Hydride Vapor Phase Epitaxy Growth of Semipolar, 10(1)over-bar(3)over-barGaN on Patterned m-Plane Sapphire

We have investigated the hydride vapor-phase epitaxy growth of (10 (1) over bar(3) over bar)-oriented GaN thick films on patterned sapphire substrates (PSSs) (10 (1) over bar0). From characterization by atomic force microscopy, scanning electron microscopy, double-crystal X-ray diffraction, and photoluminescence (PL), it is determined that the crystalline and optical qualities of (10 (1) over bar(3) over bar) GaN epilayers grown on the cylindrical PSS are better than those on the flat sapphire. However, two main crystalline orientations (10 (1) over bar(3) over bar) and (11 (2) over bar2) dominate the GaN epilayers grown on the pyramidal PSS, demonstrating poor quality. After etching in the mixed acids, these (10 (1) over bar(3) over bar) GaN films are dotted with oblique pyramids, concurrently lining along the < 30 (3) over bar2 > direction, indicative of a typical N-polarity characteristic. Defect-related optical transitions of the (10 (1) over bar(3) over bar) GaN epilayers are identified and detailedly discussed in virtue of the temperature-dependent PL. In particular, an anomalous blueshift-redshift transition appears with an increase in temperature for the broad blue luminescence due to the thermal activation of the shallow level.

Two-color quantum well infrared photodetector simultaneously working at 10-14 mu m

We have demonstrated a two-color quantum well infrared photodetector (QWIP) exhibiting simultaneous photoresponse with cutoff wavelengths at 11.8 and 14.5 mu m, respectively. Strong photocurrent signals are observed at temperature of 77 K. The simultaneous two-color photoresponse is achieved by utilizing a simple design by broadening the width of the quantum well and selecting an appropriate doping density. The two peaks are attributed to the intersubband transitions from the ground state to the first excited state (bound state) and to the fifth excited state (continuum state), respectively.

A 10 Gb/s Directly-Modulated 1.3 mu m InAs/GaAs Quantum-Dot Laser

We demonstrate 10 Gb/s directly-modulated 1.3 mu m InAs quantum-dot (QD) lasers grown on GaAs substrates by molecular beam epitaxy. The active region of the QD lasers consists of five-stacked InAs QD layers. Ridge-waveguide lasers with a ridge width of 4 mu m and a cavity length of 600 mu m are fabricated with standard lithography and wet etching techniques. It is found that the lasers emit at 1293 nm with a very low threshold current of 5 mA at room temperature. Furthermore, clear eye-opening patterns under 10 Gb/s modulation rate at temperatures of up to 50 degrees C are achieved by the QD lasers. The results presented here have important implications for realizing low-cost, low-power-consumption, and high-speed light sources for next-generation communication systems.

Highly efficient and stable organic light-emitting diodes employing MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride as hole injection layer

We report highly efficient and stable organic light-emitting diodes (OLEDs) with MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride (PTCDA) as hole injection layer (HIL). A green OLED with structure of ITO/20 wt% MoO3: PTCDA/NPB/Alq(3)/LiF/Al shows a long lifetime of 1012 h at the initial luminance of 2000 cd/m(2), which is 1.3 times more stable than that of the device with MoO3 as HIL. The current efficiency of 4.7 cd/A and power efficiency of 3.7 lm/W at about 100 cd/m(2) have been obtained. The charge transfer complex between PTCDA and MoO3 plays a decisive role in improving the performance of OLEDs.

Research on the ultrafast fluorescence property of thylakoid membranes of the wild-type and mutant rice

A high yielding rice variety mutant (Oryza sativa L., Zhenhui 249) with low chlorophyll b (Chl b) has been discovered in natural fields. It has a quality character controlled by a pair of recessive genes (nuclear gene). The partial loss of Chl b in content affects the efficiency of light harvest in a light harvest complex (LHC), thus producing the difference of the exciting energy transfer and the efficiency of photochemistry conversion between the mutant and wild-type rice in photosynthetic unit. The efficiency of utilizing light energy is higher in the mutant than that in the wildtype rice relatively. For further discussion of the above-mentioned difference and learning about the mechanism of the increase in the photochemical efficiency of the mutant, the pico-second resolution fluorescence spectrum measurement with delay-frame-scanning single photon counting technique is adopted. Thylakoid membranes of the mutant and the wild-type rice are excited by an Ar+ laser with a pulse width of 120 ps, repetition rate of 4 MHz and wavelength of 514 nm. Compared with the time and spectrum property of exciting fluorescence, conclusions of those ultrafast dynamic experiments are: 1) The speeds of the exciting energy transferred in photo-system I are faster than that in photo-system II in both samples. 2) The speeds of the exciting energy transfer of mutant sample are faster than those of the wildtype. This might be one of the major reasons why the efficiency of photosynthesis is higher in mutant than that in the wild-type rice.

结构因子相角的代数解法及K_8H_5[La(SiWMo_(10)O_(39))(SiW_3Mo_8O_(39))]·nH_2O的晶体结构

一 结构因子相角的代数解法晶体结构研究中的相角问题，一直是晶体学工作者努力探求的基本问题。几十年来，关于相角问题的研究已经取得了巨大的进展，直接法的成熟和普遍应用就是这个进展的显著标志。在直接法相角问题研究中，历来存在两种基本方法，即概率法和代数法。当前直接法的迅猛发展，则主要以概率法为基础，其应用的基本公式即是来自∑关系中的∑_2关系和由此发展出的TANGENT公式，并结合一系列的基本理论和辅助公式，从而使直接法的发展一直呈方兴未艾之势。与此形成鲜明对照的是，相角问题的代数法研究则有日趋下降之势，尤其近十年来则显著落后了。作者从近年来的∑关系研究中，看到要解决相角问题，代数法仍然有其潜在的应作价值，并认为在概率法可以得到应用的许多方面，在代数法那里都应找到对应的类似内容，而代数法在研究和应用中所表现出的不同于概率法的那些方面也正是在相角问题研究中最令人感兴趣的问题，这就是我们进行代数法研究的目的和出发点。（一）1.5和2.5阶代数式的提出及对±2~(II)型相角的估算。（二）一般类型相角的估算（三）结构相角通用代数式的推导。代数法不仅可用于结构半不变量O，π型相角的计算，而且可用于非结构半不变量的种种类型相角的估算，其中包括型和一般类型相角，而且其应用效果完全可以和概率法相比拟，在机时利用上前者有一定优势。通用代数式的获得将为代数法的普遍应用和计算机计算创造了方便条件。二稀土杂多酸根配合物K_8H_5[La(SiWMo_(10)O_(39))(SiW_3Mo_8O_(39))]·nH_2O的晶体结构采用低温技术，在-90 ℃的干燥氮气保护下，收集晶体衍射数据，以直接法解出结构。a = 17.485(5), b = 27.096(6), c = 21.642(5)A, β = 107.79(2)°, z = 4。最后的R值为0.097。中心离子La(III)同两个杂多酸根提供的8 个氧配合。而其中的W、Mo同氧的配位情况基本相同，者是与氧六配位，形成变形配位八面体。

Electronic structure of microporous titanosilicate ETS-10

The electronic structure of a microporous titanosilicate framework, ETS-10 is calculated by means of a first-principles self-consistent method. It is shown that without the inclusion of the alkali atoms whose positions in the framework are unknown, ETS-10 is an electron deficient system with 32 electrons per unit cell missing at the top of an otherwise semiconductor-like band structure. The calculated density of slates are resolved into partial components. It is shown that the states of the missing electrons primarily originate from the Ti-O bond. The local density of states of the Ti-3d orbitals in the ETS-10 framework is quite different from the perovskite BaTiO3. The possibilities of ETS-10 crystal being ferroelectric or having other interesting properties are discussed.

Low-temperature (10 K) infrared measurement of interstitial oxygen in heavily antimony-doped silicon via wafer thinning

A new technique is reported for the rapid determination of interstitial oxygen in heavily Sb-doped silicon. This technique includes wafer thinning and low-temperature 10 K infrared measurement on highly thinned wafers. The fine structure of the interstitial oxygen absorption band around 1136 cm(-1) is obtained. Our results show that this method efficiently reduces free-carrier absorption interference, allowing a high reliability of measurement, and can be used at resistivities down to 1 x 10(-2) Omega cm for heavily Sb-doped silicon.