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

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's 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 × 10 18 to 2 × 10 19 cm −3 , in good agreement with the targeted doping levels. 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 × 10 17 to 6 × 10 17 cm −3 . These findings confirm the difficulty to reach highly-doped n-type GaAs NWs, may be due to doping compensation. Notably, signatures of high concentration (5-9×10 18 cm −3 ) at the very top of NWs are unveiled.