ELECTRON AND PHONON RESONANCES OF ELECTRON-CAPTURE IN ALN GAN QUANTUM-WELLS/

We evaluate the rate of capture of electrons at the bottom of the firs t and second subbands above a GaN quantum well with AlN barriers. The capture rate is defined as the transition rate into all the subbands w ithin the quantum well by emission of either the bulk optical phonons of the well material or the confined and interface phonons of the diel ectric continuum (DC) model. Predictions of the two models are display ed and compared. We find that sharp peaks emerge at regular intervals of increasing well. width corresponding to resonances in the electron states as the initial subband energy drops into the quantum well. Othe r peaks arise when electrons begin to make transitions into the highes t subband in the well. These peaks, therefore, correspond to optical p honon emission thresholds and so depend on the model used to describe the phonon modes. The capture rate exhibits a strong dependence on wel l width, varying over four orders of magnitude, due to the large well depth characterising the AlN/GaN system. If the well width is made to vary at the scale of a monolayer thickness, this dependence becomes of great importance for the evaluation of the capture rate.