High-throughput and cost-effective method for production of high-quality semi-insulating InP substrates

A novel technique for preparation of high-resistivity indium phosphide (InP) via post-growth treatment of undoped n-type wafers is presented. The method includes the deposition of a controlled quantity of iron on both faces of as-cut wafers by a simple chemical bath, and the subsequent Fe diffusion by thermal annealing. The reproducible low - to - high resistivity conversion is explained considering two simultaneous phenomena: the annealing-controlled in-diffusion of Fe deep acceptors and the out-diffusion of hydrogen-related shallow donors. Differently from standard Fe-doped melt-grown InP single crystals, this process does not suffer from segregation, thus the Fe-concentration is constant from wafer to wafer, with no striations and radial gradients deriving from the convex solid-liquid interface during growth. Main advantages of the developed process are: i) an entire undoped InP boule may be sliced and converted to semi-insulating, which makes the process cost-effective; ii) reproducible and uniform semi-insulating properties from batch to batch of wafers; iii) the Fe incorporation is precisely controlled, and minimized, so that electrical characteristics of Fe-diffused wafers are superior to those of traditional semi-insulating melt-grown InP crystals doped via addition of elemental Fe to the melt

Slope stability and rockfall assessment of volcanic tuffs using RPAS with 2-D FEM slope modelling

Steep, hardly accessible cliffs of rhyolite tuff in NE Hungary are prone to rockfalls, endangering visitors of a castle. Remote sensing techniques were employed to obtain data on terrain morphology and to provide slope geometry for assessing the stability of these rock walls. A RPAS (Remotely Piloted Aircraft System) was used to collect images which were processed by Pix4D mapper (structure from motion technology) to generate a point cloud and mesh. The georeferencing was made by Global Navigation Satellite System (GNSS) with the use of seven ground control points. The obtained digital surface model (DSM) was processed (vegetation removal) and the derived digital terrain model (DTM) allowed cross sections to be drawn and a joint system to be detected. Joint and discontinuity system was also verified by field measurements. On-site tests as well as laboratory tests provided additional engineering geological data for slope modelling. Stability of cliffs was assessed by 2-D FEM (finite element method). Global analyses of cross sections show that weak intercalating tuff layers may serve as potential slip surfaces. However, at present the greatest hazard is related to planar failure along ENE–WSW joints and to wedge failure. The paper demonstrates that RPAS is a rapid and useful tool for generating a reliable terrain model of hardly accessible cliff faces. It also emphasizes the efficiency of RPAS in rockfall hazard assessment in comparison with other remote sensing techniques such as terrestrial laser scanning (TLS)