Abstract
Controlled doping of GaAs nanowires is crucial for the development of nanowire-based electronic and optoelectronic devices. Here, we present a noncontact method based on time-resolved terahertz photoconductivity for assessing n- and p-type doping efficiency in nanowires. Using this technique, we measure extrinsic electron and hole concentrations in excess of 10(18) cm(-3) for GaAs nanowires with n-type and p-type doped shells. Furthermore, we show that controlled doping can significantly increase the photoconductivity lifetime of GaAs nanowires by over an order of magnitude: from 0.13 ns in undoped nanowires to 3.8 and 2.5 ns in n-doped and p-doped nanowires, respectively. Thus, controlled doping can be used to reduce the effects of parasitic surface recombination in optoelectronic nanowire devices, which is promising for nanowire devices, such as solar cells and nanowire lasers.
Highlights
Semiconductor nanowires are of great interest as active components for electronic devices.[1]
GaAs nanowires were grown on p-type (111) Si substrates using molecular beam epitaxy under optimized conditions to produce a maximum yield of vertical nanowires.[49,50]
We show that the optical pump terahertz probe spectroscopy (OPTP) technique enables carrier lifetimes, carrier mobilities, and doping concentrations to be accurately determined, as well as recombination mechanisms investigated in detail using timedependent conductivity spectral data
Summary
Semiconductor nanowires are of great interest as active components for electronic devices.[1]. It has proven challenging to obtain an n-type conductivity via Si core doping of GaAs nanowires due to the amphoretic behavior of Si, as dopants incorporate both on Ga sites as donors and As sites as acceptors.[30] An n-type conductivity in GaAs nanowires has been achieved through Te core doping, yet as Te is a high vapor pressure element, its use in high-mobility molecular beam epitaxy (MBE) chambers is not ideal.[31,32] Alternatively, a shell of doped semiconductor may be grown over a nominally undoped NW core This “shell doping” technique has allowed many doped semiconductor heterostructures to be realized.[33−38] More recently, modulation doping has been achieved in GaAs/AlGaAs core−shell heterostructures. Increased impurity scattering in the heavily doped nanowires leads to an order of magnitude drop in electron mobility to ∼400 cm[2] V−1 s−1 compared with ∼1700 cm[2] V−1 s−1 for undoped reference nanowires, as expected for heavily doped structures.[43,46] Significantly, we show that for both n-type and p-type doped
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