c-Axis-tilted ScAlN films grown on silicon substrates for surface acoustic wave devices

ScAlN films are currently being investigated for their potential use in surface acoustic wave (SAW) devices for next-generation mobile networks because of their high piezoelectricity. This paper describes the numerical simulation of SAW propagation in c-axis-tilted ScAlN films on silicon substrates and a fabrication technique for preparing c-axis-tilted ScAlN films on silicon substrates. The electromechanical coupling coefficient K 2 of SAW propagating in the ScAlN film/silicon substrate increased due to the c-axis tilt angle. The maximum K 2 value is approximately 3.90%. This value is 2.6 times the maximum K 2 value of the c-axis-oriented ScAlN film/silicon substrate structure. The c-axis-tilted ScAlN films with an Sc concentration of 40% were prepared on a silicon substrate via RF magnetron sputtering based on the self-shadowing effect, and the maximum c-axis tilt angle was 57.4°. These results indicate that this device structure has potential for SAW device applications with well-established micromachining technology derived from silicon substrates.

Radiation-doped SiC*/Si heterostructure formation and defects evolution

The authors consider heterostructures of silicon carbide obtained during endotaxy on silicon substrates. The question is raised in connection with the description of the endotaxy process itself at the structural level. Authors focus on the technological aspects of the formation of a stable β-SiC/Si heterostructure by endotaxy in relation to the evolution of point defects of various nature and their probable association models with the participation of a radionuclide impurity at the micro-alloying level: 1) the growth of the SiC*/Si thin layer with C-14 atoms in the doping process; 2) physical properties of defects formation; 3) some interface between properties and efficiency.

Investigation into the InAs/GaAs quantum dot material epitaxially grown on silicon for O band lasers

InAs/GaAs quantum dot (QD) lasers were grown on silicon substrates using a thin Ge buffer and three-step growth method in the molecular beam epitaxy (MBE) system. In addition, strained superlattices were used to prevent threading dislocations from propagating to the active region of the laser. The as-grown material quality was characterized by the transmission electron microscope, scanning electron microscope, X-ray diffraction, atomic force microscope, and photoluminescence spectroscopy. The results show that a high-quality GaAs buffer with few dislocations was obtained by the growth scheme we developed. A broad-area edge-emitting laser was also fabricated. The O-band laser exhibited a threshold current density of 540 A/cm2 at room temperature under continuous wave conditions. This work demonstrates the potential of large-scale and low-cost manufacturing of the O-band InAs/GaAs quantum dot lasers on silicon substrates.

Photoconductivity of ZnS Thin Films Deposited by Solution-Processing Techniques

We have explored various solution- processing techniques to produce ZnS thin films on conducting (ITO) and silicon substrates along with ZnS-porous silicon composite films. All these samples obtained from different methods and chemical recipes were annealed under fixed ambient conditions and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and ultraviolet photocurrent response. Various characterizations reveal that the fabrication conditions and intrinsic defects of ZnS play a vital role in optoelectronic performance.

Theoretical and Experimental Analysis of Surface Roughness and Adhesion Forces of MEMS Surfaces Using a Novel Method for Making a Compound Sputtering Target

Achieving a compound thin film with uniform thickness and high purity has always been a challenge in the applications concerning micro electro mechanical systems (MEMS). Controlling the adhesion force in micro/nanoscale is also critical. In the present study, a novel method for making a sputtering compound target is proposed for coating Ag–Au thin films with thicknesses of 120 and 500 nm on silicon substrates. The surface topography and adhesion forces of the samples were obtained using atomic force microscope (AFM). Rabinovich and Rumpf models were utilized to measure the adhesion force and compare the results with the obtained experimental values. It was found that the layer with a thickness of 500 nm has a lower adhesion force than the one with 120 nm thickness. The results further indicated that due to surface asperity radius, the adhesion achieved from the Rabinovich model was closer to the experimental values. This novel method for making a compound sputtering target has led to a lower adhesion force which can be useful for coating microgripper surfaces.

Ultra-Low-Reflective, Self-Cleaning Surface by Fabrication Dual-Scale Hierarchical Optical Structures on Silicon

An integrated functional anti-reflective surface is of great significance for optical and optoelectronic devices. Hence, its preparation has attracted great attention from many researchers. This study combined wet alkaline etching approaches and reactive ion etching (RIE) techniques to create a dual-scale hierarchical anti-reflective surface on silicon substrates. The effect of RIE time on surface morphology and optical performance was investigated using multiple characterization forms. The optimal parameters for the fabrication of dual-scale structures by the composite etching process were explored. The silicon surface with a dual-scale structure indicated excellent anti-reflective properties (minimum reflectivity of 0.9%) in the 300 to 1100 nm wavelength range. In addition, the ultra-low reflection characteristic of the surface remained prominent at incident light angles up to 60°. The simulated spectra using the finite difference time domain (FDTD) method agreed with the experimental results. Superhydrophobicity and self-cleaning were also attractive properties of the surface. The functionally integrated surface enables silicon devices to have broad application prospects in solar cells, light emitting diodes (LEDs), photoelectric detectors, and outdoor equipment.

Raman area- and thermal- mapping studies of faceted nano-crystalline α-Fe2O3 thin films deposited by spray pyrolysis

Different advanced techniques including Raman area mapping and Raman thermal imaging has been used to investigate various properties of large area iron oxide thin films deposited by spray pyrolysis, on a large area of crystalline silicon substrates under controlled external parameters. Morphological studies reveal that the obtained films acquire lateral faceted crystalline structure of iron oxide. The Raman and SEM images, in unison, confirm the presence and large area distribution of the nano crystals of Fe2O3 phase. Thermal Raman imaging reveals that the obtained iron oxide thin films are robust and thus can be used for appropriate technological applications like electromagnetic shielding.

Separation of AlN layers from silicon substrates by KOH etching

In this work, the AlN/Si(111) epitaxial structures grown consistently by plasma assisted molecular beam epitaxy (PA MBE) and hydride vapour phase epitaxy (HVPE) methods were studied. The PA MBE AlN buffer layers were synthesized via coalescence overgrowth of self-catalyzed AlN nanocolumns on Si(111) substrates and were used as templates for further HVPE growth of thick AlN layer. It was shown that described approaches can be used to obtain AlN layers with sufficiently smooth morphology. It was found that HVPE AlN inherited crystallographic polarity of the AlN layer grown by PA MBE. It was demonstrated that the etching of such AlN/Si(111) epitaxial structures results in partial separation of the AlN epilayers from the Si(111) substrate and allows to form suspended structures. Moreover, the avoidance of surface damage and backside overetching was achieved by use thin Cr film as surface protective coating and by increasing the layer thickness accordingly.