Quantitative Assessment of Carrier Density by Cathodoluminescence. II. GaAs nanowires

TL;DR

This study uses cathodoluminescence to quantitatively analyze doping levels in GaAs nanowires, revealing homogeneous p-type doping and challenges in achieving high n-type doping, with detailed spatial mapping of carrier concentrations.

Contribution

It introduces a high-resolution CL mapping method for precise, spatially resolved carrier density assessment in doped GaAs nanowires, advancing nanowire doping characterization techniques.

Findings

Quantitative hole concentration range from 1×10^{18} to 2×10^{19} cm^{-3} in Be-doped NWs.

Electron concentration in Si-doped NWs is approximately 3×10^{17} to 6×10^{17} cm^{-3}.

High doping signatures (5–9×10^{18} cm^{-3}) are observed at NW tips.

Abstract

Precise control of doping in single nanowires (NWs) is essential for the development of NW-based devices. Here, we investigate a series of MBE-grown GaAs NWs with Be (p-type) and Si (n-type) doping using high-resolution cathodoluminescence (CL) mapping at low- and room-temperature. CL spectra are analyzed selectively in different regions of the NWs. Room-temperature luminescence is fitted with the generalized Planck law and an absorption model, and the bandgap and band tail width are extracted. For Be-doped GaAs NWs, the bandgap narrowing provides a quantitative determination of the hole concentration ranging from about $1\times 10^{18}$ to $2\times 10^{19}$~cm$^{-3}$, in good agreement with the targeted doping levels. High-resolution maps of the hole concentration demonstrate the homogeneous doping in the pure zinc-blende segment. For Si-doped GaAs NWs, the electron Fermi level and the full-width at half maximum of low-temperature CL spectra are used to assess the electron concentration to approximately $3\times 10^{17}$ to $6\times 10^{17}$~cm$^{-3}$. These findings confirm the difficulty to obtain highly-doped n-type GaAs NWs, maybe due to doping compensation. Notably, signatures of high concentration (5--9$\times 10^{18}$~cm$^{-3}$) at the very top of NWs are unveiled.