Type-II characteristics of photoluminescence from InGaAs/GaAs surface quantum dots due to Fermi level pinning effect

Abstract

The In(Ga)As/GaAs surface quantum dots (SQDs) have become appealing recently due to the special surface sensitivity property and consequently the advantage in developing sensors for humidity detection. This research reveals that the InGaAs/GaAs single-layer SQDs exhibit carrier separation due to Fermi level pinning, where electrons are pinned at surface but holes are confined inside the SQDs. Thus, photoluminescence (PL) features corresponding to carrier indirect transition are observed through a prominent blue-shift of ∼ 31 meV for the PL band that obeys a cube root power law over four orders of magnitude change in excitation power. The indirect transition of these SQDs is further characterized through time-resolved PL studies showing a biexponential decay with a relatively elongated carrier lifetime of ∼ 1.35 ns. This is the first time that a concept of type-II characteristic is proposed for the InGaAs SQDs, which will help to optimize the design and working principles for developing sensors with surface-sensitive InGaAs SQDs.