Determination of the transverse X-point effective mass in AlAs and its pressure dependence

We have investigated 2D-->2D magnetotunneling in a GaAs/AlAs "double barrie r structure" with 20 Angstrom AlAs layers separated by a 40 Angstrom GaAs l ayer, as a function of hydrostatic pressure and in the presence of a magnet ic field perpendicular to the interfaces (B parallel toJ). At B = 0 and at high pressures (greater than or equal to 10 kbar), resonant tunneling and i ts phonon satellites are observed between a Gamma symmetry state in the GaA s emitter and a longitudinal X-Z symmetry state in the AlAs collector. As t he pressure is increased, the hand offset between the Gamma and the X-Z sta tes is decreased, resulting in a shift of these resonances to lower bias. A t B not equal 0, clear periodic structures are observed in the current vs v oltage characteristic, which are interpreted as resonant tunneling from the lowest emitter Gamma Landau level to X-Z collector levels of increasing La ndau index. Quantitative analysis yields the energies of the phonons partic ipating in the inelastic tunneling, and the transverse mass, m(XY), at the hand edge of AlAs. Our method provides the most accurate determination to d ate of the transverse mass, and reports on its pressure dependence. We find m(XY)/m(0) = [(0.284+/-0.008) - (0.0039+/-0.0003) x P] where P is the pres sure in kbar.