Growth study of chemical beam epitaxy of GaNxP1−x using NH3 and tertiarybutylphosphine
Abstract A study in the growth of GaN x P 1 − x epilayers by chemical beam epitaxy using tertiarybutylphosphine (TBP), ammonia (NH 3 ), and elemental Ga or triethylgallium is reported. Monitoring reflection high-energy electron diffraction (RHEED) intensity oscillations, we observe that both group-III- and group-V-induced incorporation rates are increased when NH 3 is introduced into a single cracker with TBP. From the difference in the periods of group-V-induced RHEED intensity oscillations, a 16% N incorporation is expected, but X-ray rocking curve measurement shows only 0.08% N. Using separate TBP and NH 3 crackers results in no enhancement in incorporation rates. We conclude that the cracking efficiency of TBP is increased with NH 3 co-injection.
GaP1−xNx alloys formed by ion implantation
GaP1−xNx alloys (x=0.02–0.07 and x≂0.99) have been formed by ion implantation of Ga+ and N+ into GaP. X‐ray diffraction measurements proved that both a wurtzite structure and a zincblende structure of the crystals have been formed within the implanted layers. They are similar to but not the same as GaN and GaP, respectively. An emission band at an energy higher than the energy gap of GaP appeared on the photoluminescence (PL) spectra of the implanted layers and consists of several components. Formation of the alloy and origins of the PL components are discussed.
In search of optimum chest radiography techniques.
A nation-wide study of chest radiography in Sweden had previously revealed a large variation in the physical and technical factors involved, in particular the radiation dose. In this study the image quality could not be assessed unambiguously. The aim of the present study was to try to establish a correlation between visual grading of radiographs and physical and technical factors in order to find the optimum chest X-ray system. The physical and technical performance of 24 chest units was evaluated. Radiographs were taken of an anthropomorphic chest phantom supplied with test structures simulating various pathologies. Image quality was assessed by visual grading analysis of the radiographs. The physical and technical parameters of the units rated best were used to exemplify good radiographic practice. The results were in agreement with the recommendations issued by the Commission of the European Communities (CEC). It was also shown that low radiation dose is compatible with high-quality radiographic imaging of the chest.