Deterministic Fabrication of Uniform and Bright InGaN Quantum Dot Emitters toward Exciton Bohr Radius Regime by a Combination of Dry and Anisotropic, Controlled Wet Etching Techniques

Photoelectrochemical and boiling tetramethylammonium hydroxide (TMAH)-assisted etching techniques are demonstrated as controlled, anisotropic methods to reliably and deterministically fabricate uniform InGaN quantum dots (QDs) in GaN nanowires. Photoelectrochemical etching in a dilute H 2 SO 4 solution is facilitated in two possible ways. First, it ensures no chemical reaction with GaN in the absence of light. Second, under photoexcitation, H 2 SO 4 inhibits oxide accumulation on the semiconductor surface, which confirms uninterrupted QD etching. Perfect modulation of etch bias and duration, along with a gradual shrinkage in QD diameter, opens up the possibility of extremely controlled etching toward the exciton Bohr radius (∼3 nm) regime. This is being investigated for the first time to the best of my knowledge. Strong quantum confinement is observed through a significant blue shift in the photoluminescence peak with longer photoelectrochemical etching. But direct photoelectrochemical etching of large-diameter dry-etched nanowires to fabricate QDs is detrimental to QD stability. Large mechanical strain at a QD/GaN interface causes nanowires to break. Alternatively, TMAH-assisted etching causes radial decay of the entire nanowire while ensuring better uniformity of QD diameter and nanowire height across the array. It also corrects the nanowire sidewall to near-vertical. Advantages of both techniques are simultaneously availed for the first time by combining them to fabricate selectively etched, uniform and mechanically stable QDs in near-vertical nanowires. This process shows the pathway to fabricate QDs from optically written large nanodisks at low cost. This combined etching technique leads to the formation of nanowires with a high surface-to-volume ratio and enhanced emission power density from QDs. The size uniformity of these bright QDs will make them promising sources of indistinguishable single photons with a reasonable count rate for room-temperature quantum optics applications. These site-controlled QDs will also pave the way for next-generation on-chip photonic integration.