Location of quantum dots identified by microscopic photoluminescence changes during nanoprobe indentation with a horizontal scan

Abstract

The location of quantum dots ͑QDs͒ embedded in a GaAs matrix is successfully identified by microscopic photoluminescence ͑PL͒ measurement during nanoprobe indentation with a horizontal scan at low temperature ͑10 K͒. By introducing a high-sensitive load cell and a focused ion beam-fabricated flat-apex nanoprobe, the indentation force and PL of QDs are measured simultaneously at each point in the direction of the nanoprobe horizontal scanning with a constant indentation force. The experimental results show that the emission energy from QDs has a strong dependence on the location of QDs relative to the nanoprobe-indented location. Consequently, the emission energy shifts with the nanoprobe scan, generating an emission trace with a constant indentation force. Based on the energy shift of the ground state of the QD simulated by the combination of three-dimensional finite element strain calculation and strain-dependent k·p Hamiltonian, an estimation method is developed, which enables us to identify the location of the QD from its emission trace in the nanoprobe indentation experiment. Results indicate that all the emission traces clearly observed are emitted from the QDs around the edge of the nanoprobe-indented area. Further discussion reveals that the evolution of shear strain generates hole accumulation around the contact edge of the indented nanoprobe. Consequently, the high density of holes enhances the PL of the QDs in that region.

Strain Engineering of Low‐Dimensional Materials for Emerging Quantum Phenomena and Functionalities

“…Ozasa et al performed multiple studies on nanoindentation of InGaAs QDs with a variety probes, primarily to observe the resulting photoluminescence effects. [128][129][130][131][132][133] Aucoated optical fibers with apex apertures of 500-3000 nm in diameter were investigated, where the optical fiber core enabled photoluminescence measurements through the aperture. The pyramid-shaped InGaAs QDs were ≈20 nm in base width and 7 nm in height and were dispersed with an area density of ≈5-6 × 10 10 cm −2 .…”

Direct-to-indirect transition observed in quantum dot photoluminescence with nanoprobe indentation

“…6 Band gap shift induced by the strain distribution was calculated with the 6 ϫ 6 strain Hamiltonian of Pikus and Bir 11 for valence band behavior. Since the size of the nanoprobe apex was more than one order of magnitude larger than the size of the QDs, we separated the calculation into four steps: ͑1͒ indentation-induced strain distribution in uniform GaAs matrix ͑without the QDs͒ was calculated for 4.0͑x͒ ϫ 2.0͑y͒ ϫ 2.0͑z͒ m 3 , ͑2͒ the indentation-induced strain inside/ around a single QD ͑pyramidal shape of 7 nm in height and 20 nm in base width͒ at a certain horizontal distance away from the nanoprobe center ͑hereafter, the location of QD is represented as 600 nm in QD location, which means that the QD is located at the distance of 600 nm away horizontally from the nanoprobe center at 50 nm in depth͒ was calculated for 200ϫ 100ϫ 140 nm 3 with applying the displacement boundary condition derived from the first step, ͑3͒ the latticemismatched strain inside/around a single QD was calculated ͑separately from indentation-induced strains͒ for 50ϫ 25 ϫ 150 nm 3 with a periodic boundary condition along the x and y directions, and ͑4͒ the strains derived from ͑2͒ and ͑3͒ were superimposed to finalize the strain distribution induced by lattice mismatch and nanoprobe indentation.…”

“…1͑a͒. 6,7 The quenching of fine PL peaks cannot be attributed to the reverse mechanism of PL enhancement, i.e., holeaccumulation reduction, because the hole accumulation increases monotonically with indentation force for a nanoprobe with a flat cylindrical apex. 1͑b͒.…”