低温烧结0.5CaTiO3-0.5CaTiSiO5高频介质陶瓷

对添加2ZnO-B2O3玻璃实现0.5CaTiO3-0.5CaTiSiO5 高频介质材料900℃下低温烧结进行了系统研究。实验结果表明:添加质量分数为5%~10% 2ZnO-B2O3玻璃可使体积密度达到0.5CaTiO3-0.5CaTiSiO5理论密度的97%以上,且介电性能优异,r = 58~76,tg? 3.3?04,= (329~472)?06/℃,? 1012 cm。利用XRD、SEM和介电测量技术分析材料的晶相组成、显微结构和介电特性发现:材料由三种晶相组成,分别是单斜型CaTiSiO5、正交型CaTiO3以及一个新相,新相的生成可能是在液相烧结后期2ZnO-B2O3 玻璃在晶界处结晶而形成,低温烧结0.5CaTiO3-0.5CaTiSiO5 介质材料的介电性能很好地遵循李氏对数混合法则。     

复合助烧剂对0.4CaTiO3-0.6(Li1/2Nd1/2)TiO3陶瓷的低温烧结及性能的影响

采用传统的固相反应法制备了0.4CaTiO3.0.6(Li1/2Nd1/2)TiO3(CLNT)微波介质陶瓷,研究了复合添加BaCu(B2O5)(BCB)和2ZnO-B2O3(ZB)玻璃对CLNT陶瓷的烧结特性、相组成、微观形貌及介电性能的影响.结果表明:复合添加质量分数3%的ZB玻璃和5%的BCB能使CLNT陶瓷的烧...     

La2O3-B2O3玻璃添加对Zn0.5Ti0.5NbO4微波介质陶瓷结构及性能影响

利用X射线衍射、扫描电子显微镜等手段研究了添加La2O3-B2O3玻璃作为烧结助剂的Zn0.5Ti0.5NbO4微波介质陶瓷在低温烧结过程中的结构及微波介电性能变化。实验结果表明,适当的La2O3-B2O3玻璃添加不会影响Zn0.5Ti0.5NbO4陶瓷的相组成。添加质量分数2%的La2O3-B2O3烧结助剂有助于在烧结过程中形成液相,液相能有效加速Zn0.5Ti0.5NbO4陶瓷的低温烧结过程,实现Zn0.5Ti0.5NbO4陶瓷的致密化。在875℃烧结时,添加质量分数2%La2O3-B2O3玻璃的Zn0.5Ti0.5NbO4陶瓷具有优异的微波介电性能:εr=33.91,Q×f=16579 GHz(f=6.1 GHz),τf=-68.54×10-6/℃。     

球磨时间对低温烧结BaO-TiO2-Nb2O5微波陶瓷性能的影响

为实现Ba2Ti3Nb4O18(BaO-TiO2-Nb2O5)材料的低温烧结,添加质量分数为5%的ZnO-B2O3玻璃作助熔剂,研究了行星球磨时间对粉料粒径、陶瓷样品的烧结密度、显微结构和介电性能的影响。结果显示:行星球磨6h的粉料粒径适中(约90nm),用该粉料制备的样品可在900℃致密烧结(>95%理论密度),且介电性能优良(1MHz),εr约为36,tanδ小于4×10–4,电容温度系数为(–5～+5)×10–6/℃;微波介电性能如下:εr约为33,Q为2380(5.998GHz)。     

ZnO-B2O3-SiO2掺杂对锆酸钙基陶瓷性能的影响

研究了ZnO-B2O3-SiO2(ZBS)玻璃掺杂量对CaZrO3陶瓷烧结性能、物相组成、微观组织形貌和介电性能的影响。结果表明:通过掺杂ZBS,可使CaZrO3陶瓷的烧结温度由1 550℃降至1 000℃,且无第二相生成,相对密度达97.8%。当ZBS添加量为质量分数15%时,CaZrO3陶瓷在1 000℃烧结3 h获得良好的介电性能:εr=25,Q·f=8 584 GHz,τf=–45×10–6/℃。     

V_2O_5掺杂MgTiO_3-CaTiO_3陶瓷的介电性能

采用固相反应法制备了V2O5掺杂的MgTiO3-CaTiO3(MCT)介质陶瓷。研究了V2O5掺杂量对陶瓷晶相组成、烧结温度和介电性能的影响。结果表明:V2O5掺杂的MCT陶瓷的主晶相为MgTiO3和CaTiO3两相结构,当掺杂量较低时,有第二相CaVO3产生;V2O5掺杂能降低MCT陶瓷的烧结温度并使其介电性能得到改善。当x(V2O5)为1%时,在1250℃烧结2.5h获得最佳性能:εr为20.17,tanδ为2×10–3,αε为4.9×10–5/℃。     

钛酸钙对BZN-CaTiO3系统介电性能的影响

研究了利用电子陶瓷工艺制得的主晶相为Ba(Zn1/3Nb2/3)O3(BZN)和CaTiO3的新型陶瓷,BZN具有立方钙钛矿结构。通过烧结温度的改变得到不同介电性能的陶瓷材料,发现CaTiO3的添加量对系统介电性能有显著影响。在1 395℃烧结的BZN-CaTiO3陶瓷,当CaTiO3的添加量为60%(质量分数)时介电性能最佳,其εr为99.97,tgδ为0.54×10-4,αC为–13.05×10-6℃–1(25~85℃,1MHz下测量)。     

Li2O掺杂对CBS/Al2O3玻璃陶瓷性能的影响

研究了Li2O掺杂对CBS/Al2O3玻璃陶瓷烧结性能和介电性能的影响.结果表明,掺杂适量的Li2O可改善CBS/Al2O3玻璃陶瓷的烧结性能和介电性能,当掺杂Li2O的质量分数为0.5%时,CBS/Al2O3玻璃陶瓷在810 ℃可实现低温致密化烧结,试样的体积密度为2.89 g/cm3;在1 MHz的测试频率下,该材料的介电常数为8.6,介电损耗为1.0×10-3;XRD分析表明其相组成主要为CaSiO3、CaAl3BO7、残余Al2O3和玻璃相.     

ZnO-B_2O_3玻璃对Mg_2TiO_4微波介质陶瓷结构和性能的影响

利用传统固相烧结法制备了ZnO-B2O3玻璃掺杂的Mg2TiO4微波介质陶瓷,研究了ZnO-B2O3玻璃掺杂对所制陶瓷相成分、微观形貌和微波介电性能的影响。结果表明:ZnO-B2O3玻璃掺杂能使Mg2TiO4陶瓷的致密化温度降低200℃左右。当Mg2TiO4中掺杂质量分数2%的ZnO-B2O3玻璃时,经1 300℃烧结所得陶瓷微波性能较好:εr=13.62、Q.f=101 275 GHz、τf=–51×10–6/℃。     

碱金属氧化物添加剂对(Mg_(1–x)Ca_x)TiO_3陶瓷微波性能的影响

采用固相反应法制备了(Mg1–xCax)TiO3微波介质陶瓷。探讨了复合添加Na2O和K2O对(Mg1–xCax)TiO3陶瓷烧结性能和介电性能的影响。结果表明:复合添加碱金属氧化物,陶瓷的主晶相为MgTiO3和CaTiO3,同时,可以抑制中间相MgTi2O5的产生,有效降低陶瓷的烧结温度至1280℃。当Na2O和K2O添加总量为质量分数1.2%,且Na2O/K2O质量比为2∶1时,所制陶瓷介电性能最佳:εr=19.71,Q.f=3.59×104GHz(7.58 GHz),τf=–1.40×10–6/℃。     

In0.5Ga0.5As/In0.5Al0.5As应变耦合量子点的形貌和光学性质

提出了利用分子束外延方法生长In0.5Ga0.5As/In0.5Al0.5As应变耦合量子点，并分析量子点的形貌和光学性质随GaAs隔离层厚度变化的特点。实验结果表明，随着耦合量子点中的GaAs隔离层厚度从2 nm增加到10 nm，In0.5Ga0.5As量子点的密度增大、均匀性提高, Al原子扩散和浸润层对量子点PL谱的影响被消除，而且InAlAs材料的宽禁带特征使其成为InGaAs量子点红外探测器中的暗电流阻挡层。由此可见，选择合适的GaAs隔离层厚度形成InGaAs/InAlAs应变耦合量子点将有益于InGaAs量子点红外探测器的研究。     

Photo-induced magnetism in La0.5Pr0.5CrO3

In a perovskite-type chromite La_0.5Pr_0.5CrO₃, we studied the photo-induced electron-spin resonance (ESR). During the illumination of near-infrared light, the photo-induced and transient magnetization is temperature dependent with the characteristic thermal activation energy of 130 meV below the spin-canted antiferromagnetic transition temperature 261 K. At room temperature the photo-induced ESR intensity is remarkably enhanced. We interpret this is coming from the photo-excited electronic state in chromite. By analogy with the manganites, we suspect that the irradiated photons excite the t_2g electrons to the e_g state in Cr³⁺ (3d³). This kind of excitation may cause a creation of novel transient magnetic order than canted antiferromagnetism. The present results may open up an intriguing collective photo-induced magnetism, the creation and control of spin and spin-polarization dependent transport with near-infrared light illumination.     

Al0.5Ga0.5N/GaN/Al0.5Ga0.5N量子阱中依赖于表面载流子浓度的Rashba自旋劈裂

通过自洽求解薛定谔和泊松方程,计算了不同表面载流子浓度的Al0.5Ga0.5N/GaN/Al0.5Ga0.5N 量子阱中第一子带的Rashba系数和Rashba自旋劈裂。第一子带在费米能级处的Rashba自旋劈裂可观并且随Ns明显增加,因为Rashba系数特别是费米波矢增加很快。随着Ns的增加,第一子带波函数的峰朝着左异质结界面移动,且阱层的平均电场增加,所以来自阱层和异质结界面的这两个主要贡献部分增加。因而,III族氮化物异质结构中的强极化电场和高浓度的二维电子气对α至关重要,使AlGaN/GaN量子阱的Rashba自旋劈裂同窄带隙的III-V族材料可比。结果表明Ns是影响AlGaN/GaN量子阱中的Rashba系数和Rashba自旋劈裂的一个重要参数,表明这种材料可以应用到自旋电子学器件中。     

Mg掺杂Al_(0.5)Ga_(0.5)N薄膜的发光性质研究

利用MOCVD技术在c面蓝宝石衬底上采用AlN缓冲层制备了Mg掺杂Al0.5Ga0.5N薄膜。采用CL测试方法研究了Mg掺杂对Al0.5Ga0.5N薄膜光学特性的影响。测量表明,Mg掺杂导致在Al0.5Ga0.5N薄膜的发光谱中出现了3.9eV的发光带,其发光机理为束缚的施主-受主对(DAP)间的辐射复合跃迁。     

Stabilized dual-polarization oscillation in a LiNd0.5La0.5P4O12laser

Stabilized dual-polarization oscillations inc-rod LiNd0.5La0.5P4O12(abbreviated as LNLP) lasers are reported. The dual-polarization oscillation, which means the simultaneous oscillation of orthogonally polarized modes, was obtained by setting the LNLP crystal at suitable positions in the resonator without any optical device.     

Self-assembled In0.5Ga0.5As quantum-dotlasers with doped active region

Self-assembled In_0.5Ga_0.5As quantum-dot lasers with different doping schemes in the active region are investigated. Their lasing wavelength, characteristic temperature, quantum efficiency, and internal loss are characterized and correlated with the size, uniformity, and density of the quantum dots as revealed by atomic force microscopy. Continuous-wave operation of Be-doped quantum-dot lasers has been achieved. Undoped In_0.5Ga_0.5 As quantum-dot lasers with a characteristic temperature as high as 125 K above room temperature have also been demonstrated     

Temperature dependence of Al/undoped Al0.5Ga0.5As/GaAs capacitors

Undoped Al0.5Ga0.5As is used in place of the insulator layer in the fabrication of MIS-type capacitors with Schottky gates. The current-voltage and capacitance-voltage characteristics of the capacitors were measured as a function of temperature in the range 300-77 K. At high temperatures current is by thermionic emission over the barrier determined by the Schottky contact and the Al0.5Ga0.5As/ GaAs conduction band discontinuity. As the temperature is lowered, Fowler-Nordheim tunneling is observed at sufficiently large gate biases and at 77 K conduction is ohmic. Based on I-V and C-V data the electron accumulation layer density is estimated to be about 1 × 10¹²cm^-2at 77 K when the capacitor is positively biased. The results obtained indicate that for an appropriate choice of parameters it should be possible to fabricate MIS-like transistors suitable for high-speed operation at 77 K.     

晶体光谱特性

测量了0.8 at.-% Nd3+:Y0.5Gd0.5VO4的吸收光谱和荧光发射谱,光谱显示该晶体在808.5 nm有很强的偏振光吸收峰,且π偏振光(E∥C)吸收远强于σ偏振光(E⊥C)吸收,半高宽度分别为4.5 nm和12 nm,吸收截面分别为19.69×10-20 cm2和6.41×10-20 cm2;其荧光发射( 4F3/2→ 4I11/2跃迁)峰值波长在1064 nm,半高宽度为3.7 nm; 4F3/2→ 4I11/2跃迁的荧光寿命为110 μs;光谱特性表明Nd3+:Y0.5Gd0.5VO4晶体是潜在的高效率激光晶体材料.     

Novel GaAs heterojunction bipolar transistors usingIn0.5Al0.5P as emitter

We report the fabrication and characterization of the first single and double In_0.5Al_0.5P/GaAs heterojunction bipolar transistors (HBT's). These HBT's are grown by gas-source molecular beam epitaxy. The In_0.5Al_0.5P/GaAs heterostructure has the largest valence band discontinuity among all Ill-V semiconductor heterojunctions lattice-matched to GaAs. Common-emitter dc current gains as high as 300 and 400 are measured for SHBT's and DHBT's, respectively, with base doping of 1×10¹⁹ cm^-3. The corresponding offset voltage is 80 and 120 mV, respectively. These results demonstrate the advantages of the In_0.5Al_0.5 P/GaAs band alignment and make the new HBT's attractive candidates for high-speed digital circuit applications     

Investigation of Coulomb scattering on sSi/Si0.5Ge0.5/sSOI quantum-well p-MOSFETs

sSi/Si_0.5Ge_0.5/sSOI quantum-well (QW) p-MOSFETs with HfO₂/TiN gate stack were fabricated and characterized. According to the low temperature experimental results, carrier mobility of the strained Si_0.5Ge_0.5 QW p-MOSFET was mainly governed by phonon scattering from 300 to 150 K and Coulomb scattering below 150 K, respectively. Coulomb scattering was intensified by the accumulated inversion charges in the Si cap layer of this Si/SiGe heterostructure, which led to a degradation of carrier mobility in the SiGe channel, especially at low temperature.