Polaron Effect In Al_yGa_1-yN/Al_xGa_1-xN Triangle Quantum Well Structures Under Hydrostatic Pressure

Energy levels and the energy shift of Polarons in wurtzite Aly Al_yGa_1-yN/Al_xGa_1-xN triangular quantum wells are investigated in the paper.The numerical results represented with picture of the ground state energy,transition energy and contributions of different phonons to polaron energy（polaron energy shift）are given as functions of well width d,pressure p,and composition x.In the theoretical calculation,the anisotropy of the parameters,such as the phonon frequency of different optical branches,the electron effective mass,the dielectric constant,and their pressure and coordinate dependence are considered.The results show that the ground state energy and transition energy of polaron in wurtzite Aly Ga1-y N/Al0.3Ga0.7N triangular quantum well and Ga N/Al0.3Ga0.7N square quantum well decrease with the increase of pressure under the conditions of well width d = 5 nm and d = 15 nm,but the variation is small.The contribution of confined phonon,half-space phonon and the total contribution of phonons to the ground state energy（polaron energy shift）increase with the increase of the hydrostatic pressure.The ground state energy,transition energy and polaron energy shift in narrow well（d=5nm）are larger than that in width well（d=15nm）.For a given composition（0.3）and hydrostatic pressure（8Gpa）,the ground state energy and transition energy of polaron in Aly Ga1-y N/Al0.3Ga0.7N triangular quantum well and Ga N/Al0.3Ga0.7N square quantum well decrease with the increase of well width,the contribution of half-space phonon to the ground state energy decrease with the increase of well width,while the contribution of confined phonon to the ground state energy increase with the increase of well width.The contribution of half-space phonon is larger than that of confined phonon when the well width is less than 3 nm,the contribution of confined phonon is larger than that of half-space phonon when the well widthis larger than 3 nm.The total contribution of phonons to the ground state energy decrease with the increase of the well width d and then increase,the extreme value appears.the ground state energy and transition energy of polaron in Aly Ga1-y N/Al0.3Ga0.7N triangular quantum well and Ga N/Al0.3Ga0.7N square quantum well for given well width（15nm）and hydrostatic pressure（8Gpa）increase with the increase of composition x,and the variation degree in the triangular quantum well is higher than that in square quantum well.In two kinds of well,the contribution of confined phonon to the ground state energy increase with the increase of composition x,while half-space phonon to the ground state energy decrease with the increase of composition x.Total contribution of phonons to the ground state energy increase with the increase of composition x.In the wurtzite AlyGa1-y N/Alx Ga1-x N triangular quantum well structure,the change laws of the polaron energy,transition energy,and polaron energy shifts with the pressure,the well-width and composition x were found to be similar to those of the corresponding variables in a wurtzite Ga N/Alx Ga1-x N square quantum well structure.However,the variable values were different.The corresponding values in the triangular quantum well structure were obviously greater than that in the square quantum well structure.