Hexagonal boron nitride (h-BN) films were grown on c-plane sapphire substrates by low-pressure chemical vapor deposition with BCl3 and NH3 as the boron and nitrogen sources, respectively, and the influences of growth parameters on the film quality were investigated for samples with a thickness of about 1 µm. The dependence of X-ray diffraction on the growth temperature (T g) indicated that the crystalline quality is most improved in the sample grown at 1200 °C, in which the epitaxial relationship of {100}h-BN ∥ {110}sapphire and {001}h-BN ∥ {001}sapphire was confirmed. This condition enhanced lateral growth, resulting in the formation of grains with flat top surfaces. The T g dependence was discussed in relation to the amorphous AlN formed on the substrate surface and the reaction between BCl3 and NH3 in the vapor phase. The correlation between the structural and luminescent properties, which was found from the T g dependence of CL, was also discussed.

The radiative performance of hexagonal boron nitride (h-BN) was assessed by the spatio-time-resolved luminescence measurements on its microcrystals (MCs) annealed in an O2 gas ambient. The MCs exhibited distinct deep ultraviolet luminescence peaks higher than 5.7 eV, although h-BN is an indirect bandgap semiconductor. The result indicates a strong interaction between the indirect excitons (iXs) and LO/TO (and LA/TA) phonons at T points of the Brillouin zone. Such phonon replicas of free iXs and a luminescence band at 4.0 eV showed negligible thermal quenching, most probably assisted by the strong excitonic effect, enhanced phonon scattering, and formation of a surface BxOy layer that prevents excitons from surface recombination by the thermal excitation. Conversely, the luminescence band between 5.1 and 5.7 eV, which seems to consist of LO/TO phonon replicas of iXs localized at a certain structural singularity that are further scattered by multiple TO phonons at K points and another two emission peaks that originate from the singularity, showed the thermal quenching. In analogy with GaN and AlGaN, cation vacancy complexes most likely act as native nonradiative recombination centers (NRCs). In the present case, vacancy complexes that contain a boron vacancy (VB), such as divacancies with a nitrogen vacancy (VN), VBVN, are certain to act as NRCs. In this instance, iXs delocalized from the singularity are likely either captured by NRCs or the origin of the 4.0 eV-band; the latter is assigned to originate from a carbon on the N site or a complex between VB and an oxygen on the N site.

No abstract

ZnAl2O4 ultraviolet (UV) emitting phosphor has been studied for next‐generation ultraviolet emission device. In this work, to investigate the mechanism of ZnAl2O4, the phosphor was evaluated and analyzed using various methods. It is thought that the optimum ratio of source materials to obtain the single phase of ZnAl2O4 is 0.975. UV emission peak of ZnAl2O4 was changed from around 250 nm to 270 nm and the absorption edge was shifted to lower energy as increase the ratio of source materials. It is thought that bandgap of ZnAl2O4 became narrower as increase the ratio of source materials. From the results of annealing in active carbon, it became clear that the UV emission from ZnAl2O4 was caused oxygen vacancy. Additionally, from the results of sterilization examination, it is thought that the properties of ZnAl2O4 are promising for using it as candidate for sterilization. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Fe-based III-V diluted magnetic semiconductor (III-V-DMS), (Ga, Fe)As, has been grown successfully on GaAs(001) substrates by molecular beam epitaxy at a substrate temperature T s ranging from 260–350°C. Secondary ion mass spectroscopy analysis has exhibited that the film composition can be expressed by Ga1-x Fe x As. X-ray diffraction data have indicated that the lattice constant of Ga1-x Fe x As decreases with increasing Fe composition. Magnetization data have exhibited that epilayers are predominantly paramagnetic, however, their detailed behavior differs from that of Mn-based DMS systems. The work has demonstrated that the physical properties of III-V-DMS can be changed significantly by the choice of transition metals.