Growth and characterization of InAs columnar quantum dots on GaAs substrate

Abstract

The growth of InAs columnar quantum dots (CQDs) on GaAs substrates by molecular beam epitaxy was investigated. The CQDs were formed by depositing a 1.8 monolayer (ML) InAs seed dot layer and a short period GaAs/InAs superlattice (SL). It was found that the growth of the CQDs is very sensitive to growth interruption (GI) and growth temperature. Both longer GI and higher growth temperature impact the size dispersion of the CQDs, which causes the broadening of photoluminescence (PL) spectrum and the presence of the additional PL peak tails. By properly choosing the GI and the growth temperature, CQDs including GaAs (3 ML)/InAs (0.62 ML) SL with period number up to 35 without plastic relaxation were grown. The corresponding equivalent thickness of the SL is 41 nm which is two times higher than the theoretical critical thickness of the strained InGaAs layer with the same average In composition of 16%. The increase of the critical thickness is partially associated with the formation of the CQDs. Based on a five-stack CQD active region, laser diodes emitting around 1120 nm at room temperature were demonstrated, indicating a high material quality. CQDs with nearly isotropic cross section (20 nm×20 nm dimensions) were formed by depositing a 16-period GaAs (3 ML)/InAs (0.62 ML) SL on an InAs seed dot layer, indicating the feasibility of artificial shape engineering of QDs. Such a structure is expected to be very promising for polarization insensitive device applications, such as semiconductor optical amplifiers.

Polarization dependence study of electroluminescence and absorption from InAs∕GaAs columnar quantum dots

“…Due to their flat shape and quasibiaxial compressive strain, self-assembled quantum dots have a valence-band ground state of the heavyhole ͑hh͒ type, which does not couple to light polarized along the growth axis, i.e., transverse-magnetic ͑TM͒ mode in a guided-wave configuration. A hope exists, however, that both the shape of the confinement potential and the strain distribution can be changed by varying the QD aspect ratio, e.g., by changing the QD growth conditions, [4][5][6] or using a capping layer, 7 or close-stacking of several QDs. 8 In particular, depositing a short-period GaAs/ InAs superlattice ͑SL͒ on top of a seed QD layer results in the formation of columnar quantum dots ͑CQDs͒ with high aspect ratio.…”

“…8 In particular, depositing a short-period GaAs/ InAs superlattice ͑SL͒ on top of a seed QD layer results in the formation of columnar quantum dots ͑CQDs͒ with high aspect ratio. [4][5][6][9][10][11] The polarization properties of photoluminescence ͑PL͒ from the cleaved edge have been investigated for CQDs ͑Refs. 4, 12, and 13͒ and evidence of net TM gain under optical pumping has been reported very recently, 12 but no lasing.…”

Photoluminescence from a single InGaAs epitaxial quantum rod

“…The plane-view images revealed that they have a diamond ͑rhombus͒ shape with diagonals along the ͓110͔ and ͓1-10͔ directions and their length ratio is typically 1.22. 5 The cross-sectional TEM images ͑see Fig. 1͒ show they have the aspect ratio larger than 4 ͑height of 41 nm and the diagonal length of 10 nm, approximately͒ and an almost constant In content in the quantum rod ͑ϳ40% ͒ and in the surrounding two-dimensional ͑2D͒ "immersion" layer ͑ϳ15% ͒.…”

“…In this case, the preferential incorporation of In adatoms in strained areas on top of the seed QDs leads to the formation of "column-shaped" nanostructures. Recently, this technique was extended to demonstrate InGaAs QDs with an aspect ratio exceeding 1, [3][4][5][6] leading to the formation of vertical quantum rods, also called "quantum posts." Additionally, it was shown that the In content profile in the vertical direction can be controlled by varying the deposition duty cycle.…”

“…More details of the growth process have been already reported elsewhere. 5,6 Transmission electron microscopy ͑TEM͒ has been performed in order to determine the rods' geometry and composition. The plane-view images revealed that they have a diamond ͑rhombus͒ shape with diagonals along the ͓110͔ and ͓1-10͔ directions and their length ratio is typically 1.22.…”