No abstract

No abstract

No abstract

The crystal structure deformation path depending on lattice parameters and its energy barrier in group‐III nitrides are investigated by using density‐functional theory calculations. The calculations demonstrate that the energy difference in cohesive energy along the crystal structure deformation path strongly depends on the ionicity of III‐nitrides. It is also found that the lattice parameter ratio c/a of AlN and InN with Hexagonal (Hex) structure is much smaller than that of BN. Moreover, the energy barrier for structural deformation from Hex to wurtzite structures in BN is much larger than that of the other group‐III nitrides. The difference in the energy barrier originates from both the repulsive interaction among bond charges and the attractive interaction among ionic charges. These results imply that the ionicity is crucial for determining the energy change along the crystal structure deformation path as well as the structural stability of group‐III nitrides.

A micro light-emitting diode (μLED) is a key device for the future of advanced information. Owing to expand its application widely, the concept of the emission-color conversion using layered semiconductors as a color converter is proposed. In addition, it is demonstrated that layered semiconductors were transferred directly onto μLED chips, and the emission-color conversion is realized. The layered GaS1−xSex alloy, whose energy bandgap can be controlled by tuning the S and Se compositions, was selected as a color converter. The photoluminescence (PL) measurements using a blue LED as an excitation source revealed that GaS0.65Se0.35 and GaSe can show green and red luminescence with center energies of 2.34 and 1.94 eV, respectively. The emission color of gallium nitride (GaN)-based blue μLEDs covered with GaS0.65Se0.35 and GaSe thin films were clearly converted to green and red, respectively. Furthermore, the emission color could be controlled by changing the film thickness. Thus, these results suggest the possibility of emission-color conversion of blue μLED chips utilizing layered materials.