Stacking faults as quantum wells in nanowires: Density of states, oscillator strength and radiative efficiency

TL;DR

This study demonstrates that stacking faults in GaN nanowires act as quantum wells with two-dimensional exciton states, revealing insights into radiative efficiency, internal fields, and nonradiative processes through photoluminescence spectroscopy.

Contribution

It provides experimental evidence that stacking faults serve as quantum wells in GaN nanowires and quantifies their oscillator strength and radiative properties, advancing understanding of exciton behavior in these structures.

Findings

Stacking faults act as quantum wells with 2D exciton states.

Radiative recombination of (I1;X) persists up to 60 K.

Nonradiative centers are limited to 2x10^16 cm^-3.

Abstract

We investigate the nature of excitons bound to I1 basal-plane stacking faults [(I1;X)] in GaN nanowire ensembles by continuous-wave and time-resolved photoluminescence spectroscopy. Based on the linear increase of the radiative lifetime of these excitons with temperature, they are demonstrated to exhibit a two-dimensional density of states, i. e., a basal-plane stacking fault acts as a quantum well. From the slope of the linear increase, we determine the oscillator strength of the (I1;X) and show that the value obtained reflects the presence of large internal electrostatic fields across the stacking fault. While the recombination of donor-bound and free excitons in the GaN nanowire ensemble is dominated by nonradiative phenonema already at 10 K, we observe that the (I1;X) recombines purely radiatively up to 60 K. This finding provides important insight into the nonradiative recombination processes in GaN nanowires. First, the radiative lifetime of about 6 ns measured at 60 K sets an upper limit for the surface recombination velocity of 450 cm/s considering the nanowires mean diameter of 105 nm. Second, the density of nonradiative centers responsible for the fast decay of donor-bound and free excitons cannot be higher than 2x10^16 cm^-3. As a consequence, the nonradiative decay of donor-bound excitons in these GaN nanowire ensembles has to occur indirectly via the free exciton state.