高跨导氢终端多晶金刚石长沟道场效应晶体管特性研究

基于多晶金刚石制作了栅长为4 pm的铝栅氢终端金刚石场效应晶体管.器件的饱和漏源电流为160 mA/mm,导通电阻低达37.85Ω·mm,最大跨导达到32 mS/mm,且跨导高于最大值的90%的栅压(V_(GS))范围达到3 V(-2 V≤V_(GS)≤-5 V).通过传输线电阻分析以及器件的导通电阻和电容-电压特性分析,发现氢终端多晶金刚石栅下沟道中的空穴面浓度达到了1.56×10~(13)cm~(-2),有效迁移率在前述高跨导栅压范围保持在约170 cm~2/(V·s).分析认为,较低的栅源和栅漏串联电阻、沟道中高密度的载流子和在大范围栅压内的高水平迁移率是引起高而宽阔的跨导峰和低导通电阻的原因.     

单晶金刚石氢终端场效应晶体管特性

基于微波等离子体化学气相淀积生长的单晶金刚石制作了栅长为2μm的耗尽型氢终端金刚石场效应晶体管,并对器件特性进行了分析.器件的饱和漏电流在栅压为-6 V时达到了96 mA/mm,但是在-6 V时栅泄漏电流过大.在-3.5 V的安全工作栅压下,饱和漏电流达到了77 mA/mm.在器件的饱和区,宽5.9 V的栅电压范围内,跨导随着栅电压的增加而近线性增大到30 mS/mm.通过对器件导通电阻和电容-电压特性的分析,氢终端单晶金刚石的二维空穴气浓度达到了1.99×10~(13)cm~(-2),并且迁移率和载流子浓度均随着栅压向正偏方向的移动而逐渐增大.分析认为,沟道中高密度的载流子、大的栅电容以及迁移率的逐渐增加是引起跨导在很大的栅压范围内近线性增加的原因.     

氢终端单晶金刚石反相器特性

超宽禁带半导体金刚石材料在高温、高压电路中具有重要的应用潜力.本研究采用微波等离子体化学气相沉积生长的单晶金刚石衬底制备了原子层沉积(atomic layer deposition, ALD)的Al₂O₃栅介质的氢终端金刚石金属氧化物半导体场效应晶体管(metal oxide semiconductor field effect transistor, MOSFET)器件,并与负载电阻互连,成功制备了金刚石反相器. 4μm栅长的氢终端金刚石器件实现了最大113.4 m A/mm的输出饱和漏电流,器件开关比高达109,并在不同负载电阻条件下均成功测得金刚石反相器的电压反转特性,反相器的最大增益为10.     

单晶LaB_6阴极材料典型晶面的电子结构和发射性能研究

单晶LaB_6是一种理想的热发射和场发射阴极材料,其不同晶面表现出不同的发射性能.采用基于密度泛函理论的第一性原理计算分析了LaB_6单晶的(100),(110),(111),(210),(211)和(310)典型晶面的差分电子密度、能带结构和态密度,并对光学区熔法制备的高质量单晶LaB_6的上述典型晶面的热发射性能进行了测试.理论计算结果表明LaB_6各晶面结构的不同和电子结构的差异导致LaB_6发射性能具有各向异性,晶面内La原子的密度越大、费米能级进入导带越深、费米能级附近态密度越大及其在导带区域的分布宽度越宽、导带在费米能级附近分布越多,晶面的逸出功越低,发射性能越好.热发射测试结果表明,当阴极测试温度为1773 K,测试电压为1 k V时,(100),(110),(111),(210),(211)和(310)晶面的最大发射电流密度分别为42.4,36.4,18.4,32.5,30.5和32.2 A/cm~2,其中(100)晶面具有最佳的发射性能.     

硼元素对人造金刚石单晶氧化速度的影响

 本文用KNO₃溶液氧化法对人造金刚石大单晶切片进行氧化实验，用两光束干涉计测量了单晶（含硼和不含硼）(110)截平面上各晶面成长区沿(110)面法线方向的相对氧化深度，计算了其相对氧化速度，并定性的与硼元素在这些区域的浓度做了对应。     

晶面偏角对利用Voigt函数法计算硅单晶本征晶格应变的影响

研究并制备了不同晶面偏角的Si(111)单晶,经过研磨和抛光使表面粗糙度低至3.4?达到超光滑水平,消除了表面和亚表面损伤层以及其所产生的应力变化.利用高精度X射线衍射仪分别测定了在不同晶面偏角条件下衍射曲线的半高全宽和积分宽度.应用Voigt函数法分析计算了微观应变,通过理论计算和实验对比可知,Si(111)单晶在晶面偏角达到0.749o时,偏角本身所带来的衍射峰半高全宽变化使计算出的应变值误差大于5%.研究结果为其他晶体类似研究提供了重要参考.     

Si{111}晶面粒子堵塞坑的新现象

本文报道了从粒子背散射堵塞效应的实验中所发现的单晶Si的{111}晶面粒子堵塞坑的新现象。单晶Si的{111}晶面有两个面间距d_{(111)^(a)和d(111)^(b),而{110}晶面只有一个面间距d(110)。由此导致两者的堵塞坑是不同的,我们已从α粒子和质子的Si单晶堵塞效应的实验得到了证实。并由此估计了d(111)^(a)和d(111)^(b)以及d(110)的2ψ1/2角。据作者了解,到目前为止,国内外还没有人发现此现象。此现象的发现对复杂晶体的堵塞和沟道效应的研究开阔了前景。 关键词：}     

Ib型金刚石大单晶的限形生长

金刚石的限形生长有利于其后续加工.对于磨料级金刚石限形生长的研究已经比较透彻,但金刚石大单晶的限形生长尚缺乏全面系统的研究.本文以Fe Ni(64wt%:36wt%)合金为触媒,利用高温高压下的温度梯度法在5.6 GPa时对不同温度下分别沿(100)面和(111)面生长的Ib型金刚石大单晶的晶形进行了研究.研究表明:随着温度的升高,沿(100)晶面生长的金刚石大单晶的晶形分别为板状、塔状直至尖塔状,而沿(111)面生长的金刚石大单晶的晶形则分别为塔状和板状;分析了不同温度下分别沿(100)面和(111)面生长金刚石大单晶不同晶形高径比的变化情况.利用不同压力和温度下的金刚石大单晶合成实验绘制了沿(100)和(111)面生长金刚石大单晶的晶形在V形生长区域内的分布示意图,表明沿(111)面生长的金刚石大单晶V形区温度下限明显比以(100)面生长的高,而沿这两面生长金刚石大单晶的V形区温度上限差别并不明显.对不同生长面V形区温度上下限的差别进行了解释,据此实现了Ib型金刚石大单晶的限形生长.     

微波布拉格衍射中立方晶体晶面衍射测量与模型选取讨论

在微波布拉格衍射实验中,通过对立方晶体模型晶格常数参量选取,测定(110)面入射角与衍射强度变化关系,来验证衍射极大值在随入射角变化而变化的过程是否满足布拉格定律.同时可在一定入射角变化范围内,限定衍射级数的大小,讨论只改变接收端角度时,(100)面与(110)面衍射极大值时晶格常数所在范围,并从理论上给出同时测定两晶面可限定的衍射级数与晶格常量的范围.     

硼掺杂金刚石薄膜同质外延生长及肖特基势垒二极管制备

采用微波等离子体气相沉积(MPCVD)在商用3mm×3mm×1 mm高温高压合成(HPHT)Ib型(100)金刚石衬底上同质外延生长B掺杂金刚石薄膜,并在此材料的基础上用磁控溅射和电子束蒸镀技术制备了不同结构参数金刚石肖特基势垒二极管。测试结果表明:所生长的金刚石薄膜表面非常平整,可以看到比较明显的原子台阶;所制备的器件具有明显的整流特性,肖特基电极直径100μm,肖特基电极和欧姆电极间距10μm,外加电压-15V,300K时测得器件正向导通电阻20Ω,反向饱和电流近似为10-6 A,反向击穿电压大约103.5V;电极间距越大,反向击穿电压越高,器件正向电流越小。     

Vacuum relaxation and annealing-induced enhancement of mobility of regioregular poly（3-hexylthiophene） field-effect transistors

In order to enhance the performance of regioregular poly(3-hexylthiophene) (RR-P3HT) field-effect transistors (FETs), RR-P3HT FETs are prepared by the spin-coating method followed by vacuum placement and annealing. This paper reports that the crystal structure, the molecule interconnection, the surface morphology, and the charge carrier mobility of RR-P3HT films are affected by vacuum relaxation and annealing. The results reveal that the field-effect mobility of RR-P3HT FETs can reach 4.17×10^ - 2~m²/(V.s) by vacuum relaxation at room temperature due to an enhanced local self-organization. Furthermore, it reports that an appropriate annealing temperature can facilitate the crystal structure, the orientation and the interconnection of polymer molecules. These results show that the field-effect mobility of device annealed at 150~℃ for 10 minutes in vacuum at atmosphere and followed by placement for 20 hours in vacuum at room temperature is enhanced dramatically to 9.00×10^ - 2 ~cm²/(V.s).     

Low-voltage antimony-doped SnO₂ nanowire transparent transistors gated by microporous SiO₂-based proton conductors

A battery drivable low-voltage transparent lightly antimony(Sb)-doped SnO 2 nanowire electric-double-layer(EDL) field-effect transistor(FET) is fabricated on an ITO glass substrate at room temperature.An ultralow operation voltage of 1 V is obtained on account of an untralarge specific gate capacitance(～2.14 μF/cm 2) directly bound up with mobile ions-induced EDL(sandwiched between the top and bottom electrodes) effect.The transparent FET shows excellent electric characteristics with a field-effect mobility of 54.43 cm 2 /V · s,current on/off ration of 2 × 10 4,and subthreshold gate voltage swing(S = dV gs /d(log I ds)) of 140 mV/decade.The threshold voltage V th(0.1 V) is estimated which indicates that the SnO 2 namowire transistor operates in an n-type enhanced mode.Such a low-voltage transparent nanowire transistor gated by a microporous SiO 2-based solid electrolyte is very promising for battery-powered portable nanoscale sensors.     

Large‐surface‐area diamond (111) crystal plates for applications in high‐heat‐load wavefront‐preserving X‐ray crystal optics

Fabrication and results of high‐resolution X‐ray topography characterization of diamond single‐crystal plates with large surface area (10 mm × 10 mm) and (111) crystal surface orientation for applications in high‐heat‐load X‐ray crystal optics are reported. The plates were fabricated by laser‐cutting of the (111) facets of diamond crystals grown using high‐pressure high‐temperature methods. The intrinsic crystal quality of a selected 3 mm × 7 mm crystal region of one of the studied samples was found to be suitable for applications in wavefront‐preserving high‐heat‐load crystal optics. Wavefront characterization was performed using sequential X‐ray diffraction topography in the pseudo plane wave configuration and data analysis using rocking‐curve topography. The variations of the rocking‐curve width and peak position measured with a spatial resolution of 13 µm × 13 µm over the selected region were found to be less than 1 µrad.     

Demonstration of diamond field effect transistors by AlN/diamond heterostructure

This is the first report on an AlN/diamond heterojunction field effect transistor (HFET). The AlN epilayer is grown on oxygen‐terminated (111) diamond substrates using metalorganic vapor phase epitaxy at a temperature as high as 1240 °C. The transistor and gate capacitance–voltage characteristics indicate that the HFET behaves as a p‐channel FET with a normally‐on depletion mode. The HFET channel is located at the AlN/diamond interface, and holes are accumulated in diamond close to the interface. The development of the AlN/diamond HFET creates a new possibility for diamond‐based power electronics. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical strength and cleavage of diamond

The theoretical strength of diamond has been calculated for the <100>, <110>, and <111> directions using a first principles approach and is found to be strongly dependent on crystallographic direction. This elastic anisotropy, found at large strains, and particularly the pronounced minimum in cohesion in the <111> direction, is believed to be the reason for the remarkable dominance of the 111 cleavage plane when diamond is fractured. The extra energy required to cleave a crystal on planes other than 111 is discussed with reference to simple surface energy calculations and also the introduction of bond-bending terms.     

Electrical properties and memory effect in the field effect transistor based on organic ferroelectric insulator and pentacene

We have fabricated a field effect transistor (FET) based on an organic ferroelectric insulator and molecular conductor, and investigated the electrical properties and memory effects on the PEN-FET. We have observed a drastic change in the drain current at around the coercive electric fieldE _c of the organic ferroelectric insulator in not only a FET (PEN-FET) based on a pentacene (PEN) film but also a FET (IPEN-FET) based on an iodine doped PEN film. The magnitude of the change of the drain current for the IPEN-FET is 200 times larger than that for the PEN-FET. It is expected from these results that the PEN-FET (especially the IPEN-FET) is an improvement in such devices, since it operates at a low gate electric field accompanied by the appearance of the spontaneous polarization in the organic ferroelectric insulator. In addition, we have found that the drain current for the PEN-FET does not return to the initial drain current ofE _G =0 V/cm for more than one week, even if the gate electric field is changed to 0 V/cm from 500 V/cm(>E _c ). From these results, it is suggested that the PEN-FET becomes a memory device.     

一种新型高非线性色散平坦光子晶体光纤结构

提出了一种新的高非线性色散平坦光子晶体光纤结构,引入了一个衡量非线性和色散平坦的品质因子δ。采用平面波展开法,研究了气孔尺寸对光子晶体光纤色散特性和非线性的影响。新结构在第一圈空气孔的中间插入六个附加小孔,使得光子晶体光纤有更小的有效模场面积,提高了光纤的非线性。通过控制第一圈和第三圈空气孔以及附加小孔的直径,使得该光子晶体光纤在大约330 nm的波长范围内,光纤的色散系数介于±0.5 ps/(km.nm)之间,在大约230nm的波长范围内,光纤的色散系数介于±0.1 ps/(km.nm)之间,在大约200 nm的波长范围内,光纤的色散系数D的值介于±0.05 ps/(km.nm)之间。光纤的有效模场面积为2.26μm2。衡量非线性和色散平坦的品质因子δ=11.8 ps.W/μm2。     

Growth and desorption of indium epitaxial layers investigated by high field microscopy

Growth of indium single crystals on tungsten field emission tips was carried out by deposition of indium from vapour in ultra high vacuum, using substrate temperatures in the range of 293–420 K. Two different tungsten tips were used as the substrate: a perfect W single crystal in one case and a bi-crystal with a distinct grain boundary in the other. No influence of the grain boundary on the epitaxial growth was found. Two orientation relationships were observed mostly: {111}In ∥ {110}W with 〈110〉In ∥ 〈111〉W and {111}In ∥ {100}W with 〈110〉In ∥ 〈110〉W. In the first case the growth was initiated by the indium nucleus created on the ledges of the {110}W plane. A field strength of 0.9 V/Å was found for the evaporation field of indium. The field strength of the desorption of In-W interfacial layer atoms was found to be 4.4–5.2 V/Å. A mechanism of the growth of indium crystals has been proposed.