LPE growth of crack-free PbSe layers on Si(100) using MBE-Grown PbSe/BaF2CaF2 buffer layers

Crack-free PbSe on (100)-oriented Si has been obtained by a combination of liquid phase epitaxy (LPE) and molecular beam epitaxy (MBE) techniques. MBE is employed first to grow a PbSe/BaF₂/CaF₂ buffer structure on the (100)-oriented Si. A 2.5 μm thick PbSe layer is then grown by LPE. The LPE-grown PbSe displays excellent surface morphology and is continuous over the entire 8×8 mm² area of growth. This result is surprising because of the large mismatch in thermal expansion coefficients between PbSe and Si. Previous attempts to grow crack-free PbSe by MBE alone using similar buffer structures on (100)-oriented Si have been unsuccessful. It is speculated that the large concentration of Se vacancies in the LPE-grown PbSe layer may allow dislocation climb along higher order slip planes, providing strain relaxation.     

Transmission electron microscopy study of the effect of selenium doping on the ordering of GalnP2

Selenium doped Ga_0.51In_0.49P films have been grown by metalorganic chemical vapour deposition at 600, 670 and 740° C. The extent of ordering of the Group III sublattice has been monitored by transmission electron microscopy. Ordering disappears at carrier concentrations on the order of 10¹⁸ cm⁻³ for samples grown at 600 and 740° C although a small degree of ordering persists in the samples grown at 670° C up to a carrier concentration of 10¹⁹ cm⁻³. At each growth temperature, the ordering observed decreased and the bandgap measured increased with increasing Se doping.     

Characterization of electron traps in plasma-treated AlInAs

Electron traps have been investigated for molecular beam epitaxially grown n-AlInAs by isothermal capacitance transient spectroscopy measurement. Two traps, EOl(Ec−0.44 eV) and EO2(Ec−0.52 eV), appear for oxygen-plasma treated samples in addition to El(Ec−0.47 eV) and E2(Ec−0.69 eV) traps detected for control (as-chemically etched) sample. On the other hand, the EO1 trap is not detected for Ar plasma-treated sample. This suggests that the EO1 is generated by reaction of atomic oxygen with AllnAs and that the EO2 trap is induced by plasma damage. It is found that a reduction in the densities of the four traps occurs due to annealing subsequently after oxygen plasma treatment.     

The electron trapping behavior of silicon dioxide with ion implanted aluminum

The electron trapping behavior of SiO₂ films implanted with Al has been studied by Johnson, Johnson, and Lampert¹ and they conclude that the trapping is occuring in damage sites resulting from the implantation. They used annealing temperatures up to 600C. We find that the trapping is reduced further as we increase the annealing temperature up to 1050C. We have characterized the traps and find that the predominate traps have cross sections of 1.26 × 10⁻¹⁶ and 1.4 × 10⁻¹⁷cm². The trapping is proportional to the fluence and is not a strong function of the measuring temperature. The centroid of the trapped charge is close to the centroid of the implanted Al as predicted by the LSS theory⁶.     

(NH4)2Sx-treated InP(100) surfaces studied by soft x-ray photoelectron spectroscopy

The sulfur chemical bonding state on (NH₄)₂S_x-treated InP(100) surfaces has been studied by S 1s core-level photoelectron measurements using synchrotron radiation soft x-rays. The change in the sulfur chemical bonding states caused by rinsing with water and annealing in vacuum after the (NH₄)₂S_x-treatment was observed clearly in the S 1s spectra. Four kinds of sulfur bonding states were resolved in the S 1s spectrum of the as-treated surface. Only one sulfur bonding state was detected on the surfaces with and without the water rinse after annealing, indicating that the InP surfaces were terminated by the S-In bond. The effect of rinsing the (NH_j4)₂S_x-treated InP surface is discussed by comparison with the (NH₄)₂S_x-treated GaAs surface.     

A langmuir probe investigation of electron cyclotron resonance argon-hydrogen plasmas

We report on the physical attributes of an argon-hydrogen plasma and the effects that induced changes in these attributes have on the physical and electrical characteristics of the plasma itself. Changes in the plasma conditions of these argon-hydrogen plasmas due to variations in microwave power, DC biasing, gas concentrations, and pressures were measured. We determined that increasing the hydrogen flow increases the sheath potential of the plasma, thereby increasing the arrival energy of ions at the surface of a sample placed in the plasma. Even with the decrease in plasma density from an increase in hydrogen input flow, we found the ion current is maintained in the predominately hydrogen plasma and is likely compensated by the high velocity and long mean free path of the hydrogen. We also observed that increasing total pressure also results in hydrogen ions dominating the total number of ions reaching the Langmuir probe and therefore the sample during processing. Last, a model based on the ion/electron energy ratio was developed and used to determine the relative ion concentrations of hydrogen and argon ions.     

Low temperature cleaning of Si by a H2/AsH3 plasma prior to heteroepitaxial growth of GaAs by metalorganic chemical vapor deposition (MOCVD)

A method using a H₂/AsH₃ plasma to clean the Si surface before GaAs heteroepitaxy was investigated and the dependence of the effectiveness of this treatment on arsine partial pressure was studied. Thin GaAs-on-Si films deposited on the plasma-cleaned Si were analyzed using plan-view TEM, HRXTEM and SIMS. Although not optimized, this method of Si cleaning makes heteroepitaxial deposition of GaAs possible. Some roughening of the Si surface was observed and a possible explanation is offered. Using the results of this study, thick (2.5–3.0μm) epitaxial GaAs films were then deposited and their quality was evaluated using RBS, XTEM and optical Nomarski observation. All Si surface cleaning and GaAs deposition were carried out at temperatures at or below 650°.     

基于Bphen:BCP:Cs2CO3作为电子传输层的OLED性能研究

为了进一步平衡OLED器件内部空穴和电子载流子 的注入,制备了结构为ITO/NPB(40nm)/Alq₃(45nm)/Bphen:(X%)BCP:(5%)Cs₂CO₃(15nm)/Cs₂CO₃(1.5 nm)/Al(100nm)的OLED器件,通过改变BCP 的掺杂浓度,研究了以Bphen:BCP:Cs₂CO₃作为电子传输层对OLED器件发光亮度、电流 密度和效率等性能 的影响。结果表明,采用Bphen:BCP:Cs₂CO₃作为电子传输层能提高器件的电子注入能力 ,改善器件的性能, 相比于未引入BCP的器件,采用BCP掺杂浓度为10%的Bphen:BCP:Cs₂CO₃作为电子传输层 ,可以使器件 的最大电流效率提高46%,达到3.89cd/A,且 在电压从为5V上升至10V的过程中,器件的色坐标一直为 (0.35,0.55),具有很高的稳定性。原因是由于BCP的高LUMO能级和高 HOMO能级,能够有 效阻挡空穴到达阴极,减小空穴漏电流,同时使电子的注入更容易,电子和空穴的注入更加 平衡,发光也更加稳定。     

Photoluminescent properties of ZnO thin films grown on SiO2/Si(100) by metal-organic chemical vapor deposition

We report on the photoluminescent (PL) properties of ZnO thin films grown on SiO₂/Si(100) substrates using low pressure metal-organic chemical vapor deposition. The growth temperature of the films was as low as 400°C. From the PL spectra of the films at 10–300 K, strong PL peaks due to free and bound excitons were observed. The origin of the near bandedge emission peaks was investigated measuring temperature-dependent PL spectra. In addition, the Zn O films demonstrated a stimulated emission peak at room temperature. Upon illumination with an excitation density of 1 MW/cm², a strong, sharp peak was observed at 3.181 eV.     

Applications of electron paramagnetic resonance to studies of defects in insulators and semiconductors

Electron paramagnetic resonance (EPR) which is the absorption of electromagnetic waves in the microwave frequency domain has been used for many years to study magnetic dipoles in crystals subjected to magnetic fields. These magnetic dipoles arise from electrons in the material whose intrinsic spin is exposed due to processes such as doping with transition metal ions, doping with ions whose spin is not locked up with chemical bonding and irradiation with bond breaking energy. The sensitivity of the EPR technique depends on such experimental parameters as, incident microwave power, size of the sample, quality of the microwave cavity, number of paramagnetic spins participating in the absorption, width of the EPR resonance line, temperature of the sample and relaxation time of the spin system to the lattice. The experimental spectrum is described by parameters which by the application of basic quantum mechanics can be related to properties of the wave function of the electron spin in the crystal environment such as bonding directions to neighboring ions in the crystal lattice. Some examples of this analysis will be presented to show how EPR is used in the study of defects in Si and SiO₂.     

电子束蒸发方法研究Mg2Si的薄膜及其光学带隙

Mg_2Si材料作为一种新型环境友好半导体材料,其薄膜制备方法及其光学性质的研究对其应用研发起到基础性作用.采用电子束蒸发方法在Si(111)衬底上沉积Mg膜,在氩气环境下进行热处理以制备Mg_2Si半导体薄膜.采用X射线衍射仪(XRD)、扫描电镜(SEM)、分光光度计对制备的Mg_2Si薄膜进行表征.在氩气环境、温度500℃、压强200 Pa下,研究热处理时间(时间3-7 h)对Mg_2Si薄膜形成的影响.XRD和SEM结果表明:通过电子束蒸发沉积方法在500℃、热处理时间为3~7 h能够得到Mg_2Si薄膜.热处理温度是500时,最佳热处理时间是4 h,得到致密度好的薄膜.通过对薄膜的红外透射谱测试,得到了Mg_2Si薄膜的光学带隙,其间接光学带隙值为0.9433 eV,直接光学带隙值为1.1580 eV.实验数据为Mg_2Si薄膜的研发在制备工艺和光学性质方面提供参考.     

Deterioration of insulating films on silicon wafer due to surface charging during ion implantation

Charge-up phenomena during ion implantation were studied using the wafers (1) covered with the 1 μm thick photoresist and (2) fabricated with the MOS capacitor devices. The wafers were implanted with 35 keV As⁺ at the beam currents of 1 mA to 10 mA. The surface potential was measured by a capacitive probe set in the chamber. The ion distribution was also measured by a beam profile monitor placed behind the rotating disc. Surface charging on the photoresist wafers in some cases led to the puncture of the resist layer. Probe measurement showed that the charge-up phenomena were to a large extent governed by the behavior of the secondary electrons generated at ion implantation. The wafers with the MOS devices hardly failed by the charge build-up because of the bulk conduction through the thin oxide. However, the C-V measurement indicated that the deterioration of the oxide were influenced by the beam distribution.     

Chemistry of electron doped Ln2−xCexCuO4 superconductors

The electron doped Ln_2−xCe_xCuO₄ (Ln=lanthanide) oxides have intergrowth structures consisting of superconductively active CuO₂ sheets alternating with inactive (Ln, Ce)₂O₂ fluorite layers along the c-axis. Stabilization of such intergrowth structures requires bond length matching across the intergrowth interface. The bond length matching criterion causes a monotonic decrease in the Ce solubility limit from x=0.24 to x=0.15 as the size of Ln³⁺ decreased from Ln=La_0.5Nd_0.5 to Ln=Gd. Annealing in N₂ atm of Ln_2−xCe_xCuO₄ at temperatures above 900°C creates oxygen vacancies and the number of vacancies decreases with increasing Ce content. The value of x at which a semiconductor to superconductor transition occurs in Ln_2−xCe_xCuO₄ increases with decreasing size of Ln³⁺ due to an increasing Madelung energy caused by a decreasing Cu−O bond length.     

Ballistic electron emission microscopy studies of the temperature dependence of Schottky barrier height distribution in CoSi2/n-Si(1 0 0) diodes formed by solid phase reaction

Ballistic electron emission microscopy (BEEM) and ballistic electron emission spectroscopy have been performed on polycrystalline and epitaxial CoSi₂/n-Si(1 0 0) contacts at temperatures ranging from −144°C to −20°C. The ultra-thin CoSi₂ films (10 nm) were fabricated by solid state reaction of a single layer of Co (3 nm) or a multilayer of Ti (1 nm)/Co (3 nm)/amorphous-Si(1 nm)/Ti (1 nm) with a Si substrate, respectively. The spatial distribution of barrier height over the contact area obeys a Gaussian function at each temperature. The mean barrier height increases almost linearly with decreasing temperature with a coefficient of −0.23±0.02 meV/K for polycrystalline CoSi₂/Si diodes and −0.13±0.03 meV/K for epitaxial diodes. This is approximately equal to one or one-half of the temperature coefficient of the indirect energy gap in Si, respectively. It suggests that the Fermi level is pinned to different band positions of Si. The width of the Gaussian distribution is about 30–40 meV, without clear dependence on the temperature. The results obtained from conventional current–voltage and capacitance–voltage (I–V/C–V) measurements are compared to BEEM results.     

Deep level transient spectroscopy study of electron-irradiated CuInSe<Subscript>2</Subscript> thin films

Irradiation of high-energy (2-MeV and 3-MeV) electrons on single-crystalline n-CuInSe₂ films has been investigated. From Hall-effect measurements of the film, the carrier density and mobility were decreased by increasing the electron fluence above 1×10¹⁷ cm⁻². In both as-grown and electron-irradiated CuInSe₂ films, the deep level transient spectroscopy (DLTS) peak, indicating electron trap, was found at around 180 K. However, Arrhenius plots of the observed DLTS peaks in as-grown and electron-irradiated films showed different behavior, suggesting the presence of electron traps introduced by high-energy electron irradiation.     

In-situ cleaning and passivation of oxidized Cu surfaces by alkanethiols and its application to wire bonding

The treatment of oxidized Cu surfaces using an alkanethiol as a reducing agent has been investigated. Exposure to a dilute solution of 1-decanethiol resulted in the complete removal and/or conversion of CuO and subsequent formation of a passivating thiolate film, a so-called self-assembled monolayer (SAM), on the underlying Cu/Cu₂O surface as evidenced by x-ray photoelectron spectroscopy (XPS) analysis. Morphological changes, monitored by scanning electron microscopy (SEM) and atomic force microscopy (AFM), revealed transformation of the rough, porous CuO layer into a comparatively smooth Cu/Cu₂O surface. Experiments performed on integrated circuit back-end-of-line (BEOL) die structures, comprising Cu/SiO₂ bond pads used as substrates for Cu wire bonding, demonstrate the potential application of a thiol-based in-situ cleaning-passivation procedure in microelectronics.     

Temperature dependence of Rresistivities of SnO2-based gas sensors exposed to Co,H2, and C3H8 gases

The temperature dependence of resistivities of gas sensors made of SnO₂, Pd-doped SnO₂, and ThO₂-doped SnO₂ with Pd has been investigated in air containing reducing gases such as CO, H₂, and C₃H₈. The curves for ThO₂-doped sensors were significantly influenced by the reducing gases as compared to the sensors without ThO₂. From these results, it is found that in Pd-doped SnO₂ sensors the dopant plays an important role in oxidizing the surface of SnO₂ above 170°C, and that the addition of ThO₂ to Pd-doped SnO₂ enhances the effects of Pd by removing the adsorbed hydroxyl on SnO₂. It is also apparent that the interactions between reducing gases in air and SnO₂-based sensors depend upon the oxidizing rates of the surface of SnO₂, as well as the amounts of the adsorbed hydroxyl on SnO₂.     

Epitaxial growth of Dy2O3 thin films on epitaxial Dy-germanide films on Ge(0 0 1) substrates

Ultra-thin films of Dy are grown on Ge(0 0 1) substrates by molecular beam deposition near room temperature and immediately annealed for solid phase epitaxy at higher temperatures, leading to the formation of DyGe_x films. Thin films of Dy₂O₃ are grown on the DyGe_x film on Ge(0 0 1) substrates by molecular beam epitaxy. Streaky reflection high energy electron diffraction (RHEED) patterns reveal that epitaxial DyGe_x films grow on Ge(0 0 1) substrates with flat surfaces. X-ray diffraction (XRD) spectrum suggests the growth of an orthorhombic phase of DyGe_x films with (0 0 1) orientations. After the growth of Dy₂O₃ films, there is a change in RHEED patterns to spotty features, revealing the growth of 3D crystalline islands. XRD spectrum shows the presence of a cubic phase with (1 0 0) and (1 1 1) orientations. Atomic force microscopy image shows that the surface morphology of Dy₂O₃ films is smooth with a root mean square roughness of 10 Å.     

Characterization of AlGaN/GaN structures on various substrates grown by radio frequency-plasma assisted molecular beam epitaxy

The structural properties and surface morphology of AlGaN/GaN structures grown on LiGaO₂ (LGO), sapphire, and hydride vapor phase epitaxy (HVPE)-grown GaN templates are compared. AlGaN grown on LGO substrates shows the narrowest x-ray full width at half maximum (FWHM) for both symmetric 〈00.4〉 and asymmetric 〈10.5〉 reflections. Atomic force microscopy (AFM) analysis on AlGaN surfaces on LGO substrates also show the smoothest morphology as determined by grain size and rms roughness. The small lattice mismatch of LGO to nitrides and easily achievable Ga-polarity of the grown films are the primary reasons for the smoother surface of AlGaN/GaN structure on this alternative substrate. Optimizations of growth conditions and substrate preparation results in step flow growth for an AlGaN/GaN structure with 300 Å thick Al_0.25Ga_0.75N on 2.4 μm thick GaN. A high III/V flux ratio during growth and recently improved polishing of LGO substrates aids in promoting two dimensional step flow growth. The GaN nucleation layer directly on the LGO substrate showed no evidence of mixed phase cubic and hexagonal structure that is typically observed in the nucleation buffer on sapphire substrates. Cross-sectional high-resolution transmission electron microscopy (HRTEM) was performed on an AlGaN/GaN heterostructure grown on LGO. The atomic arrangement at the AlGaN/GaN interface was sharp and regular, with locally observed monolayer and bilayer steps.