Influence of phosphine flow rate on Si growth rate in gas source molecular beam epitaxy

As reported by other authors, we have also observed that the Si growth rate decreases with increasing phosphine (PH3) flow rate in gas source-Si molecular beam epitaxy using phosphorous (P) as a n-type dopant. Why small quantity PH3 can affect Si growth rate? Up to now, the quantitative characterization of PH3 flow influence on Si growth rate is little known. In this letter, the PH, influence will be analyzed in detail and a model considering strong P surface segregation and its absorption of hydrogen will be proposed to characterize the effect. (C) 2000 Elsevier Science B.V. All rights reserved.

1.55 mu m Ge islands resonant-cavity-enhanced narrowband detector

The high quality Ge islands material with 1.55 mu m photo-response grown on Sol substrate is reported. Due to the modulation of the cavity formed by the mirrors at the surface and the buried SiO2 interface, seven sharp and strong peaks with narrow linewidth are found. And a 1.55 mu m Ge islands resonant-cavity-enhanced (RCE) detector with narrowband was fabricated by a simple method. The bottom mirror was deposited in the hole formed by anisotropically etching, in a basic solution from the backside of the sample with the buried SiO2 layer in silicon-on-insulator substrate as the etch-stop layer. Reflectivity spectrum indicates that the mirror deposited in the hole has a reflectivity as high as 99% in the range of 1.2-1.65 mu m. The peak responsivity of the RCE detector at 1543.8 nm is 0.028 mA/W and a full width at half maximum of 5 nm is obtained. Compared with the conventional p-i-n photodetector, the responsivity of RCE detector has a nearly threefold enhancement.

两种高分子保水材料对盆栽甘蓝影响研究

采用盆栽试验,研究了两种高分子化合物聚丙烯酸钠(sodium polyacrylate,SP)与聚丙烯酰胺(Polyacrylamide,PAM)对甘蓝生长的影响。结果表明:在土壤中施入2/1000的两种高分子材料均能抑制土壤蒸发,砂土、粘土蒸发强度分别较对照降低35.5%、22.8%;甘蓝叶绿素受两种材料的影响不显著,受肥料影响较大;两种高分子材料施入土壤中增加了甘蓝产量、降低了根冠比,地上、地下生物量砂土较对照分别增加了61.1%、16.1%,粘土分别增加了55.2%、28.7%,根冠比砂土较对照平均降低了26.9%,粘土降低16%;PAM与SP使砂土容重较对照降低了13.9%,而粘土仅降低了4.1%;单施高分子处理水分利用效率平均较对照增加59.1%,与肥料混合使用时增加77.1%。总体来看,PAM与SP作用效果相近。

INFLUENCES OF ALLOY DISORDER AND INTERFACE ROUGHNESS ON OPTICAL-SPECTRA OF INGAAS/GAAS STRAINED-LAYER QUANTUM-WELLS

We present studies of alloy composition and layer thickness dependences of excitonic linewidths in InGaAs/GaAs strained-layer quantum wells grown by MBE, using both photoluminescence and optical absorption. It is observed that linewidths of exciton spectra increase with indium content and well size. Using the virtual crystal approximation, the experimental data are analyzed. The results obtained show that the alloy disorder is the dominant mechanism for line broadening at low temperature. In addition, it is found that the absorption spectra related to light hole transitions have varied from a peak to a step-like structure as temperature increases. This behavior can be understood by the indirect space transitions of light holes.

Analysis of directional emission in square resonator lasers with an output waveguide

Square microcavity laser with an output waveguide is proposed and analyzed by the finite-difference time-domain (FDTD) technique. For a square resonator with refractive index of 3.2, side length of 4 microns, and output waveguide of 0.4-micron width, we have got the quality factors (Q factors) of 6.7×10~2 and 7.3×10~3 for the fundamental and first-order transverse magnetic (TM) mode near the wavelength of 1.5 microns, respectively. The simulated intensity distribution for the first-order TM mode shows that the coupling efficiency in the waveguide reaches 53%. The numerical simulation shows that the first-order transverse modes have fairly high Q factor and high coupling efficiency to the output waveguide. Therefore the square resonator with an output waveguide is a promising candidate to realize single-mode directional emission microcavity lasers.

激光雷达中雪崩光电二极管的智能应用

以激光雷达为应用目标,提出单片机反馈控制方案,智能化地调整雪崩光电二极管(APD)的工作状态,主要是在实时监测噪声和环境温度的条件下,自动设置APD的反向工作电压得到最大信噪比,自动调整滤出噪声的最低门限电压以利于有效信号的探测,从而保证系统安全可靠地工作。