Formation of twin boundaries during the growth of semiconductor nanowires is very common. However, the effects of such planar defects on the electronic and optical properties of nanowires are not very well understood. Here, we use a combination of ab initio simulation and experimental techniques to study these effects. Twin boundaries in GaP are shown to act as an atomically-narrow plane of wurtzite phase with a type-I homostructure band alignment. Twin boundaries and stacking faults (wider regions of the wurtzite phase) lead to the introduction of shallow trap states observed in photoluminescence studies. These effects should have a profound impact on the efficiency of nanowire-based devices. * rubelo@mcmaster.ca 1 arXiv:1810.01194v2 [cond-mat.mtrl-sci] 11 Mar 2019 III-V semiconductor nanowires (NWs) have applications in electronic, optoelectronic, and photonic devices [1]. III-V NWs can be grown epitaxially on Si making integration of III-V optoelectronic devices with Si-based technology possible [2][3][4]. NWs with embedded quantum dots (e.g.GaAs quantum dots in GaP NWs) have shown potential for use in light-emitting diodes (LEDs), lasers and photodetectors [5].Crystal imperfections in 111 oriented III-V NWs is one of the factors that can limit the performance of optoelectronic devices. Twin boundaries (TBs) are one of the most abundant planar defects observed in NWs [6] as well as bulk semiconductors [7]. A very high twin plane density is usually observed in NWs due to their relatively low stacking fault energy, especially for GaP (30 meV/atom) [8], which can be easily overcome at typical NW synthesis temperatures. Planar crystal defects, such as TBs and stacking faults, can affect electron transport by acting as a carrier scattering source [9, 10], a recombination center [11-13] or a trap [14, 15]. Unwanted radiative or non-radiative recombination associated with mid-gap states can be detrimental to the efficiency of optoelectronic devices such as removing carriers from the desired recombination channel in lasers or LEDs or reducing carrier collection in photovoltaic cells. Understanding the potential effects of such defects on the electronic and optical properties of NWs is critical for NW optoelectronic devices.Here, we present structural and optical studies of GaP NWs combined with ab initio calculations to establish a structure-property relationship. Despite GaP being an indirect semiconductor, photoluminescence (PL) spectra of GaP NWs show optical transitions at energies lower than the fundamental band gap of bulk GaP. Transmission electron microscopy (TEM) analysis of NWs indicates that GaP is present in the zinc blende (ZB) phase along with the existence of TBs. We use a density functional theory (DFT) to establish a model of the 111 TB in GaP and propose an effective band diagram that explains the origin of sub-band gap optical transitions. II. METHOD A. Experimental detailsGaP NWs were grown on (111) Si by the self-assisted (seeded by a Ga droplet) selective-area epitaxy method using a multi-source ...

No abstract

No abstract

No abstract