Zhixun Ma

Zincblende-wurtzite phase transformation of ZnSe films by pulsed laser deposition with nitrogen doping

Nitrogen-doped ZnSe films have been fabricated by pulsed laser deposition. It is found that the incorporation of nitrogen has resulted in a phase transformation from zincblende to wurtzite. By first-principles total energy calculations, two newly observed Raman peaks at 555 cm−1 and 602 cm−1 are assigned to vibration modes of N substituting Se in wurtzite and zincblende structures, respectively. This preference of wurtzite phase is consistent with previous prediction of the energy difference ΔEWZ−ZB between wurtzite structure and zincblende structure. This work opens a way to achieve stable ZnSe-based polytypism and may help understand the mechanisms of nitrogen doping in wide-bandgap semiconductors.

Effect of Cu doping on Hole Mobility in CdTe

High quality CdTe thin films grown by laser deposition technique and heavily doped with Cu have recently been reported to have resistivity and hole mobility comparable to those of bulk single crystals. To explain the experimental results we have calculated the effect of Cu on the band structure and phonon spectrum of CdTe using the density functional theory (DFT) and the linearized augmented plane wave (LAPW) method. We found that the introduction of a high density of Cu can lead to a reduction in the hole‐LO phonon scattering. In addition, Cu doping can remove Cd vacancies in CdTe and thereby enhance the hole mobility in CdTe.

A Density Functional Theory Study of Ferromagnetism in GaN:Gd

First principle calculations of the electronic structure and magnetic interaction of GaN:Gd have shown that the ferromagnetic p–d coupling is over two orders of magnitude larger than the s–d exchange coupling. The experimental room temperature ferromagnetism in GaN:Gd are explained by the interaction of Gd 4f spins via p–d coupling involving localized holes introduced by intrinsic defects such as Ga vacancies.

Temperature Dependence of Optical Transitions of One Dimensional InGaAs/GaAs Quantum Structures

We have studied the temperature dependence of CER spectra of layered InGaAs QWRs and QDCs and found strain-induced splitting of lh and hh states occur in both InGsAs and GaAs layers. By fitting experimental data using Varshni law and Bose-Einstein type relation, various parameters are obtained, which are similar to those of bulk GaAs. We pointed out that a caution must be excised when extracting the electron-phonon interaction parameters by subtracting the thermal dilation part from the experimental data of the embedded semiconductor microstructures because in these structures the temperature-induced lattice-dilation may produce additional strain besides the lattice mismatch.