Be-Doping of MBE-Grown InP Nanowires

Abstract

<p>Be-doped InP nanowires were grown by the gold-assisted vapour-liquid-solid mechanism in a gas source molecular beam epitaxy system. The nanowires were characterized by scanning and transmission electron microscopy. With increased doping, the dependence of the length on diameter [L(D)] underwent an unusual transition from the diffusion-limited 1/D² relationship to one that increased before saturating. Doping influences on crystal structure and radial growth have been reported previously, but in the absence of these effects it is speculated that the beryllium introduces an increase in the steady-state chemical potential of the catalyst, and a barrier to nucleation. A model is presented relating the diffusion- and nucleation-limited regimes.</p> <p>Additionally, the progressive increase of dopant incorporation was verified by secondary ion mass spectrometry. Samples were transformed into a "bulk-like" material by spin-coating with cyclotene to enable depth profiling. Carrier concentrations were inferred through comparison with a thin film reference, and agreed in order of magnitude with the nominal doping values.</p> <p>Dopant activation was investigated through micro-photoluminescence experiments, and showed peak emissions between 1.49 eV and 1.50 eV for undoped samples, transitioning with increased doping to 1.45-1.46 eV. The difference between the dominant peak energies was consistent with differences reported for comparable epitaxially-grown thin film samples. Bandgap narrowing was also observed at high levels of doping, and was consistent with theoretical predictions.</p> <p>As a whole, the work presented here provides a different perspective on the effects of doping on nanowire growth, demonstrated through the specific system of Be-doped InP. The findings have implications for predictable and consistent nanowire device design, and suggestions for avenues of future research are provided.</p>