In islands and their conversion to InAs quantum dots on GaAs (100): Structural and optical properties

Abstract

We report growth of crystalline In islands on GaAs ͑100͒ by molecular beam epitaxy at low temperatures. The islands have a pyramidlike shape with well defined facets and epitaxial relation with the substrate. They are of nanoscale dimensions with high density. Above a certain substrate temperature, associated with the melting point of In, noncrystalline round shaped islands form with larger size and lower density. Upon conversion of the In islands into InAs islands under As flux, the final shape does not depend on the original crystalline state but on the annealing temperature of the InAs islands. Clear photoluminescence is observed from InAs quantum dots after conversion of the crystalline In islands.

Low-density InAs QDs with subcritical coverage obtained by conversion of In nanocrystals

“…There is oneto-one In nanocrystal to InAs island correspondence, because the initial and final densities match. In accordance with previous reports [10], the InAs islands flatten and develop a local wetting layer elongated along [0][1][2][3][4][5][6][7][8][9][10][11]. For the symmetric In nanocrystals on the c(4 x 4) reconstructed surface ( Fig.…”

“…The As 4 background pressure was low enough that the respective surface reconstructions were stable for at least 30 min, also in the (2 x 4) case. Indium was deposited at a growth rate of 0.01 ML/s to form In nanocrystals with well defined epitaxial relationship, evidenced by the observation of a spotty RHEED transmission diffraction pattern (reported previously in [10]). The nanocrystals were transformed to InAs QDs by annealing under As 4 flux, initially at 100 °C and then at 420 °C for lOmin.…”

“…Low-density InAs/GaAs QDs can be obtained by molecular beam epitaxy (MBE) using the Stransld-Krastanov (SK) growth mode and small InAs coverage above the critical thickness [6] or extremely small growth rates [7]. An alternative, yet so far widely unexplored route to achieve this is to use droplet epitaxy [8][9][10], where one first deposits metallic liquid In droplets or, in our case epitaxial In nanocrystals and afterwards recrystalizes them under As flux. This offers a very robust and reproducible way to grow low-density QDs without relying on extremely low flux or precise coverage control.…”

Strain-driven alignment of In nanocrystals on InGaAs quantum dot arrays and coupled plasmon-quantum dot emission

“…After this the samples were cooled down to 100 or 120°C and In nanocrystals with 4 or 12 monolayers ͑ML͒ In amount were deposited. 14 The growth rates for GaAs and InAs were 0.054 and 0.0375 nm/s. The surface morphology of the In nanocrystals was characterized by tapping-mode atomic force microscopy ͑AFM͒ in air.…”

“…This is attributed to the crystalline nature of the In nanocrystals with the shape of a truncated pyramid and a clear epitaxial relationship with the GaAs ͑100͒ surface. 14 Figure 2 shows the temperature dependent PL spectra of the InGaAs QD arrays capped with 3-nm GaAs and 4 ML In nanocrystals grown at 120°C on top. The average base size and height of the In nanocrystal grown under these conditions are 40 and 30 nm, respectively, and their density is 5.1 m −2 .…”