Hot Electron Dynamics in InAs–AlAsSb Core–Shell Nanowires

Abstract

Semiconductor nanowires (NWs) have shown evidence of robust hot-carrier effects due to their small dimensions, making them attractive for advanced photoenergy conversion concepts. Especially, indium arsenide (InAs) NWs are promising candidates for harvesting hot carriers due to their high absorption coefficient, high carrier mobility, and large effective electron-to-hole mass difference. Here, we investigate the cooling and recombination dynamics of photoexcited hot carriers in pure and passivated InAs NWs by using ultrafast near-infrared pump−probe spectroscopy. We observe reduced Auger recombination in pure InAs NWs compared to that in passivated ones and associate this with charge-carrier separation by surface band bending. Similarly, faster carrier cooling by electron−hole scattering is observed in passivated InAs−AlAsSb NWs at high carrier densities in excess of 10 18 cm −3 , where hot electron lifetimes in this regime increase substantially with the pump fluence due to Auger heating. These results emphasize the importance of type-II alignment for charge-carrier separation in hot-carrier devices to suppress carriermediated cooling channels. In addition, a separate charge-carrier population lasting up to several nanoseconds is observed for photoexcitation of the NW shell. Despite the high conduction band offset, carrier migration is not observed in the range of 40 ps to 2 ns. This observation may open avenues for core−shell NW multijunction solar cells.

Strong Dimensional and Structural Dependencies of Hot Carrier Effects in InGaAs Nanowires: Implications for Photovoltaic Solar Cells

“…However, the large surface-to-volume ratio of NWs can increase the influence of surface states on hot carriers and their thermalization rates . Sandner et al studied therefore the effects of surface passivation of NWs on their hot carrier properties using transient absorption pump–probe spectroscopy. Comparison of bare-core InAs and InAs-AlAsSb core–shell NWs showed that the passivation layer reduces Fermi-level pinning effects (lowering band bending) at the interface of the InAs absorber, while the rate of Auger recombination increases, both of which lead to an increase in hot carrier effects.…”

“…Hot carrier effects in NWs have been further studied using steady-state and time-resolved optical spectroscopy. − Tedeschi et al studied the effects of hot carriers in NWs under continuous wave excitation and found that there is a reciprocal relationship between hot carrier temperature and NW diameter. One of the main characteristics of NWs is their large surface-to-volume ratio, which can improve photoabsorption for solar cell applications .…”