半绝缘GaAs中的深能级

在180-500 K温度范围测量了不掺杂半绝缘GaAs晶体的电阻率和霍耳系数.按结果可把样品分为两类:(一)高阻样品,激活能为0.71-0.64eV,由EL2能级决定;(二)中阻样品,激活能为 0.43 eV和 0.37 eV,由 EL5和 EL6能级决定,这与 Martin 等报道的结果有所不同.热处理实验进一步证实了我们的分析.     

未掺杂半绝缘砷化镓中EL2能级的光电离截面谱

采用恒流光电导方法,在不同温度下测量了未掺杂半绝缘LEC砷化镓中EL2能级的光电离截面谱σ_n~0-hv。发现截面谱中有三个上升较快的台阶,认为它们来源于EL2能级上的电子向导带上三个极点Γ、L、X的光跃迁。σ_n~0-hv的理论计算和实验曲线符合得很好,并得出有关EL2能级的物理量即束缚能E_T、Frank-Condon移动d_(FC)和波函数扩展长度α~(-1)。     

激光晶体钼酸钆

一、引言铁电晶体钼酸钆Ga_2(MoO_4)_3(简称GMO),掺钕已经实现1.06微米激光输出。1976年美国Jackiec报导了GMO:Tb光讼,~5D_4亚稳态寿命0.7毫秒,~5D_4→~7F_5跃迁截面为4×10~(-21)厘米~2,是已经实现0.5445微米激光的YLiF_4:Tb晶体的两倍。预计GMO:Tb晶体室温有可能产生0.5430微米四能级激光跃迁,低温77K可能产生0.4870微米三能级激光跃迁。认为它是一种有希望的兰绿激光工作物质。此外,钼酸钆作为非线性晶体在电光开关和声光调制方面国外已有应用的报导,并且有可能实现激光自倍频作用。     

利用HCD灯测量Gu亚稳态寿命

铜原子能级中存在着两个亚稳态能级(4d~94s~(22)D_(3/2)和4d~94s~(22)D_(5/2)。它们分别是铜蒸气激光器578.2nm和510.6nm激光跃迁的下能级。过去已经在CuCl正柱放电管中测量过这二个亚稳态能级的寿命,在不同的条件下,得到的结果也不尽相同,大致在10到100μs的范围内。利用HCD灯,我们发展了一种新的利用窄脉冲放电激发HCD灯产生Cu亚稳态粒子并在放电结束后测量共振激光感生荧光强度随激光脉冲对放电脉冲延迟时间的衰减关系来测量亚稳态寿命的方法。这里的激光波长共振于下能级为亚稳态的跃迁,即510.6nm:     

阿符科试验可能产生X射线激光的两级泵浦方案

阿符科·埃佛雷特研究室将试验两级光泵装置，这样，用目前激光器的水平可能产生X射线激光。第一级泵浦是由激光产生的等离子体的非相干软X射线发射；这些X射线将优先地光致电离中性锂的K壳层电子，产生处于亚稳的1s2s态的高度受激的离子。在亚稳态离子的密度达到足够程度后，调谐至958.41毫微米1s2s1S→1s2p1P跃迁的染料激光器将激发锂离子的19.9毫微米共振线的反斯托克斯-喇曼发射。     

GaAs中由磁场引起的与Si施主有关的高亚稳态

本文报道了GaAs中Si浅施主的博里叶变换红外（FTIR）磁光电导谱．观察到非零磁场下从类氢束缚基态到施主高亚稳态的跃迁．采用变分方法计算了跃迁能量以及这些高亚稳态的离化能的磁场关系，并与实验结果进行了比较．     

自终止跃迁机制和R-M激光

众所周知,以铜蒸气激光器为代表的脉冲放电激励的金属蒸气激光器件属于通常的三能级系统,其激光上能级应是与基态有最强光学联系的共振态,而激光下能级则是与基态光学跃迁禁戒的亚稳态,在玻恩近似得以成立的条件下,同一能级的电子碰撞激发速率与自发跃迁速率正关联,因此共振态有可能优于亚稳态被布居形成粒子数反转导致激光．由于激光下能级与基态之间的光学跃迁禁戒,所以激光跃迁将造成其粒子数堆积,激光最终必将自动终止,因此习惯上称作为“自终止跃迁激光器”． 我们完成了包括铜蒸气激光器在内的脉冲放电激励的多种金属蒸气“…     

多光子Buck—Sukumar模型中原子反转的量子崩溃和再生

为了反映原子与光场的多光子相互作用对光场强度的依赖性,我们最近将Buck—Sukumar模型推广到多光子跃迁过程: H=ωa~+a+ω_oS_z+ε(S+a~K(a~+a)~(1/2)+(a~+a)~(1/2)a~(+K)S_-)(1)式中a~+和a是频率为ω的光场的产生和消灭算符,S_z和S±是二能级原子的反转和跃迁算符,其跃迁频率为ω,ε是原子和场的耦合系数,k是原子每跃迁一次吸收或发射的光     

用近红外光谱技术快速测定聚氯乙稀K值的新方法——正交信号校正法

本文基于正交投影的正交校正算法(OSC),建立了聚氯乙稀近红外光谱与其K值之间关系的数学模型,提出了用近红外漫反射光谱技术快速检测聚氯乙稀K值的新方法。研究结果表明,原始光谱经正交信号校正处理后,聚氯乙稀K值化学测定值与近红外预测值的相关系数和标准差为R=0.9825、RMSEP=0.5933,预测结果的相对误差在0.5%以内,且正交信号校正算法能取得比单纯使用偏最小二乘回归更好的预测效果,模型更为简单。为用近红外光谱快速测定聚氯乙稀的K值提供了一条新途径。     

YGG:Cr~(3+)晶体的光谱特性研究

本文通过实验研究了YGG:Cr~(3+)晶体的光谱特性。报道了室温下的吸收谱;10K、133K、300K的荧光谱;以及荧光寿命,无辐射跃迁几率,辐射量子效率与温度之间的依赖关系。从吸收谱及荧光谱中确定在C_(31)(S_6)低对称场微扰下,Cr~(3+)离子在基质YGG中2T_1能级分裂的子能级及基态~4A_2←→~2E零声子跃迁R线的位置。     

Absorption and photoionization of the donor level in CdF2 semiconductor crystals

A model of strong vibronic interaction is proposed to interpret the specific features of infrared absorption and photoionization in CdF₂ semiconductor crystals. The model takes into account the polaronic nature of the conductivity in these crystals and the profound configuration shift of the free and bound polaron states. It is shown that the intense infrared absorption band in the crystals is not due to the transitions of charge carriers from hydrogen-like donor levels to the conduction band, but is caused by the phonon replicas of intracenter transitions. The low-temperature photoconductivity (in the temperature range 0–70 K) is a result of tunneling transitions between the phonon states of bound and free polarons, since these states are separated by rather high potential barriers. Overcoming the barriers in both directions is responsible for equilibration in the polaron subsystem upon the photoexcitation of charge carriers. The tunneling character of this process is responsible for the slight variation in the equilibration time in the above-indicated temperature range.     

EL2缺陷能级及光电离截面的计算(英文)

In the present work, the electronic level associated with the arsenic-antisite-arsenic-interstitial model for the structure of EL2 has been calculated by using the EHT method. Fourty-two atoms are contained in the cluster and the location of arsenic-interstitial in the EL2 stable state is at two bond lengths distant from arsenic-antisite along the (111) direction, surrounded by four nearest arsenic neighbors. The defect complex has C3V symmetry and the group theory is applied to reduce the secular equation. The optical cross section associated with EL2 is also calculated. The theoretical results revealed that the EL2 defect is the complex arsenic-antisite-arsenic-interstitial.     

First direct observation of EL2-like defect levels in annealed LT-GaAS

Nonstoichiometric arsenic-rich GaAs grown at low temperatures by molecular beam epitaxy (LT-GaAs) has been found to be semi-insulating after high-temperature annealing. The origin of this technologically important conversion is not yet fully understood. In order to study this effect, we performed photocurrent measurements on p-LT GaAs-n diodes in the spectral range between 0.75 and 1.5eV at 8K. The photocurrent spectra revealed the following features which are unique to the EL2 level: photoquenching, characteristic photoionization transitions to conduction band minima and a presence of a broad band due to the effect of auto-ionization from the excited state. Moreover, modeling of the optical excitation process using realistic band structure demonstrates that these features cannot be explained by “internal photoemission” originating from As precipitates, as the “buried Schottky barrier model” predicts. This is the first direct experimental evidence for the existence of EL2-like defect levels and their importance for understanding the optical and electronic properties of annealed LT-GaAs.     

Influence of electronic (charge) state of <Emphasis Type="Italic">E</Emphasis> traps on their introduction rate in irradiated <Emphasis Type="Italic">n</Emphasis>-GaAs

A complex temperature dependence of the introduction rate of E traps in the neutral and space-charge regions of Schottky diodes based on n-GaAs and subjected to high-energy irradiation was observed at 77–580 K in the situation where the recoil-atom energies were close to the threshold energies for radiation-defect production. The experimental data were interpreted quantitatively using a model of metastable Frenkel pairs. This model accounts for the processes of annihilation, recharging, and stabilization of a Frenkel pair in the material in relation to the electronic (charge) state of the Frenkel pair components; this state is governed by the position of the Fermi (quasi-Fermi) level and the sample temperature.     

Temperature,injection level,and frequency dependences of some extrinsic luminescence bands in ZnTe

Using cathodoluminescence measurements between 80 and 300 K, we have investigated the temperature, injection level, and frequency dependences of three extrinsic luminescence bands in nominally undoped ZnTe. At 80 K, our material shows strong edge emission and broad extrinsic bands near 1.59 eV and 2.08 eV. The peak position and band shape are independent of injection level for both these extrinsic bands. 80 K measurements of frequency response from 50 Hz to 50 MHz show that the 2.08 eV band has an exponential time decay with a time constant of 0.045 μsec. The 1.59 eV band shows a more complex frequency dependence which indicates that one component of the response has a time constant of 1.85 μsec. At temperatures above 80 K the 2.08 eV band quenches with an activation energy of 0.22 eV which indicates that the transition originates near a band edge. In contrast, the 1.59 eV band does not quench with a well-defined activation energy. The peak of the 2.08 eV band follows the temperature dependence of the edge emission energy, whereas the peak of the 1.59 eV band shows the opposite behavior. From the 80 K measurements, we conclude that the 2.08 eV band results from a conduction-band-to-acceptor transition, and that the 1.59 eV band results from an intracenter transition between localized levels of a compact complex. Above 160 K, a third extrinsic band begins to appear near 1.80 eV. This band becanes increasingly prominent with increasing temperature. The frequency dependence of the 1.80 eV band at 166 K indicates an exponential time decay with a time constant of 0.37 μsec. However, the frequency dependence changes with temperature and a faster component appears in the response at 300 K. We conclude that 1.80 eV band near 160 K results primarily from an intracenter transition in a compact complex, and that there is a contribution from free-to-bound transitions at 300 K.     

Relationship between near bandedge absorption and photoluminescence efficiency in semi-insulating GaAs

We demonstrate that near bandedge photoluminescence efficiency in SI bulk GaAs can be increased by low temperature photo-quenching of native point defects in the material. These defects cause infrared absorption at photon energies just below the bandgap energy in cooled samples and their concentrations anti-correlate with those of EL2 in unannealed crystals. This absorption has been previously termed “Reverse Contrast.” The increase in PL efficiency is almost an exponential function of the photoquenching time and proportional to the Reverse Contrast absorption coefficient.     

Observation of differences in the quenching of the Photocurrent in GaAs containing EL2 and EL0

The quenching of the photocurrent and photo-Hall effect of several undoped semi-insulating gallium arsenide samples has been measured and compared with the deep-level photoluminescence spectra from neighboring samples. Samples that show either EL2 (0.68 eV) or ELO (0.63 eV) photoluminescence have distinctly different photocurrent quenching behaviors. EL2 samples show a photocurrent decrease of several orders of magnitude, and a change fromn-type to p-type conduction during quenching at 80 K with 1.1 eV light. ELO samples show a reduction in photocurrent of less than an order of magnitude with no change in the carrier type at this temperature. Photo-Hall effect experiments at 80 K indicate that the conduction isn-type for the ELO samples, but changes fromn- to p-type during the quench for the EL2 samples. The temperature dependence of the quenching has also been studied. EL2 samples show little variation in the range 10-80 K, while ELO samples show significant quenching similar to EL2 after the temperature is reduced below 70 K. These results indicate that defects other than EL2 can significantly affect photocurrent quenching experiments.     

Optical an photoelectric properties odf ZnSe:Ti crystals

The photoconductivity and photoluminescence spectra of ZnSe:Ti crystals in the visible and infrared spectral regions are studied. It is established that the high-temperature impurity-induced photoconductivity of ZnSe:Ti crystals is defined by the optical transitions of electrons from the ³ A ₂(F) ground state to highenergy excited states, with the subsequent thermal transitions of electrons to the conduction band. The efficient excitation of intracenter luminescence of ZnSe:Ti crystals is achieved by light from the region of the intrinsic absorption of Ti²⁺ ions.     

Hopping conduction and its photoquenching in molecular beam epitaxial GaAs grown at low temperatures

As the growth temperature of molecular beam epitaxial GaAs is increased from 250 to 400°C, the dominant conduction changes from hopping conduction to band conduction with a donor activation energy of 0.65 eV. A 300°C grown layer is especially interesting because each conduction mechanism is dominant in a particular temperature range, hopping below 300K and band conduction above. Below 140K, the hopping conduction is greatly diminished (quenched) by irradiation with either infrared (hv≤1.12 eV) or 1.46 eV light, but then recovers above 140K with exactly the same thermal kinetics as are found for the famous EL2. Thus, the 0.65 eV donor, which is responsible for both the hopping and band conduction, is very similar to EL2, but not identical because of the different activation energy (0.65 eV vs 0.75 eV for EL2).     

Enhancing the Infrared Photoresponse of Silicon by Controlling the Fermi Level Location within an Impurity Band

Strong absorption of sub‐band gap radiation by an impurity band has recently been demonstrated in silicon supersaturated with chalcogen impurities. However, despite the enhanced absorption in this material, the transformation of infrared radiation into an electrical signal via extrinsic photoconductivity—the critical performance requirement for many optoelectronic applications—has only been reported at low temperature because thermal impurity ionization overwhelms photoionization at room temperature. Here, dopant compensation is used to manipulate the optical and electronic properties and thereby improve the room‐temperature infrared photoresponse. Silicon co‐doped with boron and sulfur is fabricated using ion implantation and nanosecond pulsed laser melting to achieve supersaturated sulfur concentrations and a matched boron distribution. The location of the Fermi level within the sulfur‐induced impurity band is controlled by tuning the acceptor‐to‐donor ratio, and through this dopant compensation, three orders of magnitude improvement in infrared detection at 1550 nm is demonstrated.