Synthesis and systematic optical investigation of selective area droplet epitaxy of InAs/InP quantum dots assisted by block copolymer lithography

Abstract

We report on the systematic investigation of the optical properties of a selectively grown quantum dot gain material assisted by block-copolymer lithography for potential applications in active optical devices operating in the wavelength range around 1.55 µm and above. We investigated a new type of diblock copolymer PS-b-PDMS (polystyrene-blockpolydimethylsiloxane) for the fabrication of silicon oxycarbide hard mask for selective area epitaxy of InAs/InP quantum dots. An array of InAs/InP quantum dots was selectively grown via droplet epitaxy. Our detailed investigation of the quantum dot carrier dynamics in the 10-300 K temperature range indicates the presence of a density of states located within the InP bandgap in the vicinity of quantum dots. Those defects have a substantial impact on the optical properties of quantum dots.

Optical Properties of Site-Selectively Grown InAs/InP Quantum Dots with Predefined Positioning by Block Copolymer Lithography

“…The extracted PL rise times are collected in Figure 5 d, showing monotonic increase from at , to beyond at . A similar observation has been recently made for an ensemble of SAG InAs/InP QDs [ 29 ], and we believe that these statements apply to the investigated dots as well. The PL rise time is contributed by two independent times: the carrier capture time, and intradot relaxation time.…”

“…Second, quantitative similarities among the values of activation energies may point to the same PL quench mechanism independent of the dot size, which is opposite to SK InAs/InP QDs where the PL intensity quench energy scales with the QD potential depth [ 1 ]. Third, the activation energies are comparable to those previously obtained for the ensemble of SAG InAs/InP QDs [ 29 ]. They are attributed to carrier quench mechanisms in the InP barrier which seems to be also active for the studied dots.…”

“…The mask fabrication is described in Ref. [ 29 ] and starts with the spin-casting the PS- b -PDMS powder (61–111 K, purchased from Sigma-Aldrich, St. Louis, MO, USA) dissolved in cyclohexane 1/400 mg/mL onto the InP(100) oriented wafer with a predeposited InP epitaxial buffer layer ( of InP grown with flow of TMIn and of PH ). The solvent annealing (methylcyclohexane saturated vapor) promotes the formation of the pattern of standing PS cylinders in the PDMS matrix.…”

“…Several techniques have been used for site selection in InP material, including local atomic-force-microscopy oxidation [23] or nanopatterning by electronic lithography [24]. Block copolymer lithography was previously used to form a mask for selective-area growth (SAG) of In(Ga)As QDs in both GaAs [25][26][27] and InP [13,25,26,28,29] material systems. This method can result in establishing a dense ensemble of InAs/InP QDs [13,26,[28][29][30].…”

“…Block copolymer lithography was previously used to form a mask for selective-area growth (SAG) of In(Ga)As QDs in both GaAs [25][26][27] and InP [13,25,26,28,29] material systems. This method can result in establishing a dense ensemble of InAs/InP QDs [13,26,[28][29][30]. Within this growth approach, the nucleation of QDs occurs in openings of a few tens of nanometers in size.…”