ABSTRACT
First-step nucleation growth has an important impact on the two-step growth of high-quality mid-infrared emissive InAs/InGaAs/InP quantum dots (QDs). It has been found that an optimized growth rate for first-step nucleation is critical for forming QDs with narrow size distribution, high dot density and high crystal quality. High growth temperature has an advantage in removing defects in the QDs formed, but the dot density will be reduced. Contrasting behavior in forming InAs QDs using metal-organic vapor phase epitaxy (MOVPE) by varying the input flux ratio of group-V versus group-III source (V/III ratio) in the first-step nucleation growth has been observed and investigated. High-density, 2.5 × 10(10) cm(-2), InAs QDs emitting at>2.15 µm have been formed with narrow size distribution, â¼1 nm standard deviation, by reducing the V/III ratio to zero in first-step nucleation growth.
ABSTRACT
We report the first study of argon (Ar)-plasma-enhanced intermixing of InAs/InGaAs/InP self-assembled quantum dots (QDs) in an inductively coupled plasma reactive ion etch system. The Ar-plasma exposure creates point defects, which propagate into the QD structure and enhance the intermixing between the QDs and their barrier layers, hence tuning the energy bandgap of the QDs. By optimizing the plasma exposure time and the annealing temperature, we observe (i) a blueshift of 160 nm and an increase in the photoluminescence (PL) intensity of the QD samples immediately after Ar-plasma exposure for 90 s, and (ii) a further increase in the blueshift of 330 nm, accompanied by 2.5-times increase in the PL intensity and 37 nm narrowing in the PL linewidth after subsequent rapid thermal annealing at 720 °C. The ability to generate a large blueshift without degrading the material quality shows that Ar-plasma exposure is an efficient post-growth technique for tuning the energy bandgap of QD structures.
