Suppression of Nonradiative Recombination by V-Shaped Pits in $\mathrm{GaInN}/\mathrm{GaN}$ Quantum Wells Produces a Large Increase in the Light Emission Efficiency

Despite the high density of threading dislocations generally found in (AlGaIn)N heterostructures, the light emission efficiency of such structures is exceptionally high. It has become common to attribute the high efficiency to compositional fluctuations or even phase separation in the active GaInN quantum well region. The resulting localization of charge carriers is thought to keep them from recombining nonradiatively at the defects. Here, we show that random disorder is not the key but that under suitable growth conditions hexagonal V-shaped pits decorating the defects exhibit narrow sidewall quantum wells with an effective band gap significantly larger than that of the regular $c$-plane quantum wells. Thereby nature provides a unique, hitherto unrecognized mechanism generating a potential landscape which effectively screens the defects themselves by providing an energy barrier around every defect.

Figure 1

Schematic view of a hexagonal V-shaped pit emerging at the apex of a threading dislocation in a GaInN-based heterostructure.

Figure 2

Transmission electron microscope image (a) of a $\mathrm{GaInN}/\mathrm{GaN}$ multiple quantum well structure. In the planar region high quality QW’s with well-defined sharp interfaces are visible. In the vicinity of a threading dislocation, a V-shaped pit appears with sidewall QW’s with a thickness and spacing much lower than for the (0001) QW’s. This is also schematically shown in (b).

Figure 3

Comparison of TEM and near-field PL data: (a) shows low-temperature emission spectra obtained from nm-size areas close to threading dislocations with a near-field microscope [24]. Besides the main emission at 430 nm multiple sharp peaks from different locations appear in the range 380–410 nm. Utilizing the calculated emission wavelength vs QW width we compare the $c$-plane QW and the sidewall QW widths (reduction ratio from Fig. 2) with the main emission and the short wavelength emissions observed in SNOM measurements.

Figure 4

Visualization of the energy landscape resulting from V-shaped hexagonal pits exhibiting increased band gap in the sidewalls. Carriers in the regular $c$-plane QW’s (with lower band gap) in between have to overcome a large energy barrier to reach the defects and to recombine nonradiatively.