ZnCdSe/ZnSe多量子阱的生长和激子光学性质的研究

用分子束外延在GaAs衬底上生长了ZnCdSe/ZnSe多量子阱结构.利用X射线衍射(XRD)、变温度PL光谱和ps发光衰减等研究了ZnCdSe/ZnSe多量子阱结构和激子复合特性.由变温PL光谱讨论了随温度升高辐射线宽展宽和辐射复合效率降低的机理.     

GaAs/Al0.23Ga0.77As双量子阱的带边不连续性和阱间耦合

本文报道在300和77K对一组具有不同垒宽L_b0.23Ga_0.77As双量子阱样品的光调制反射谱(PR)的研究结果。除观察到11H,11L和22H等容许跃迁外,同时还识别一个从Al_0.23Ga_0.77As价带顶至量子阱第一电子束缚能级的跃迁,另一个从量子阱第一轻空穴束缚能级至Al_0.23Ga_0.77As导带底的跃迁。利用这些跃迁确定导带边不连续性为0.63。对L_{b关键词：}     

ZnCdSe／ZnSe多量子阱的生长和激光光学性质的研究

用分子束外延在GaAs衬底上生长了ZnCdSe/ZnSe多量子阱结构,利用X射线衍射（XRD）、变温度PL光谱和ps发光衰减等研究了ZnCdSe/ZnSe多量子阱结构和激子复合特性,由变温PL光谱讨论了随温度升高辐射线宽展宽和辐射复合效率降低的机理。     

CdSe/CdMnSe多量子阱的激子光学性质的研究

用分子束外延在GaAs衬底上生长了CdSe/CdMnSe多量子阱结构.利用X射线衍射(XRD)、变密度激发的PL光谱、变温度PL光谱和变密度激发的ps时间分辨光谱研究了CdSe/CdMnSe多量子阱结构和激子复合特性.讨论了随温度升高辐射线宽展宽和辐射复合效率降低的机理.发现不同激发密度下发光衰减时间不同,认为它的机理可能是无辐射复合引起的.在该材料中观测到激子激子散射发射峰,它被变密度激发和变温度PL光谱所证实. 关键词： CdSe/CdMnSe 量子阱 光学性质     

基于量子限制的受主带间跃迁太赫兹探测器的制备与测量

使用分子束外延生长设备,在GaAs（100）衬底上生长了量子阱宽度为3 nm的GaAs/AlAs多量子阱样品,并在量子阱层中央进行了Be受主的δ-掺杂。根据量子限制受主从束缚态到非束缚态之间的跃迁,设计并制备了δ-掺杂Be受主GaAs/AlAs多量子阱太赫兹光探测器原型器件。在4.2 K温度下,分别对器件进行了太赫兹光电流谱和暗电流-电压曲线的测量。在6 V直流偏压下,空穴载流子沿量子阱层方向输运。当正入射激光频率为6.8 THz时,器件响应率为2×10^-4 V/W（2 μA/W）。通过器件的暗电流-电压曲线计算了器件全散粒噪声电流,在4.2 K、6 V直流偏压下,全散粒噪声电流为5.03 fA·Hz^-1/2。     

GaAs/Al_(0.23)Ga_(0.77)As双量子阱的带边不连续性和阱间耦合

本文报道在300和77K对一组具有不同垒宽Lb的GaAs/Al_(0.23)Ga_(0.77)As双量子阱样品的光调制反射谱(PR)的研究结果。除观察到11H,11L和22H等容许跃迁外,同时还识别一个从Al_(0.23)Ga_(0.77)As价带顶至量子阱第一电子束缚能级的跃迁,另一个从量子阱第一轻空穴束缚能级至Al_(0.23)Ga_(0.77)As导带底的跃迁。利用这些跃迁确定导带边不连续性为0.63。对Lb≤40实验观察到11H和11L跃迁都明显地分裂成对称和反对称分量,对分裂大小的实验值与理论计算作了比较。在77K的11H的PR谱中在高能端明显地出现一个肩形峰,其形状不能用PR标准线形来拟合。如认为它对应于带间跃迁,并由此估计激子的束缚能约为8meV。     

InGaAs/GaAs应变量子阱的光谱研究

分别用光致发光谱（PL），光伏谱（PV）及时间分辨谱（TRPL）的方法，测量了应变InGaAs/GaAs单量子阱和多量子阱在不同温度下的光谱，发现单量子阱与多量子阱有不同的光学4性质。多量子阱PL谱发光峰和PV谱激子峰的强度与半高宽都比单量子阱的大，但单量子阱的半高宽随着温度的升高增大很快，这是由激子－声子耦合引起的，通过时间分辨谱研究发现了量子阱子能级之间的跃迁，多量子阱的发光寿命明显比单量子阱的长，我们利用形变势模型对量子阱的能带进行了计算，很好地解释了实验结果。     

δ-掺杂Be受主GaAs/AlAs多量子阱的空穴共振隧穿（英文）

三个具有不同量子阱宽度的GaAs/AlAs多量子阱结构样品通过分子束外延生长设备生长在半绝缘的(100)p-型GaAs衬底上,并且在量子阱层结构的生长过程中,在GaAs阱层中央进行了Be受主的δ-掺杂。基于这3个结构样品,通过光刻技术和半导体加工工艺制备了相应的两端器件。在4～200 K的温度范围内,我们分别测量了器件的电流-电压特征曲线,清楚地观察到了重、轻空穴通过δ-掺杂Be受主GaAs/AlAs多量子阱结构的共振隧穿现象。发现随着GaAs量子阱层宽的逐渐减小,轻空穴的共振隧穿峰向着高电压方向移动,这个结果和通过AlAs/GaAs/AlAs双势垒结构模型计算的结果是一致的。然而,随着测量温度的进一步升高,两个轻空穴共振峰都朝着低电压的方向移动,并且在150 K温度下,其中一个共振遂穿峰表现为一种振动模式。     

内节流式冷指型液氮杜瓦瓶及其在多量子阱荧光研究中的应用

本文介绍了适用于光学测量的经过特别设计的液氮杜瓦瓶。作为一个应用例子,讨论了液氮温度下GaAs/GaAlAs多量子阱荧光谱的测量。     

生长温度和结构参数对InGaAs／GaAs量子阱光学特性的影响

研究了不同生长温度下制备的In0.15Ga0.85As/GaAs应变量子阱的PL谱,结果表明,生长温度越高,In偏析和In-Ga互混越严重,同时,导致更多的In脱附,PL谱发光峰蓝移。对不同In含量的和不同InGaAs厚度的InGaAs/GaAs量子阱进行PL谱测试,分析表明In含量<0.2,生长温度低于560℃时,In含量和InGaAs层量子阱的厚度对In偏析、脱附和In-Ga互混基本没有影响。     

Electric and photoelectric properties of GaAs/ZnSe-Ge/ZnSe/Al structures with Ge quantum dots

Current-voltage characteristics and spectral dependences of photovoltage are investigated at T=4.2 and 300 K in stress-free structures with germanium quantum dots (QDs) in the GaAs/ZnSe/QD-Ge/ZnSe/Al system. The “Coulomb staircase” type features in the current-voltage characteristic observed at room temperature without illumination are due to the Coulomb interaction of electrons in resonant tunneling through intrinsic levels in QDs. The features in the photovoltage spectra are related to the absorption of radiation in the system of discrete levels of QDs. An energy band diagram of the structure is constructed based on the experimental data.     

GaAs,InP, and CdSe photovoltage transients

The response of the photovoltage of GaAs, InP, and CdSe to changes in the incident light intensity are examined with the retarding potential electron beam technique. It is demonstrated that the dynamics of the photovoltage transients are sensitive to the surface conditions. This is discussed in terms of a theoretical model which involved the capture of both electrons and holes at the semiconductor surface.     

Comparative research for transmission-mode GaAs photocathodes of different doping structures on surface photovoltage

In order to well study the internal body performance for transmission-mode GaAs photocathode of different varied doping structures, two GaAs photocathodes of exponential doping structure and gradient doping structure were designed respectively. Because surface photovoltage spectrum has close relation with the internal properties of GaAs photocathodes, the connection between surface photovoltage and internal electronic field was well discussed through deduction and calculation. The difference of two structures and the value of internal electronic energy were exactly calculated and verified by experiments. The internal band bending energy could form an internal electronic field with the same direction, which could help the photo-excited electrons to move toward surface barrier layer. This research shows a better method to well study the varied doping structures for GaAs photocathode materials and will help to improve the growth structure for transmission-mode GaAs photocathode module in the future.     

发射层厚度对透射式GaAs光电阴极表面光电压谱的影响

通过求解一维稳态少子扩散方程,推导了含有后界面复合速率和发射层厚度的透射式GaAs光电阴极表面光电压谱理论方程.通过对发射层厚度分别为1.6 μm和2.0 μm,掺杂浓度为1×1019 cm－3的GaAs透射式阴极样品测试,理论曲线和实验曲线基本一致.通过引入表面光电压谱积分灵敏度公式,仿真探讨了表面光电压谱在一定体材料参量条件下,积分灵敏度受发射层厚度的影响|发现在体材料参量一定条件下,透射式GaAs光电阴极具有最佳厚度,同时最佳厚度受后界面复合速率的影响更大,同时GaAlAs窗口层也能很好降低发射层后界面复合速率.     

Electron propagation from a photo-excited surface: implications for time-resolved photoemission

We perform time- and angle-resolved photoelectron spectroscopy on p-type GaAs(110). We observe an optically excited population in the conduction band, from which the time scales of intraband relaxation and surface photovoltage decay are both extracted. Moreover, the photovoltage shift of the valence band intriguingly persists for hundreds of picoseconds at negative delays. By comparing to a recent theoretical study, we reveal that the negative-delay dynamics reflects the interaction of the photoelectrons with a photovoltage-induced electric field outside the sample surface. We develop a conceptual framework to disentangle the intrinsic electron dynamics from this long-range field effect, which sets the foundation for understanding time-resolved photoemission experiments on a broad range of materials in which poor electronic screening leads to surface photovoltage. Finally, we demonstrate how the long-lasting negative-delay dynamics in GaAs can be utilized to conveniently establish the temporal overlap of pump and probe pulses in a time-resolved photoemission setup.     

[5‐(p‐alkoxy)phenyl‐10, 15, 20‐tri‐phenyl] porphyrin and their rare earth complex liquid crystalline

Three series of porphyrin liquid crystalline compounds, [5‐(p‐alkoxy)phenyl‐10, 15, 20‐tri‐phenyl] porphyrin and their rare earth complexes (Tb (III), Dy (III), Er (III), Yb (III)), with a hexagonal columnar discotic columnar(Col_h) phase have been synthesized. These compounds were characterized by elemental analysis, molar conductances, UV‐visible spectra, infrared spectra, luminescence spectra, and cyclic voltammetry. These compounds exhibit more than one mesophases, which transition points of temperature change from ?33.6 to 16.0 °C, and transition points of temperature for isotropic liquid also increase from 4.9 to 38.2 °C, with increasing chain length. Their surface photovoltage (SPV) response have also been investigated by the means of surface photovoltage spectroscopy (SPS) and field‐induced surface photovoltage spectroscopy (EFISPS). It was found that their SPV bands are analogous with the UV‐visible absorption spectra and derived from the same transition. Copyright © 2007 John Wiley & Sons, Ltd.     

Investigation on electronic transitions in Co-doped ZnO by surface photovoltage spectra

Surface photovoltage spectrum (SPS) technique is one of the powerful experimental methods for studying the attribution of electronic transition. The SPS investigation on Zn_0.97Co_0.03O system has been reported here. The different transitions in the material are distinguished by the electric field-induced surface photovoltage spectra (EFISPS), in which SPS is combined with the electric field-modified technique. The presence of the interaction between defects (excitonic transition) and Co²⁺ (charge-transfer transition) is confirmed by EFISPS. The magnetic properties are measured as a function of magnetic field and temperature. No hysteresis is observed, but Curie–Weiss temperature for Co-doped ZnO is positive.     

Enhanced infrared response of Si base p-n diode with self-assembled Ge quantum dots by thermal annealing

The effects of thermal annealing in Si base p-n diode with self-assembled Ge dots stacked in eight layers structure are investigated. The effects of annealing are discussed based on the photovoltage spectra, the PL spectra and the Raman spectra. Three main effects occur after thermal annealing: the reduction of point defects, the intermixing of Si-Ge and the strain relaxation. The experimental result shows that 800 °C might be a suitable annealing temperature for photovoltaic applications.     

Temperature- and illumination-dependence of the work function of gallium arsenide

Contact potentials of vacuum-cleaved (110) surfaces of GaAs have been measured as functions of temperature (77 < T < 400 K) and illumination intensity by means of a transparent vibrating capacitor. Surface photovoltage as a function of wavelength and intensity of light, as well as relaxation times, have been measured at various temperatures. Samples of greater than 10¹⁸ cm⁻³ doping exhibit photovoltages of 1–2 mV or less and little variation of work function with temperature. At a doping level of 10¹⁷ cm⁻³ p-type samples display photovoltages of more than 50 mV at 77 K and up to 10 mV at room temperature. Moderately doped n-type samples (1.8 × 10¹⁶ and 2.7 × 10¹⁷) exhibit photovoltages up to 0.25 eV at room temperature. At low temperatures, their work function can have two apparently stable values: upon rapid cooling in total darkness, the work function decreases about 80 mV, but during illumination at 77 K, however weak, it decreases by an additional 0.5 V to a new value at which it remains in the dark. This behavior can be accounted for by surface photovoltage according to a simple model not requiring a temperature dependence of surface state spectra. Light is absorbed through interband transitions in the bulk, the surface charge is altered by surface recombination and the return to equilibrium occurs by thermal excitation and tunneling of carriers.     

Study of Be δ-doped GaAs/AlAs multiple quantum wells by the surface photovoltage spectroscopy

We report a surface photovoltage and differential surface photovoltage (DSPV) study of Be δ-doped GaAs/AlAs multiple quantum wells (QWs) with widths ranging from 3 to 20 nm and sheet doping densities from 2 × 10¹⁰ to 2.5 × 10¹² cm⁻² per well aiming to characterize their electronic properties and structural quality. From a line shape analysis of room temperature DSPV spectra the interband excitonic transition energies and broadening parameters for a large number of QW-related subbands have been established. A study of well-width and quantum number dependencies of the excitonic linewidths allowed us to evaluate the various broadening contributions to the spectral line shapes in QWs of different design. It was found that an average half monolayer well-width fluctuations are the dominant broadening mechanism of the excitonic line for QWs thinner than 10 nm. In QWs thicker than 10 nm, the spectral line broadening originates mainly from thermal broadening as well as Stark broadening due to random electric fields of ionized impurities and exciton scattering by free holes.