The nature of defects in 4H SiC was studied by means of low temperature photoluminescence before and after energy-controlled electron irradiation. Analysis of experimental data from irradiation at energies above and below the Si displacement energy together with subsequent annealing leads to the conclusion that Si Frenkel defects have been detected experimentally in this material. Reasons why these are formed in some cases rather than carbon vacancy carbon antisite pairs are explored.

The impurity distribution of different growth sectors in high temperature high pressure (HTHP) synthesized boron (B)-doped diamond has been investigated, after electron irradiation, at higher spatial resolution than in previous work that relied on absorption spectroscopy. Although high quantitative accuracy is claimed for absorption spectroscopy measurements, it should be borne in mind that this claim is only valid if the region studied is homogeneous, a situation that is not easily established. In this paper, micro–photoluminescence (PL) was employed to investigate the distribution of impurities in HTHP B-doped diamond, and the inhomogeneity within {100}, {111}, and {311} sectors but particularly in {311} sectors where alternations between B-rich and N-rich regions was observed together with decoration of growth horizons. It follows that it may not be reliable, as in the past, to describe a particular growth sector as enriched with a particular dopant.

Mixed-habit growth of natural diamond is relatively uncommon and the reasons why it occurs are not well-understood. The diamond studied here, unusually, alternated between cuboidal and octahedral growth over a very long period making it possible, using a variety of high resolution analytical techniques, to establish the properties of the different phases of growth. In particular, nickel, in the form of NE centres, was restricted the cuboidal regions which also contained very high levels of hydrogen. There was a high concentration of nitrogen in the sample, but photoluminescence microscopy revealed it was incorporated in the two different regions of growth in very different forms with strong N3 emission from the octahedral regions, but in the hydrogen-related 3107 cm(-1) infra-red and NE centres in the cuboidal regions. These results suggest that the traditional means of assaying nitrogen levels by A- and B-centre absorption may require additions. The section of the sample studied was quite close to the nucleation of growth and study of this region by high spatial resolution photo- and cathodoluminescence microscopy revealed previously unreported aspects of this critical growth step. The experimental results also indicate that a major fracture occurred with new diamond grown between the mixed-habit and the later octahedral growth.

The migration of vacancies in diamond is of considerable fundamental interest and has been widely studied previously, while the involvement of self-interstitials in diamond is less common except through centers such as 3H, 515.8 nm, 533.5 nm, and 580 nm. In this paper, the annealing and lateral migration of some interstitial-related centers in type IIa diamond are investigated by low temperature photoluminescence (PL) microscopy, and the distributions of interstitial- and vacancy-related centers are also clearly presented and discussed.

Cubic boron nitride (cBN) as the outstanding representative of the family of semiconducting wide bandgap nitrides and the closest analogue of diamond, is produced and investigated. XRD as method for doping control of cBN with impurities of large atomic sizes, is suggested. The larger an atomic size mismatch between doping and intrinsic atoms of a semiconductor’s crystal lattice, the stronger its response through own strains and distortions. The distortions are expected to be notable in the case of the smallest intrinsic atoms of cBN and diamond. The light-emitting cBN doped with various rare-earth elements (RE) in different concentrations under high pressure conditions is synthesized in form of the cBN: RE single phase micropowders. The micro-powders showed the discrete photoluminescence spectra in IR-, red and green spectral ranges which were attributed to the intra-electronic transitions of RE3+ ions located in cBN crystal lattice. The locations of the RE3+ ions in cBN crystal lattice are discussed. The data of XRD (CuKα) analysis of the cBN:RE micropowders are repre- sented. Extra-splits (as the additional ones to the α1-α2-splits on CuKα) of the cBN parent peaks in XRD patterns of the cBN: RE, are discovered and analyzed using appropriate computer programs. As established, crystal lattice of cBN due to the incorporation of RE3+ ions, represents a disordered solid solutions which are nonuniformly distorted in dependence on the ions’ size and their concentrations in cBN. Results of the present work can be useful to manufacture cBN with predictable functional properties, as well as for in situ doping control of cBN and diamond.

In this study low temperature micro-photoluminescence technology was employed to investigate effects of the irradiation and nitrogen concentration on nitrogen-vacancy (NV) luminescence, with the photochromic and vibronic properties of the NV defects. Results showed that the NV luminescence was weakened due to recombination of self-interstitials created by electron irradiation in diamond and the vacancies within the structure of NV centers. For very pure diamond, the vacancies migrated the long distance to get trapped by N atoms only after sufficient high temperature annealing. As with the increase in nitrogen content, the migration distance of vacancies got smaller. The nitrogen also favored the formation of negatively charged NV centers with the donating electrons. Under the high-energy ultraviolet laser excitation, the photochromic property of the NV- center was also observed, though it was not stable. Besides, the NV centers showed very strong broad sidebands, and the vibrations involved one phonon with energy of ~42 meV and another with ~67 meV energy.

The photoluminescence technology previously employed to investigate the boron distribution of type IIb diamond has now been applied to study the nitrogen distribution of type Ib diamond. All growth sectors were clearly distinguished by the characteristic colors and the brightness of the synthetic Ib diamond's cathodoluminescence topography. As a measure of the concentration of nitrogen impurity, the nitrogen-vacancy luminescence gave relative concentrations in different growth sectors as: the {111} sector was the highest, followed by the {311}, {100} and {511} sectors. The results were reconfirmed by the evidence of the broadened and strengthened zero phonon lines of nitrogen-vacancy center with the increase of nitrogen concentration of type Ib diamond.

The diffusion of vacancies in diamond is of considerable practical and fundamental interest. This work undertakes a new investigation of this property, based on photoluminescence of electron irradiated and annealed samples, exploiting the recent availability of ultra-pure diamond where the very low nitrogen level dictates the necessity for long-distance migration of vacancies on annealing if nitrogen-vacancy complexes are to be formed. The results reveal that an annealing temperature of 850 degrees C is required for long-range vacancy diffusion rather higher than the generally accepted 700 degrees C, but that in Ib samples with high nitrogen concentrations marked reductions of vacancy concentrations can occur at temperatures as low as 500 degrees C by short range diffusion to nearby nitrogen atoms. As a result of this study, two new optical centres have been discovered and evidence is provided for the hypotheses that they are the divacancy and the positively charged nitrogen-vacancy complex.Interstitials created by the electron irradiation are well known to produce several optically active defects, but in particular, the centre known in the literature as 3H exhibits properties that have so far eluded convincing explanations. As a by-product of this investigation, a number of the properties of this centre were encountered that may assist a final determination of the atomic structure of this complex but very common defect. It is deduced that, contrary to conclusions in the literature, the centre is negatively charged. (C) 2014 Elsevier B.V. All rights reserved.

The 523.7nm centre is very commonly observed in electron irradiated HPHT synthetic diamond, but not in CVD samples with high N content up to 50ppm. Absorption studies indicated that the 523.7nm centre was caused by nitrogen-interstitials complexes, and this hypothesis was supported by the insensitivity of its zero phonon line to stress. However, its high annealing temperature, strong broad phonon sideband and lack of high energy local vibrational modes suggest that the 523.7nm centre was more probably vacancy-related.

A technique previously employed to investigate photochromic effects in 4H SiC has now been applied to various high pressure and high temperature (HPHT) and chemical vapour deposition (CVD) diamond samples. After electron irradiation with 250–300keV electrons the irradiated region is first investigated for uniformity of defects created by low-temperature (7K) microscopic photoluminescence (PL) using a 488nm laser. It is then subjected to an intense focused 325nm laser beam in a square raster of points with 40μm spacing and finally re-examined with 488nm excitation. Periodic changes of the intensities of particular optical centres identify photochromic behaviour. The samples studied by this technique were low-nitrogen CVD and HPHT samples and a boron doped HPHT sample. The restoration of photochromically quenched centres by thermal annealing has also been investigated.

Rare-earth (RE) activated cBN-based materials were produced as cBN–Tb, cBN–Ce, cBN–Eu, and cBN–Tm micropowders with 0.1 at.% RE in HPHT conditions. Their X-ray diffraction spectra are compared with those of a standard unactivated cBN micropowder. It is established that structurally cBN–RE materials are interstitial solid solutions based on interstitial solid solutions because there is initial distortion in the unactivated cBN due to its nonstoichiometry. The atomic displacements in the cBN crystal lattice caused by interstitial RE ions are calculated from XRD reflection intensities. The displacements correlate with the cBN lattice distortions evaluated from the regularly nonlinear relationship between the cBN–RE lattice parameters (calculated for each reflection) and the Nelson–Riley function, unlike the unactivated cBN micropowder where this relationship is linear. The degree of nonlinearity depends on the RE content of cBN and the size of RE ions and can correlate with larger shifts of the (111), (220), and (331) reflections toward smaller angles, compared with the shift of (331). The XRD and Raman spectra of cBN micropowders with 0.1 at.% RE of the same kind reveal no stacking faults in the crystal lattice. However, it is not improbable that such faults might form in cBN in which the concentration of RE of one kind is higher than 0.1 at.% or there are different kinds of RE ions. The latter is supported by the TO–LO splitting in the Raman spectra of cBN–Ce–Tb (~0.1 at.% RE) micropowders, which has never been observed in cBN. The RE concentration in cBN is no higher than 0.1 at.%, which is less than that (10 at.% Er) in cBN nanopowders achieved so far by another scientific group using the plasma method. Therefore, studies aimed at obtaining light-emitting materials based on cBN will be continued to reach higher luminescence of RE ions in cBN. Since no data have been previously provided on the crystal structure of light-emitting materials based on RE-activated cBN, it is concluded that structurally new cBN-based materials have been produced.

A series of irradiations has been performed mainly on some very high purity CVD single crystal diamonds but also on some other diamond specimens at various electron doses and dose rates. The electron energies were sufficient to cause atomic displacements creating vacancies and self-interstitials in the irradiated samples. The 515.8nm, 533.5nm and 580nm centres were commonly observed in low temperature photoluminescence examination of electron-irradiated type IIa diamonds. Details of their spectra indicate that they are all related to interstitial complexes.

CdTe/Cd1−xMnxTe superlattices with well/barrier thicknesses ranging from 20Å to 300Å were examined via plan and cross section TEM in analytical instruments capable of EDX and CL. Misfit dislocations, inclined dislocations and stacking faults were observed with a net density of around 109cm−2. It was observed that the dislocations originated near the substrate/epilayer interface and that stacking faults appeared preferrentially on the pair of {111}B (tellurium terminated) planes in the growth direction rather than on the {111}A planes. It is suggested that this is due to a difference in mobility between α and β dislocations originating at or near the substrate.

In the course of studying by low temperature photoluminescence spectroscopy a wide range of electron-irradiated samples of p(Al)-type epitaxial layers of 4H SiC, from a variety of different sources of supply, the results were found to fit into two very different categories. The origin of these differences has been explored using a wide range of experimental techniques and found to result from the degree of compensation of the aluminium by nitrogen in the layers. Nitrogen concentrations deduced by SIMS experiments on these materials were found to be unreliable. The two different categories of material, called V and AB here, showed marked differences in their subsequent annealing behaviour and the implications of this distinction are discussed.

Transmission electron microscopy at 300kV has been used in a thorough examination of CMO3 and bipolar processed wafers of Czochralski silicon. Diffraction contrast and tilting experiments have been performed on the defects which were observed and a number of new observations have been made on stacking faults and {001} platelets induced by oxygen precipitation.

A new hexagonal crystal structure modification of the rhombohedral Mu phase with A7B6 stoichiometry was observed in a cast alloy C-276. The hexagonal structure was determined to share the same lattice parameter along the a axis, while the dimension along the c axis was such that chex = 2/3crhomb. The space group of the hexagonal phase is suggested to be P 63/mmc and forms by a four-layer ABAB repeat, where A and B represent Zr4Al3 and MgCu2 structures, respectively. Details of the diffraction analysis are presented in this article.

Development of high performance dielectric materials is required to facilitate the trend towards miniaturization of microwave communications circuits. A novel two-step sintering process has been found that enhances the value of (Q-factor) (frequency) (QF)product of Ba(Mg 1/3 Ta 2/3)O3 (BMT). Detailed examination of samples densified in this way gives not only details of the grain size, defect content and state of order of the ordered perovskite grains but also reveals the presence of a number of previously unreported phases. These new phases have been examined by TEM using energy dispersive X-ray analysis to give them approximate chemical composition and convergent beam electron diffraction to determine their crystallography. Large unit cells are found which are evidently related to compounds studied previously in the BaMnO3-x - system. The results will be discussed in relation to the enhanced performance of the materials.

P doping of gallium nitride by incorporation of magnesium in the layers was controlled recently. Only Popovici et al. [1] have published the results of a Raman study on p type GaN. In the present communication, we report on the interaction of the free hole gas with the axial A1(LO) or planar E1(LO) phonon modes, evidenced by Raman scattering: the observed coupled phononplasmon mode is found very different from the corresponding one evidenced in silicon doped (n type) GaN. We compare the experimental data with the lineshape calculated within a dielectric model, using the results of electrical measurements. These results are also compared with infrared reflectivity spectra.