Application of selective implantation in Al0.5Ga0.5As/In0.25Ga0.75As/GaAs pseudomorphic single quantum wire structures

A pseudomorphic Al0.5Ga0.5As/In0.25Ga0.75As/GaAs asymmetric quantum wire (QWR) structure was grown on GaAs V-grooved substrate by low pressure metal organic vapor phase epitaxy. The formation of crescent shaped QWRs at the bottom of the V-grooves was confirmed by both transmission electron microscopy and photoluminescence (PL) spectra. The temperature dependence of PL spectra demonstrated a fast decrease of the sidewall quantum well PL intensity with increasing temperature, which originates from relaxation of carriers from well to wire region. The self-aligned dual implantation technique was successfully used to selectively disable the adjacent quantum structures. Decrease of the PL intensity of QWR at 8 K was observed after selective implantation, which resulted from a decreased number of carriers relaxed from adjacent quantum structures.     

A highly efficient graphene oxide absorber for Q-switched Nd:GdVO4 lasers

We demonstrated that graphene oxide material could be used as a highly efficient saturable absorber for the Q-switched Nd:GdVO4 laser. A novel and low-cost graphene oxide (GO) absorber was fabricated by a vertical evaporation technique and high viscosity of polyvinyl alcohol (PVA) aqueous solution. A piece of GO/PVA absorber, a piece of round quartz, and an output coupler mirror were combined to be a sandwich structure passive component. Using such a structure, 104 ns pulses and 1.22 W average output power were obtained with the maximum pulse energy at 2 μJ and a slope efficiency of 17%.     

Enhanced energy storage and photoluminescence properties in ErBiO3-doped (Na0.5Bi0.5)TiO3-SrTiO3 ceramics

Journal of Materials Science - (1-x)(0.75Na0.5Bi0.5TiO3-0.25SrTiO3)-xErBiO3 (NBST-xEB, x?=?0–0.04) ceramics were fabricated through a solid state reaction method. Scanning...     

CIGS thin films, solar cells, and submodules fabricated using a rf-plasma cracked Se-radical beam source

Coevaporated Cu(In,Ga)Se₂ (CIGS) film growth using a rf-plasma cracked Se-radical beam (R-Se) source leads to a significant reduction in the amount of raw Se source material wasted during growth and exhibits unique film properties such as highly dense, smooth surfaces and large grain size. R-Se grown CIGS solar cells also show concomitant unique properties different from conventional evaporative Se (E-Se) source grown CIGS cells. In the present work, the impact of modified surfaces, interfaces, and bulk crystal properties of R-Se grown CIGS films on the solar cell performance was studied. When a R-Se source was used, Na diffusion into CIGS layers was enhanced while a remarkable diffusion of elemental Ga and Se into Mo back contact layers was observed. Improvements in the bulk crystal quality as manifested by large grain size and increased Na concentration with the use of a R-Se source is expected to be effective to improve photovoltaic performance. Using a R-Se source for the growth of CIGS absorber layers at a relatively low growth temperature, we have successfully demonstrated a monolithically integrated submodule efficiency of 15.0% (17 cells, aperture area of 76.5 cm²) on 0.25-mm thick soda-lime glass substrates.     

Magnetic transition behavior and electromagnetic properties of Zr substituted Bi0.5Y1.5−xCa1+xZrxV0.5Fe4.5−xO12 garnets

Journal of Materials Science: Materials in Electronics - Zr substituted Bi0.5Y1.5?xCa1+xZrxV0.5Fe4.5?xO12 (x?=?0.00, 0.25, 0.50, 0.75, 1.00) samples were prepared via...     

Crystal Structure and Optical Absorption Spectra of Ga0.5Fe0.5InS3 and Ga0.5Fe0.25In1.25S3 Crystals

Ga_0.5Fe_0.5InS₃ and Ga_0.5Fe_0.25In_1.25S₃ crystals are grown by chemical vapor transport and the Bridgman method, respectively. As determined by x-ray diffraction analysis, they have trigonal (sp. gr. P3m1, a= 3.796 × 2 Å, c = 12.210 Å) and rhombohedral (sp. gr. R3m, a= 3.786 × 2 Å, c = 36.606 Å) structures, respectively. From edge absorption data, the band gap is determined to be E _g = 1.885 eV in Ga_0.5Fe_0.5InS₃ and 1.843 eV in Ga_0.5Fe_0.25In_1.25S₃.     

Holographic recording with orthogonally polarized beams in a cesium-doped (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 crystal

Holographic recording with orthogonally polarized beams in a cesium-doped KNSBN [(K(0.5)Na(0.5))(0.2)(Sr(0.75)Ba(0.25))(0.9)Nb(2)O(6)] crystal has been studied. It was found that this kind of photorefractive crystal possesses high linear dichroism, which makes it suitable for use in polarization holography. The diffraction efficiency as a function of the polarization orientation of the reference beam and as a function of the fringe modulation at the optimum polarization orientation of the reference beam is experimentally investigated. Theoretical fitting based on Kahmann models was performed and agrees well with the experimental data. In the experiments, both polarization holography and conventional holography are used to record a binary object. The reconstruction shows that polarization holography with Ce:KNSBN is highly effective, exhibiting high diffraction efficiency and reduced fanning noise.     

Optoelectronic characteristics of Cu(In,Ga)(S,Se)2 thin film solar cells obtained from varied chalcogenization processes

We investigated industrially produced chalcopyrite solar cells based on the absorber modifications Cu(In,Ga)Se₂ and Cu(In,Ga)(S,Se)₂ in order to study the nature of the experimentally verified efficiency improvement, mainly caused by an increased open circuit voltage. We show that the introduction of sulfur during the absorber formation via rapid thermal processing leads to a substantial lowering of the surface doping concentration and widening of the space charge region (SCR). Temperature dependent diode analysis revealed a reduction of the SCR recombination in (Se,S) devices which would lead to a larger splitting of quasi-Fermi levels and hence to an increased open circuit voltage as compared to neat Cu(In,Ga)Se₂ devices.     

新型SOFC阳极材料La0.75Sr0.25Mn0.5Cr0.5-xCuxO3-δ的合成与表征

合成了新型固体氧化物燃料电池(SOFC)阳极材料La_0.75Sr_0.25Mn_0.5Cr_0.5-xCu_xO_3-δ (LSMCr_0.5-xCu_x, x=0、0.05、0.10、0.20)。通过X射线衍射(XRD)表征其物相结构和与电解质的化学相容性, 通过透射电子显微镜(TEM)表征其微观形貌。用直流四探针法测试了材料的电导率; 交流阻抗法表征了材料的阳极阻抗特性。结果表明: LSMCr_0.5-xCu_x材料均为菱方钙钛矿晶相, Cu的掺入导致晶胞体积和粉体粒径增大。x≤0.10时, 阳极粉体与YSZ在1200℃烧结3 h无第三相生成, 具有良好的化学相容性。LSMCr_0.5-xCu_x 在空气和5%H₂-Ar气氛下的电导率均随x的增加而增大; 在湿润的5%H₂-Ar气氛下的阳极极化面电阻(ASR)均低于未掺杂的LSCM, x =0.05时ASR最低, 900℃时仅有0.38 Ω·cm²。     

光纤饱和吸收体稳频窄线宽光纤激光器

结合光纤饱和吸收体与光纤光栅法布里-珀罗标准具,研制出了全光纤结构1550nm单频窄线宽掺铒光纤环形激光器.采用两个976nm激光二极管双向抽运作为抽运源,高掺杂浓度铒光纤作为增益介质,以行波腔消除空间烧孔效应,利用光纤光栅法布里-珀罗标准具窄带选模特性,以10m长低掺铒光纤饱和吸收体稳频,得到了十分稳定的窄线宽激光输出.激光器抽运阈值功率21mW,在抽运光功率为145mW时输出光功率39mW,斜率效率30%,信噪比大于50dB.采用延迟自外差方法精确测量光纤激光器线宽小于10kHz.     

Modification of the three-stage evaporation process for CuIn1−xGaxSe2 absorber deposition

CuIn_1−xGa_xSe₂ absorbers for highest efficiency state-of-the-art solar cells are generally deposited by a sequential three-stage coevaporation process from elemental sources. We investigated the influence of the maximum copper concentration used during processing in the second stage of the growth process. The impact on the Ga grading in the deposited layer was measured by SIMS. The position and slope of the Ga grading profiles were optimized for high efficiency solar cells. Effects on the phases found in the absorber layer were investigated by Raman spectroscopy. The recorded spectra show the formation of a group III rich phase in layers grown at high maximum Cu contents. Best PV parameters were achieved for solar cells developed with absorbers grown with [Cu]/[In + Ga] = 1.05 at the end of the 2nd stage.     

Spatial variations of optoelectronic properties in single crystalline CuGaSe2 thin films studied by photoluminescence

Single crystal CuGaSe₂ (CGSe) thin films were grown epitaxially on GaAs substrates with different compositions and studied with spatially resolved photoluminescence with micrometer resolution (μPL). Polycrystalline counterparts grown on glass were studied for comparison. μPL performed at room temperature is used to analyze spatial variations of the band gap (?Eg) and the splitting of quasi-Fermi levels (?(E_Fn − E_Fp)) of the absorber. In contrast to earlier studies on Cu(In,Ga)Se₂ (CIGSe) we have concentrated on inhomogeneities occurring in the absence of alloying effects due to the In and Ga mixture.The epitaxially grown specimen exhibited a significantly smaller amount of variations than the polycrystalline counterparts. Cu-rich samples showed higher variation of ?(E_Fn − E_Fp) compared to the Cu-poor counterparts. It is suggested that this is related to formation of a secondary phase Cu_xSe under Cu-rich conditions giving rise to spatially fluctuating Cu-excess. The observed band gap variations could be attributed to strain effects in the absorber layer, and do not indicate any variations of the electronic structure of the absorber.     

Observation of e2/h Conductance Steps in a Side-Gate Point Contact on In0.75Ga0.25As/In0.75Al0.25As Heterostructure

In 1996, it was suggested by K. J. Thomas et al. (Phys. Rev. Lett. 77, 135 (1996)) that 0.7(2e²/h) conductance structure in Quasi-1DEG (Q1DEG) at GaAs/AlGaAs heterostructure might be related to spin polarization at zero magnetic field. We have recently studied spontaneous spin-splitting in the 2DEGs formed at normal metamorphic In_0.75Ga_0.25As/In_0.75Al_0.25As heterojunctions grown on GaAs substrates and obtained the value of ?10 meV as the zero-field splitting at Fermi level (Y. Sato et al., J. Appl. Phys. 89, 8017 (2001)). In this work, we attempted to observe spin-related phenomena in this heterojunction Q1DEGs at zero magnetic field. We observed e²/h conductance steps in low electron concentration side-gate point contact.     

Passive Q Switching of a Diode-Pumped 946-nm Nd:YAG Laser with 1.6-W Average Output Power

As much as 1.6-W average output power was emitted in a simple setup from a diffusion-bonded Nd:YAG rod with 70-100-ns Q-switched pulses at 946 nm and repetition frequencies between 15 and 45 kHz at 22-W incident diode-pump power. A Cr(4+):YAG crystal with a bleachable loss of approximately 2.5% and a length of 0.5 mm was used as a saturable absorber. The extraction efficiency was 47% in comparison with the continuous-wave laser output power of 3.37 W in the free-running regime.     

Positive delayed photoconductivity in double heterostructures Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As of the p-type

Positive delayed photoconductivity was observed for the first time in double p-type heterostructures Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5 As upon exposure to the radiation of a red light-emitting diode. In this state, the concentration and mobility of two-dimensional holes are increased 1.5 and 1.7 times, respectively, as compared to the initial dark values. The delayed photoconductivity can be explained by the presence of deep electron traps located above the Fermi level at the inverted heterointerface.     

Direct observation of a noncatalytic growth regime for GaAs nanowires

We identify a new noncatalytic growth regime for molecular beam epitaxially grown GaAs nanowires (NWs) that may provide a route toward axial heterostructures with discrete material boundaries and atomically sharp doping profiles. Upon increase of the As/Ga flux ratio, the growth mode of self-induced GaAs NWs on SiO(2)-masked Si(111) is found to exhibit a surprising discontinuous transition in morphology and aspect ratio. For effective As/Ga ratios <1, in situ reflection high-energy electron diffraction measurements reveal clear NW growth delay due to formation of liquid Ga droplets since the growth proceeds via the vapor-liquid-solid mechanism. In contrast, for effective As/Ga ratios >1 an immediate onset of NW growth is observed indicating a transition to droplet-free, facet-driven selective area growth with low vertical growth rates. Distinctly different microstructures, facet formation and either the presence or absence of Ga droplets at the apex of NWs, are further elucidated by transmission electron microscopy. The results show that the growth mode transition is caused by an abrupt change from As- to Ga-limited conditions at the (111)-oriented NW growth front, allowing precise tuning of the dominant growth mode.     

Diode-end-pumped passively Q-switched 1.34 μm Nd:Gd0.5Y0.5VO4 laser with Co:LMA saturable absorber

In this paper, the output performances at 1.34 μm in continuous wave operation and passive Q-switching regime of a diode-end-pumped Nd:Gd_0.5Y_0.5VO₄ laser have been investigated. The passive Q-switching regime was achieved with Co²⁺:LaMgAl₁₁O₁₉ (Co²⁺:LMA) saturable absorbers crystals. A maximum average output power of 230 mW was recorded with a Co²⁺:LMA with initial transmission of 81%. The minimum pulse duration was 116 ns, which corresponded to a repetition rate of 360 kHz, the single pulse energy of 2.1 μJ and the pulse peak power of 5.5 W.     

Tip-enhanced Rayleigh scattering and photoluminescence from semiconductor nanoparticles

Tip-enhanced Rayleigh scattering images of Ge quantum dots grown on a Si substrate have been observed at room temperature. Changing the wavelength of the incidence light from 405 to 590 nm, the contrast of the images is reversed. It is found that the scattering intensity depends on the dielectric constants of the materials under the probe. By changing the wavelength of the incident light, we have obtained information about the dielectric constant dispersion of single Ge quantum dots. The spectral peak position of single Ge quantum dots is found to shift to higher energy, compared to that of bulk Ge. Tip-enhanced photoluminescence from an In0.25Ga0.75N film at room temperature has also been reported. The strong local enhancement of the photoluminescence of the localized excitons has been observed in the vicinity of a gold nano-particle attached to the end of the probe. A coupling to plasmons in the gold nano-particle yields strong enhancement of the photoluminescence.     

Observation of e2/h Conductance Steps in a Side-Gate Point Contact on In0.75Ga0.25As/In0.75Al0.25As Heterostructure

In 1996, it was suggested by K. J. Thomas et al. (Phys. Rev. Lett. 77, 135 (1996)) that 0.7(2e²/h) conductance structure in Quasi-1DEG (Q1DEG) at GaAs/AlGaAs heterostructure might be related to spin polarization at zero magnetic field. We have recently studied spontaneous spin-splitting in the 2DEGs formed at normal metamorphic In_0.75Ga_0.25As/In_0.75Al_0.25As heterojunctions grown on GaAs substrates and obtained the value of 10 meV as the zero-field splitting at Fermi level (Y. Sato et al., J. Appl. Phys. 89, 8017 (2001)). In this work, we attempted to observe spin-related phenomena in this heterojunction Q1DEGs at zero magnetic field. We observed e²/h conductance steps in low electron concentration side-gate point contact.     

Influence of the internal photoinduced electric field on the formation of self-pumped phase conjugation in doped (K(0.5)Na(0.5))(0.2)(Sr(0.75)Ba(0.25))(0.9)Nb(2)O(6) crystals

The obvious influence of the internal photoinduced electric field on the formation of self-pumped phase conjugation in doped (K(0.5) Na(0.5))(0.2) (Sr(0.75) Ba(0.25))(0.9) Nb(2)O(6) crystals has been investigated with intermittent and continuous laser beams. An analysis is given that involves the migration of charge carriers driven by the photovoltaic (PV) and the pyroelectric (PY) electric field. Deviation from the optimal state of energy transfer owing to the PV effect and the self-adjusting of holograms owing to the PY field are the two important dominant processes in the self-pumped phase conjugator. The influence of the photoinduced electric field on the conjugation fidelity and the stability of the phase-conjugate output is also observed and analyzed. The bump feature of the two-wave mixing and the oscillating situation of the self-pumped phase conjugator are observed and are explained in view of the photoinduced internal field.