Final report to the Department of Energy, Basic Energy Sciences, Grant No. DE-FG02-97ER45649 [Theoretical study of phonon modes and electron-phonon scattering]

We have studied the effect of additional layering within a semiconductor quantum well on carrier mobility compared to a simple quantum well. The previous report indicated results concerning modification of the phonon dispersion of the quantum well with additional layering and enhanced scattering from interface phonons accompanied by a reduction in confined phonon scattering. New results for this report are calculated relaxation times for transitions into all subbands of the quantum well structures and subsequent mobilities. We have found that mobilities are enhanced in structurally modified quantum well systems compared to simple quantum wells. Structurally modified quantum wells have additional thin layers of barrier material inside the well regions. For the case considered here, we have studied GaAs/AlAs quantum wells with thin AlAs layers, 8 {angstrom} in width, at room temperature. We have found that structurally modified quantum wells in the approximate ranges of 50-90 {angstrom}, 200-250 {angstrom}, and 370-400 {angstrom} show higher mobilities when compared to simple quantum wells of comparable widths. Mobilities increase when the separation between subbands is unfavorable for single phonon emission or absorption. Upon reaching resonance there is a sharp decrease in the mobilities until conditions become favorable again. This is a final report on the theoretical study of phonon modes and electron-phonon scattering in structurally modified electronic materials