A strong limitation for the quantum efficiency of group III-nitride based light emitters is the spatial electron-hole separation due to the quantum-confined Stark effect (QCSE). To overcome this problem, Hönig et al.  proposed a concept, the Internal-Field-Guarded-Active-Region Design (IFGARD), which enables quasi electric-field free active regions in polar heterostructures. Here, we show how the encapsulation of the active region by additional guard layers results in a strong reduction of the built-in electric field in c-plane wurtzite nanostructures. In particular, we demonstrate experimental evidence for the successful realization of an IFGARD structure based on GaN/AlN heterostructures embedded in GaN nanowires. By means of power-dependent and time-resolved µ-photoluminescence (µ-PL) we experimentally proof the validity of the IFGARD structure. We managed to tune the emission of 4-nm-thick GaN nano-discs up to 3.32 eV at low excitation powers, which is just 150 meV below the bulk GaN bandgap . Our results demonstrate an almost complete elimination of the QCSE in comparison to conventional structures which show approximately 1 eV red-shifted emission. The reduction of the QCSE results in a significant increase of the radiative exciton decay rates by orders of magnitude and demonstrates the potential of IFGARD structures for future light sources based on polar heterostructures.
 Hönig et al., Phys. Rev. Applied 7, 024004 (2017)
 Schlichting et al., arXiv:1707.06882 (2017).
Gerald Hönig, Sarah Schlichting, Markus R. Wagner, Jan Müssener, Pascal Hille, Tim Grieb, Jörg Teubert, Jörg Schörmann, Andreas Rosenauer, Martin Eickhoff, Axel Hoffmann, and Gordon Callsen, "QCSE tuning in polar GaN/AlN heterostructures (Conference Presentation)," Proc. SPIE 10554, Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXII, 105540B (Presented at SPIE OPTO: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2295328.5751487339001.
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