We present the theoretical results of the electronic band structure of wurtzite GaN films under biaxial strains in the (11■2)-plane.The calculations are performed by the k · p perturbation theory approach through using the effective-mass Hamiltonian for an arbitrary direction.The results show that the transition energies decrease with the biaxial strains changing from 0.5% to 0.5%.For films of (11■2)-plane,the strains are expected to be anisotropic in the growth plane.Such anisotropic strains give rise to valence band mixing which results in dramatic change in optical polarisation property.The strain can also result in optical polarisation switching phenomena.Finally,we discuss the applications of these properties to the (11■2) plane GaN-based light-emitting diode and lase diode.
With ZnO nanorods doped in only one poly(vinyl alcohol)(PVA) layer,we observed different threshold voltages with reverse DC voltages for a liquid crystal cell.The length and diameter of the ZnO nanorod used in our experiment were about 180 nm and 20 nm,respectively.When the PVA layer on the anodic side was doped, the threshold voltage was larger than that of the pure cell;conversely,when the PVA layer on the cathodic side was doped,the threshold voltage was smaller than that of the pure cell.These results can be explained by the internal electric field model.We also observed a resonance phenomenon with a low frequency AC voltage.
We observe obviously different diffraction efficiencies with forward and reverse dc voltages in a forced-light-scattering(FLS)experiment for a cell with ZnO nanorod doped in only one poly(vinyl alcohol)(PVA)layer.When a dc voltage with a positive pole on the ZnO nanorod doped side is applied,the excited charge carriers primarily move along the transverse direction,which results in a higher diffraction efficiency.Conversely,when the dc voltage with a negative pole on the ZnO nanorod doped side is applied,the excited charge carriers primarily move along the longitudinal direction,which leads to a lower diffraction efficiency.A largest diffraction efficiency of about 9%is achieved in the ZnO nanorod doped liquid crystal cell.
The InGaN/GaN blue light emitting diode(LED) is numerically investigated using a triangular-shaped quantum well model,which involves analysis on its energy band,carrier concentration,overlap of electron and hole wave functions,radiative recombination rate,and internal quantum efficiency.The simulation results reveal that the InGaN/GaN blue light emitting diode with triangular quantum wells exhibits a higher radiative recombination rate than the conventional light emitting diode with rectangular quantum wells due to the enhanced overlap of electron and hole wave functions(above 90%) under the polarization field.Consequently,the efficiency droop is only 18% in the light emitting diode with triangular-shaped quantum wells,which is three times lower than that in a conventional LED.
We have measured the in-plane optical anisotropy(IPOA) of(1120) ZnO(a-plane) on(1012) sapphire(r-plane) by reflectance difference spectroscopy(RDS) at room temperature.Giant IPOA has been observed between the light polarized direction parallel and perpendicular to the c axis of ZnO,since the symmetry of a-plane is C2v.A sharp resonance has been observed near the fundamental band gap,which is induced by the polarizationdepend band gap shift.The sharp line shape is attributed to the exciton transition.The spectra fitting and differential spectra indicate the polarization-depend band energies.The giant IPOA is possible enhanced by anisotropy strain along and perpendicular to the c axis in the a-plane.
