Carrier relaxation in GaAs v-groove quantum wires and the effects of localization

Carrier relaxation processes have been investigated in $\mathrm{GaAs}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ v-groove quantum wires (QWRs) with a large subband separation $(\ensuremath{\Delta}E\ensuremath{\simeq}46\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$. Signatures of inhibited carrier relaxation mechanisms are seen in temperature-dependent photoluminescence (PL) and photoluminescence-excitation measurements; we observe strong emission from the first excited state of the QWR below $\ensuremath{\sim}50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This is attributed to reduced intersubband relaxation via phonon scattering between localized states. Theoretical calculations and experimental results indicate that the pinch-off regions, which provide additional two-dimensional confinement for the QWR structure, have a blocking effect on relaxation mechanisms for certain structures within the v groove. Time-resolved PL measurements show that efficient carrier relaxation from excited QWR states into the ground state occurs only at temperatures $\ensuremath{\gtrsim}30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Values for the low-temperature radiative lifetimes of the ground- and first excited-state excitons have been obtained ($340\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ and $160\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$, respectively), and their corresponding localization lengths along the wire estimated.