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 barrier structure" with 20 Å AlAs layers separated by a 40 Å GaAs layer, as a function of hydrostatic pressure and in the presence of a magnetic field perpendicular to the interfaces (B∥J). At B=0 and at high pressures (≥10 kbar), resonant tunneling and its phonon satellites are observed between a Γ symmetry state in the GaAs emitter and a longitudinal X_z symmetry state in the AlAs collector. As the pressure is increased, the band offset between the Γ and the X_z states is decreased, resulting in a shift of these resonances to lower bias. At B≠0, clear periodic structures are observed in the current vs voltage characteristic, which are interpreted as resonant tunneling from the lowest emitter Γ Landau level to X_z collector levels of increasing Landau index. Quantitative analysis yields the energies of the phonons participating in the inelastic tunneling, and the transverse mass, m_XY, at the band edge of AlAs. Our method provides the most accurate determination to date of the transverse mass, and reports on its pressure dependence. We find m_XY/m₀=[(0.284±0.008) - (0.0039±0.0003) × P] where P is the pressure in kbar.