首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   444篇
  国内免费   20篇
  完全免费   53篇
  无线电   517篇
  2017年   2篇
  2016年   3篇
  2015年   4篇
  2014年   5篇
  2013年   4篇
  2012年   3篇
  2011年   19篇
  2010年   6篇
  2009年   18篇
  2008年   28篇
  2007年   27篇
  2006年   33篇
  2005年   30篇
  2004年   21篇
  2003年   26篇
  2002年   14篇
  2001年   17篇
  2000年   23篇
  1999年   25篇
  1998年   33篇
  1997年   40篇
  1996年   35篇
  1995年   28篇
  1994年   17篇
  1993年   20篇
  1992年   10篇
  1991年   3篇
  1990年   8篇
  1989年   4篇
  1988年   5篇
  1987年   2篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
排序方式: 共有517条查询结果,搜索用时 31 毫秒
1.
980 nm高功率垂直腔面发射激光器   总被引:14,自引:6,他引:8  
研究了 980nm垂直腔面发射激光器 (VCSEL)的结构设计和器件制作 ,实现了室温下的脉冲激射。在脉宽为 5 0 μs,占空比为 5∶10 0 0的脉冲电流下 ,直径 4 0 0 μm的器件输出光功率最高可达 380mW ,发散角小于 10° ,光谱的半高全宽为 0 8nm。  相似文献
2.
MBE growth and properties of ZnO on sapphire and SiC substrates   总被引:9,自引:0,他引:9  
Molecular beam epitaxy (MBE) of ZnO on both sapphire and SiC substrates has been demonstrated. ZnO was used as a buffer layer for the epitaxial growth of GaN. ZnO is a würtzite crystal with a close lattice match (<2% mismatch) to GaN, an energy gap of 3.3 eV at room temperature, a low predicted conduction band offset to both GaN and SiC, and high electron conductivity. ZnO is relatively soft compared to the nitride semiconductors and is expected to act as a compliant buffer layer. Inductively coupled radio frequency plasma sources were used to generate active beams of nitrogen and oxygen for MBE growth. Characterization of the oxygen plasma by optical emission spectroscopy clearly indicated significant dissociation of O2 into atomic oxygen. Reflected high energy electron diffraction (RHEED) of the ZnO growth surface showed a two-dimensional growth. ZnO layers had n-type carrier concentration of 9 × 1018 cm−3 with an electron mobility of 260 cm2/V-s. Initial I-V measurements displayed ohmic behavior across the SiC/ZnO and the ZnO/GaN heterointerfaces. RHEED of GaN growth by MBE on the ZnO buffer layers also exhibited a two-dimensional growth. We have demonstrated the viability of using ZnO as a buffer layer for the MBE growth of GaN.  相似文献
3.
ZnO材料的生长及表征   总被引:7,自引:4,他引:3  
氧化锌材料是新一代宽禁带光电子半导体材料和场致发射材料,通过等离子体分子束外延设备,在a-plane的蓝宝石衬底上生长了高质量的氧化锌外延材料。在生长过程中用反射高能电子束衍射仪(RHEED),研究了生长时材料薄膜的表面形貌。为了使材料更好地应用于器件,研究了材料的掺杂性质。研究了给体束缚激子(Donor bound exeiton (DX))、自由激子(Free exciton(EX))和受体束缚激子(Aeeeptor bound exciton (AX))随温度变化的发光过程。用紫外-可见透射光谱研究了ZnO薄膜材料的透射光谱性质。结果表明,用分子束外延生长设备成功地生长了高质量的氧化锌薄膜材料。  相似文献
4.
脉冲激光纳米薄膜制备技术   总被引:7,自引:1,他引:6  
脉冲激光薄膜沉积(PLD)是近年来受到普遍关注的制膜新技术。简要介绍了该技术的物理原理;探讨了脉冲激光沉积制膜的物理过程,激光作用的极端条件及等离子体羽辉形成的控制对薄膜成长的影响;评价了脉冲激光沉积技术在多种功能材料薄膜,特别是纳米薄膜及多层结构薄膜的制备方面的特点和优势,结合自行研制的设备,介绍了在PLD基础上发展起来的兼具分子束外延(MBE)技术特点的激光分子束外延技术(L-MBE),指出脉冲激光沉积技术在探讨激光与物理相互作用和薄膜成膜机理方面的作用,尤其是激光分子束外延技术在高质量的纳米薄膜和超晶格等人工设计薄膜的制备上显现出的巨大潜力。  相似文献
5.
Improving material characteristics and reproducibility of MBE HgCdTe   总被引:5,自引:0,他引:5  
This paper describes our progress to improve the material quality, reproducibility, and flexibility of molecular beam epitaxial (MBE) growth of HgCdTe. Data, statistics, and yields according to defined screen criteria are presented for n-type layer carrier concentration and mobility, void defect density, and dislocation density for more than 100 layers. Minority carrier lifetime data are also presented. Continued improvements in impurity reductiont have allowed us to achieve, for the first time, reproducible, low n-type carrier concentration in the mid-1014 cnr−3 range with high electron mobility. Data are presented that show that low dislocation density films are obtained for growth on CdZnTe substrates with a wide range of Zn concentration. Results are presented from a nine-growth run first pass success demonstration run to further assess material quality reproducibility and flexibility of wavelength band tuning. These results demonstrate the promising potential of MBE growth for flexible manufacturing of HgCdTe for infrared focal plane arrays.  相似文献
6.
Mode of arsenic incorporation in HgCdTe grown by MBE   总被引:5,自引:0,他引:5  
The results of arsenic incorporation in HgCdTe layers grown by molecular beam epitaxy (MBE) are reported. Obtained results indicate that arsenic was successfully incorporated as acceptors in MBE-HgCdTe layers after a low temperature anneal. Secondary ion mass spectrometry and Hall effect measurements confirm that arsenic is incorporated with an activation yield of up to 100%. This work confirms that arsenic can be used as an effective dopant of MBE-HgCdTe after a low temperature annealing under Hg-saturated conditions.  相似文献
7.
应变补偿InGaAs/InAlAs量子级联激光器   总被引:5,自引:4,他引:1       下载免费PDF全文
利用应变补偿的方法研制出激射波长 λ≈ 3.5— 3.7μm的量子级联激光器 .条宽 2 0 μm,腔长 1 .6mm的 Inx Ga1- x As/Iny Al1- y As量子级联激光器已实现室温准连续激射 .在最大输出功率处的准连续激射可持续 30 min以上 .  相似文献
8.
This paper will address features of plasma-assisted molecular beam epitaxial growth of ZnO and related materials and their characteristics. Two-dimensional, layer-by-layer growth is achieved both on c-plane sampphire by employing MgO buffer layer growth and on (0001) GaN/Al2O3 template by predepositing a low-temperature buffer layer followed by high-temperature annealing. Such two-dimensional growth results in the growth of high-quality heteroepitaxial ZnO epilayers. Biexciton emission is obtained from such high quality epilayers The polarity of heteroepitaxial ZnO epilayers is controlled by engineering the heterointerfaces. We achieved selective growth of Zn-polar and O-polar ZnO heteroepitaxial layers. The origin of different polarities can be successfully explained by an interface bonding sequence model. N-type conductivity in Gadoped ZnO epilayers is successfully controlled. High conductivity, enough to be applicable to devices, is achieved. MgxZn1-xO/ZnO heterostructures are grown and emission from a ZnO quantum well is observed. Mg incorporation in a MgZnO alloy is determined by in-situ reflection high-energy electron diffraction intensity oscillations, which enables precise control of the composition. Homoepitaxy on commericial ZnO substrates has been examined. Reflection high-energy electron diffraction intensity oscillations during homoepitaxy growth are observed.  相似文献
9.
SiGe/Si异质结双极晶体管研究   总被引:4,自引:1,他引:3  
李开成  刘道广  张静  易强 《微电子学》2000,30(3):144-146
介绍了一咱SiGe/Si分子束外延异质结双极晶体管(HBT)的研制。该器件采用3μm工艺制作,测量得其电流放大系数β为50,截止效率fr为5.1GHz,表明器件的直流特性和交流特性良好。器件的音片成品率在90%以上。  相似文献
10.
Epitaxial growth of (211)B CdTe/HgCdTe has been achieved on two inch germanium (Ge) by molecular beam epitaxy (MBE). Germanium was chosen as an alternative substrate to circumvent the weaknesses of CdZnTe wafers. The ease of surface preparation makes Ge an attractive candidate among many other alternative substrates. Best MBE CdTe growth results were obtained on (211) Ge surfaces which were exposed to arsenic and zinc fluxes prior to the MBE growth. This surface preparation enabled CdTe growth with B-face crystallographic polarity necessary for the HgCdTe growth. This process was reproducible, and produced a smooth and mirror-like surface morphology. The best value of the {422} x-ray double diffraction full width at half maximum measured from the HgCdTe layer was 68 arc-s. We present the 486 point maps of FWHM statistical values obtained from CdTe/Ge and HgCdTe/CdTe/Ge. High resolution microscopy electron transmission and secondary ion mass spectroscopy characterization results are also presented in this paper. High-performance middle wavelength infrared HgCdTe 32-element photodiode linear arrays, using the standard LETI/LIR planar n-on-p ion implanted technology, were fabricated on CdTe/Ge substrates. At 78K, photodiodes exhibited very high R0A figure of merit higher than 106 Ωcm−2 for a cutoff wavelength of 4.8 μm. Excess low frequency noise was not observed below 150K.  相似文献
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号