Pressure Effect On The Mobility Of Electrons In Quantum Wells With Finite Barriers

The dielectric continuum phonon model and force balance equation are adopted to investigate the electronic mobility parallel to the interfaces of AlAs/Al_xGa_1-xAs semiconductor quantum wells with finite barriers under hydrostatic pressure by taking the influence of three kinds of optical phonon modes into account. The temperature dependence of the electronic mobility is also studied. Our result is in good agreement with the experimental data at zero pressure. Meanwhile, the effect of ternary mixed crystals on the mobility is discussed.In this thesis, a model of square quantum wells(QWs) is adopted to discuss pressure effect on the electronic mobility by assuming that only the lowest subband is occupied by the electrons. The scattering from the confined longitudinal optical(LO) phonon modes, half-space LO phonon modes and interface optical(IO) phonon modes is considered by using Frohlich interaction matrix to deal with the interaction of electrons and phonons. The numerical results for Al_xGa_1-xAs/GaAs QWs show that the three kinds of phonons respectively limit the mobility at different width of QWs. It is found that the confined modes play an important role in wide QWs, but the interface modes are dominant in narrow QWs, the half-space modes in the barrier material hardly influence the electronic mobility expect for very narrow QWs. For the given well wide L=124A, the scattering from the IO phonon modes are more important than that from the confined LO modes in lower temperature, whereas the effect of confined LO modes increase with increasing temperature, and both influences from the two kinds of phonons can not be neglected. All of the effects from the three kinds of phonons mentioned above decrease the electronic mobility as pressure increases. We also calculated the electron mobility in Alo.3Gao.7As/GaAs QWs and compared it with that in AlAs/GaAs ones. The results show that the electron mobility in former system is lower than that in the latter for narrow QWs, higher than that for middle wide QWs, and reaches a same saturated value for wide QWs.