Magnetic field effects and k∥-filtering in BEEM on GaAsAlGaAs resonant tunneling structures

In this work, GaAsAlGaAs double barrier resonant tunneling diodes (RTDs) are investigated by ballistic electron emission microscopy (BEEM). RTDs grown directly below the sample surface exhibit characteristic steplike features in the BEEM spectrum, whereas for buried RTDs, a linear spectrum is observed. Moreover, the BEEM spectra of sub-surface RTDs show Shubnikov-de Haas-like oscillations in magnetic fields. To investigate the origin of these effects, the BEEM spectra were calculated using a scattering formalism within the framework of a semi-empirical tight binding method. As a main result we found that, independent of the applied bias, only electrons within a narrow k∥ distribution are transferred resonantly through the RTD. Hence, a k∥ filter is established for ballistic electrons close to k∥=0. The calculated filter width is consistent with the magnetic field data.