C. Netzel

Optimization scheme for the quantum efficiency of GaInN-based green-light-emitting diodes

We have optimized the internal quantum efficiency (IQE) of GaInN∕GaN quantum-well (QW) structures. For an emission wavelength of 460nm, a high IQE of 73% was achieved. For a longer emission wavelength, calculations predict higher oscillator strength for thinner QWs but higher In content. We observe an improvement in IQE of almost 50% when reducing the QW width from 2.7nmto1.8nm, and increasing the In content for the whole blue to green spectral region with IQE=40% at 525nm. The typical saturation of the output power with increasing current that occurs, particularly for green-light-emitting diodes, is extremely weak in our structures.

Anti-localization suppresses non-radiative recombination in GaInN/GaN quantum wells

The light emission efficiency of (AlGaIn)N heterostructures and light-emitting diodes is exceptionally high, despite the high density of threading dislocations generally found in such structures. 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 non-radiatively at the defects. Here, we show that carriers are mobile at room temperature rather than localized and that under suitable growth conditions hexagonal V-shaped pits decorating the defects exhibit narrow sidewall quantum wells with an effective bandgap 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. Thus even for mobile charge carriers non-radiative recombination is effectively suppressed leading to the unexpectedly high emission efficiency.