Role of hole confinement in the recombination properties of InGaN quantum structures

Abstract

We study the isolated contribution of hole localization for well-known charge carrier recombination properties observed in conventional, polar InGaN quantum wells (QWs). This involves the interplay of charge carrier localization and non-radiative transitions, a non-exponential decay of the emission and a specific temperature dependence of the emission, denoted as “s-shape”. We investigate two dimensional In 0.25 Ga 0.75 N QWs of single monolayer (ML) thickness, stacked in a superlattice with GaN barriers of 6, 12, 25 and 50 MLs. Our results are based on scanning and high-resolution transmission electron microscopy (STEM and HR-TEM), continuous-wave (CW) and time-resolved photoluminescence (TRPL) measurements as well as density functional theory (DFT) calculations. We show that the recombination processes in our structures are not affected by polarization fields and electron localization. Nevertheless, we observe all the aforementioned recombination properties typically found in standard polar InGaN quantum wells. Via decreasing the GaN barrier width to 6 MLs and below, the localization of holes in our QWs is strongly reduced. This enhances the influence of non-radiative recombination, resulting in a decreased lifetime of the emission, a weaker spectral dependence of the decay time and a reduced s- shape of the emission peak. These findings suggest that single exponential decay observed in non-polar QWs might be related to an increasing influence of non-radiative transitions.

Substitutional synthesis of sub-nanometer InGaN/GaN quantum wells with high indium content

“…In previous work, we determined directly the indium content of QWs grown at 680 °C using quantitative high-resolution scanning transmission electron microscopy (HRSTEM) observations, and again yielded x In < 35% 25 . Photoluminescence (PL) measurements performed on such SLs revealed emission peaks ranging between 2.8 and 3.4 eV 17 , 21 , 24 , 26 – 29 , when first principle calculations predict ≈2.1 eV for 1InN/ n GaN SLs in the limit of a large number, n , of GaN barrier MLs 7 , 30 . This deviation has been attributed either to formation of In x Ga 1− x N alloy or to reduced spatial localization of excitons 17 , 30 .…”