Abstract
We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.
Highlights
Bob Sinclair and Nestor Zaluzec have pioneered the use of electron microscopy and analysis to characterise the structure of materials at the nanoscale
The present paper reports some of our research on the unusual atomic structure of InGaN quantum wells, which relates to the work of Zaluzec [4] and for which aberration-corrected electron microscopy has been essential
It is worth noting that this detailed understanding of electrons and holes in polar InGaN quantum wells (QWs) is based upon observations of the atomic structure of the wells using high resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT), these experimental results being input as data into theoretical calculations
Summary
Bob Sinclair and Nestor Zaluzec have pioneered the use of electron microscopy and analysis to characterise the structure of materials at the nanoscale. Has been central to the research of Sinclair, aberrationcorrected transmission electron microscopy He has utilised high resolution electron microscopy to analyse a wide range of materials and devices, from seminal work on silicide thin-films on silicon [1] to quantum dots in living mice [2]. Zaluzec has developed state-of-the-art instrumentation for electron and X-ray spectroscopy, and analytical electron microscopy He has recently investigated how aberration-corrected transmission electron microscopes can be re-engineered to improve the sensitivity of spectroscopy in analytical modes. He has studied a wide range of materials, from ground-breaking research on high-Tc superconductors [3] to InGaN quantum wells in light emitting diodes [4].
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