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Becker, J.; Morkoetter, S.; Treu, J.; Sonner, M.; Speckbacher, M.; Doeblinger, M.; Abstreiter, G.; Finley, J. J.; Koblmüller, G. (2018): Carrier trapping and activation at short-period wurtzite/zinc-blende stacking sequences in polytypic InAs nanowires. In: Physical Review B, Vol. 97, No. 11, 115306
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Abstract

We explore the effects of random and short-period crystal-phase intermixing in InAs nanowires (NW) on the carrier trapping and thermal activation behavior using correlated optical and electrical transport spectroscopy. The polytypic InAs NWs are grown by catalyst-free molecular beam epitaxy under different temperatures, resulting in different fractions of wurtzite (WZ) and zincblende (ZB) and variable short-period (similar to 1-4 nm) WZ/ZBstacking sequences. Temperature-dependent microphotoluminescence (mu PL) studies reveal that variations in the WZ/ZB stacking govern the emission energy and carrier confinement properties. The optical transition energies are modeled for a wide range of WZ/ZB stacking sequences using a Kronig-Penney type effective mass approximation, while comparison with experimental results suggests that polarization sheet charges on the order of similar to 0.0016-0.08 C/m along the WZ/ZB interfaces need to be considered to best describe the data. The thermal activation characteristics of carriers trapped inside the short-period WZ/ZB structure are directly reproduced in the temperature-dependent carrier density evolution (4-300 K) probed by four-terminal (4T) NW-field effect transistor measurements. In particular, we find that activation of carriers in-between similar to 10(16)-10(17) cm(-3) follows a two-step process, with activation at low temperature attributed to WZ/ZB traps and activation at high temperature being linked to surface states and electron accumulation at the InAs NW surface.