Probing carrier dynamics in nanostructures by picosecond cathodoluminescence

Abstract

Picosecond and femtosecond spectroscopy allow the detailed study of carrier dynamics in nanostructured materials. In such experiments, a laser pulse normally excites several nanostructures at once. However, spectroscopic information may also be acquired using pulses from an electron beam in a modern electron microscope, exploiting a phenomenon called cathodoluminescence. This approach offers several advantages. The multimode imaging capabilities of the electron microscope enable the correlation of optical properties (via cathodoluminescence) with surface morphology (secondary electron mode) at the nanometre scale. The broad energy range of the electrons can excite wide-bandgap materials, such as diamond- or gallium-nitride-based structures that are not easily excited by conventional optical means. But perhaps most intriguingly, the small beam can probe a single selected nanostructure. Here we apply an original time-resolved cathodoluminescence set-up to describe carrier dynamics within single gallium-arsenide-based pyramidal nanostructures with a time resolution of 10 picoseconds and a spatial resolution of 50 nanometres. The behaviour of such charge carriers could be useful for evaluating elementary components in quantum computers, optical quantum gates or single photon sources for quantum cryptography.

High spatial resolution picosecond cathodoluminescence of InGaN quantum wells

“…We have developed an original pTRCL setup using an ultrafast pulsed electron gun described elsewhere. 14,15 Our setup reaches remarkable spatial and temporal resolutions of 50 nm and 10 ps, respectively. The samples were grown by metal-organic vapor phase epitaxy ͑MOVPE͒ in an AIXTRON 200/ 4 RF-S reactor on 2 in.…”

In-Situ Analysis of Optoelectronic Properties of Semiconductor Nanostructures and Defects in Transmission Electron Microscopes

“…CL intensity measurements have been applied to assess the density of point defects acting as radiative recombination center (e.g., Graham et al, 1994, Mitsui et al, 1996 and those acting as non-radiative one (e.g., Ohno et al, 1999, Ohno & Takeda, 1996. Also, the techniques have been used to assess the carrier dynamics such as excited carrier paths towards the lower energy states (e.g., Akiba et al, 2004, Merano et al, 2005, Sonderegger et al, 2006, as well as carrier lifetimes. Some extended defects such as dislocations (Yamamoto et al, 1984, Mitsui & Yamamoto, 1997, twins (Ohno et al, 2007b), platelets (Ohno, 2005a) and strains induced by a uniaxial stress , Ohno, 2005b, as well as low-dimensional nanostructures such as nanowires (Ishikawa et al, 2008, Yamamoto et al, 2006, quantum wells (Ohno, 2005a) and superlattices (Ohno & Takeda, 2002, Ohno et al, 2007b, form anisotropic defect levels, and electronic transitions via the levels result in the emission of polarized CL lights.…”

The role of transition radiation in cathodoluminescence imaging and spectroscopy of thin-foils

“…Cathodoluminescence (CL) in the electron microscope is a powerful technique for probing radiative transitions in dielectrics [1], plasmons [2][3], defect properties [4][5][6], strain [7] and carrier lifetime [8][9][10] at high spatial resolution. CL is typically implemented in a scanning electron microscope (SEM), but recently there has been renewed interest in its application as a transmission electron microscope (TEM) technique.…”