Exciton States And Hydrogenic Donor Impurity States In Wurtzite Structure InGaN/GaN Quantum Wells

In wurtzite （WZ） InGaN/GaN quantum wells （QWs） structure, there is a strong built-in electricfield caused by the spontaneous and piezoelectric polarization, which affects the properties of the QWsstrongly. In this thesis, within the framework of the effective-mass theory, the ground exciton states in WZInGaN/GaN QWs, the ground states in WZ InGaN/GaN QWs with finite barrier width model and thehydrogenic donor impurity states in WZ staggered InGaN/GaN QWs are investigated variationally,considering the built-in electric field. Their related properties are calculated as functions of structureparameters of the WZ InGaN/GaN QWs, and the competition effects between built-in electric field andquantum confinement are studied intensively. Numerical result shows the following conclusions.In WZ In_xGa_1-xN/GaN QWs, the built-in electric field, well width and In composition affect theground-state exciton binding energy, interband transition energy and integrated absorption probabilitystrongly. With the increase of the well width, the exciton binding energy has a maximum. And the built-inelectric field leads to a remarkable reduction of the exciton binding energy, interband transition energy andintegrated absorption probability in the QWs in any case. The variation of the In composition have aintensively effect on the exciton states and related optical properties when well width is narrow; while thebuilt-in electric field affect the exciton states and associated optical properties violently when the wellwidth is wide. In particular, the integrated absorption probability in WZ InGaN/GaN single QWs is reducedto zero with well width wider than4nm when the built-in electric field is considered, which is quitedifferent from that in the absence of the built-in electric field.Within finite barrier width model, the ground-state exciton binding energy, interband transitionenergy and integrated absorption probability in WZ InGaN/GaN QWs depend on the barrier width andother structure parameters. With the increase of the barrier width, the exciton binding energy and integratedabsorption probability are both decreased firstly and then insensitive to the variation of the barrier widthwhen barrier width wider than8nm; while the interband transition energy is not sensitive to the variationof the barrier width when the barrier width is wide than some value, and this value is increased with the increase of the well width. With the increase of the well width, the exciton binding energy and integratedabsorption probability both have a maximum and the interband transition energy decreases continuously.Especially, when the well width is wider than6nm, the integrated absorption probability decreases to zero.When In composition is increased, for the narrow QWs, the exciton binding energy increases firstly andthen decreases for the competition effect between built-in electric field and quantum confinement; while forthe wide QW, the exciton binding energy decreases all the time.In WZ structure staggered In_0.2Ga_0.8N/In_yGa_1-yN QWs, donnr binding energy of hydrogenic donorimpurity has a maximum with some the impurity position, and this impurity position is at the In_yGa_1-yNwell layer. When the In composition y higher than0.125, the donor binding energy is insensitive to thevariation of the In composition y for any impurity position. With the increase of the well width, donorbinding energy is decreased for the impurity located at z_i=-L,-L/2,0and L/2; while for the impuritylocated at the right edge of the In_yGa_1-yN （y=0.1）, because of the quantum confinement of the staggeredwell and the built-in electric field, the donor binding energy has a minimum with well width at about2nmand when the well width wider than3nm, the donor binding energy is not sensitive to the variation of thewell width.