Change Of Valence Band Structure Research Articles

Electronic structure of the Ga 1 − xCr xN studied by high-energy photoemission spectroscopy

Valence band spectra of Ga 1 − x Cr x N have been investigated by high-energy photoemission spectroscopy at the photon energy of 5.95 keV. Cr doping does introduce a novel electronic structure in the bandgap and causes some change in valence band structure. Based on the first-principle calculation, Cr-associated electronic levels in the bandgap are assigned to nonbonding and antibonding d states while the change of the valence band suggests that the Ga 4s originated states are significantly modified through hybridization with the Cr 3d orbital. The present result evidences that the Ga valence electrons are considerably modified through the interaction with the second nearest-neighbour Cr atoms.

In-situ spectroscopic investigations of silver electrodes on stabilized zirconia

In situ spectroscopic investigations of evaporated silver films as oxygen electrodes on yttria stabilized zirconia (YSZ) have been performed at 550°C under UHV conditions. For this purpose a new three-electrode galvanic cell with oxygen gas on the reference side has been developed. The oxygen activity at the working electrode was changed by controlling the electrode potential between working and reference electrode. Ultraviolet photoelectron spectroscopy (UPS) was used to determine the work function change during pumping oxygen to the surface of the silver electrode. A change in valence band structure was observed during oxygen pumping. The work function increases and a new electronic state attributed to surface oxygen appears at a binding energy of 3.3 eV below the Fermi energy. With X-ray photoelectron spectroscopy (XPS) the chemical nature of this surface oxygen species was further investigated. A binding energy of the O 1s core electrons was observed at 529 eV indicating the occurrence of subsurface oxygen. Scanning electron micrographs show characteristic changes in the electrode morphology after polarization.

Vertex Correction for a Quasi-Two-Dimensional Electron-Hole Plasma Including Strain Effects

The contribution of the second-order self-energy to the band-gap reduction due to exchange and correlation effects is evaluated by including the valence-band mixing for a quasi-two-dimensional electron–hole plasma. Based on the screened, effective interaction within the random-phase approximation, the change of valence band structure due to band mixing has been discussed by using the Luttinger-Kohn Hamiltonian as a function of the compressive strain. The present results applied to the InxGa1−xAs/InGaAsP quantum well systems lattice-matched to InP exhibit that the vertex correction due to second-order self-energy is enhanced with increasing compressive strain and sheet carrier density, and in addition, with decreasing carrier density, it is significantly contributive to the band-gap reduction due to exchange and correlation effects.

Optical gain control model of the quantum-well laser diode

The effects of various structure parameters such as graded potential, strain, quantum-well size, barrier heights, and temperature on the optical gain of single quantum-well lasers are studied for a potential solution to the problem of device optimization from the unified point of view with a rigorous model for gain. This study on the structure parameter dependence of the gain with the valence band mixing as well as intraband relaxation is new and presents a unified scheme for the optical gain control. Significant enhancement of gain in the graded quantum well as compared with that of the ordinary square quantum well is predicted. With the uniaxial stress, the TE mode gain is suppressed while the TM mode gain is enhanced due to the change of valence band structure. Calculated results show that the roles played by structure parameters such as well width, barrier heights, and temperature on the optical gain becomes of great importance for the device optimization.