Radial Stark Effect in (In,Ga)N Nanowires

Abstract

We study the luminescence of unintentionally doped and Si-doped InxGa1-xN nanowires with a low In content (x < 0.2) grown by molecular beam epitaxy on Si substrates. The emission band observed at 300 K from the unintentionally doped samples is centered at much lower energies (800 meV) than expected from the In content measured by X-ray diffractometry and energy dispersive X-ray spectroscopy. This discrepancy arises from the pinning of the Fermi level at the sidewalls of the nanowires, which gives rise to strong radial built-in electric fields. The combination of the built-in electric fields with the compositional fluctuations inherent to (In,Ga)N alloys induces a competition between spatially direct and indirect recombination channels. At elevated temperatures, electrons at the core of the nanowire recombine with holes close to the surface, and the emission from unintentionally doped nanowires exhibits a Stark shift of several hundreds of meV. The competition between spatially direct and indirect transitions is analyzed as a function of temperature for samples with various Si concentrations. We propose that the radial Stark effect is responsible for the broadband absorption of (In,Ga)N nanowires across the entire visible range, which makes these nanostructures a promising platform for solar energy applications.

Electronic properties of air-exposed GaN(11-00) and (0001) surfaces after several device processing compatible cleaning steps

“…Therefore, we propose that •ClO n H m and/or •H terminations at the GaN(1 100) and (0001) surfaces act as surface donors. Overall, as shown in Table I, it is clear that the three cleaning steps investigated here can be used to tailor the GaN surface BB over several hundreds of meV, as qualitatively intended in other reports [7,51].…”

A generalized model for time-resolved luminescence of localized carriers and applications: Dispersive thermodynamics of localized carriers

“…With the rapid development of the InGaN alloy based blue-green light emitting diodes, recently, the CL effect induced by structural imperfections has been increasingly addressed 19–21 . For example, it has been well shown that localized carriers due to alloy disorder, especially indium content fluctuation, can produce efficient luminescence and unusual thermodynamic behaviors 19–28 .…”

Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

“…This effect can be moderately mitigated in the NW geometry as a result of lateral strain relief during growth. Several efforts already have been made to understand the QCSE for GaN/InGaN-based LEDs, 96,99,101,[103][104][105][106][107] but there were limited related studies on GaN/AlN or GaN/AlGaN-based UV LEDs. 108,109 In this regards, Leroux et al reported an internal electric field strength of 0.45 MV∕cm in AlGaN/GaN structures by varying the well thickness.…”

“…The excited carriers may pass through an intermediate energy state induced by the localized defects, 64 and other nonradiative recombination sites, thereby resulting in a reduction in the light-emitter performances. 107 To solve this problem, we have recently demonstrated that the use of long-carbon chained octadecanethiol (ODT) surface treatment of group-III nitride NWs-LED improves the light emission intensity due to a reduction in the SRH recombination and an increase in carrier lifetime. 64 InGaN/GaN NWs were soaked in a mix of ODT, ethanol, and NH 4 OH and kept at 60°C.…”