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.
This paper mainly describes fabrication of two-dimensional GaAs-based photonic crystals with low nanometer scale air-hole arrays using an inductively coupled plasma(ICP) etching system.The sidewall profile and surface characteristics of the photonic crystals are systematically investigated as a function of process parameters including ICP power,RF power and pressure.Various ICP powers have no significant effect on the verticality of air-hole sidewall and surface smoothness.In contrast,RF power and chamber pressure play a remarkable role in improving sidewall verticality and surface characteristics of photonic crystals indicating different etching mechanisms for low nanometer scale photonic crystals.The desired photonic crystals have been achieved with hole diameters as low as 130 nm with smooth and vertical profiles by developing a suitable ICP processes.The influence of the ICP parameters on this device system are analyzed mainly by scanning electron microscopy.This fabrication approach is not limited to GaAs material,and may be efficiently applied to the development of most two-dimensional photonic crystal slabs.
Spin splitting of conduction subbands in Al0.3Ga0.7As/GaAs/AlxGa1-xAs/Al0.3Ga0.7As step quantum wells induced by interface and electric field related Rashba effects is investigated theoretically by the method of finite difference.The dependence of the spin splitting on the electric field and the well structure,which is controlled by the well width and the step width,is investigated in detail.Without an external electric field,the spin splitting is induced by an interface related Rashba term due to the built-in structure inversion asymmetry.Applying the external electric field to the step QW,the Rashba effect can be enhanced or weakened,depending on the well structure as well as the direction and the magnitude of the electric field.The spin splitting is mainly controlled by the interface related Rashba term under a negative and a stronger positive electric field,and the contribution of the electric field related Rashba term dominates in a small range of a weaker positive electric field.A method to determine the interface parameter is proposed.The results show that the step QWs might be used as spin switches.
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.
