An advanced theoretical approach to study super-multiperiod superlattices:theory vs experiments

A new theoretical method to study super-multiperiod superlattices has been developed.The method combines the precision of the 8-band kp-method with the flexibility of the shooting method and the Monte Carlo approach.This method was applied to examine the finest quality samples of super-multiperiod Al_(0.3)Ga_(0.7)As/GaAs superlattices grown by molecular beam epitaxy.The express photoreflectance spectroscopy method was utilized to validate the proposed theoretical method.For the first time,the accurate theoretical analysis of the energy band diagram of super-multiperiod superlattices with experimental verification has been conducted.The proposed approach highly accurately determines transition peak positions and enables the calculation of the energy band diagram,transition energies,relaxation rates,and gain estimation.It has achieved a remarkably low 5%error compared to the commonly used method,which typically results in a 25%error,and allowed to recover the superlattice parameters.The retrieved intrinsic parameters of the samples aligned with XRD data and growth parameters.The proposed method also accurately predicted the escape of the second energy level for quantum well thicknesses less than 5 nm,as was observed in photoreflectance experiments.The new designs of THz light-emitting devices operating at room temperature were suggested by the developed method.

Domain formation on the nonpolar lithium niobate surfaces under electron-beam irradiation:A review

In this review,our recent results on the electron-beam domain writing(EBDW)on the nonpolar surfaces of LiNbO_(3) crystals of different compositions are presented.Under EB irradiation of the nonpolar surfaces,domains nucleated in irradiation points grow frontally along the polar Z-direction in a thin(of microns in thickness)surface layer;the driving force is the tangential component of space-charge fields induced by EB in irradiation points.This geometry of the experiment provides a possibility of three-dimensional(3D)characterization of domain patterns using the combination of atomic force microscopy(AFM)and second harmonic generation(SHG)confocal microscopy methods.The obtained results permitted us to relate the main characteristics of domain formation(the domain sizes and velocity Vf of the frontal motion)to the irradiation conditions(the accelerating voltage U of scanning electron microscopy(SEM),EB current I,the inserted charge Q).The domain depth Td is controlled by U via the electron penetration depth;the domain length Ld increases linearly with Q owing to the domain frontal growth by the viscous friction law.The electron emission coefficient
affects the domain formation due to the fundamental dependence of
on U.In the framework of current approach to EB charging of insulators,the effect of an enhanced conductance on EBDW characteristics is analyzed.The difference between EBDW characteristics observed in varied LiNbO_(3) compositions is discussed in the framework of the intrinsic defect structure of LiNbO_(3).The obtained results extend the possibility of EBDW application to a wider range of crystals.