relaxation via scattering by long-wavelength acoustic phonons, a process which is strongly energy dependent. In addition, resonant Raman scattering observed for excitation in the zero-phonon absorption suggests study for the first time of the mode behaviour of certain off-zone center phonons in this system.