InP based semiconductor structures for radiation detection

We report the preparation of semi-insulating InP single crystals of p-type conductivity and intentionally undoped p-type epitaxial layers for radiation detection. We focus on (i) the growth of InP single crystals doped with copper by the Czochralski technique and their subsequent temperature annealing to convert them to a semi-insulating (SI) state of p-type conductivity, and (ii) the growth of thick (>10 μm) p-type InP layers by liquid phase epitaxy with an admixture of Pr and Dy. Grown layers and single crystals were examined by low-temperature photoluminescence spectroscopy, capacitance-voltage and temperature dependent Hall measurements. An efficient purification due to rare earth (RE) admixture has been observed and layers grown with the addition of Pr and Dy exhibit the change of electrical conductivity from n to p at certain RE concentration in the melt. Dominant acceptors responsible for conductivity conversion have been identified. Three types of detection structures exploiting the Schottky or Schottky like contacts on pure and SI p-type InP or exploiting the p–n junction were designed.     

Absolute-Type Shaft Encoding Using LFSR Sequences With a Prescribed Length

Maximal-length binary sequences have existed for a long time. They have many interesting properties, and one of them is that, when taken in blocks of n consecutive positions, they form 2ⁿ - 1 different codes in a closed circular sequence. This property can be used to measure absolute angular positions as the circle can be divided into as many parts as different codes can be retrieved. This paper describes how a closed binary sequence with an arbitrary length can be effectively designed with the minimal possible block length using linear feedback shift registers. Such sequences can be used to measure a specified exact number of angular positions using the minimal possible number of sensors that linear methods allow.     

Estimation of Rock Aggregates Quality Using Analyses of Drill Cuttings

There is a need for an effective method to estimate the quality of crushed rock aggregates and its usability in the early stages of project planning, e.g., for road and railway constructions and quarry prospecting. The proposed method is based on mineralogical and petrographic analyses of drill cuttings and analysis of the coarse fraction to estimate the homogeneity/heterogeneity of the bedrock. The geological analyses are followed by an estimation of the rock materials’ mechanical properties and their potential technical usability. Development and practical applicability (field and laboratory) of the method have been performed and correlated to three road projects from regions of different geological and climatic zones in Sweden. The study confirms the capability of the proposed method as a surveying tool.     

The oxidation resistance of Nb-20Mo-15Si-5B-20Cr up to 1,300°C

Nb-20Mo-15Si-5B-20Cr alloy has been oxidized in air in a range of temperatures from 700 to 1,300°C. A 24 hour exposure to air shows a minimum in weight gain per unit area at 900 and 1,000°C. Below and above this temperature the alloy has an oxide scale composed of oxide-metal interface which has been characterized by x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and x-ray mapping. Formation of CrNbO₄ appears to be beneficial for the oxidation resistance while another Cr oxide, Cr₂O₃, may form mainly at temperatures below 1,000°C. SiO₂ formation has been restricted to temperatures above 1,000°C. Long term oxidation consisting of seven successive 24 hour cycles of heating shows better oxidation resistance at 1,300°C for times longer than 96 hours but below that usual lower weight gain per unit area at lower temperature has been observed.     

Photoluminescence of rare-earth/transition metal-doped transparent/translucent polycrystalline Al2O3 ceramics: A review

Transparent alumina doped with rare-earth or transition metal oxides represents a group of materials suitable for optical applications. Because of the birefringence of alumina, their preparation is demanding on the quality of starting materials, their advanced shaping, and pressure-assisted sintering. Spark plasma sintering and hot isostatic pressing have proven at achieving pore-free fine microstructures exhibiting high in-line transmission and a sufficient intensity of emitted light. The present review aims to summarize the results published on this topic, to compare them and on this base to propose other possible and/or appropriate approaches to future.     

A New,Thorough Look on Unusual and Neglected Group III-VI Compounds Toward Novel Perusals

The attention on group III-VI compounds in the last decades has been centered on the optoelectronic properties of indium and gallium chalcogenides. These outstanding properties are leading to novel advancements in terms of fundamental and applied science. One of the advantages of these compounds is to present laminated structures, which can be exfoliated down to monolayers. Despite the large knowledge gathered toward indium and gallium chalcogenides, the family of the group III-VI compounds embraces several other noncommon compounds formed by the other group III elements. These compounds present various crystal lattices, among which a great deal is offered from layered structures. Studies on aluminium chalcogenides show interesting potential as anodes in batteries and as semiconductors. Thallium (Tl), which is commonly present in the +1 oxidation state, is one of the key components in ternary chalcogenides. However, binary Tl–Q (Q = S, Se, Te) systems and derived films are still studied for their semiconducting and thermoelectric properties. This review aims to summarize the biggest features of these unusual materials and to shed some new light on them with the perspective that in the future, novel studies can revive these compounds in order to give rise to a new generation of technology.     

LiF enhanced nucleation of the low temperature microcrystalline silicon prepared by plasma enhanced chemical vapour deposition

A 15-nm lithium fluoride (LiF) thin film evaporated on glass substrate is shown to enhance the nucleation of microcrystalline Si grown by plasma enhanced chemical vapour deposition at the amorphous/microcrystalline boundary conditions. The effect is more pronounced at low substrate temperatures, nucleation density being 10 times higher at ∼ 80 °C. The effect is ascribed to the ionic chemical nature of LiF, the low work function material used in organic electronic devices, and we propose its use for micro patterning crystalline Si regions in otherwise amorphous Si film.