Exciton States And Interband Transitions In The Direct-gap Ge/Si_1-xGe_x And ZnO/Be_xZn_1-xO Quantum Well

In recent decades, the low-dimensional semiconductor heterostructures have a rapiddevelopment because of their specific physical properties. It not only promoted the developmentof electronics and optoelectronics physics, but accelerated the development of world’s economic,finance and industry etc. In this paper, based on the framework of the effective-massapproximation and variational approach, the exciton state and interband transition is investigatedin the direct-gap Ge/Si1-xGexquantum wells(QWs), in addition, the exciton state and interbandtransition is investigated in the direct-gap ZnO/BexZn1-xO QWs too.(1) Based on the framework of effective-mass approximation and variational approach, theground-state exciton and interband transition in the direct-gap Ge/Si1-xGexQWs are investigated.We have calculated the interband transition energy, recombination time of exciton and oscillatorstrength as functions of the well width and Ge content in the direct-gap Ge/Si1-xGexQWs, as wellas the imaginary part of the ground state linear light polarization as functions of the photon energyand Ge content in the direct-gap Ge/Si1-xGexquantum well. Numerical results show that the wellwidth and Ge content have an important effect on the exciton state and optical properties of thedirect-gap Ge/Si1-xGexQWs. The interband transition energy, recombination time of exciton andoscillator strength can be tuned effectively by the well width and Ge content in the direct-gapGe/Si1-xGexQWs, when the well width is more than30nm, the interband transition energy,exciton recombination time and oscillator strength are insensitive for well width and Ge content inthe Si1-xGexbarrier layer. The imaginary part of the ground state linear light polarization decreaseswith the increase of Ge content in the Si1-xGexbarrier layer, while the photon energy corresponds to the summit of the optical polarizability reduces.(2) Based on the framework of the effective-mass approximation and variational approach,with or no the built-in electric field, the exciton binding energy, integral absorption probability andthe interband transition energy in the direct-gap ZnO/BexZn1-xO QWs are investigated anddiscussed. Calculating the built-in electric field, integral absorption probability and the interbandtransition energy as functions of the Be content and well width in the direct-gap ZnO/BexZn1-xOQWs. Numerical results show that the built-in electric field gives rise to a marked significantrection of the exciton binding energy, the integral absorption probability and interband transitionenergy for any Be content and well width in the direct-gap ZnO/BexZn1-xO QWs. The variation ofBe content has an important influence on the exciton states and optical properties of in the narrowwell, but the built-in electric field has a strong influence on the exciton states and opticalproperties of in the wide well. Especially, considering the built-in electric field, when the wellwidth is greater than7nm, the integral absorption probability approaches zero, which is obviouslydifferent from that by taking into account the built-in electric field.The well width and Be content in the direct-gap ZnO/BexZn1-xO quantum well have animportant effect on the optical properties of the direct-gap ZnO/BexZn1-xO and Ge/Si1-xGexquantum well. Through the study to the kinds of quantum wells, the structure parameters and thebarrier height can change the quantum well exciton state and optical properties. These results willbe of great significance for the design and manufacture of the low dimensional optical devicesbased on the direct-gap ZnO/BexZn1-xO quantum well.