金刚石膜和类金刚石膜的电子能量损失谱和喇曼光谱的研究

用电子能量损失谱(EELS)研究了金刚石膜、类金刚石膜和高取向石墨的特征能量损失峰.金刚石膜的特征峰主要是5.4eV和15eV的带间跃迁,23eV和34eV的表面等离子激元和体等离子激元.类金刚石膜的特征峰主要是 4.5eV的π电子的体等离子激元,13eV的带间跃迁,22.4eV的(π+ σ)电子的体等离子激元.石墨的特征峰主要是6eV的π电子的等离子激元,13eV带间跃迁和C轴方向等离子激元,20eV的C轴方向的等离子激元和25.6eV的基面等离子激元.比较了α-C和α-C:H能量损失谱和喇曼光谱,利用hω_(p(π+σ))和hω_(p(x))峰位计算了类金刚石膜中sp~3键和sp~2键的比例.研究了不同CH_4浓度生长的金刚石膜的能量损失谱,利用hω_(p(π+σ))和hω_(p(x))峰位计算金刚石膜中类金刚石第二相内的sp~2键和sp~3键的比例,利用第二相的体等离子激元损失峰hω_(p(π+σ))与金刚石的体等离子激元损失峰hω_(p(σ))的强度比来估价第二相的多少.     

等离子平板显示中冷阴极纳米金刚石膜的制备

讨论大面积 4 cm×4 cm 纳米金刚石膜制备工艺.采用电子辅助-热丝化学气相沉积法(EA-HFCVD)在硅片上沉积纳米金刚石膜.生长过程中,预先加 6 安培偏流生长 1 小时,然后在 0.8 千帕条件下,无偏流生长 3 小时.原子力镜表征晶粒尺寸为 30 纳米.样品上任意三点采用原子力镜表征,表现出良好均匀性.采用偏振光椭圆率测量仪和分光计分别表征样品的折射率和透射率.红外波段透过率超过 50%.金刚石膜表面分别进行氢化和氧化处理.通过表征,氢化处理后膜比氧化处理后膜对应的γ值大,约为 0.45.     

生长温度对类金刚石膜结构和发光性质的影响

使用脉冲激光沉积技术制备了系列无氢类金刚石薄膜,测量了样品的Raman光谱、光吸收光谱和光致发光光谱,研究了薄膜结构和光致发光性质与制备条件的依赖关系。结果表明,这种薄膜是由少量sp2键和大量sp3键组成的非晶碳膜。薄膜的光学带隙在1.68~2.46eV,发光在可见光区呈宽带结构。生长温度能够对类金刚石薄膜的结构和发光性质产生较大影响。当生长温度从室温升高至400℃时,sp2团簇的变大使C原子的有序度增强,从而导致薄膜的光学带隙变窄,发光峰红移且半高宽变小。     

SiC基GaN上多晶金刚石散热膜生长及其影响

通过微波等离子体化学气相沉积(MPCVD)法,在SiC基GaN高电子迁移率晶体管(HEMT)异质结构材料上生长多晶金刚石散热膜,采用光学显微镜(OM)、拉曼光谱、非接触霍尔测试系统、X射线衍射(XRD)和扫描电子显微镜(SEM)对生长样品进行表征,研究了生长温度、多晶金刚石散热膜厚度对GaN HEMT异质结构材料性能的影响。测试结果表明,当多晶金刚石生长温度为625℃,散热膜厚度为20μm时,GaN材料载流子迁移率降低9.8%,载流子浓度上升5.3%,(002)衍射峰半高宽增加40%。生长温度越高,金刚石散热膜的生长速率越快。当金刚石散热膜厚度相差不大时,生长温度越高,GaN所受拉应力越大,材料电特性衰退越明显。多晶金刚石高温生长过程中,金刚石引入的应力未对GaN结构产生破坏作用,GaN材料中没有出现孔洞等缺陷。     

未掺杂GaN外延膜的结晶特性与蓝带发光关系的研究

采用卢瑟福背散射／沟道技术，X射线双晶衍射技术和光致发光技术对几个以MOCVD技术生长的蓝带发光差异明显的未掺杂GaN外延膜和GaN：Mg外延膜进行了测试。结果表明，未掺杂GaN薄膜中出现的2．9eV左右的蓝带发光与薄膜的结晶品质密切相关。随未掺杂GaN的蓝带强度与带边强度之比增大，GaN的卢瑟福背散射／沟道谱最低产额增大，X射线双晶衍射峰半高宽增大。未掺杂GaN薄膜的蓝带发光与薄膜中的某种本征缺陷有关。研究还表明，未掺杂GaN中出现的蓝带与GaN：Mg外延膜中出现的2．9eV左右的发光峰的发光机理不同。     

Ge覆盖多孔硅结构的桔绿光发射

使用514.5nm Ar+激光检测了Ge覆盖多孔硅结构的光致发光谱(PL),观察到峰位2.25eV,半峰宽约0.1eV的一个新的桔绿发光峰.随着覆盖Ge薄膜的加厚,这个桔绿发光峰的峰位保持不变,但发光强度显著下降.实验和分析结果表明,该桔绿发光峰源于多孔硅和嵌于其孔中的Ge纳米晶粒两者界面中的Ge相关缺陷.     

PLD方法在CVD金刚石膜上生长ZnO薄膜及其特性研究

采用脉冲激光沉积(PLD)技术,在(110)和(100)织构金刚石膜上成功制备出高度c-轴取向的ZnO薄膜,然后在纯氮气氛条件下对ZnO薄膜进行退火处理.作为比较,也在(100)Si上生长的ZnO薄膜进行了相同的处理.通过测量X射线衍射(XRD)谱和光致发光(PL)谱,研究了不同衬底性质和退火对薄膜结构和发光特性的影响.实验结果表明,在(100)织构金刚石上的ZnO膜具有最好的结晶质量,其半高宽只有0.2°.退火之后近紫外发光峰明显减弱的同时,绿色发光峰得到增强.这里归结为氮气退火后氧空位的增加,这点从退火后的XPS谱中可以得到进一步的确认.     

InGaN/GaN多量子阱LED电致发光谱中双峰起源的研究

研究了MOCVD生长的具有双发射峰结构的InGaN/GaN多量子阱发光二极管(LED)的结构和发光特性.在透射电子显微镜(TEM)下可以发现量子阱的宽度不一致,电致发光谱(EL)发现了位于2.45eV的绿光发光峰和2.81eV处的蓝光发光峰.随着电流密度增加,双峰的峰位没有移动,直到注入电流密度达到2×104 mA/cm2时,绿光发光峰发生蓝移,而蓝光发光峰没有变化.单色的阴极荧光谱(CL)发现绿光发射对应的发光区包括絮状区域和发光点,而蓝光发射对应的发光区仅包含絮状区域.通过以上的结果,我们认为蓝光发射基本上源于InGaN量子阱发光,而绿光发射则起源于量子阱和量子点的发光.     

InGaN/GaN多量子阱LED电致发光谱中双峰起源的研究

研究了MOCVD生长的具有双发射峰结构的InGaN/GaN多量子阱发光二极管(LED)的结构和发光特性.在透射电子显微镜(TEM)下可以发现量子阱的宽度不一致,电致发光谱(EL)发现了位于2.45eV的绿光发光峰和2.81eV处的蓝光发光峰.随着电流密度增加,双峰的峰位没有移动,直到注入电流密度达到2×104 mA/cm2时,绿光发光峰发生蓝移,而蓝光发光峰没有变化.单色的阴极荧光谱(CL)发现绿光发射对应的发光区包括絮状区域和发光点,而蓝光发射对应的发光区仅包含絮状区域.通过以上的结果,我们认为蓝光发射基本上源于InGaN量子阱发光,而绿光发射则起源于量子阱和量子点的发光.     

HVPE生长GaN厚膜光致发光特性研究

利用吸收光谱和光致发光(PL)光谱研究了氢化物气相外延(HVPE)法生长的GaN厚膜材料发光特性。研究发现当激发脉冲光源的重复频率较低时,PL光谱中仅能观察到带边发光峰,当重复频率增加时,PL光谱中不仅出现带边发光峰,还可观察到蓝带发光峰和黄带发光峰;随着光源重复频率的增加,带边发光峰与黄带发光峰、蓝带发光峰的光强之比也随着增大。分析认为蓝带发光起源于材料中碳杂质缺陷而黄带发光可能与位错等结构缺陷有关。     

微量Co2+掺杂ZnO粉体的结构和光学性能研究

采用球磨法制备了Zn1-xCoxO(x=0,0.004,0.008)纳米粉体,分别利用XRD,PL光谱和紫外-可见吸收光谱对样品进行了表征。XRD图谱显示样品呈六方纤锌矿结构,随着Co2+离子掺杂量的增加,晶格常数和平均晶粒尺寸略有减小。在PL光谱上观察到三个发光带:370nm处的本征发光峰、468nm附近的强蓝光发光峰,以及533nm附近的绿光发光峰。和球磨样品相比,1 200℃退火的样品的发光强度明显增强,这归因于退火使样品晶粒长大。在紫外-可见吸收谱上可以观察到两个吸收带:由ZnO的带隙吸收引起的360～388nm的强紫外吸收带和由Co2+离子的d-d跃迁引起的565nm附近的可见光吸收带。因此通过调节Co2+掺杂量和选择适当的退火温度可制备高质量的发光材料。     

Comparative study of the carbon nanofilm and nanodots grown by plasma-enhanced hot filament chemical vapor deposition

Carbon nanofilm and nanodots were grown by plasma-enhanced hot filament chemical vapor deposition using methane, hydrogen and nitrogen as the reactive gases. The results of field emission scanning electron microscopy, micro-Raman spectroscopy and X-ray photoelectron spectroscopy indicate that the amorphous carbon nanofilm and nanodots are formed without and with nitrogen, respectively. The formation of carbon nanofilm and nanodots is the consequence of different sputtering-etching effects. The photoluminescence (PL) of carbon nanofilm and nanodots was studied in a SPEX 1403 Ramalog system using a 325 nm He–Cd laser as an excitation source and the PL spectra show the PL bands centered at about 411 and 513 nm for the carbon nanofilm and 405 and 504 nm for the carbon nanodots. Simultaneously, the PL results also indicate that the intensity of PL bands of carbon nanofilm is lower than that of carbon nanodots. The generation of different PL bands was interpreted by the transition mechanism. The difference in the intensity of PL bands is related to the size of carbon nanodots. The electron field emission (EFE) characteristics of carbon nanofilm and nanodots were investigated in a high-vacuum system. The results show that Fowler–Nordhelm curves are composed of two or three straight lines and the carbon nanofilm can emit a high current density, which originate from the diversification of carbon nanodots. The difference in the EFE results of carbon nanofilm and nanodots is associated to the size and number of carbon nanodots. These results can enrich our knowledge about carbon-based nanomaterials and are important to fabricate the carbon-based solid nanodevices in the field of optoelectronics.     

刻划的富硅二氧化硅／p-Si结构的光致发光和电致发光

以磁控溅射方法于p-Si上淀积富硅二氧化硅,形成富硅二氧化硅／p-Si结构,用金刚刀在其正面刻划出方形网格后在N2气氛中退火,其光致发光(PL)谱与未刻划的经同样条件退火的对比样品的PL谱有很大不同.未刻划样品的PL谱只有一个峰,位于840nm(1.48eV),而刻划样品的PL谱是双峰结构,峰位分别位于630nm(1.97eV)和840nm.800℃退火的刻划富硅二氧化硅/p-Si样品在背面蒸铝制成欧姆接触和正面蒸上半透明金电极后在正向偏压10V下的电致发光(EL)强度约为同样制备的未经刻划样品在同样测试条件下的EL强度的6倍.EL谱形状也有明显不同,表现在：未经刻划样品的EL谱可以分解为两个高斯峰,峰位分别位于1.83eV和2.23eV;而在刻划样品EL谱中1.83eV发光峰大幅度增强,还产生了一个新的能量为3.0eV的发光峰.认为刻划造成的高密度缺陷区为氧化硅提供了新的发光中心并对其中某些杂质起了吸除作用,导致PL和EL光谱改变.     

GaAs中缺陷的光致发光研究

用光致发光技术研究了未掺杂半绝缘砷化镓中的深能级缺陷,观察到一系列与其有关的光致发光.其中0.69eV发射带是源自EL2的辐射复合发光,0.77eV带是由导带至As_(Ga)施主能级的跃迁.认为1.447eV和1.32eV荧光带系分别对应于与Ga_(As)的两个电子态(38meV和203meV)有关的辐射复合.     

Characterization of undoped and silicon-doped InGaN/GaN single quantum wells

We investigated the influence of doping and InGaN layer thickness on the emission wavelength and full width at half maximum (FWHM) of InGaN/GaN single quantum wells (SQW) of thicknesses between 1 nm and 5 nm by temperature and intensity resolved photoluminescence (PL). The crystalline quality of the GaN claddings was assessed by low temperature PL. The emission energy of 5 nm Si doped SQW could be tuned from 3.24 eV to 2.98 eV by reducing the deposition temperature. An increase of piezoelectric (PE) field screening with increasing deposition temperature is attributed to an increase of the SiH₄ decomposition efficiency. Piezoelectric (PE) fields between 0.5 MV/cm and 1.2 MV/cm in undoped structures of varying SQW thicknesses were calculated. Two activation energies of 15 meV and 46 meV of the SQW emission could be observed in temperature resolved measurements. The higher value was assigned to the confined exciton binding energy, whereas the activation energy of 15 meV is probably due to a decrease in carrier supply from the absorption zone in the GaN cladding into the SQW.     

Ultralow-voltage boron-doped diamond field emitter vacuum diode

A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp² content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters     

Field- and photon-enhanced field emission from thin-film field-emission devices

Thin-film sandwich devices of CdS-SiO-metal have been made. They have current/voltage behaviour characteristics of field emission from semiconductors. With reverse bias, the current is very much smaller. The field-emission current is greatly enhanced by illuminating the device with 2.41 and 2.54eV photons (from an argon-ion laser). Under pulsed laser excitation (pulse duration 1 ?s) the enhanced emission persisted for more than 20ms. These experiments are analogous to some previous work on vacuum field emission. A possible mechanism for the enhanced emission is discussed.     

Optical and electrical characterization of thin films based on anthracene polyether polymers

Two new anthracene derivatives were characterized to improve the optoelectronic properties of π-conjugated anthracene polymers. The optical properties of the polymers were investigated by UV-visible absorption and photoluminescence (PL) spectroscopy. The energy bandgaps of anthracene-based polyether thin films were in the range 2.8–2.97 eV. Green emission (504 nm) was observed for anthracene/bisphenol A (An-BPA) and green-yellow emission (563 nm) for anthracene/fluorinated bisphenol A. (An-BPAF) Organic diodes formed by sandwiching anthracene layers between indium–tin oxide (ITO) and aluminum contacts were characterized. The dc electrical properties of ITO/anthracene derivatives/Al diodes were studied using current–voltage measurements and showed ohmic behavior at low voltage. The conduction mechanism seems to be a space-charge-limited current with exponential trap distribution at high applied bias voltage. The ac electrical transport of the anthracene derivatives was studied as a function of frequency (100 Hz–10 MHz) and applied bias in impedance spectroscopy analyses. We interpreted Cole–Cole plots in terms of the equivalent circuit model as a single parallel resistance and a capacitance network in series with a relatively small resistance. The evolution of the electrical parameters deduced from fitting of the experimental data is discussed. The conduction mechanism revealed by I–V characteristics is in agreement with the impedance spectroscopy results.     

Increase in photoluminescence of Zn-doped p-type InP after hydrogenation

The authors report on the effect of hydrogenation on the low-temperature (5.5 K) photoluminescence properties of Zn-doped p-type (p approximately 3*10/sup 18/ cm/sup -3/) InP substrates. The photoluminescence spectrum of the as-grown sample shows a Zn/sub In/ acceptor-related transition near the band-edge at 1.386 eV, a Zn-related PL band at 1.214 eV and a phosphorus vacancy V/sub P/-related PL band at 1.01 eV. After hydrogenation of the samples by exposure to hydrogen plasma, which completely passivates the Zn/sub In/ acceptors over a depth of more than 1 mu m, the deep luminescence bands (1.214 and 1.01 eV) disappeared, with a concomitant approximately 2000-fold increase in the intensity of the near-band-edge emission. Such a large increase in radiative efficiency together with the elimination of the deep luminescence bands indicates hydrogen passivation of deep nonradiative centers in addition to passivation of shallow acceptors.<>