ZnO薄膜紫外光敏特性及晶界势垒的研究

以二水合醋酸锌为原料,采用sol-gel法在石英衬底上制备了ZnO薄膜。用AFM观察表面形貌,通过测量真空条件下不同温度热处理后薄膜的I-V特性,拟合计算晶界势垒高度。研究了热处理温度对ZnO薄膜性能的影响。结果表明:经650℃热处理制备的ZnO薄膜样品具有较佳性能,结构均匀致密,粒径分布为20～32nm。在10V偏压和1.24×10–3W/cm2光强下,紫外光灵敏度为43.95;无光照条件下晶界势垒高度为0.079eV。紫外光照使晶界势垒高度下降为0.011eV,薄膜的紫外光灵敏度与势垒高度的相对变化密切相关。     

用于GaAs数字IC的难熔栅自对准技术研究

本文用直流磁控溅射方法在离子注入n型GaAs衬底上制备了WSi_xN_y难熔金属膜,研究了它的热稳定性、界面和势垒特性.同时对WSi_(0.6),W,WN等难熔栅金属膜也进行了研究.AES和SIMS分析表明,WSiN/GaAs的界面通过1000℃,10秒钟快速退火(RTA)或850℃,20分钟常规炉退火处理仍保持稳定,势垒高度达到0.8V,理想因子n=1.1.制作了WSiN栅自对准(SAG)增强和耗尽型MESFET.其跨导分别为154mS/mm和250mS/mm.用这一工艺制作的运放差分输入电路从直流到1千兆赫增益达29.5dB.     

Ultraviolet ZnO Photodetectors with High Gain

Fabrication and characterization of metal-semiconductor-metal ultraviolet(MSM UV) photodetector based on ZnO ultra thin(nano scale) films with Pd Schottky contact are reported.The ZnO thin film was grown on glass substrate by thermal oxidation of pre-deposited zinc films using vacuum deposition technique.With applied voltage in the range from -3V to 3V,the contrast ratio,responsivity,and detectivity for an incident radiation of 0.1 mW at 365 nm wavelength were estimated.The proposed device exhibited a high ...     

Effect of annealing atmosphere on the electrical properties of nickel oxide/zinc oxide p–n junction grown by sol–gel technique

Zinc oxide (ZnO) and nickel oxide (NiO) thin films were prepared on glass substrates by a sol–gel method. Spin coating was used to fabricate a p-NiO/n-ZnO junction. The influence of the post annealing atmosphere (air or nitrogen) on the microstructure and surface morphology of NiO and ZnO thin films and the p-NiO/n-ZnO junction are examined. The structural properties are characterized by X-ray diffraction (XRD) and the surface morphology of the thin films and the p–n junction are investigated by atomic force microscopy (AFM). Optical properties are investigated by UV–visible spectroscopy and the electrical properties, such as I–V photocurrent, are characterized by a voltage source meter instrument. XRD patterns show that the films are polycrystalline with preferred orientation in the (002) direction for the ZnO films and the (200) direction for the NiO films. The AFM results indicate that the morphology of the ZnO and NiO films and the p-NiO/n-ZnO junction are mainly influenced by the annealing atmosphere. All films have a high optical transmittance of about 80% in the visible region and a sharp absorption edge. The optical band gaps of the two materials change with the annealing atmosphere (air or nitrogen). The p-NiO/n-ZnO heterojunction device has an average transmittance of over 80% in the visible region, which lies between the transmittance of the ZnO and NiO films separately. The ideality factor, barrier height, and series resistance of the heterojunction treated in different annealing atmospheres are determined by using conventional forward bias I–V characteristics and also Norde׳s and Cheung׳s methods.     

退火温度对Au/Ti/4H-SiC肖特基接触特性的影响

采用电子束蒸发法在4H-SiC表面制备了Ti/Au肖特基电极,研究了退火温度对Au/Ti/4H-SiC肖特基接触电学特性的影响.对比分析了不同退火温度下样品的电流密度-电压(J-V)和电容-电压(C-V)特性曲线,实验结果表明退火温度为500℃时Au/Ti/4H-SiC肖特基势垒高度最大,在.J-V测试和C-V测试中分别达到0.933 eV和1.447 eV,且获得理想因子最小值为1.053,反向泄漏电流密度也实现了最小值1.97×10-8 A/cm2,击穿电压达到最大值660 V.对退火温度为500℃的Au/Ti/4H-SiC样品进行J-V变温测试.测试结果表明,随着测试温度的升高,肖特基势垒高度不断升高而理想因子不断减小,说明肖特基接触界面仍然存在缺陷或者横向不均匀性,高温下的测试进一步证明肖特基接触界面还有很大的改善空间.     

退火对Pt/TiO2肖特基二极管结构及电学性能的影响

以硅为衬底,采用射频磁控溅射技术制备了TiO2薄膜,利用扫描电子显微镜及拉曼光谱对退火前后的TiO2进行表征与结构分析.结果表明,退火后的TiO2具有良好的结晶特性,且呈锐钛矿结构.在此薄膜工艺条件下,以TiO2为半导体层在玻璃基底上制备了Al/TiO2/Pt肖特基二极管,并在153～433 K温度范围内对其进行了I-V测试,得到以下结果:在整个温度范围内,A1/TiO2/Pt肖特基二极管均表现出良好的整流特性;其理想因子随温度升高而降低,势垒高度随温度升高而升高;在433 K下,理想因子为1.31,势垒高度为0.73,表明此肖特基二极管已接近理想的肖特基二极管.     

Al-N共掺杂ZnO:Mn稀磁半导体薄膜的结构与性能

采用反应磁控溅射法在室温下沉积前驱体氮化物,在大气环境、500℃下氧化退火30min后获得了Al-N共掺杂ZnO:Mn薄膜。研究了直流与射频反应磁控溅射对氧化退火薄膜结构和性能的影响。结果表明:两种工艺制备的退火薄膜均具有ZnO纤锌矿结构,且均为n型导电。射频溅射退火样品具有很好的c-轴择优取向,其表面光滑平整,表面粗糙度RMS值为1.2nm,且具有室温铁磁性,饱和磁化强度(Ms)和矫顽力(Hc)分别为46.8A·m–1和4.9×103A·m–1;而直流溅射退火样品表面凹凸不平,RMS值为25.8nm,室温下是反铁磁性的。     

GaAs surface plasma treatments for Schottky contacts

The properties of different rectifying metallizations (Al, Ti/Pt, WN_x) on GaAs have been investigated for various surface preparation procedures. In particular, in situ hydrogen plasma treatments were used to remove residual surface contamination (mainly O and C) and a nitrogen plasma to grow a thin mixed nitride layer. Al and Ti/Pt Schottky diodes with an ideality factor very close to 1, but with reduced barrier height, were found after the H₂ plasma as a consequence of H diffusion into GaAs. The Schottky barrier height was further reduced if a H₂ + N₂ plasma was performed. The N content in the sputtering environment during the WN_x deposition affects the diode properties of plasma-treated WN_x contacts. By increasing the N₂ partial pressure, the diode barrier height is reduced, probably due to nitridization of the GaAs surface. Such differences disappear after annealing the diodes in arsine overpressure at 800°C. WN_x contacts deposited under different conditions on H₂ plasma treated substrates also show a similar Schottky barrier height after such annealing.     

Electrical characteristics of Pd Schottky contacts on ZnO films

The electrical characteristics of Pd Schottky contacts on ZnO films have been investigated by current-voltage (I–V) and capacitance–voltage (C–V) measurements at different temperatures. ZnO films of two thicknesses (400 nm and 1000 nm) were grown by DC-magnetron sputtering on n-Si substrates. The basic structural, optical and electrical properties of these films are also reported. We compared the two Schottky diodes by means of characteristic parameters, such as rectification ratio, ideality factor (η), barrier height (Φ_b) and series resistance and obtained better results for the 1000 nm-ZnO Schottky diodes. We also discussed the dependence of I‐V characteristics on temperature and the two distinct linear regions observed at low temperatures are attributed to the existence of two different inhomogeneous barrier heights. From I–V plots in a log-log scale we found that the dominant current-transport mechanism at large forward bias is space-charge limited current (SCLC) controlled by the presence of traps within the ZnO bandgap. The existence of such traps (deep states or interface states) is demonstrated by frequency-dependent capacitance and deep-level transient spectroscopy (DLTS) measurements.     

用弹道电子发射显微术研究超薄金属硅化物/硅肖特基接触

采用弹道电子发射显微术 ( BEEM)技术对超薄 Pt Si/Si、Co Si2 /Si肖特基接触特性进行了研究 ,并与电流 -电压 ( I- V)及电容 -电压 ( C- V)测试结果进行了对比 .研究了 Ar离子轰击对超薄Pt Si/n- Si肖特基接触特性的影响 .BEEM、I- V/C- V技术对多种样品的研究结果表明 ,I- V/C- V测试会由于超薄硅化物层串联电阻的影响而使测试结果产生严重误差 ;BEEM测试则不受影响 .随着离子轰击能量增大 ,肖特基势垒高度降低 ,且其不均匀性也越大 .用 BEEM和变温 I- V对超薄 Co Si2 /n- Si肖特基二极管的研究结果表明 ,变温 I- V测试可在一定程度上获得肖特基势垒     

ZnO薄膜的结构与光学性能研究

采用sol-gel法在石英衬底上制备了ZnO薄膜,通过改变溶胶浓度、涂敷层数及退火温度,研究了ZnO薄膜的形貌、结构性能及光学性能。结果表明,薄膜具有六方纤锌矿结构,表面均匀致密,晶粒大小在25～35nm之间,Zn含量为0.8mol/L的溶胶经旋涂并在500℃下退火1h后可获得最高的可见光透射率,平均透射率约为94%。获得的ZnO薄膜的光学带隙在3.27～3.29eV之间。     

Gate formation in GaAs MESFET's using ion-beam etching technology

The use of ion-beam etching for the controllable formation of very thin active channel layers in GaAs MESFET's is investigated and compared with chemical and plasma etching techniques. The Schottky gate diodes associated with ion-beam etched surfaces show significant surface damage, a substantial part of which can be removed by annealing. Typical annealed diodes exhibit a barrier height of 0.53 eV and an ideality factor of 1.22. A modified Schottky theory is presented which includes the effects of surface damage and a thin interfacial layer between the metal and semiconductor. This model appears to account for most of the observed behavior. Capacitance-voltage-and current-voltage characteristics are presented for both large-area diodes on ion-beam etched surfaces and for MESFET's with gate lengths of 3 and 0.15 µm.     

退火温度对ZnO掺杂ITO薄膜性能的影响

利用电子束蒸镀方法,在K8玻璃衬底上沉积ZnO掺杂ITO(ZnO-ITO)与ITO薄膜。研究不同退火温度对ZnO-ITO薄膜的微观结构的影响;对比分析了在不同退火温度条件下,ZnO-ITO和无掺杂ITO薄膜的光电性能。结果发现,ZnO-ITO薄膜具有较大的晶粒尺寸,随着退火温度的上升,晶体结构得到改善,表面粗糙度减小,薄膜的光电性能显著提高。ZnO-ITO薄膜经过500℃退火后得到最佳的综合性能,其表面均方根粗糙度(RMS)为32.52nm,电阻率为1.43×10-4Ω.cm;对442nm波长的光,透射率可达98.37%;与ITO薄膜相比,ZnO-ITO薄膜具有显著的抗PEDOT:PSS溶液腐蚀的能力。     

Ultraviolet photodetectors based on low temperature processed ZnO/PEDOT:PSS Schottky barrier diodes

In this work, vertical Schottky barrier diodes (SBDs) were fabricated using a thin film of ZnO (50 nm) and PEDOT:PSS deposited by RF Sputtering and micro-drop casting, respectively. ITO and Au were used as ohmic contacts to ZnO and PEDOT:PSS films, respectively. The final structure consisted on Glass/ITO/ZnO/PEDOT:PSS/Au. The SBDs performance was characterized under dark and four different wavelengths conditions. From current–voltage characteristics, under dark and ambient conditions, a diode ideality factor of 1.4; a saturation current density of 1×10⁻⁹ A/cm²; a Schottky barrier height of 0.9 eV and a rectification ratio of 5 orders of magnitude at ±1 V were obtained. A carrier density of 5×10¹⁷ cm⁻³ for the ZnO film was estimated from capacitance–voltage measurements. For their characterization as photodiodes, the SBDs were illuminated with an ultra-bright UV (~380 nm) LED. A maximum UV responsivity of 0.013 A/W was obtained. The transient response of the SBDs was also analyzed with the UV LED connected to a pulsed signal of 0.5 Hz, demonstrating rise and fall times in the order of 200 ms. With a low temperature processing (<80 °C), visible-blind and UV photon-detection characteristics, the fabricated SBDs are candidates for flexible optoelectronics devices such as optical receivers for digital signal processing and measurement of light intensity.     

Photoelectrochemical Study of Nanostructured ZnO Thin Films for Hydrogen Generation from Water Splitting

Photoelectrochemical cells based on traditional and nanostructured ZnO thin films are investigated for hydrogen generation from water splitting. The ZnO thin films are fabricated using three different deposition geometries: normal pulsed laser deposition, pulsed laser oblique‐angle deposition, and electron‐beam glancing‐angle deposition. The nanostructured films are characterized by scanning electron microscopy, X‐ray diffraction, UV‐vis spectroscopy and photoelectrochemical techniques. Normal pulsed laser deposition produces dense thin films with ca. 200 nm grain sizes, while oblique‐angle deposition produces nanoplatelets with a fishscale morphology and individual features measuring ca. 900 by 450 nm on average. In contrast, glancing‐angle deposition generates a highly porous, interconnected network of spherical nanoparticles of 15–40 nm diameter. Mott‐Schottky plots show the flat band potential of pulsed laser deposition, oblique‐angle deposition, and glancing‐angle deposition samples to be ?0.29, ?0.28 and +0.20 V, respectively. Generation of photocurrent is observed at anodic potentials and no limiting photocurrents were observed with applied potentials up to 1.3 V for all photoelectrochemical cells. The effective photon‐to‐hydrogen efficiency is found to be 0.1%, 0.2% and 0.6% for pulsed laser deposition, oblique‐angle deposition and glancing‐angle deposition samples, respectively. The photoelectrochemical properties of the three types of films are understood to be a function of porosity, crystal defect concentration, charge transport properties and space charge layer characteristics.     

Effect of annealing on the Richardson constant of Al-GaAs Schottky diodes

Effect of heat-treatment on near-ideal Al-GaAs Schottky barrier diodes has been studied. Forward current-voltage and capacitance-voltage characteristics are used to determine Richardson constant and barrier height. It is shown that due to annealing at 250°C, the Richardson constant reduces by a factor of 2–3. Also, the difference between barrier heights measured from I–V and C–V characteristics is found to increase after heat-treatment. The results are interpreted in terms of an interfacial Al_xGa_1-xAs layer which gets formed during annealing.     

Effect of annealing on electrical properties of radio-frequency-sputtered ZnO films

We report on the electrical properties of ZnO films and devices grown on different substrates by radio-frequency magnetron sputtering. The films grown on c-plane sapphire were annealed in the range 800–1,000°C. The electron concentration increased with annealing temperature reaching 1.4×10¹⁹ cm^?3 for 1,000°C. Mobility also increased, however, reaching its maximum value 64.4 cm²/V · sec for 950°C anneal. High-performance Schottky diodes were fabricated on ZnO films grown on n-type 6H-SiC by depositing Au/Ni(300/300 Å). After annealing at 900°C, the leakage current (at ?5 V reverse bias) decreased from 2.2 × 10^?7 A to ～5.0 × 10^?8 A after annealing at 900°C, the forward current increased by a factor of 2, and the ideality factor decreased from 1.5 to 1.03. The ZnO films were also grown on p-type 6H-SiC, and n-ZnO/p-SiC heterostructure diodes were fabricated. The p-n diode performance increased dramatically after annealing at 950°C. The leakage current decreased from 2.0×10^?4 A to 3.0×10^?7 A at ?10 V reverse bias, and the forward current increased slightly from 2.7 mA to 3.9 mA at 7 V forward bias; the ideality factor of the annealed diode was estimated as 2.2, while that for the as-grown sample was considerably higher.     

SBH adjustment characteristic of the dopant segregation process for NiSi/n-Si SJDs

By means of analyzing the Ⅰ-Ⅴ characteristic curve of NiSi/n-Si Schottky junction diodes(NiSi/n-Si SJDs), abstracting the effective Schottky barrier height (φB,eff) and the ideal factor of NiSi/n-Si SJDs and measuring the sheet resistance of NiSi films (RNiSi),we study the effects of different dopant segregation process parameters,including impurity implantation dose,segregation annealing temperature and segregation annealing time,on the φB,eff of NiSi/n-Si SJDs and the resistance characteristic of NiSi films.In addition,the changing rules of φB,eff and RNiSi are discussed.     

Spin-coated ZnO thin films using ZnO nano-colloid

Using ZnO nano-colloids, thin films of ZnO have been deposited and characterized. The nano-colloid has been synthesized using a top-down wet chemistry method starting from submicron ZnO particles. The steric stabilization technique is implemented using stearic acid as a capping agent to prevent agglomeration of the ZnO nanoparticles. A stable suspension is achieved, exhibiting strong optical absorbance and a band edge at 376 nm. The simple chemistry enables a uniform film on a variety of substrates using spin coating. Current-voltage (I–V) measurements of ZnO films deposited on quartz after annealing treatment show a resistivity of 1.89×10⁵ Ω · cm.     

GaN紫外探测器的Ti/Al接触的电学特性

在非故意掺杂的和掺Si的GaN薄膜上蒸镀Ti(24nm)/Al(nm)薄膜,氮气环境下400～800℃范围内进行退火。实验结果表明,在非故意掺杂的样品上,随退火温度的升高,肖特基势垒高度下降,理想因子升高,表面状况逐渐变差,600℃退火形成较低接触电阻的欧姆接触,比接触电阻率为3.03×10-4Ωcm2,而载流子浓度为5.88×1018cm-3的掺Si的样品未退火就形成欧姆接触,比接触电阻可达到4.03×10-4Ωcm2。