Formation and properties of InGaN QDs: Influence of substrates

Abstract

We examine the formation and properties of InGaN quantum dots (QDs) on free-standing GaN and GaN/sapphire templates, with and without buried InGaN/GaN QD superlattices (SLs). We use scanning tunneling microscopy (STM) and scanning tunneling spectroscopy to image the QDs and measure their electronic states. As the number of layers preceding the QDs increases (i.e., increasing substrate complexity), the total QD density increases. For free-standing GaN, STM reveals a mono-modal QD-size-distribution, consistent with a limited density of substrate threading dislocations serving as heterogeneous nucleation sites. For GaN/sapphire templates, STM reveals a bimodal QD-size-distribution, presumably due to the nucleation of additional ultra-small InN-rich QDs near threading dislocations. For multi-period QD SLs on GaN/sapphire templates, an ultra-high density of QDs, with a mono-modal size distribution is apparent, suggesting that QD nucleation is enhanced by preferential nucleation at strain energy minima directly above buried QDs. We discuss the relative influences of strain fields associated with threading dislocations and buried QD SLs on the formation of InGaN QDs and their effective bandgaps.

Enhanced Photoluminescence of 1.3 μm InAs Quantum Dots Grown on Ultrathin GaAs Buffer/Si Templates by Suppressing Interfacial Defect Emission

“…The higher TDD in the coalescence-rich thin buffer strongly suggests that TDs are the main root of defective QD formation. Previously, TDs have been associated with the nucleation of normal-sized GaN, Ge, and InGaN QDs. − We suspect that the strain field near the TDs led to the nucleation, overgrowth, and coalescence of QDs in our samples. For both 250 and 1000 nm samples, the defective QD density is larger than the TDD by roughly 5 × 10 8 cm –2 .…”