Spontaneous polarization and piezoelectric effects on intraband relaxation time in a wurtzite GaN/AlGaN quantum well

Spontaneous (SP) and piezoelectric (PZ) polarization effects on the intraband relaxation time for a wurtzite (WZ) GaN/AlGaN quantum well (QW) are investigated theoretically as functions of the sheet carrier density and well thickness. The self-consistent (SC) model with the SP and PZ polarizations shows that linewidths for carrier-carrier and carrier-phonon scatterings are significantly reduced compared to those for the flat-band (FB) model without SP and PZ polarization. In particular, line-widths for the e-h and h-e scatterings are reduced by about two orders of magnitude at a sheet carrier density as low as 2×10¹² cm^-2 compared to the case of the FB model. This is attributed to the decrease of the matrix element due to the spatial separation between electron and hole wave functions. In the case of the e-e and h-h scatterings, the reduction of linewidths is mainly attributed to the decrease of the scattering matrix element due to the increase of the inverse screening length. Linewidths for e-h and h-e scatterings gradually increase with the sheet carrier density since the screening field increases, while linewidths for the other scatterings are almost independent of the sheet carrier density. The SC model also shows that linewidths for the carrier-carrier and carrier-phonon scatterings are nearly, constant irrespective of well thickness except for e-h and h-e scatterings. In the case of e-h and h-e scatterings, linewidths greatly decrease with the well width because of the increase of the spatial separation of wave functions.