Surface Roughness Rms Value Research Articles

Effects of multi-layer Ti/Al electrode and ohmic groove etching on ohmic characteristics of AlGaN/GaN HEMT devices

This experiment studied the effects of multi-layer Ti/Al electrodes, ohmic groove etching, and annealing temperature on the ohmic characteristics, output characteristics, and surface topography of AlGaN/GaN high electron mobility transistor (HEMT) devices. In the experiment, we prepared the device structure through the linear transmission model. We then used an atomic force microscope, B1500A, and other instruments to test the output characteristic curve and surface roughness of the device under each temperature and structure. After analysis and calculation, it is found that the device with an etched depth of 10 nm in the ohmic groove of the multi-layer Ti/Al electrode obtains the best characteristics when fast annealed at 850 °C for 30 s. The contact resistance value of the improved device is only 54.3% of that of the traditional structure, and the specific contact resistivity is reduced by 71.8% compared with that of the traditional structure. The surface morphology of the improved device is also smoother, and the surface roughness rms value is only 40.5% of that of the traditional structure. When it is applied to the HEMT device, the output current is increased by 40.7% compared with the traditional structure.

A nano-imprint method analysis of the optical subsurface quality processed by hydrodynamic effect polishing

Hydrodynamic effect polishing (HEP), in which the material is removed in elastic region by chemical impact reaction, can effectively remove the surface/subsurface damage to get an ultrasmooth surface. However subsurface damage contains scratches and machining residual stress are hidden below the surface and can’t be easily detected. The subsurface/surface properties such as hardness and elastic modulus have direct relationship with the subsurface damage. Therefore, a nano-imprint method analysis of the optical subsurface quality was presented to evaluate the hydrodynamic effect polishing process effect. Polishing experiment was conducted on a conventional pad pre-polished silica glass. The surface before and after polishing process was firstly observed by atomic force microscope and ZYGO white-light interferometer. The observation shows the surface damage such as the scratches and bump structures are completely removed by HEP process, and the surface roughness rms value decreased to near 0.3 nm. To evaluate the subsurface damage, nano-imprint was conducted on the processed and unprocessed area under different load with different impressed depth. The imprint results show the processed surface become soft and easily be impressed, while the unprocessed surface becomes hard. The processed and unprocessed surface shows the same impress depth when impressed depth exceeded 200 nm. Analysis shows the surface becomes hard under the effect of the residual stress in subsurface damage which is generated in the traditional machining process with material removal in brittle or plastic mode. Material is removed in elastic mode by chemical impact reaction in HEP, and the surface/subsurface damage can be effectively removed. It demonstrates that HEP processed surface properties are much close to the bulk material.

Acceptor-modulated optical enhancements and band-gap narrowing in ZnO thin films

Fermi-Dirac distribution for doped semiconductors and Burstein-Moss effect have been correlated first time to figure out the conductivity type of ZnO. Hall Effect in the Van der Pauw configuration has been applied to reconcile our theoretical estimations which evince our assumption. Band-gap narrowing has been found in all p-type samples, whereas blue Burstein-Moss shift has been recorded in the n-type films. Atomic Force Microscopic (AFM) analysis shows that both p-type and n-type films have almost same granular-like structure with minor change in average grain size (∼ 6 nm to 10 nm) and surface roughness rms value 3 nm for thickness ∼315 nm which points that grain size and surface roughness did not play any significant role in order to modulate the conductivity type of ZnO. X-ray diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) have been employed to perform the structural, chemical and elemental analysis. Hexagonal wurtzite structure has been observed in all samples. The introduction of nitrogen reduces the crystallinity of host lattice. 97% transmittance in the visible range with 1.4 × 107 Ω-1cm-1 optical conductivity have been detected. High absorption value in the ultra-violet (UV) region reveals that NZOs thin films can be used to fabricate next-generation high-performance UV detectors.

Electrical, Magnetic and Morphological Properties of E-Beam Evaporated Ni Thin Films

Nickel (Ni) thin films in the thickness range 50?80 nm have been prepared by electron beam evaporation method at a base pressure of 4x10-5 mbar on silicon and glass substrates. Some samples have been annealed at 573 K for 1.5 h in open air. The resistivity of Ni films on silicon substrate is higher than the resistivity of Ni films on glass substrate. The TCR of Ni films is found to be positive which indicates that the Ni samples are metallic in nature. Coercivity of Ni films increases with increasing film thickness. The coercivity of 80 nm as-deposited Ni film on glass substrate is found to be ~ 9 Oe. The rms value of the surface roughness of 150 nm as-deposited Ni film on glass substrate is ~12 nm and it becomes ~ 7 nm after annealing. On the other hand, the coercivity of 90 nm and 160 nm as-deposited Ni films on silicon substrate are 50 Oe and 85 Oe, respectively. The rms value of surface roughness of 120 nm as-deposited Ni film on Si substrate is ~ 16 nm. It becomes ~ 3 nm after annealing.

Growth and characterization of an In0.53Ga0.47As-based Metal-Oxide-Semiconductor Capacitor (MOSCAP) structure on 300 mm on-axis Si (001) wafers by MOCVD

We report on the development of a metamorphic In0.53Ga0.47As-based heterostructure grown on 300mm on-axis Si (001) wafers by metal-organic chemical vapor deposition (MOCVD), and the fabrication of a Metal-Oxide-Semiconductor Capacitor (MOSCAP) with C–V characteristics and interfacial trap density (Dit) values comparable to those of an equivalent structure grown on an InP substrate. A 1.15µm thick GaAs/InP buffer with a defect density in the low 109cm−2 range and a surface roughness rms value <2nm was used to accommodate the large lattice mismatch between In0.53Ga0.47As and Si.

Analysis of a New Processing Method for Small Curvature Aaspheric

For the aspheric processing is complex , time consuming and difficult to guarantte the eccentricity ,this paper introduce a new method of aspheric processing --repairing and polishing methed and describe the principle . Best fit radius, removal function were computed by mathematical model method and the respective performance curves were given by simulation. This methed has the particular advantage of shortening the working time ,reducing the eccentric amount of the element and improving the processing efficiency. Through this processing method, do a series of processing experiments on the smaller aspheric tolerance single crystal silicon aspheric.As the result indicated , plane surface shape error PV 0.52 μm,surface roughness RMS value of single-crystal silicon 0.09 μm ,the center deviation was less than1μm and the surface smoothness meet the standard above the grade Π.

Ultra-smooth polishing of high-precision optical surface

A new method of ultra-smooth uniform polishing was presented, which can avoid high-precision surface figure getting worse after ultra-smooth polishing. At first, the fundamental and process were introduced. Then the process was simulated with “Gauss” and “V” type removal function. It shows that there will be no significant influence on optical surface figure after ultra-smooth uniform polishing with any type removal function. To demonstrate the process, a high-precision Ø100mm fused silica flat optical element was polished, which was prior figured by IBF. Its surface figure accuracy root-mean-square (rms) value is improved from initial 3.624nm to final 3.393nm, the mid-spatial frequency surface roughness rms value is improved from initial 0.477nm to final 0.309nm, and the high-spatial frequency surface roughness rms value is improved from initial 0.167nm to final 0.0802nm. At last, the surface quality of the lens was analyzed by power spectral density (PSD). The result indicates that the surface roughness of high-precision optical element could be improved by ultra-smooth uniform polishing method without the surface figure destroyed.

Effect of Cr and V dopants on the chemical stability of AZO thin film

The effect of the dopants of Cr and V on the optoelectronic properties of AZO thin film by pulsed DC magnetron sputtering has been investigated. We also use HCl and KOH solutions to conduct the chemical stability of AZO:Cr:V thin film. The experimental results show that the optimum AZO optoelectronic properties without Cr and V doping obtain the resistivity of 9.87×10−4Ωcm, optical transmittance of 84% and surface roughness rms value of 2.6nm. The chemical stability of AZO will increase after Cr and V doping. Under the added V=0.19wt.%, Cr=0.56wt.%, AZO:Cr:V thin film showed 52% increased chemical stability and 128% decrease in surface roughness after etching (the resistivity was 3.62×10−3Ωcm and optical transmittance 81%). From the experimental results, the higher resistivity obtained after KOH etching compared with after HCl etching. The reason is that the Zn/Al ratio will reduce after etching and cause the AZO film carrier density to reduce as well. However, the optical transmittance obtained after KOH etching will be higher than that after HCl etching. This is because that a better surface roughness after KOH etching obtained than after HCl etching.

Pulse plated zinc sulphide films and their characteristics

Zinc sulphide thin films were deposited by the pulse plating technique using AR grade Zinc sulphate and sodium thiosulphate precursors. The pH of the deposition bath was adjusted to 2. The duty cycle was varied in the range of 20–60%. Total deposition time was kept constant as 60 min in all the cases. X-ray diffraction studies indicated the formation of single phase cubic zinc sulphide films. After heat treatment the crystal structure transformed to hexagonal structure. Optical absorption measurements indicated a band gap values in the range of 3.6–4.0 eV as the duty cycle decreased. EDAX studies yielded a composition of the films deposited at 50% duty cycle is Zn = 48%, S = 52%. XPS studies indicated the formation of ZnS. The Zn 2p and S 3p peaks are observed. AFM studies indicated a rms value of surface roughness of 55 nm for the films deposited at a duty cycle of 60%.

Pulsed laser deposited nanostructured InN thin films as field emitters

InN thin films were deposited on c -cut Al 2O 3 substrates using the DC plasma assisted pulsed laser deposition technique. X-ray diffraction (XRD) studies showed the single phase, polycrystalline nature of the InN thin films with wurtzite structure. Surface morphology of the films, as seen by atomic force microscopy (AFM), consisted of densely packed nanocrystalline grains of InN. The rms value of surface roughness was found to be ∼35 nm. AFM images also revealed the hexagonal features with sharp edges and protrusions of InN. The field emission characteristics of InN/Al 2O 3 were investigated in ultra high vacuum (1×10 −8 Torr) using the diode configuration. The turn-on field, required to draw an emission current density of 10 μA/cm 2, was observed to be ∼3.5 V/μm. The maximum emission current density obtained was 230 μA/cm 2 when the applied electric field strength was ∼4 V/μm. The Fowler–Nordheim (FN) plot obtained from the current–voltage characteristic was found to be linear in accordance with the quantum mechanical tunneling phenomenon. The field enhancement factor, β , estimated from the slope of the FN plot was 21,167 cm -1. To the best of our knowledge this is the first report of field emission studies of InN/Al 2O 3 with such high values of β , which is comparable to that obtained for GaN or IrO 2.

Roughness control of polycrystalline diamond films grown by bias-enhanced microwave plasma-assisted CVD

A simple growth technique to control the surface roughness of polycrystalline diamond films is proposed. The films are grown using a microwave plasma-assisted chemical vapor deposition method, with varying the methane (CH 4) concentration at the stage of bias-enhanced nucleation. It is found from the field-emission scanning electron microscope spectra that nanocrystalline diamond nuclei are formed at a relatively high methane concentration, causing a secondary nucleation at the accompanying growth step. The RMS value of surface roughness for grown films, which is estimated from the atomic force microscope images, monotonically decreases from 165 to 53 nm with methane concentration. It is also observed that the surface roughness is closely related to the nucleation density. In addition, employing a two-step growth method, which consists of first-growth at 500 W and subsequent second-growth at 800 W, enables the as-grown polycrystalline diamond film to have a smaller roughness of approximately 46 nm. This is believed to be due to the secondary nucleation effect induced during the growth step.

Scattering pattern measurement and analysis of sputtered-glass optical waveguides for integrated optics

The radiation patterns from optical waveguides prepared by sputtered 7059 glass thin film onto pyrex glass substrates are measured in order to clarify the loss mechanisms producing the scattering. The angular distributions of the scattered light can be explained by the presence of its surface roughness at film-substrate and film-air interfaces and/or of bulk inhomogeneities of the waveguide core. For waveguides with a relatively high loss of several dB/cm, for example, the patterns are consistent with the theory based on a cross-correlated model of these imperfections, assuming correlation lengths of the order of 0.1λ in the normal direction and of the same order as the wavelength λ in the parallel direction to the waveguide. The rms value of surface roughness to that of bulk inhomogeneities divided by λ is also determined by comparing the measured scattering curves with the theoretically calculated curves.

Scattering Pattern Measurement and Analysis of Sputtered-Glass Optical Waveguides for Integrated Optics

The radiation patterns from optical waveguides prepared by sputtered 7059 glass thin film onto pyrex glass substrates are measured in order to clarify the loss mechanisms producing the scattering. The angular distributions of the scattered light can be explained by the presence of its surface roughness at film-substrate and film-air inter-faces and/or of bulk inhomogeneities of the waveguide core. For waveguides with a relatively high loss of several dB/cm, for example, the patterns are consistent with the theory based on a cross-correlated model of these imperfections, assuming correlation lengths of the order of 0.1Lambda in the normal direction and of the same order as the wavelength Lambda in the parallel direction to the waveguide. The rms value of surface roughness to that of bulk inhomogeneities divided by alpha is also determined by comparing the measured scattering curves with the theoretically calculated curves.