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. [1] 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 [2]. 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.
[1] Hönig et al., Phys. Rev. Applied 7, 024004 (2017)
[2] Schlichting et al., arXiv:1707.06882 (2017).
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