Γ-X Transfer in Tunneling through Single AlAs Barriers

When electrons tunnel through a single barrier of AlAs between GaAs contact layers there is a possibility of transfer from the Γ-conduction band to the X-band.1,2,3 The basic mechanism for Γ-X transfer based on the model of Liu 3 is shown in Fig. 1 along with Γ (solid lines) and X (dashed lines) conduction-band profiles for a 5.2 nm AlAs barrier. A Γ-electron can (1) tunnel through the entire structure without transfer, it can (2) transfer to the X-minimum at the first interface and propagate through the AlAs layer before transferring back to the Γ-minimum, or it can (3) transfer to the X-minimum at the first interface and propagate through the whole structure. The transfer at the interfaces is described by an interaction vertex VΓX or a coupling parameter α as described in Ref. 3. The process (2) is relatively unimportant at low applied potentials but becomes dominant above about 0.3 V where the Fermi energy has crossed the X-band in the AlAs.