Metal-insulator transition in amorphous Si1−xCrx films

The electrical conductivity of the amorphous Si_1−xCr_x films prepared by vacuum evaporation and sputtering was measured down to 40mK. In both films we observed a continuous metal-insulator transition. The electrical conductivity at low temperatures and the critical behavior are explained in terms of the scaling theory for interacting electrons. Whereas, present results support neither the scaling law proposed by Möbius et al. nor the existance of σ_min reported in the same system.     

The Hall effect in selectively doped strained-layer Ge-Ge1−xSix superlattices superlattices

For the first time, research on the unique galvanomagnetic properties of the hole gas in the channels of selectively doped CVD Ge-Ge_1−XSi_X (X≤0, 2) superlattices with strained Ge layers was carried out. We have obtained a high value of the hole mobility 1.5 × 10⁴ cm²/V s (T = 4, 2 K) at a hole concentrations of (1–5) × 10¹⁷ cm⁻³ in SLs channels. It is shown that the main contribution into the longitudinal conductivity of strained Ge-Ge_1−XSi_X SL due to light hole band splitting under the strains in Ge layers.     

1.55μmSi_(1-x)Ge_x光波导与Si_(1-x)Ge_x/Si多量子阱探测器集成的优化设计

对１．５５μｍ波长的Ｓｉ１－ｘＧｅｘ光波导和Ｓｉ１－ｘＧｅｘ／Ｓｉ多量子阱（ＭＱＷ）红外探测器的集成器件结构进行了系统的分析和优化设计。优化结果为：１）对Ｓｉ１－ｘＧｅｘ光波导，Ｇｅ含量ｘ＝０．０５，脊宽、高和腐蚀深度分别为８、３和２．６μｍ；２）对Ｓｉ１－ｘＧｅｘ／Ｓｉ多量子阱红外探测器，Ｇｅ含量ｘ＝０．５，探测器由厚度为５５０ｎｍ、２３个周期的６ｎｍＳｉ０．５Ｇｅ０．５＋１７ｎｍＳｉ组成，长度约２ｍｍ。结果表明，这种结构器件的内量子效率可达８８％。     

Morphology of GaAs1−xPx superlattices grown by MOCVD and chloride VPE

Distorted layer growth manifested by nonuniform etching may occur in GaAs_1−xP_x superlattices grown by MOCVD and VPE. The distortion was found to be more severe for MOCVD growth than for VPE. The distortion is decreased by decreasing the magnitude of the interlayer strain in the superlattice but does not depend upon the layer thickness. The rate of crystal growth, the temperature of growth and the strain rate in the layer supporting the superlattice also influence the distortion. Several possible causes of the effect are discussed, including nonuniform elastic stress and/or compositional nonuniformity.     

Spin fluctuations of Y(Mn1−xAlx)2 and Y1−xScxMn2

The thermal expansion and low temperature and low temperature specific heat were measured for Y_1−xScxMn2. The results are discussed in terms of spin fluctuations and compared with those of Y(Mn_1−xAl_x)₂, which show al local moment character. It is revealed that Y_1−xSc_xMn₂ is a typical nearly antiferromagnet in which giant spin fluctuations are thermally excited.     

Si1−xGex/Si multi-quantum well phototransistor for near-infrared operation

For the first time in the literature, we report the monolithic integration of SiGe near-infrared phototransistor and planar hetero-junction bipolar transistor (HBT). The phototransistor is made with SiGe/Si multi-quantum well structure (MQW_PHT). At room temperature, the MQW_PHT reveals an optical responsivity of 1904 mW/A at 0.85 μm and 1.25 mW/A at 1.3 μm under the reversed bias of V_CE=1.5 V. For electrical DC and microwave performance, the SiGe HBT has a current gain of 160 and a cut-off frequency (f_T) of 25 GHz, respectively.     

硅锗量子阱结构在硅异质结太阳电池中应用的数值模拟

利用半导体工艺和器件仿真软件silvaco TCAD(Technology Computer Aided Design),模拟研究了采用硅/硅锗合金(silicon/silicon germanium alloy,Si/Si_(1-x)Ge_x)量子阱结构作为吸收层的薄膜晶体硅异质结太阳电池各项性能.模拟结果显示,长波波段光学吸收随锗含量的增加而增加,而开路电压则因Si_(1-x)Ge_x)层带隙的降低而下降.锗含量为0.25时,短路电流密度的增加补偿了开路电压的衰减,效率提升0.2%.氢化非晶硅/晶体硅(a-Si:H/c-Si)界面空穴密度以及Si_(1-x)Ge_x)量子阱的体空穴载流子浓度制约着空穴费米能级的位置,进而影响到开路电压的大小.随着锗含量增加,a-Si:H/c-Si界面缺陷对开压的影响降低,Si_(1-x)Ge_x)量子阱的体缺陷对开压的影响则相应增加.高效率含Si_(1-x)Ge_x)量子阱结构的硅异质结太阳电池的制备需要a-Si:H/c-Si界面缺陷的良好钝化以及高质量Si_(1-x)Ge_x)量子阱的生长.     

A k·p analytical model for valence band of biaxial strained Ge on（001） Si1-xGex

In this paper,the dispersion relationship is derived by using the k·p method with the help of the perturbation theory,and we obtain the analytical expression in connection with the deformation potential.The calculation of the valence band of the biaxial strained Ge/（001）Si1-xGex is then performed.The results show that the first valence band edge moves up as Ge fraction x decreases,while the second valence band edge moves down.The band structures in the strained Ge/（001）Si 0.4 Ge 0.6 exhibit significant changes with x decreasing in the relaxed Ge along the [0,0,k] and the [k,0,0] directions.Furthermore,we employ a pseudo-potential total energy package（CASTEP） approach to calculate the band structure with the Ge fraction ranging from x = 0.6 to 1.Our analytical results of the splitting energy accord with the CASTEP-extracted results.The quantitative results obtained in this work can provide some theoretical references to the understanding of the strained Ge materials and the conduction channel design related to stress and orientation in the strained Ge pMOSFET.     

Metastable impurity bands: Conduction in Si1−xCox and Si1−xNix alloy films

Conductivity data for silicon-nickel and silicon-cobalt films prepared by electron beam evaporation shows a hopping conduction at metal concentrations in the range of 1 to 6 at.%. A semiconductor-to-metal transition was observed at metal concentrations of 15 at.% Co for SiCo and 13 at.% Ni for SiNi films.     

Photoluminescence and X-ray characterisation of Si/Si1−xGex multiple quantum wells

We present an experimental approach to correlate optical and structural properties of Si/Si_1−xGe_x multiple quantum wells as determined by photoluminescence (PL) and X-ray diffraction, respectively. The optical properties of the quantum wells were characterised by studying the dependence of luminescence on temperature and excitation density. An enhanced PL yield and an increased quenching temperature were observed for a sample grown at 650°C as compared to one grown at 600°C. Pronounced interdiffusion across the multiple quantum well interfaces as well as significant lattice distortions within the SiGe layers have been observed.     

Ge组分对应变Si1-xGe x 沟道p-MOSFET电学特性影响

利用二维数值模拟方法,研究了不同Ge组分应变Si_1-xGe _x 沟道p-MOSFET的电容-电压特性以及阈值电压的变化情况.计算结果表明:提高应变Si_1-xGe _x 沟道层中的Ge组分,器件亚阈值电流明显增大;栅电容在器件进入反型状态时产生显著变化;阈值电压的改变量与Ge组分基本成线性关系.通过改变Si_1-xGe _x 沟道的长度,并结 关键词： 1-xGe _x 沟道')" href="#">应变Si_1-xGe _x 沟道 p-MOSFET 空穴迁移率 栅电容     

Hyperfine investigations of the magnetic state in ordered Pt3−xFe1+x

Mössbauer effect studies of Pt_3−xFe_1+x fcc ordered alloys in the range 4.2 K <T<300 K, in zero and in external magnetic field, for samples with x = 0.16 to 0.28, are reported. The low-temperature spectra show several satellite lines which are related to different excess-Fe nearest-neighbor configurations. Experiments in external fields give information on the different local spin structure at different concentrations.     

Mössbauer studies of CoxFe1−xCr2S4

The mixed spinel systems Co_xFe_1−xCr₂S₄ has been studied using the Mössbauer effect. Spectra have been collected over the temperature range 83–300 K. The isomer shifts indicate that the charge states of Fe ions are ferrous in character throughout the series. Absence of quadrupole splitting above the magnetic ordering temperature T_c suggests that iron ions occupy only tetrahedral sites. It is notable that as the temperature decreases below T_c, both quadrupole shift and asymmetrical line-broadening appear and increase with decreasing temperature, suggesting the presence of electric field gradient and accompanying relaxation effects.     

Linear and nonlinear optical properties of CdSexS1−x microcrystallites

Microcrystals of CdSe_xS_1−x (x≈0.6) with nanometer dimensions have been investigated experimentally by a range of optical techniques. This system of ‘quantum dot’ consists of nanometer sized semiconductor particles embedded within an insulating glass matrix. The existence of microscopic CdSeS crystals within the glass matrix is demonstrated by the observation of Raman scattering from the ‘CdSe-like’ and ‘CdS-like’ LO phonons. The nature of the electronic states within these three dimensionally confined systems is investigated by linear absorption and photoluminescence spectroscopy. The photoluminescence spectra show features which are attributed to direct electron-hole recombination and recombination via states within the ‘blue shifted’ energy gap (which are possibly surface related). Carrier relaxation is also investigated by a pump-probe experiment whereby the absorption is partially bleached by a short pump pulse then probed some variable time later by a delayed probe pulse of much lower intensity. Fast and slow components in the carrier relaxation process are identified, and a relationship is suggested between the carrier relaxation and the features observed in the photoluminescence spectra. The well known ‘photodarkening’ properties of such materials are also investigated by the above techniques.     

Thermoelectric power of Y(Mn1−xAlx)2

Electrical resistivity and thermoelectric power of Y(Mn_1−xAl_x2 and (Y_1−xSc_x)Mn₂ were measured from 2 to room temperature. Anomalous behavior of the thermoelectric power of YMn₂ disappears rapidly with the increase of Al content in Y(Mn_1−xAl_x)₂. Based upon spin fluctuations of the itinerant antiferromagnetism of the samples, the anomaly of the thermoelectric power is discussed.     

Spectroscopic study of BixEu1−xVO4 and BiyGd1−yVO4 mixed oxides

The mixed oxides Bi_xEu_1−xVO₄ and Bi_yGd_1−yVO₄ crystallize in a zircon-type structure, for 0 <x < 0.6 and 0 < y < 0.64, and in a fergusonite-type structure, for 0.94 < x < 1 and 0.93 < y < 1. A process of competition between the dominant and the constrained effects of the lone-pair 6s² of Bi³⁺ is discussed. The diffuse reflectance spectroscopic studies of these mixed oxides are presented. The observed broad bands are attributed to charge transfer processes and the sharp peaks in the Bi_xEu_1−xVO₄ spectra are ascribed to intra-configurational 4f – 4ftransitions of the Eu³⁺ ion. The broad absorption shift in BiLnVO₄ (Ln : Eu and Gd) compounds to the longer wavelengths range, when Bi is introduced in the LnVO₄ lattice, is ascribed to charge transfer processes in a Bi-VO₄ center and are interpreted assuming a Jahn-Teller effect in the excited state of Bi³⁺. The concept of an internal pressure of Bi³⁺ ions is also used to explain the broad A-band shifts.     

Low temperature photoluminescence of GaxIn1−xAs/GaAs strained layer superlattices

The low temperature photoluminescence spectra of several Ga_xIn_1−xAs/GaAs strained layer superlattices have been measured. Excitomic recombination between electrons and holes confined in the ternary layers and conduction band-acceptor transitions have been observed. The excitonic transition energies calculated with a simple model which takes into account both strain and quantization are in good agreement with the measured values provided the additional strain due to the mismatch between the SLS and the buffer layer is taken into account. The hydrogenic acceptor binding energy is smaller in the SLS than in the bulk ternary because the reduction due to the decrease of the hole mass under strain appears to be more important than the two dimensional quantization enhancement in the present samples.     

Raman spectroscopy of pseudomorphic Si0.989C0.011/Si superlattices

Raman spectroscopy is used here to study pseudomorphic Si_0.989C_0.011/Si superlattices grown by molecular beam epitaxy. The high crystalline quality of the samples was tested by a high resolution X-ray diffraction experiment. The lineshape of the LO Si-Si peak shows an asymmetry, which correlates with the increase of the alloy layer width. The Raman spectra show three additional peaks in the high energy side above the LO mode of Si. One of them is due to the local vibration of the C substitutional atoms, and the other two can be attributed to the formation of short range order with C atoms occupying second and third nearest-neighbor places. On the low energy side of the LO Si-Si mode, we have observed two other peaks associated with the relaxation of the Si atoms around the substitutional C. Although the X-ray experiments show clear evidence of superperiodicity, no indication of the superlattice formation could be observed in the parallel polarized Raman spectra, where the folded acoustic modes are allowed.