Hydrostatic Pressure Effect On Donor And Exciton In Semiconductors Quantum Wells

In the recent years, the research of the hydrostatic pressure effect on properties of semiconductor materials and relation low dimensional systems (for instance quantum dot, quantum well and superlattices and so on) are widely interested. The semiconductor band structure, lattice vibrations and relative physical problem have been studied both theoretical and experimental physicists. Further, the investigation of the pressure effect on the donor and exciton in quantum well, especially in the case of the electron-phonon interaction need to be clarified.In present paper, we investigated the problem of the donor and exciton in the finite barrier quantum well under hydrostatic pressure. In our investigation, the electron (hole) and optical phonon modes in quantum well interaction have been considered. Adopted the pressure coefficients of some physical parameter of the semiconductor materials, we calculated the donor and exciton binding energy used a variational method under isotropic effective band mass approximation. The computation calculation of the donor and exciton binding energy as function of pressure, well width and Al concentration (potential height) for GaAs/AlxGa1-xAs and GaN/AlxGa1-xN quantum well has been performed.The numerical results shown that the binding energy of donor and exciton increase with pressure. In our calculation range of pressure, the enhancements of the donor binding energy with pressure is about 35%, and 31% for the exciton in GaAs/AlxGa1-xAs quantum well. For the case of GaN/AlxGa1-xN quantum well this value is smaller than in GaAs/AlxGa1-xAs quantum well, but cannot be neglected.The results of binding energy as function of quantum well width indicated that the donor and exciton binding energy vary tendency with well width is similar to each other. It can be seen thatthe binding energy first increase rapidly, reach a maximum value, then slowly decrease with increasing the well width, finally trend to the effective Rydberg energy of the well material. With increasing the well width, the pressure effect on binding energy also increases firstly, and then decreases. The position of maximum is near the maximum of binding energy increasing with well width.In present paper, the barrier materials of two quantum well system are ternary mixed crystal. The potential height is determined by the Al concentration on mixed crystal. The results of the binding energy vary with the Al concentration (potential height) shown that the donor and exciton binding energy nonlinear monotony increase with increasing Al concentration from 0 to 0.45.For the case of donor, the dependence of binding energy on the impurity-center position was also considered. For the given well width and pressure, the donor binding energy firstly increases, and then decreases with moving the impurity position from well center to edge. It gets a maximum value when the impurity center is at the well center, and symmetry to the well center.We also considered the optical phonon modes in quantum well system (include the confined LO phonon, the half space LO phonon and interface optical phonon) influence on the exciton binding energy and exciton phonon interaction energy under pressure, the results shown that the polaron effect cannot be neglected. After considered the effect of phonon, exciton binding energy still increases with pressure, but the enhancement is weakened, exciton phonon interaction screens the Coulomb interaction between electron and hole. The interaction energy of the exciton with the confined LO phonon, the half space LO phonon and interface optical phonon are increase with pressure. In different well width range, the contribution of three phonon are different: in the case of small well width contribution of the half space LO phonon is important, in contrasts, contribution of the confined LO phonon is remarkable in the wide well width case, as the media well width, the IO phonon contribution is significant.