Structural and optical investigation of non-polar (1-100) GaN grown by the ammonothermal method

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 113, 203513 (2013) and may be found at https://doi.org/10.1063/1.4807581.We studied the structural and optical properties of state-of-the-art non-polar bulk GaN grown by the ammonothermal method. The investigated samples have an extremely low dislocation density (DD) of less than 5 × 104 cm−2, which results in very narrow high-resolution x-ray rocking curves. The a and c lattice parameters of these stress-free GaN samples were precisely determined by using an x-ray diffraction technique based on the modified Bond method. The obtained values are compared to the lattice parameters of free-standing GaN from different methods and sources. The observed differences are discussed in terms of free-electron concentrations, point defects, and DD. Micro Raman spectroscopy revealed a very narrow phonon linewidth and negligible built-in strain in accordance with the high-resolution x-ray diffraction data. The optical transitions were investigated by cathodoluminescence measurements. The analysis of the experimental data clearly demonstrates the excellent crystalline perfection of ammonothermal GaN material and its potential for fabrication of non-polar substrates for homoepitaxial growth of GaN based device structures

Intrinsic electronic properties of high-quality wurtzite InN

Recent reports suggested that InN is a highly unusual III-V semiconductor, whose behavior fundamentally differs from that of others. We therefore analyzed its intrinsic electronic properties on the highest available quality InN layers, demonstrating the absence of electron accumulation at the (101¯0) cleavage surface and in the bulk. The bulk electron density is governed solely by dopants. Hence, we conclude that InN acts similarly to the other III-V semiconductors and previously reported intriguing effects are related to low crystallinity, surface decomposition, nonstoichiometry, and/or In adlayers

Chapter 11: Emerging approaches in the analysis of inks on questioned documents

Questioned document is one of the oldest fields of examination reported in forensic science. Documents are used as physical (nowadays sometimes virtual) traces of human transactions, thus questioning, falsification and counterfeiting certainly have existed since their invention and routine use. This is also the case for biblical texts and art pieces for which authenticity and authorship are often disputed. While mainly handwriting comparison was reported in early works, the composition and characteristics of inks on paper were often briefly discussed (see for example the early works of Demelle or Raveneau in the XVIIe century ). Since then, many technological developments have impacted questioned document examination, both with regard to the ink and paper production, as well as to the writing instruments or printing techniques. Nowadays, further progress have changed the world of (questioned) documents, through the introduction of virtual documents using electronic signatures and security documents such as passports using mixed physical and digital biometric data. Thus, the document examiner' expertise has to quickly evolve and adapt to such developments, sometimes necessitating the combination of skills from different disciplines not always co-existing in forensic laboratories (such as chemistry, physics, statistics, engineering, material science, computer science). After a brief overview of the historical development in both ink formulation and analysis, this chapter will investigate the relevance of rapidly evolving technologies for application to the examination of questioned documents in a forensic perspective