Temperature behavior of Franz-Keldysh oscillation and evaluation of interface electric fields attributed to strain effect of InAs/GaAs quantum dot

In this work, the electric field-induced Franz-Keldysh effect was used to investigate the localized electric fields in GaAs interfaces attributed to strain effect of InAs/GaAs quantum dots (QD). The electric fields were investigated by photoreflectance spectroscopy (PR). PR spectra of the InAs/GaAs QDs showed complex Franz-Keldysh oscillations (FKOs) with various temperatures. It is suggested that the FKOs originated from the interface electric fields predominately caused by the strain-induced polarization at GaAs interface near the InAs QDs. The InAs/GaAs QDs have a broad range of interface electric fields from ～10⁴ V/cm to ～2х10⁵ V/cm. Temperature behavior of FKO amplitude distribution is explained by temperature dependent carrier confinement effect.     

On the properties of photovoltaic X-ray detectors based on GaAs epitaxial structures

Operation of a new photovoltaic detector of X-ray bremsstrahlung based on GaAs epitaxial structures at room temperature without bias is studied. The efficiency of the absorbed energy conversion into short-circuit current is calculated from the measured photoresponses for the photon energies in the range from 12 to 120 keV. In this energy range, the absorption in GaAs is governed by photoelectric effect. The efficiency of the X-ray bremsstrahlung energy conversion in GaAs peaks at 80 keV. It is suggested that the X-ray absorption of a thin 50-μm detector can be enhanced by applying an inclined irradiation scheme. The effect is most pronounced in the region of hard X-rays.     

Raman piezospectroscopic study of indium-hardened GaAs

We have investigated the effect of a uniaxial stress on the transverse optical and longitudinal optical phonon frequencies of In-hardened GaAs using a cw Nd:YAG laser. We find that for a stress along [1 1 1] the single-doublet phonon frequency splittings are smaller in comparison with those in pure GaAs. A possible explanation of this effect may lie in a hardening of the internal stress parameter ζ due, at least in part, to the increase in lattice constant. Plastic deformation and fracture at the highest stresses reached is also discussed and compared with observations for pure GaAs.     

Impurity effect on the creation of point-defects in GaAs and InP investigated by a slow positron beam

The impurity effect on the creation of point-defects in 60-keV Be⁺-ion implanted GaAs and InP has been studied by a slow positron beam. Vacancy-type defects introduced by ion implantation were observed in n-type GaAs. For p-type GaAs, however, this was not the case. This can be attributed to the recombination of vacancy-type defects with pre-existing interstitial defects in p-type GaAs. In the case of InP, the vacancy-type defects were created by ion implantation and increased with the implantation dose. However, no significant doping effect was observed in InP.     

Control of unpolarized emission in closely stacked InAs quantum dot structure

In this work, we studied the effect of some growth parameters on the polarization behavior of InAs/GaAs closely stacked quantum dot (CSQDs). In particular, we focused on the surface reconstruction time of GaAs spacer, its thickness and the number of QD layers. We found that the most effective parameter to enhance the TM/TE intensity ratio is the surface reconstruction time of the GaAs spacer before the subsequent QD deposition. By varying this parameter between 20 s and 120 s, a TM/TE ratio as high as 0.86 has been achieved. A further fine tuning of GaAs spacer thickness and QD layer number increased this ratio up to a value of 0.92 in structures containing only 3 QD layers.     

Investigation of an InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) with reduced potential spike

In this work, an improved InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) with an InGaP wide-bandgap collector is investigated. In the emitter–base region, the thin narrow bandgap n-type GaAs layer is sandwiched between a wide-bandgap N-type InGaP confinement layer and a narrow-bandgap p-type GaAs base layer. In the collector–base structure, an undoped 30 Å-thick GaAs spacer and a heavily doped 30 Å-thick GaAs are inserted between the base and collector. Due to the absence of a potential spike both at the base–emitter and base–collector junctions, the studied device shows lower offset and saturation voltages. In addition, not only are the excellent current–voltage characteristics observed, but also the undesired effects, e.g. the electron blocking effect, are completely eliminated.     

Numerical Comparisons of Terahertz Radiation from GaAs and GaAs: As+ Substrates

In this paper, we have numerically analyzed the ultrafast change of local fields on the surfaces of a large-aperture photoconducting (LA-PC) antenna with GaAs and GaAs: As+ substrates. We find that the ultrafast screening of photogenerated carriers to the externally applied electric field has different effects on the saturation of THz radiation as the function of the laser fluence in the near and far field, respectively. Both screening effect of photocarriers and radiation effect are important in forming the saturation phenomena in the case of near field. But in far field, only the radiation effect is important.     

Near-field photoluminescence of Si-doped GaAs

We have measured surface photoluminescence properties of Si-doped bulk GaAs using a near-field scanning optical microscope. An apertured fiber probe tip is used as an emitter of excitation laser as well as a collector of luminescence from GaAs. Due to the Fabry-Perot etalon effect, the excitation laser is reflected or transmitted with an oscillation period of λ._He-Ne/2 as the gap between the tip and the GaAs surface varies. The luminescence from GaAs also varies with an oscillation period of λ_GaAs/2 due to the same etalon effect. Therefore, the intensity of luminescence light collected by the probe tip shows a beating between two oscillations of different periods. When the probe approaches the GaAs surface, the collected luminescence intensity increases due to tunneling of evanescent wave. On the other hand, when we collect the luminescence using a lens, the intensity also increases due to similar coupling of evanescent wave into propagating wave in spite of a shadowing effect of the wide metal coating.     

1.3-μm InAs/GaAs quantum dots grown on Si substrates

We compare the effect of InGaAs/GaAs strained-layer superlattice(SLS) with that of GaAs thick buffer layer(TBL)serving as a dislocation filter layer. The InGaAs/GaAs SLS is found to be more effective than GaAs TBL in blocking the propagation of threading dislocations, which are generated at the interface between the GaAs buffer layer and the Si substrate. Through testing and analysis, we conclude that the weaker photoluminescence for quantum dots(QDs) on Si substrate is caused by the quality of capping In_(0.15)Ga_(0.85)As and upper GaAs. We also find that the periodic misfits at the interface are related to the initial stress release of GaAs islands, which guarantees that the upper layers are stress-free.     

中子辐照高掺硅砷化镓的光致发光研究

研究了高掺硅的n型GaAs在中子辐照前后和150℃-500℃等时热退火以后的光致发光光谱。观察到在中子辐照后积分发光强度降低为辐照前的1/36。在退火温度超过250℃时,积分发光强度显著增长,当退火温度达400℃以上时,在带边峰的低能侧出现能量为1.35eV、1.30eV和1.26eV的发光峰。假设250℃退火阶段对应于较大的空位团分解为较小的空位团,400℃退火阶段对应于较小的空位团分解出VGa,可以较好地解释实验现象。     

加偏置电场的抛物量子阱中的电光效应

本文利用密度矩阵方法得到了加偏置电场的抛物量子阱中电光效应的解析表达式,并以典型的GaAs抛物量子阱为例进行了数值计算研究结果表明,电光效应随偏置电场和抛物势频率的增大而增强,同时也表明GaAs量子阱中的电光效应比体GaAs中的要强一个数量级以上。     

Broadband light emitting from multilayer-stacked InAs/GaAs quantum dots

We report the effect of the GaAs spacer layer thickness on the photoluminescence(PL) spectral bandwidth of InAs/GaAs self-assembled quantum dots(QDs).A PL spectral bandwidth of 158 nm is achieved with a five-layer stack of InAs QDs which has a 11-nm thick GaAs spacer layer.We investigate the optical and the structural properties of the multilayer-stacked InAs/GaAs QDs with different GaAs spacer layer thicknesses.The results show that the spacer thickness is a key parameter affecting the multi-stacked InAs/GaAs QDs for wide-spectrum emission.     

Influence of the cap layer thickness on photoluminescence properties in strained InGaAs/GaAs single quantum wells

The influence of the GaAs cap layer thickness on the luminescence properties in strained In_0.20Ga_0.80As/GaAs single quantum well (SQW) structures has been investigated using temperature-dependent photoluminescence (PL) spectroscopy. The luminescence peak is shifted to lower energy as the GaAs cap layer thickness decreases, which demonstrates the effect of the GaAs cap layer thickness on the strain of InGaAs/GaAs single quantum wells (SQW). We find the PL quenching mechanism is the thermal activation of electron hole pairs from the wells into the GaAs cap layer for the samples with thicker GaAs cap layer, while in sample with thinner GaAs cap layer exciton trapping on misfit dislocations is dominated.     

Decrease in the bond energy of arsenic atoms on the GaAs(100)-(2×4)/c(2×8) surface due to the effect of adsorbed cesium

It has been found experimentally that the bond energy of arsenic atoms on the GaAs(100) surface decreases under the influence of adsorbed cesium. This is manifested in the disordering of the As-stabilized surface and in a decrease of ～(100 K in the temperature of the transition to the Ga-stabilized (100)GaAs(4×2)/c(8×2) surface. This effect is caused by the redistribution of the valence electron density between the arsenic atoms in the upper layer and the gallium atoms in the lower-lying layer as a result of charge transfer from the electropositive adsorbate to the semiconductor. In combination with the analogous effect of a decrease in the bonding energy of gallium atoms on the Ga-stabilized GaAs surface upon the adsorption of electronegative adsorbates (halogens), the effect observed allows the atomic layer etching of the polar GaAs(100) face.     

Effects of hydrogen on the electronic properties of dilute GaAsN alloys

Nitrogen has profound effects on the electronic structure of GaAs, as only a few percent of N can drastically lower the band gap. It is, however, not recognized that the same amount of N can also qualitatively alter the electronic behavior of hydrogen: First-principles calculations reveal that, in GaAsN, a H atom bonds to N and can act as a donor in its own right, whereas in GaAs and GaN, H is amphoteric, causing passivation instead. At high Fermi energy and H concentration, a N complex with two H was found to have lower energy than the single-H configuration. By removing the effect of N, this electrically inactive complex restores the gap of GaAs.     

氢对GaAs薄膜的钝化作用

报导了射频磁控溅射与沉积气氛掺氢相结合制备单层(13~20 nm厚)高质量GaAs多晶态纳米薄膜的方法,研究了氢钝化对薄膜微观结构及光学性质的影响.对GaAs薄膜进行了X射线衍射、原子力显微镜、吸收光谱、光致荧光谱的研究分析.结果表明,衬底温度500℃的掺氢薄膜和520℃的薄膜呈面心立方闪锌矿结构,薄膜的晶团尺寸较大,微观表面较为粗糙,其吸收光谱出现了吸收边蓝移和明显的激子峰,带隙光致荧光峰强明显增加,说明氢在衬底温度500℃~520℃下对薄膜有重要的钝化作用.     

GaAs衬底上生长的GaInP_2外延单晶薄膜的杂质污染研究

各种外延技术已被用来在ＧａＡｓ衬底上生长ＧａｘＩｎ１－ｘＰ外延单晶薄膜（ＧａＩｎＰ２／ＧａＡｓ）．很多文献认为,在ＧａＩｎＰ２／ＧａＡｓ生长过程中会被Ｃ杂质污染．我们用高灵敏的ＣＡＭＥＣＡＩＭＳ４Ｆ型二次离子质谱仪直接测量的结果表明,污染ＧａＩｎＰ２／ＧａＡｓ的微量杂质是Ｓｉ,而不是Ｃ．由ＧａＩｎＰ２／ＧａＡｓ在１．１７ｅＶ附近的光致发光峰的峰值随激发强度的变化形状表明了它应属于施主－受主对复合发光．进一步分析表明,施主为处在Ｇａ格位上的Ｓｉ杂质（ＳｉＧａ）,受主为Ｇａ空位（ＶＧａ）．     

Effect of high‐energy light‐ion irradiation on SI‐GaAs and GaAs:Cr as observed by Raman spectroscopy

The structural evolutions of high‐energy (50 MeV) lithium ion (Li³⁺) irradiated undoped semi‐insulating GaAs (SI‐GaAs) and chromium‐doped SI‐GaAs (GaAs:Cr) were investigated by Raman measurements. It is shown that high‐energy Li³⁺ irradiation causes amorphization beyond a fluence of 3 × 10¹³ ions/cm² in undoped SI‐GaAs. Interestingly, the same fluence of ions does not seem to affect the crystallinity in GaAs:Cr appreciably. The effect of ion irradiation on the change in lattice ordering and anharmonicity of the phonon modes of undoped SI‐GaAs and GaAs:Cr is also compared. Copyright © 2011 John Wiley & Sons, Ltd.     

Superior Mechanical Properties of GaAs Driven by Lattice Nanotwinning

Gallium arsenide(GaAs),a typical covalent semiconductor,is widely used in the electronic industry,owing to its superior electron transport properties.However,its brittle nature is a drawback that has so far significantly limited its application.An exploration of the structural deformation modes of GaAs under large strain at the atomic level,and the formulation of strategies to enhance its mechanical properties is highly desirable.The stressstrain relations and deformation modes of single-crystal and nanotwinned GaAs under various loading conditions are systematically investigated,using first-principles calculations.Our results show that the ideal strengths of nanotwinned GaAs are 14% and 15% higher than that of single-crystal GaAs under pure and indentation shear strains,respectively,without producing a significantly negative effect in terms of its electronic performance.The enhancement in strength stems from the rearrangement of directional covalent bonds at the twin boundary.Our results offer a fundamental understanding of the mechanical properties of single crystal GaAs,and provide insights into the strengthening mechanism of nanotwinned GaAs,which could prove highly beneficial in terms of developing reliable electronic devices.     

Plasmon-induced transparency effect in hybrid terahertz metamaterials with active control and multi-dark modes

We numerically demonstrate a photo-excited plasmon-induced transparency (PIT) effect in hybrid terahertz (THz) metamaterials. The proposed metamaterials are regular arrays of hybrid unit cells composed of a metallic cut wire and four metallic split-ring resonators (SRRs) whose gaps are filled with photosensitive semiconductor gallium arsenide (GaAs) patches. We simulate the PIT effect controlled by external infrared light intensity to change the conductivity of GaAs. In the absence of photo excitation, the conductivity of GaAs is 0, thus the SRR gaps are disconnected, and the PIT effect is not observed since the dark resonator (supported by the hybrid SRRs) cannot be stimulated. When the conductivity of GaAs is increased via photo excitation, the conductivity of GaAs can increase rapidly from 0 S/m to 1×10⁶ S/m and GaAs can connect the metal aluminum SRR gaps, and the dark resonator is excited through coupling with the bright resonator (supported by the cut wire), which leads to the PIT effect. Therefore, the PIT effect can be dynamically tuned between the on and off states by controlling the intensity of the external infrared light. We also discuss couplings between one bright mode (CW) and several dark modes (SRRs) with different sizes. The interference analytically described by the coupled Lorentz oscillator model elucidates the coupling mechanism between one bright mode and two dark modes. The phenomenon can be considered the result of linear superposition of the coupling between the bright mode and each dark mode. The proposed metamaterials are promising for application in the fields of THz communications, optical storage, optical display, and imaging.