Effective Surface Passivation of InP Nanowires byAtomic-Layer-Deposited Al2O3 with POx Interlayer

摘要

III/V semiconductor nanostructures have significant potential in device applications, but effective surface passivation is critical due to their large surface-to-volume ratio. For InP such passivation has proven particularly difficult, with substantial depassivation generally observed following dielectric deposition on InP surfaces. We present a novel approach based on passivation with a phosphorus-rich interfacial oxide deposited using a low-temperature process, which is critical to avoid P-desorption. For this purpose we have chosen a POx layer deposited in a plasma-assisted atomic layer deposition (ALD) system at room temperature. Since POx is known to be hygroscopic and therefore unstable in atmosphere, we encapsulate this layer with a thin ALD Al2O3 capping layer to form a POx/Al2O3 stack. This passivation scheme is capable of improving the photoluminescence (PL) efficiency of our state-of-the-art wurtzite (WZ) InP nanowires by a factor of ∼20 at low excitation. If we apply the rate equation analysis advocated by some authors, we derive a PL internal quantum efficiency (IQE) of 75% for our passivated wires at high excitation. Our resultsindicate that it is more reliable to calculate the IQE as the ratioof the integrated PL intensity at room temperature to that at 10 K.By this means we derive an IQE of 27% for the passivated wires athigh excitation (>10 kW cm^–2), which constitutesan unprecedented level of performance for undoped InP nanowires. Thisconclusion is supported by time-resolved PL decay lifetimes, whichare also shown to be significantly higher than previously reportedfor similar wires. The passivation scheme displays excellent long-termstability (>7 months) and is additionally shown to substantiallyimprovethe thermal stability of InP surfaces (>300 °C), significantlyexpanding the temperature window for device processing. Such effectivesurface passivation is a key enabling technology for InP nanowiredevices such as nanolasers and solar cells.