Ballistic Electron Emission Microscopy and Spectroscopy BEEM/BEES

Figures (a) and (b) show the SEM and STM images of the self-assembled InP quantum dots and Figure (c) displays the resonant tunneling effects in InP QDs, as observed by BEEM spectroscopy.

Narayanamurti has used Ballistic Electron Emission Microscopy and Spectroscopy to make the first transport studies of self assembled InP and AlInP quantum dots (QDs) embedded in double barrier heterostructures. QD-based light emitters are expected to out-perform conventional devices by having lower current thresholds and higher characteristic temperatures. In spite of tremendous progress in controlling the size and density of self-assembled QDs, their quantum efficiency has been quite low. The solution to this problem will be better carrier confinement in QDs through the construction of better barriers. As shown above, BEEM spectroscopy performed on an individual dot revealed a strong resonant transmission through a quantized state 100 meV above the ground state, instead of the usual flow over a barrier. These results show that novel structures with multiple quantum barriers may achieve higher carrier confinement higher quantum efficiencies.

Harvard MRSEC (DMR-0820484)