高灵敏度Sb基量子阱2DEG的霍尔器件

用分子束外延技术将高灵敏度的InAs/AlSb量子阱结构的Hall器件赝配生长在GaAs衬底上。设计了由双δ掺杂构成的Hall器件的新结构,有效地提高了器件的面电子浓度。与传统的没有掺杂的InAs/AlSb量子阱结构的Hall器件相比,室温下器件电子迁移率从15 000 cm²·V^-1·s^-1 提高到16 000 cm²·V^-1·s^-1。AFM测试表明材料有好的表面形态和结晶质量。从77 K 到300 K对Hall器件进行霍尔测试,结果显示器件不同温度范围有不同散射机构。双δ掺杂结构形成高灵敏度、高二维电子气（2DEG）浓度的InAs/AlSb异质结Hall器件具有广阔的应用前景。     

基于聚(4-乙烯基苯酚)衬底修饰层喷墨打印的小分子有机半导体薄膜制备和表征

采用旋涂法预先在SiO₂衬底表面形成一层聚（4-乙烯基苯酚）（PVP）作为表面修饰层,以喷墨打印的6,13-双（三异丙基甲硅烷基乙炔基）并五苯（TIPS并五苯）作为有源层制作有机薄膜晶体管,有效改善了有机半导体薄膜的形貌。采用真空热蒸镀工艺制备源漏电极,形成底栅顶接触结构的有机薄膜晶体管（OTFT）器件。作为对比,在未经过表面修饰的SiO₂衬底上采用相同条件打印TIPS并五苯薄膜晶体管,发现在经过PVP修饰的SiO₂衬底上打印的单点厚度更均匀,咖啡环效应被抑制或被消除;而通过多点交叠打印形成的矩形薄膜的晶粒尺寸更大,相应的OTFT器件具有更高的场效应迁移率。在有PVP修饰层的衬底上制作的OTFT,器件在饱和区的平均场效应迁移率达到了0.065 cm²·V^-1·s^-1;而直接在SiO₂衬底上制作的器件,相应的平均场效应迁移率仅为0.02 cm²·V^-1·s^-1。     

退火温度对溶胶-凝胶法制备锌锡氧化物薄膜晶体管的影响

采用溶胶-凝胶法制备了非晶锌锡氧化物(ZTO)薄膜晶体管(TFT),通过热重-差热分析(TG-DTA)对ZTO胶体中的化学反应进行了分析,研究了不同退火温度对ZTO TFTs性能的影响。结果表明:当退火温度在300~500℃范围内时,薄膜为非晶态结构,薄膜表面致密、平整。当退火温度达到400℃时,薄膜在可见光范围内具有高透过率(>85%)。随着退火温度的升高,器件阈值电压明显降低,由15.85 V降至3.76 V,载流子迁移率由0.004 cm²·V^-1·s^-1提高到5.16 cm²·V^-1·s^-1,开关电流比达到10⁵。退火温度的升高明显改善了ZTO TFT的电学性能。     

Growth condition optimization and mobility enhancement through inserting AlAs monolayer in the InP-based In_xGa_(1-x)As/In_(0.52)Al_(0.48)As HEMT structures

The structure of In P-based In_xGa_(1-x) As/In0.52Al0.48 As pseudomorphic high electron mobility transistor(PHEMT)was optimized in detail.Effects of growth temperature,growth interruption time,Si δ-doping condition,channel thickness and In content,and inserted Al As monolayer(ML) on the two-dimensional electron gas(2DEG) performance were investigated carefully.It was found that the use of the inserted Al As monolayer has an enhancement effect on the mobility due to the reduction of interface roughness and the suppression of Si movement.With optimization of the growth parameters,the structures composed of a 10 nm thick In0.75Ga0.25 As channel layer and a 3 nm thick Al As/In0.52Al0.48 As superlattices spacer layer exhibited electron mobilities as high as 12500 cm~2·V-1·s~(-1)(300 K) and 53500 cm~2·V~(-1_·s~(-1)(77 K) and the corresponding sheet carrier concentrations(Ns) of 2.8×10~(12)cm~(-2)and 2.9×1012cm~(-2),respectively.To the best of the authors' knowledge,this is the highest reported room temperature mobility for In P-based HEMTs with a spacer of 3 nm to date.     

超薄EuF3电极修饰层对有机场效应晶体管性能的提升

采用EuF₃薄层修饰低功函数金属Ag源、漏电极,制备了CuPc有机场效应晶体管,研究了不同厚度EuF₃对器件性能的影响。结果表明,EuF₃的厚度由0 nm增至0.6 nm时,接触电阻由23.65×10⁵ Ω·cm减 至3.86×10⁵ Ω·cm,使得器件载流子迁移率由1.5×10^-3 cm²·V^-1·s^-1提高到4.65×10^-3 cm²·V^-1·s^-1。 UPS测试结果表明,薄层EuF₃在Ag与有机半导体间形成了界面偶极势垒,使源漏电极表面功函数增大,空穴注入势垒降低,Ag电极与有机半导体层界面的接触电阻减小,进而提升了空穴的注入效率。     

单层二硫化钼多相性质及相变的第一性原理研究

本文基于密度泛函的第一性原理,并引入范德瓦耳斯力修正,研究了单层二硫化钼2H,1T,ZT三种相的电学性质及相变原理.首先通过结构弛豫确定了三种相的几何结构,能带和态密度计算证实1T相具有金属性质,ZT相具有半导体性质,带隙为0.01 eV.然后结合变形势理论计算了2H和ZT相的迁移率,ZT相的迁移率高达104cm~2·V~(-1)·s~(-1),进一步拓展了单层二硫化钼的应用范围.最后通过对比三种相吸附锂原子结合能,计算2H-1T相变能量曲线,解释了引起二硫化钼相变的原因.本文的研究结果将对单层二硫化钼实验制备表征以及相关光电器件性能分析提供重要参考.     

沟道层厚度对室温制备的In2O3薄膜晶体管器件性能的影响

在室温下采用直流磁控溅射以SiO₂/Si为衬底制备了不同沟道层厚度的底栅式In₂O₃薄膜晶体管,讨论了沟道层厚度对底栅In₂O₃薄膜晶体管的电学性能的影响。实验结果表明:器件的特性与沟道层厚度有关,最优沟道层厚度的In₂O₃薄膜晶体管为增强型,其阈值电压为2.5 V,开关电流比约为10⁶,场效应迁移率为6.2 cm²·V^-1·s^-1。     

拓扑绝缘体Bi_2Se_3中层堆垛效应的第一性原理研究

运用第一性原理方法,研究了拓扑绝缘体Bi_2Se_3块体和薄膜中的层堆垛对其结构、电子态、拓扑态和自旋劈裂的影响.发现不同的堆垛会引起Bi_2Se_3层间的相互作用,改变系统的中心对称性.块体的ABC和AAA堆垛都具有中心对称性和相似的能带结构.ABA堆垛破坏了体系的中心对称性,能带发生很大改变,并且产生了很大的能带自旋劈裂.用能带反转的方法判定体系的拓扑相,在不同堆垛的Bi_2Se_3块体中,考虑自旋轨道耦合时都发生了能带反转,因而具有不同堆垛的Bi2Se3仍是拓扑绝缘体.进一步研究了Bi_2Se_3薄膜中的堆垛效应,发现非中心对称的ABA堆垛在Bi_2Se_3薄膜中引起明显的自旋劈裂,并且提出和验证了用应变调控自旋劈裂的方法.     

非晶铟镓锌氧薄膜晶体管钼/铜源漏电极的研究

针对非晶铟镓锌氧薄膜晶体管（a-IGZO TFT）的钼/铜源漏电极开展研究。实验证明,单层Mo源漏电极与栅绝缘层之间的粘附性好、表面粗糙度较小、电阻率较大,而单层Cu源漏电极与栅绝缘层之间的结合性差且Cu原子扩散问题严重、表面粗糙度较大、电阻率较小。为了实现优势互补,我们设计了双层Mo（20 nm）/Cu（80 nm）源漏电极,并采用优化工艺制备了包含该电极结构的a-IGZO TFT。器件具有良好的电学特性,场效应迁移率为 8.33 cm²·V^-1·s^-1, 阈值电压为6.0 V,亚阈值摆幅为2.0 V/dec,开关比为 1.3×10⁷,证明了双层Mo/Cu源漏电极的可行性和实用性。     

Electronic transport properties of silicon junctionless nanowire transistors fabricated by femtosecond laser direct writing

Silicon junctionless nanowire transistor(JNT) is fabricated by femtosecond laser direct writing on a heavily n-doped SOI substrate.The performances of the transistor,i.e.,current drive,threshold voltage,subthreshold swing(SS),and electron mobility are evaluated.The device shows good gate control ability and low-temperature instability in a temperature range from 10 K to 300 K.The drain currents increasing by steps with the gate voltage are clearly observed from 10 K to50 K,which is attributed to the electron transport through one-dimensional(1D) subbands formed in the nanowire.Besides,the device exhibits a better low-field electron mobility of 290 cm~2·V~(-1)·s~(-1),implying that the silicon nanowires fabricated by femtosecond laser have good electrical properties.This approach provides a potential application for nanoscale device patterning.     

PVA栅绝缘层浓度对P3HT有机场效应晶体管性能的影响

采用溶液制备法制备了用PVA作为绝缘层、P3HT作为有源层的有机场效应晶体管,,研究了不同浓度PVA栅绝缘层对器件性能的影响。实验结果显示,以质量分数为8%的PVA溶液制备的栅绝缘层具有最好的性能,器件的场效应迁移率为0.31 cm²·V^-1·s^-1,阈值电压为-6 V。进一步分析了PVA栅绝缘层浓度对器件性能提高的原因,结果表明,对于制备溶液化的有机场效应晶体管,选取合适的PVA栅绝缘层浓度非常重要。     

Scalable fabrication of Bi_2O_2Se polycrystalline thin film for near-infrared optoelectronic devices applications

We present a controlled, stepwise formation of layered semiconductor Bi_2O_2 Se thin films prepared via the vapour process by annealing topological insulator Bi_2Se_3 thin films in low oxygen atmosphere for different reactions. Photodetectors based on Bi_2O_2 Se thin film show a responsivity of 1.7×10~4 A/W at a wavelength of 980 nm. Field-effect transistors based on Bi_2O_2 Se thin film exhibit n-type behavior and present a high electron mobility of 17 cm~2/V·s. In addition, the electrical properties of the devices after 4 months keeping in the air shows little change, implying outstanding air-stability of our Bi_2O_2 Se thin films. From the obtained results, it is evident that low oxygen annealing is a surprisingly effective method to fabricate Bi_2O_2 Se thin films for integrated optoelectronic applications.     

High sensitivity Hall devices with AlSb/InAs quantum well structures

AlSb/InAs quantum well (QW) structures and InAs films on GaAs (001) substrates were grown by molecular beam epitaxy (MBE). We investigated the dependence of electron mobility and two-dimensional electron gas (2DEG) concentration on the thickness of an InAs channel. It is found that electron mobility as high as 19050 cm2·V-1·s-1 has been achieved for an InAs channel of 22.5 nm. The Hall devices with high sensitivity and good temperature stability were fabricated based on the AlSb/InAs QW structures. Their sensitivity is markedly superior to Hall devices of InAs films.     

AlN隔离层生长时间对AlGaN/AlN/GaN HEMT材料电学性能的影响

利用金属有机化学气相沉积（MOCVD）设备,在蓝宝石（0001）面上外延不同生长时间AlN隔离层的Al_xGa_1-xN/AlN/GaN结构的高电子迁移率的晶体管（HEMT）,研究了AlN隔离层厚度对HEMT材料电学性能的影响。研究发现采用脉冲法外延（PALE）技术生长AlN隔离层的时间为12 s（1 nm左右）时,HEMT材料的方块电阻最小,电子迁移率为1 500 cm²·V^-1·s^-1,二维电子气（2DEG）浓度为1.16×10¹³ cm^-2。AFM测试结果表明,一定厚度范围内的AlN隔离层并不会对材料的表面形貌产生重大的影响。HRXRD测试结果表明,AlGaN/AlN/GaN具有好的异质结界面。     

Fabrication and characterization of the normally-off N-channel lateral 4H–SiC metal–oxide–semiconductor field-effect transistors

In this paper, the normally-off N-channel lateral 4H–Si C metal–oxide–semiconductor field-effect transistors(MOSFFETs) have been fabricated and characterized. A sandwich-(nitridation–oxidation–nitridation) type process was used to grow the gate dielectric film to obtain high channel mobility. The interface properties of 4H–Si C/SiO_2 were examined by the measurement of HF I–V, G–V, and C–V over a range of frequencies. The ideal C–V curve with little hysteresis and the frequency dispersion were observed. As a result, the interface state density near the conduction band edge of 4H–Si C was reduced to 2 × 10~(11) e V~(-1)·cm~(-2), the breakdown field of the grown oxides was about 9.8 MV/cm, the median peak fieldeffect mobility is about 32.5 cm~2·V~(-1)·s~(-1), and the maximum peak field-effect mobility of 38 cm~2·V~(-1)·s~(-1) was achieved in fabricated lateral 4H–Si C MOSFFETs.     

AlN插入层对AlxGa1-xN/GaN界面电子散射的影响

本文研究AlN作为Al_xGa_1-xN/GaN插入层引起的电子输运性质的变化, 考虑了Al_xGa_1-xN和AlN势垒层的自发极化、压电极化对Al_xGa_1-xN/AlN/GaN双异质结高电子迁移率晶体管(HEMT)中极化电荷面密度、二维电子气(2DEG) 浓度的影响, 分析了AlN厚度与界面粗糙度散射和合金无序散射的关系; 结果表明, 2DEG 浓度、界面粗糙度散射和合金无序散射依赖于AlN层厚度, 插入一层1–3 nm薄的AlN层, 可以明显提高电子迁移率.     

单轴压力下Ge2X2Te5(X=Sb,Bi)薄膜拓扑相变的第一性原理研究

随着拓扑绝缘体的发现, 材料拓扑物性的研究成为凝聚态物理研究的热点领域. 本文基于第一性原理计算, 研究了化合物Ge₂X₂Te₅ (X=Sb, Bi) 的块体结构和二维单层和双层薄膜结构的拓扑物性, 以及单双层薄膜在垂直方向单轴压力下的拓扑量子相变. 研究发现, A型原子序列排列的这两种化合物都是拓扑绝缘体, 其单层薄膜都是普通金属, 而双层薄膜都是拓扑金属, 单层和双层薄膜在单轴加压过程中都没有发生拓扑量子相变; 这两种化合物的B型原子序列的晶体是普通绝缘体, 其所对应的薄膜, Ge₂Sb₂Te₅单层是普通金属, 双层薄膜和Ge₂Bi₂Te₅的单层和双层薄膜均为普通绝缘体, 但是在单轴加压过程中B 型原子序列所对应的单层和双层薄膜都转变为拓扑金属.     

硅掺杂氧化锡柔性薄膜晶体管的制备与特性

研究了柔性非晶硅掺杂氧化锡（SiSnO,STO）薄膜晶体管的电学特性及其在弯曲状态下的电学特性。通过射频磁控溅射在聚酰亚胺（Polyimide,PI）衬底上制备出了柔性非晶硅掺杂氧化锡薄膜晶体管。通过对比不同退火温度的器件性能,发现在300℃能获得最佳器件性能,其饱和迁移率达到2.71 cm²·V^-1·s^-1,开关比高于10⁶,亚阈值摆幅为1.95 V·dec^-1,阈值电压为2.42 V。对器件在不同曲率半径（5,10,20,30 mm）状态下进行输出特性和转移特性测试,发现其在弯曲状态下仍具有良好的电学性能。     

Tunable topological quantum states in three- and two-dimensional materials

We review our theoretical advances in tunable topological quantum states in three- and twodimensional materials with strong spin–orbital couplings. In three-dimensional systems, we propose a new tunable topological insulator, bismuth-based skutterudites in which topological insulating states can be induced by external strains. The orbitals involved in the topological band-inversion process are the d- and p-orbitals, unlike typical topological insulators such as Bi₂Se₃and BiTeI, where only the p-orbitals are involved in the band-inversion process. Owing to the presence of large d-electronic states, the electronic interaction in our proposed topological insulator is much stronger than that in other conventional topological insulators. In two-dimensional systems, we investigated 3d-transition-metal-doped silicene. Using both an analytical model and first-principles Wannier interpolation, we demonstrate that silicene decorated with certain 3d transition metals such as vanadium can sustain a stable quantum anomalous Hall effect. We also predict that the quantum valley Hall effect and electrically tunable topological states could be realized in certain transition-metal-doped silicenes where the energy band inversion occurs. These findings provide realistic materials in which topological states could be arbitrarily controlled.     

铟锡氧化物薄膜表面等离子体损耗降低的研究

本文采用直流磁控溅射方法在普通浮法玻璃基底上制备了立方多晶铁锰矿结构的铟锡氧化物(indium tin oxide, ITO)薄膜,并对其进行了结晶性、表面粗糙度、紫外-可见吸收光谱、折射率、介电常数及霍尔效应的测试.研究了溅射时基底温度的改变对于ITO薄膜的光电、表面等离子体性质的影响.随着基底温度由100?C升高至500?C,其光学带隙(3.64—3.97eV)展宽,减少了电子带间跃迁的概率,有效降低了ITO薄膜的光学损耗.与此同时,对应ITO薄膜的载流子浓度(4.1×10~(20)-—2.48×10~(21)cm~(-3))与迁移率(24.6—32.2 cm~2·V~(-1)·s~(-1))得到提高,电学损耗明显降低.