Quantitative Assessment of Carrier Density by Cathodoluminescence. II. Nanowires

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 temperatures. 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 x 10(18) to 2 x 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 zincblende 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 x 10(17) to 6 x 10(17) cm(-3). These findings confirm the difficulty in obtaining highly doped n-type GaAs NWs, maybe due to doping compensation. Notably, signatures of high concentration [(5-9)x 10(18) cm(-3)] at the very top of NWs are unveiled.