Carrier diffusion in low-dimensional semiconductors: A comparison of quantum wells, disordered quantum wells, and quantum dots

Abstract

We present a comparative study of carrier diffusion in semiconductor heterostructures with different dimensionality [$\mathrm{InGaAs}$ quantum wells (QWs), $\mathrm{InAs}$ quantum dots (QDs), and disordered $\mathrm{InGaNAs}$ QWs (DQWs)]. In order to evaluate the diffusion length in the active region of device structures, we introduce a method based on the measurement of the current-voltage and light-current characteristics in light-emitting diodes where current is injected in an area $<1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}{\mathrm{m}}^{2}$. By analyzing the scaling behavior of devices with different sizes, we deduce the effective active area, and thus the diffusion length. A strong reduction in the diffusion length is observed going from QWs $({L}_{d}\ensuremath{\approx}2.7\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m})$ to QDs $({L}_{d}<100\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$, DQWs being an intermediate case (${L}_{\mathrm{diff}}\ensuremath{\approx}0--200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ depending on the carrier density). These results show that lateral composition fluctuations, either intended or unintended, produce strong carrier localization and significantly affect the carrier profile in a device even at room temperature.