nanowires; semiconductors; heterostructures; high resolution electron microscopy; photoluminescence; cathodoluminescence; structural properties; optical properties; nanostructures
Ketterer B, Heiss M, Livrozet MJ, Rudolph A, Reiger E, Morral AFI (2011), Determination of the band gap and the split-off band in wurtzite GaAs using Raman and photoluminescence excitation spectroscopy, in PHYSICAL REVIEW B
, 83(12), 1-4.
Heiss M, Conesa-Boj S, Ren J, Tseng HH, Gali A, Rudolph A, Uccelli E, Peiro F, Morante JR, Schuh D, Reiger E, Kaxiras E, Arbiol J, Morral AFI (2011), Direct correlation of crystal structure and optical properties in wurtzite/zinc-blende GaAs nanowire heterostructures, in PHYSICAL REVIEW B
, 83(4), 1-10.
Ketterer B, Heiss M, Uccelli E, Arbiol J, Morral AFI (2011), Untangling the Electronic Band Structure of Wurtzite GaAs Nanowires by Resonant Raman Spectroscopy, in ACS NANO
, 5(9), 7585-7592.
Semiconductor nanowires are filamentary crystals with a diameter of the order of few nanometers. In the last decade, they have opened up new directions in optoelectronic, sensing and energy harvesting applications. Their large surface-to-volume ratio has revealed and/or amplified phenomena such as the existence of other crystalline phases and scattering of free-carriers by the surface states. The direct relation between structure and functional properties is in nanowires clearly an important issue. As an example, differences in the exact structure within nanowires obtained in the same processing may explain the lack of 100% reproducibility that is observed today. Moreover, the investigation of a novel type of ‘heterostructures’ combining wurtzite and zinc-blende phases of one same material necessitate a direct correlation between structure and properties. An unambiguous correlation between structure and optical properties will bring understanding and open new directions in the area of nano-science and technology. We propose to simultaneously study the structure and optical properties of the same nanowire respectively by high-resolution transmission electron microscopy (HRTEM), confocal photoluminescence and cathodoluminescence. The structures investigated will be mainly heterostructures formed by wurtzite and zinc-blende structure in catalyst-free GaAs nanowires [ , ]. Bulk GaAs is stable zinc-blende structure. In the form of nanowire, GaAs can crystallize in the wurtzite form. Nanowires formed by a combination of the two structures have interesting optical properties that are still to date not fully understood. Additionally, the effect of the diameter and surface morphology on the luminescence efficiency will be studied. Here, we want to understand the reason why not 100% of the nanowires fabricated in one process have equal luminescence properties. For a reliable correlation between the structure and optical properties, a statistical study on numerous nanowires will be realized. This project will be developed in three main phases. First, a reliable method to study the same nanowire simultaneously by photoluminescence spectroscopy and HRTEM will be developed. Once this is achieved, measurements on the different types of samples will be realized and the physical mechanisms underlined. The effect of nanowire morphology and diameter on the luminescence efficiency will be first studied, followed by the investigation of nanowires with various percentages of wurtzite and zinc-blende structure. The following outcomes are expected from this project: (i) band alignment and exciton binding energy in wurtzite and zinc-blende GaAs quantum ‘heterostructures’ (ii) role of strain in the optical properties (iii) role of nanowire surface morphology and diameter in the luminescence efficiency, (iv) determination of the possible electric field at the interface and (iv) reproducibility of the properties of nanowires. Finally, we expect that the outcomes will also be useful for better controlling the structure -and functional properties- of nanowires