基于三组分共轭聚合物的高灵敏度有机晶体管二氧化氮传感器

研究了基于联噻吩-氮杂异靛蓝-双(2-氧代二氢-7-氮杂吲哚-3-亚基)苯并二呋喃二酮的三组分给体-受体共轭聚合物(BTNIDNBIBDF-50)薄膜对二氧化氮气体传感特性。通过控制半导体浓度调控半导体薄膜表面形貌,研究其对二氧化氮气体灵敏度的影响。聚合物半导体BTNIDNBIBDF-50的浓度为2 mg/m L时对NO₂气体表现出最优的传感性能,对体积分数为10×10^-6NO₂气体的灵敏度为121.44%。实验结果表明：三组分共轭聚合物BTNIDNBIBDF-50呈现双极型半导体特性,降低聚合物半导体浓度会使薄膜表面出现明显的孔洞结构,提高传感器对NO₂气体的灵敏度。但过多的孔洞又会使气体解吸附速率的变化大于吸附速率变化,导致传感器灵敏度降低。     

氟取代聚苯基噻吩系列衍生物的合成及应用

介绍了用于超级电容器电极材料的氟取代聚苯基噻吩系列聚合物,包括聚3-(4-氟苯基)噻吩(P-4-FPT)、聚3-(3-氟苯基)噻吩(P-3-FPT)、聚3-(3,4-二氟苯基)噻吩(P-3,4-DFPT)、聚3-(3,5-二氟苯基)噻吩(P-3,5-DFPT)、聚3-(3,4,5-三氟苯基)噻吩(P-3,4,5-TFPT)等的单体及其聚合物的合成方法及研究进展,并对该类聚合物电极材料的电化学性能进行了比较。     

溶液法制备环保型高分子聚合物薄膜晶体管

基于一种新型的稠合噻吩-吡咯并吡咯二酮聚合物半导体(PTDPPTFT4),采用溶液法工艺制作了高性能环保型、空穴型有机薄膜晶体管。通过尝试不同的半导体层退火温度及退火时间,优化了有机薄膜晶体管的性能。当采用对二甲苯溶剂,退火温度为190℃,退火时间为60min时,迁移率为2.1cm2·V-1·s-1,电流开关比大于106。通过X射线掠入射角衍射法测试,得到高温退火后聚合物薄膜的结构特点,进而揭示了退火条件改变后,薄膜晶体管拥有高迁移率的原因。     

III型聚合物超电容器国外研究进展

评述了国外在III型聚合物超电容器方面的研究进展。目前,国外一些主要研究单位已经进展到研制模型电容器的阶段。III型聚合物超电容器所用的导电高分子主要包括聚噻吩衍生物类,如:聚-3-(4-氟苯基)噻吩、聚二噻吩[3,4-b;3,4-d]噻吩,聚苯胺类等。在用这些聚合物所组装的超电容器中,能量密度最大可达68 Wh/kg,功率密度最大可达30.5?03 W/kg。     

主、侧链修饰对异靛蓝基共轭聚合物结构及电学性能的影响

研究了基于异靛蓝及其衍生物的给-受体共轭聚合物主、侧链修饰对电学性能的影响。采用掠入射X射线衍射、原子力显微镜和4200半导体参数测试仪对聚合物结构与形貌以及电学性能进行了表征。实验结果表明,烷基侧链的加入会增大空间位阻,使得分子堆积从较为有序的edge-on结构变得混乱无序,导致结晶性和电学性能的下降。平均空穴迁移率从0.05cm~2·V~(-1)·s~(-1)下降至2.11×10~(-3) cm~2·V~(-1)·s~(-1)。但当主链用苯并二呋喃二酮(BIBDF)这一强吸电子的长共轭单元替代异靛蓝单元之后,由于主链平面性的提高,引起分子堆积变好,结晶性和电学性能显著提高,并不影响溶液加工性且该聚合物显示出良好的双极型传输特性。空气中电子与空穴平均迁移率可以达到0.29cm2·V~(-1)·s~(-1)和0.49cm2·V~(-1)·s~(-1)。     

硅纳米管结构和电子性质的第一性原理研究

基于密度泛函理论的第一性原理方法,在广义梯度近似下,研究了(5,0)和(5,5)硅纳米管结构和电子性质。计算结果表明:(5,0)管硅原子相邻键长波动范围为0.068 nm,大于(5,5)管的0.006 nm;通过对(5,0)管的分波态密度进行分析发现,其3s电子和2p电子能量分布在-13～3 eV,但2p电子集中分布在能量较高的-6～3 eV,出现了明显的sp3轨道杂化。同时对(5,0)和(5,5)硅纳米管最高占据轨道和最低未占据轨道的能隙进行了分析,发现两种管导电性能与结构的手性相关,锯齿型(5,0)管能带交叠具有明显的金属性,而扶手型(5,5)管能隙为0.151 eV是半导体纳米管。     

基于异靛蓝的供体-受体型共聚物忆阻器的构建及性能

由于供体-受体型聚合物具有较强的诱捕和释放电荷的能力,在忆阻器的研究方面具有很大的潜力。利用异靛蓝、丙烯二氧噻吩和噻吩合成了低带隙的供体-受体半导体聚合物(IPDT)(异靛蓝/噻吩/丙烯二氧噻吩的摩尔比率为x/1/1-x),构建了有机电子器件Al/IPDT/ITO,发现器件具有较稳定的忆阻特性。x=0.5时器件的开、关电压分别为8和-7.5 V,高低电阻比达到102,室温下的忍耐力循环测量超过2 000次。x=0.25时器件的开、关电压分别减小为2.2/-1.6 V,最大电流下降了5个量级。x=0.2时器件的开、关电压分别为1.9和-1.1 V,高低电阻比提高到103,最大电流仍为纳安量级。结果表明供体单元的占比越高,器件的开关电压越低,且较低的电流更有利于降低功耗。发现器件的忆阻特性是由聚合物材料内部电子通道的形成与断裂引起的。     

有机/无机复合体异质结太阳电池

利用简单的低温工艺制备了纳米晶纤锌矿结构的ZnO,用高分辨透射电镜(HRTEM)、X射线衍射(XRD)和光致发光(PL)技术进行了表征.利用纳米晶ZnO和共轭聚合物2-甲氧基-5-(3,7.二甲基辛氧基)对苯撑乙烯(MDMO-PPV)制备了结构为ITO/PEDOT:PSS/ZnO:MDMO-PPV/Al的有机/无机复合体异质结太阳电池,作为对比,同时制备了ITO/PEDOT:PSS/MDMO-PPV/Al结构的纯有机聚合物电池.实验结果表明,添加纳米晶ZnO使其能量转换效率提高了约550倍.PL谱测试结果表明这是由于有高电子亲合能的ZnO提高了电子空穴对分离的能力.另外,光伏性能的提高可能也与ZnO引起的电子传输能力的提高有关.此外,本文分析了ZnO:MDMOPPV体异质结电池性能低于传统电池的原因,并提出了进一步提高其性能的方法.     

有机/无机复合体异质结太阳电池

利用简单的低温工艺制备了纳米晶纤锌矿结构的ZnO,用高分辨透射电镜(HRTEM)、X射线衍射(XRD)和光致发光(PL)技术进行了表征.利用纳米晶ZnO和共轭聚合物2-甲氧基-5-(3,7.二甲基辛氧基)对苯撑乙烯(MDMO-PPV)制备了结构为ITO/PEDOT:PSS/ZnO:MDMO-PPV/Al的有机/无机复合体异质结太阳电池,作为对比,同时制备了ITO/PEDOT:PSS/MDMO-PPV/Al结构的纯有机聚合物电池.实验结果表明,添加纳米晶ZnO使其能量转换效率提高了约550倍.PL谱测试结果表明这是由于有高电子亲合能的ZnO提高了电子空穴对分离的能力.另外,光伏性能的提高可能也与ZnO引起的电子传输能力的提高有关.此外,本文分析了ZnO:MDMOPPV体异质结电池性能低于传统电池的原因,并提出了进一步提高其性能的方法.     

波长可调谐聚合膜/无机膜异质结电致发光

针对聚合物电致发光材料缺乏可用的电子型聚合物半导体材料的现状 ,采用无机电子型半导体材料 Zn O∶Zn与空穴型聚合物材料 PDDOPV [poly (2 ,5 - bis (dodecyloxy) - phenylenevinylene) ]成功制备了结构为 ITO/PDDOPV/Zn O∶ Zn/Al的异质结双层器件 .异质结器件的发光效率与亮度较单层器件提高 1个数量级以上 .该异质结器件的发光颜色是随着电压的增加而蓝移的 ,其光致发光光谱也随着激发波长的改变而改变 ,可能形成了新的发光基团 .     

Ta2O5/silicon barrier height measured fromMOSFETs fabricated with Ta2O5 gate dielectric

N-channel metal oxide semiconductor field effect transistors with Ta₂O₅ gate dielectric were fabricated. The Ta₂O₅/silicon barrier height was calculated using both the lucky electron model and the thermionic emission model. Based on the lucky electron model, a barrier height of 0.77 eV was extracted from the slope of the ln(I_g/I_d) versus ln(I_sub/I_d) plot using an impact ionization energy of 1.3 eV. Due to the low barrier height, the application of Ta₂ O₅ gate dielectric transistors is limited to low supply voltage preferably less than 2.0 V     

Fabrication and characterization of metal-oxide-semiconductorfield-effect transistors and gated diodes using Ta2O5 gate oxide

N-channel metal oxide semiconductor field effect transistors (MOSFETs) using Ta₂O₅, gate oxide were fabricated. The Ta₂O₅ films were deposited by plasma enhanced chemical vapor deposition. The I_DS-V_DS and I_DS-V_GS characteristics mere measured. The electron mobility was 333 cm²/V·s. The subthreshold swing was 73 mV/dec. The interface trapped charge density, the surface recombination velocity, and the minority carrier lifetime in the field-induced depletion region measured from gated diodes were 9.5×10¹² cm^-2 eV^-1, 780 cm/s and 3×10^-6 sec, respectively. A comparison with conventional MOSFETs using SiO₂ gate oxide was made     

Hot electron energy relaxation via acoustic phonon emission in GaAs/Al0.24Ga0.76As single and multiple quantum wells

The energy relaxation associated with acoustic phonons has been investigated in a series of modulation doped GaAs/AlGaAs single and multiple quantum wells grown by molecular beam epitaxy, using the hot electron Shubnikov — de Haas effect. The power loss is shown to be proportional to (T_e² − T_L²) for electron temperatures 2.2K < T_e < 8K and proportional to (T_e³ − T_L³) for 8K < T_e < 20K. The energy loss rates due to acoustic phonon scattering via both deformation potential coupling and piezoelectric coupling have been calculated. The total energy loss rate as a function of electron temperature is compared with the experimental results. Good agreement is obtained for 2.2K < T_e < 8K. Above 8K the energy loss rate is seen to rise above the predicted values, indicating the onset of an extra energy relaxation mechanism. The application of a high electric field (E = 3kV/cm) at low lattice temperatures is shown to induce persistent parallel conduction and a subsequent reduction of the low field well mobility.     

Hot phonons and Auger related carrier heating in semiconductoroptical amplifiers

We have directly measured the carrier temperature in semiconductor optical amplifiers (SOAs) via spontaneous emission and we demonstrate an unexpectedly high carrier temperature. The direct correlation of the temperature increase with the carrier density suggests Auger recombination as the main heating mechanism. We have developed a model based on rate equations for the total energy density of electrons, holes, and longitudinal-optical phonons. This model allows us to explain the thermal behavior of carrier and phonon populations. The strong heating observed is shown to be due to the combined effects of hot phonon and Auger recombination in the valence band. We also observe an evolution of the Auger process, as the density is increased, from cubic to square dependence with coefficients C₃ = 0.9 10^-28 cm⁶ s^-1 and C₂ = 2.4 10^-10 cm³ s^-1. This change is explained by the hole quasi-Fermi level entering the valence band     

A study of noise in surface and buried channel SiGe MOSFETs with gate oxide grown by low temperature plasma anodization

A study is made of noise in p- and n-channel transistors incorporating SiGe surface and buried channels, over the frequency range f=1 Hz–100 kHz. The gate oxide is grown by low temperature plasma oxidation. Surface n-channel devices are found to exhibit two noise components namely 1/f and generation–recombination (GR) noise. It is shown that the 1/f noise component is due to fluctuations of charge in slow oxide traps whilst bulk centers located in a thin layer of the semiconductor close to the channel, give rise to the GR noise component. The analysis of the noise data gives values for the density D_ot of the oxide traps in the SiGe and Si nMOSFETs of the order 1.8×10¹² and 2.5×10¹⁰ cm⁻² (eV)⁻¹, respectively. The density D_GR of the bulk GR centres is equal to 3×10¹⁰ cm⁻² in both the SiGe and Si devices. The electron and hole capture cross-sections for these centres as well as their energy level and their depth below the oxide/semiconductor interface are also the same in the devices of both types. This suggests that those GR centers are of the same nature in all devices studied. p-Channel devices show different behaviour with only a 1/f noise component apparent in the data over the same frequency range. Buried SiGe channel and Si control devices exhibit quite low and similar slow state densities of the order low to mid 10¹⁰ cm⁻² (eV)⁻¹ whereas surface p-channel devices show even higher slow state densities than n-channel counterparts. The Hooge noise characterized by the Hooge coefficient _H=2×10⁻⁵ is also detected in some buried p-channel SiGe devices.     

Interface characteristics of Ge3N4-(n-type) GaAs MIS devices

Passivation of GaAs surfaces was achieved by the deposition of Ge₃N₄ dielectric films at low temperatures. Electrical characteristics of MIS devices were measured to determine the interface parameters. From C-V-f and G-V-f measurements, density of interface states has been obtained as (4–6)×10¹¹ cm⁻² eV⁻¹ at the semiconductor mid-gap. Some inversion charge buildup was seen in the C-V plot although the strong inversion regime is absent. Thermally stimulated current measurements indicate a trap density of 5×10¹⁸−10¹⁹ cm⁻³ in the dielectric film, with their energy level at 0.59 eV.     

Low Dit, thermodynamically stable Ga2O3-GaAs interfaces: fabrication, characterization, and modeling

Thermodynamically stable, low D_it amorphous Ga₂ O₃-(100) GaAs interfaces have been fabricated by extending molecular beam epitaxy (MBE) related techniques. We have investigated both in situ and ex situ Ga₂O₃ deposition schemes utilizing molecular beams of gallium oxide. The in situ technique employs Ga₂O₃ deposition on freshly grown, atomically ordered (100) GaAs epitaxial films in ultrahigh vacuum (UHV); the ex situ approach is based on thermal desorption of native GaAs oxides in UHV prior to Ga₂O₃ deposition. Unique electronic interface properties have been demonstrated for in situ fabricated Ga₂O₃-GaAs interfaces including a midgap interface state density D_it in the low 10¹⁰ cm^-2 eV^-1 range and an interface recombination velocity S of 4000 cm/s. The existence of strong inversion in both n- and p-type GaAs has been clearly established. We will also discuss the excellent thermodynamic and photochemical interface stability. Ex situ fabricated Ga₂O₃-GaAs interfaces are inferior but still of a high quality with S=9000 cm/s and a corresponding D_it in the upper 10¹⁰ cm^-2 eV^-1 range. We also developed a new numerical heterostructure model for the evaluation of capacitance-voltage (C-V), conductance-voltage (G-V), and photoluminescence (PL) data. The model involves selfconsistent interface analysis of electrical and optoelectronic measurement data and is tailored to the specifics of GaAs such as band-to-band luminescence and long minority carrier response time τ_R. We will further discuss equivalent circuits in strong inversion considering minority carrier generation using low-intensity light illumination     

Experimental evidence of surface conduction contributing totransconductance dispersion in GaAs MESFETs

Low-frequency transconductance dispersion in GaAs metal semiconductor field effect transistors (MESFET's) is commonly attributed to the presence of a high density of surface states under the passivated source-gate and gate-drain separation regions. In this paper, we have found that they also contribute to a temperature dependent surface reverse leakage current with a thermal activation energy of 0.43 eV and a surface electron concentration (2.5×10¹² cm² ). Conductance deep-level transient spectroscopy (DLTS) spectra of these MESFETs have shown apparent “hole-like” peaks with emission energy of 0.48 eV and capture activation energy of 0.05 eV. These data were used for a model-based simulation and the results were compared with those obtained from experimental transconductance versus temperature measurements performed at various frequencies. A close agreement between these provides conclusive proof that the surface conduction at the GaAs-passivant interface is the major cause of the low-frequency transconductance dispersion observed. Finally, a possible explanation for the characteristic activation energy of 0.43 eV for Si ₃N₄ passivant film on GaAs has been presented     

The coordinated tunning optical,electrical and thermal properties of spiro-configured phenyl acridophopsphine oxide and sulfide for host materials

Two spiro-configured phenyl acridophopsphine-based oxide and sulfide host materials, named 5-phenyl-5H-spiro[acridophosphine- 10,9′-fluorene]-5-oxide (PSAFO) and 5-phenyl-5H-spiro [acridopho-sphine-10,9′-fluorene]5-sulfide (PSAFS), were synthesized by convenient method. The lowest unoccupied molecular orbital (LUMO) energy level and electron mobility could be decreased and improved as the S-atom replaced O-atom, respectively. Then, the electron injecting/transporting ability of PSAFS is expected to be enhanced. Moreover, the S-atom would provide PSAFS with better electron-donating capability and heavier molecular weight compared with that of PSAFO. Thus, a higher HOMO (the highest occupied molecular orbital) energy level and thermal stability can be achieved due to the shallower onset of oxidation potential and increased molecular weight. Consequently, a narrower energy gap between HOMO and LUMO of PSAFS would be obtained, and its thermal stability could be improved, which is beneficial to constructing high performance device. Although the frontier molecular orbitals and thermal stability were finely controlled by molecular modification, the high triplet (T₁) energy level was still retained due to the limited π-conjugation. With the high T₁, HOMO and LUMO energy levels of 2.83/2.82, −6.19/-5.66 and −2.12/-2.19 eV, PSAFO and PSAFS based blue TADF OLEDs with low driving voltages of 2.9/3.1 V and maximum EQEs of 12.4/13.8% are successfully realized.     

Subnanosecond multi-gigawatt CO2 laser

A semiconductor switching technique has been utilized to produce 30-300 ps variable duration CO₂ laser pulses of 0.5-MW peak power. Eight passes through a 1.2-m long, UV-preionized, 3-atm TE CO₂ amplifier raise the output laser peak power to the 10¹⁰ W level. Sampling the amplifier gain in linear and saturated regimes using CO₂ laser radiation ranging from CW to 30 ps pulse length permits comparison with computer modeling of picosecond CO₂ pulse amplification. The potential for further peak power scaling of picosecond molecular lasers is discussed