InAs island-to-ring transformation by a partial capping layer

Transformation of InAs islands into quantum rings (QRs) by metal organic vapor phase epitaxy is investigated by using a GaAs partial capping layer followed by annealing under tertiarybutylarsine (TBAs) flow. QRs with the density of 107–109cm-2 are obtained at 500–600∘C. The optimum values for the annealing time and the partial capping layer thickness are found to be 60–120 s and 0.5–2.0 nm, respectively. Both a thicker cap layer and shorter annealing time produce an obvious suppression of the ring evolution. The geometric shape of the rings is elongated in [1 1 0] direction due to the anisotropy of the diffusion rate of the indium atoms. However, this elongation is reduced in the QRs annealed at higher temperatures. Low-temperature (10 K) photoluminescence (PL) peak at 1.22 eV with the full width at half maximum of about 80 meV is obtained from the buried QRs grown at 550∘C. A blue shift of the PL peak is observed when the annealing temperature is increased. This energy shift is probably due to the changes in the ring size and in the indium composition of the ring.