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．     

Zn1—xMnx／ZnSe应变超晶格分子束外延生长及光学特性研究

用分子束外延方法在ＧａＡｓ（１００）衬底上成功生长了高质量的Ｚｎ１－ｘＭｎｘＳｅ／ＺｎＳｅ（ｘ＝０．１６），超晶格结构，用Ｘ射线衍射和低温光致发光（ＰＬ）对其结构，应变分布以及光学性能进行了研究，结果表明，２Ｋ温度下，Ｚｎ１－ｘＭｎｘＳｅ／ＺｎＳｅ超晶格的光致发光中主发光峰对应于ＺｎＳｅ阱中基态电子和基态轻空穴之间的自由激子跃迁，而且其峰位相对于ＺｎＳｅ薄膜材料的自由激子峰有明显移动。其中，当超晶     

高分子中的激子激子复合过程

高分子的一维特性使电子激发产生显著的自陷（ｓｅｌｆｔｒａｐｐｉｎｇ）效应，两个单激子（ｅｘｃｉｔｏｎ）会复合形成双激子（ｂｉｅｘｃｉｔｏｎ），这是形成双激子的重要通道，其效率高于双光子过程．这种复合过程伴随着晶格畸变，需要了解其演变过程并确定其弛豫时间．本文利用动力学方程研究了激子激子复合的弛豫过程，确定了它的弛豫时间为１６０ｆｓ，同时还研究了外电场Ｅ对复合过程的影响，结果表明，当Ｅ大于０５ＭＶ／ｃｍ时，两个单激子不能复合成双激子，而是解离成正负双极化子．     

Cs3Cu2I5晶体薄膜吸收谱的研究

本文测定了Ｃｓ３Ｃｕ２ Ｉ５ 晶体薄膜在室温及液氮温度下的吸收谱,并依此计算出该材料的激子参数,即激子束缚能ΔＥ（１）ｅｘ ＝ （０．５３±０．０７）ｅＶ,激子半径ａｅｘ ＝ ０．３２６ ｎｍ ,禁带宽度Ｅｇ ＝ （５．００±０．０７）ｅＶ。在谱分析的基础上,论证了Ｃｓ３Ｃｕ２Ｉ５ 的电子和激子激发定域在该晶体的ＣｕＩ亚晶格之中,同时,揭示了在低温下Ｃｓｘ Ｃｕ１－ ｘ Ｉ系列化合物的第一激子峰位置随其摩尔组分变化的规律。     

类锂铝离子能级结构及光谱线性质的理论计算

用Ｈａｒｔｒｃｅ－Ｆｏｃｋ－Ｒｅｌａｔｉｖｉｓｔｉｃ（ＨＦＲ）自洽场方法,计算类锂铝离子１ｓ＾２ｎｌ（ｎ＝２～７,ｌ＝０～５）,１ｓｎｌｎ’ｌ’（ｎ,ｎ’＝２～３,ｌ,ｌ’＝０～２）各能级值,电偶极跃迁谱线的光谱线性质（波长、振子强度和跃迁几率）,其波长计算值和现有文献结果符合得较好。特别是实验中已观察到的软Ｘ射线激光跃迁（３ｄ－４ｆ,３ｄ－５ｆ）的波长值与我们的计算值符合得也很好。     

InCI分子C^1Ⅱ1态光谱研究

采用激光诱导荧光技术对ＩｎＣ１分子Ｃ＾１Ⅱ１→Ｘ＾１∑＾＋荧光光谱进行了分析和归属,在发射谱中探测到ｖ′＝１向下的跃迁,证明Ｃ态预离解只能发生在ｖ′＝１之上。并对Ｃ＾１Ⅱ１→Ｘ＾１∑＾＋的荧光衰变曲线进行了观测,得到ＩｎＣ１分子Ｃ＾１Ⅱ１（ｖ′＝１）态的无碰撞辐射寿命τ０≈１１ｎｓ及电子跃迁矩│Ｒｅ│＾２≈５．９５Ｄ＾２。     

类锂V^20＋—Cu^26＋离子的谱线波长和振子强度

用多组态ＨＸＲ方法计算了类Ｌｉ离子Ｖ２０＋－Ｃｕ２６＋１ｓ２ｎｌ（ｎ＝２～６，ｌ＝０～４）组态能级之间的电偶极跃迁波长和振子强度，并和已有的实验结果进行了比较。     

Ar^1^6^＋离子双激发态的新量子数描述和跃迁规律

此文采用ＣＩ方法计算了类氦Ａｒ１６＋离子双激发态能级和波函数，并向ＤＥＳＢ（Ｄｏｕｂｌｙ－ｅｘｅｃｉｔｅｄｓｔａｔｅｓｂａｓｉｓ）做投影，求出表征这些双激发态的新量子数Ｋ、Ｔ和Ａ。计算和比较了初态ｎ（ｎ－１，０）ｎ＋１Ｓｅ的辐射和Ａｕｇｅｒ跃迁率，发现辐射跃迁随初态主量子数ｎ的变化是光滑的，而Ａｕｇｅｒ跃迁则随ｎ的变化是不光滑的。     

超声射流冷却SO2^—A2—^1A1激光诱导荧光激发谱

测得了３１５￣３３０ｎｍ超声射流冷却下ＳＯ２＾１Ａ２－＾１Ａ１激光诱导荧光（ＬＩＦ）激发谱，获得了７个有明显Ｋ结构的Ｃ型跃迁的转动子带分辨谱，并将７０个转动子带归属为（１，ｍ，１）－（０，０，０）和（０，ｎ，１）－（０，０，０）（４≤ｍ≤７，８≤ｎ≤１０）的跃迁带系。光谱分析得到ＳＯ２＾１Ａ２－＾１Ａ１跃迁的带源ｖ００、＾１Ａ２态弯曲振动频率ｖ′２，非谐性常数Ｘ２２′分别为（２７９５０±５）、（２     

类氦铷、铌离子光电离截面的细致计算

采用ＨＦ加相对论修正的ＨＦＲ方法，考虑束缚组态间的相互作用，计算了类氦铷与类氦铌离子各能级间跃迁的光电截面，所包括的离子组态为１ｓｎｌ—１ｓεｌ±１（１≤ｎ≤６、０≤ｌ≤ｎ－１），取自由电子能量区间为０～１０倍的离化能，分析了系统计算误差与计算精度，给出了对未态求和及三次样条插值后的结果。     

Recombination dynamics of free and bound excitons in bulk GaN

We report new data on the transient photoluminescence behaviour of free and donor bound excitons in high quality bulk GaN material grown by HVPE. With 266 nm photoexcitation the no-phonon free exciton has a short decay time, about 100 ps at 2 K, assigned to nonradiative surface recombination. The LO replicas of the free exciton have a much longer decay at 2 K, about 1.4 ns, believed to be a lower bound for the bulk radiative lifetimes of the free excitons at 2 K. The donor bound exciton no-phonon lines exhibit a rather short (about 300 ps) nonexponential decay at 2 K, which appears to be dominated by a scattering process. The corresponding LO replicas and the two-electron transitions have a much longer decay. From the latter, the lower bound of the radiative lifetime of the O- and Si-bound excitons are 1800 ps and 1100 ps, respectively.     

Temperature dependent effects on luminescence polarization and recombination lifetime in serpentine superlattice quantum wire arrays

We have measured photoluminescence excitation (PLE) spectra and radiative lifetimes as functions of temperature for serpentine superlattice quantum-wire arrays. The (Al, Ga)As arrays have lateral periods near 10 nm, and lateral confining potentials of 120 meV in the conduction band. At low temperature the excitons are strongly localized within potential fluctuations along the wires. The radiative lifetime of these localized states is 340 ps at 2 K. The degree of exciton localization decreases with increasing temperature, from which we estimate the strongly-localizing potential fluctuations to be approximately 10 meV deep. Above 80 K the excitons have sufficient thermal energy for motion along the wires. The radiative lifetimes increase with temperature, to 20 ns for free carriers at 325 K. The lateral potential barriers inhibit diffusion to non-radiative recombination sites.     

Picosecond excitonic luminescence in ZnO and other wide-gap semiconductors

Radiative lifetimes of free-atom transitions, scaled by ω³ for comparison at 368 nm, are not faster than about 6.9 ns. BaF₂ core-valence luminescence, scaled in the same way from 220 to 368 nm, corresponds to 4.1 ns. In contrast, excitonic transitions in wide-gap semiconductors display subnanosecond radiative lifetimes, and in particular ZnO has radiative lifetimes measured at 50–300 ps for D^o,X and 400–900 ps for free excitons. The “giant oscillator strength” corresponding to these lifetimes can be explained by theories developed initially for defect-bound excitons, then quantum wells, and nanoparticles. An exciton is a coherent array of N dipoles, where N is the number of sites covered by coherent translational motion of the exciton. This is not essentially a phenomenon of multiple excitons, but applies as well to single-exciton decay. It differs in that regard from the more familiar Dicke giant dipole of N coherently excited atoms lacking translational periodicity. The phenomenon suggests possibilities for achieving ultrafast scintillators and high light yield.     

用MOCVD技术在Al2O3衬底上外延GaN的光致发光研究

本文通过变温和变激发强度的光致发光研究了用ＭＯＣＶＤ在Ａｌ２Ｏ３上生长ＧａＮ单晶薄膜的带边发射，通过分峰拟合得到Ａ，Ｂ，Ｃ，Ｄ四个谱峰，其中半峰宽分别为１３．８ｍｅＶ，１０．８ｍｅＶ，１５．６ｍｅＶ，和５０ｍｅＶ。Ａ对应自由激子谱，Ｂ，Ｃ为两种束缚激子的跃迁，Ｄ与氧杂质谱有关。     

Lifetimes of bound excitons in CdSe

Lifetime measurements have been made on bound excitons in CdSe, by using the time-correlated single photon counting and a cw mode-locked dye laser. The lifetimes of the T₂ (an exciton bound to a neutral donor) and I₁ (an exciton bound to be a neutral acceptor) bound excitons have been determined to be 0.50±0.05 and 0.80±0.05 ns, respectively. These values are in good agreement with those predicted by the model of Rashba and Gurgenishvili.     

镓铟磷三元化合物中的自由激子和杂质N发光中心的结构位形

我们研究了GaxIn1-xP:N(x=0.99,0.98,0.96)的发光光谱,用Ar+离子激光器的458nm线激发。N的浓度为5×1017cm-3。图1示出了在6K下Ga0.99In0.01P:N的发光光谱。Mariette和Chevallier[1,2]以及Nelson和Holonyak,Jr[3]。认为Nx0带起源于束缚在孤立N中心上激子的辐射复合。     

Metastable optical absorption of relaxed electronic excitations in BeO-Zn crystals

Spectra of metastable optical absorption and its relaxation kinetics have been studied in zinc-doped BeO crystals by time-resolved pulsed absorption spectroscopy. A comparison of the observed induced optical absorption of self-trapped excitons and small-radius excitons bound to the zinc impurity suggests that their hole components have similar structures and reveals distinctive features of “forbidden” optical transitions in the electronic components. Metastable optical absorption in Zn⁺ centers has been discovered. It is shown that the small-radius excitons bound to the zinc impurity form in the hole stages of thermally stimulated tunneling recombination processes involving Zn⁺ electronic centers. It has been found that the high recombination probability of the electronic and hole centers created in BeO-Zn crystals by an electron beam may be due to the high degree of their spatial correlation. Fiz. Tverd. Tela (St. Petersburg) 41, 601–605 (April 1999)     

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。     

Frequency and density dependent radiative recombination processes in III–V semiconductor quantum wells and superlattices

In this paper we review the radiative recombination processes occurring in semiconductor quantum wells and superlattices under different excitation conditions. We consider processes whose radiative efficiency depends on the photogenerated density of elementary excitations and on the frequency of the exciting field, including luminescence induced by multiphoton absorption, exciton and biexciton radiative decay, luminescence arising from inelastic excitonic scattering, and electron-hole plasma recombination.

Semiconductor quantum wells are ideal systems for the investigation of radiative recombination processes at different carrier densities owing to the peculiar wavefunction confinement which enhances the optical non-linearities and the bistable behaviour of the crystal. Radiative recombination processes induced by multi-photon absorption processes can be studied by exciting the crystal in the transparency region under an intense photon flux. The application of this non-linear spectroscopy gives direct access to the excited excitonic states in the quantum wells owing to the symmetry properties and the selection rules for artificially layered semiconductor heterostructures.

Different radiative recombination processes can be selectively tuned at exciting photon energies resonant with real states or in the continuum of the conduction band depending on the actual density of photogenerated carriers. We define three density regimes in which different quasi-particles are responsible for the dominant radiative recombination mechanisms of the crystal: (i) The dilute boson gas regime, in which exciton density is lower than 10¹⁰ cm^-2. Under this condition the decay of free and bound excitons is the main radiative recombination channel in the crystal. (ii) The intermediate density range (n < 10¹¹ cm^-2) at which excitonic molecules (biexcitons) and inelastic excitonic scattering processes contribute with additional decay mechanisms to the characteristic luminescence spectra. (iii) The high density range (n ?10¹² cm^-2) where screening of the Coulomb interaction leads to exciton ionization. The optical transitions hence originate from the radiative decay of free-carriers in a dense electron-hole plasma.

The fundamental theoretical and experimental aspects of the radiative recombination processes are discussed with special attention to the GaAs/Al _x Ga_1-x As and Ga _x In_1-x As/Al _y In_1-y As materials systems. The experimental investigations of these effects are performed in the limit of intense exciting fields by tuning the density of photogenerated quasi-particles and the frequency of the exciting photons. Under these conditions the optical response of the quantum well strongly deviates from the well-known linear excitonic behaviour. The optical properties of the crystal are then no longer controlled by the transverse dielectric constant or by the first-order dielectric susceptibility. They are strongly affected by many-body interactions between the different species of photogenerated quasi-particles, resulting in dramatic changes of the emission properties of the semiconductor.

The systematic investigation of these radiative recombination processes allows us to selectively monitor the many-body induced changes in the linear and non-linear optical transitions involving quantized states of the quantum wells. The importance of these effects, belonging to the physics of highly excited semiconductors, lies in the possibility of achieving population inversion of states associated with different radiative recombination channels and strong optical non-linearities causing laser action and bistable behaviour of two-dimensional heterostructures, respectively.     

Radiative and non-radiative relaxation of excitons in strain-compensated quantum dots

We have investigated the population dynamics of excitons in strain-compensated InAs quantum dots (QDs) using a pump–probe technique under resonant excitation. Precise control of polarization directions of incident pulses enabled us to selectively estimate population lifetimes for two orthogonally polarized exciton ground states according to polarization selection rules. Measured decay times of the probe transmissions were highly dependent on the polarization directions of the exciton states. We found that the ratio of the decay times for the orthogonally polarized states is in quantitative agreement with the ratio of square of the transition dipole moments. This indicates that radiative recombination processes have a dominant effect on the population dynamics and that non-radiative and spin relaxations are negligible in our QDs. As a result, we can estimate the radiative lifetimes to be 1.0±0.1 and 1.7±0.2 ns for orthogonally polarized exciton ground states.