Probing of superlattice minibands by ballistic electron emission microscopy

Metal–insulator–metal injector for ballistic electron emission spectroscopy

“…The measured height of the AlGaAs barrier of g232 is thus 310 meV, in good agreement with the results obtained earlier on the same samples by STM-based BEEM measurements. 19 The shape of the BEES curves and the values of the onset voltages were reproduced on several samples and also agree excellently with the calculated results. It must be pointed out, however, that the total amount of the ballistic electron current shows large deviations when measured on different samples.…”

Hot electron spectroscopy and microscopy

“…To compare the spectroscopic capabilities of BEEM and hot electron spectroscopy with HET devices, we now discuss some spectroscopic results obtained on GaAs-AlGaAs superlattices. In our group, STM based ballistic transport through the lowest miniband of a buried GaAs-AlGaAs superlattice was studied already some time ago [155,86]. In this work, we had shown that the miniband transport results in a BEEM current threshold clearly below the height of the AlGaAs barriers, and that the measured and calculated miniband position in the GaAs-AlGaAs superlattice are in very good agreement [155].…”

“…In our group, STM based ballistic transport through the lowest miniband of a buried GaAs-AlGaAs superlattice was studied already some time ago [155,86]. In this work, we had shown that the miniband transport results in a BEEM current threshold clearly below the height of the AlGaAs barriers, and that the measured and calculated miniband position in the GaAs-AlGaAs superlattice are in very good agreement [155]. Like the DBRTs discussed in the previous sections, the miniband in the superlattice also acts as tunable energy filter, where both the position and the transmission of the miniband are a function of the applied bias voltage V c .…”

“…The main reason for this somewhat surprising behaviour can be found in the phonon scattering time, which has been determined to be ≈185 fs [27] in undoped GaAs. Looking at typical heterostructure samples investigated by BEEM, like buried double-barrier resonant tunnelling diodes and superlattices [86,155,156], one can see that the classical electron transfer time through the active region of the corresponding samples is usually only up to ≈100 fs and is, therefore, well below the phonon scattering time. Thus, LO phonon emission will not occur in the active region of the sample.…”