Abstract
Nanowires require surface passivation due to their inherent large surface to volume ratio. We investigate the effect of embedding InP nanowires in different oxides with respect to surface passivation by use of electron beam induced current measurements enabled by a nanoprobe based system inside a scanning electron microscope. The measurements reveal remote doping due to fixed charge carriers in the passivating POx/Al2O3 shell in contrast to results using SiOx. We used time-resolved photoluminescence to characterize the lifetime of charge carriers to evaluate the success of surface passivation. In addition, spatially resolved internal quantum efficiency simulations support and correlate the two applied techniques. We find that atomic-layer deposited POx/Al2O3 has the potential to passivate the surface of InP nanowires, but at the cost of inducing a field-effect on the nanowires, altering their electrostatic potential profile. The results show the importance of using complementary techniques to correctly evaluate and interpret processing related effects for optimization of nanowire-based optoelectronic devices.
Highlights
Nanowire (NW) solar cells have the potential to reach similar or even higher efficiencies as thin-film solar cells while at the same time only using fractions of the expensive III-V semiconductor materials [1]
At an excitation flux of 3 × 1012 photons·cm−2·pulse−1 the charge carrier lifetime decreases from 650 ps for as-grown NWs to 507 ps for SiOx covered NWs and 474 ps for POx/Al2O3 covered NWs (see Table S1 in the Electronic Supplementary Material (ESM))
By measuring time-resolved photoluminescence (TRPL) on nominally intrinsic and doped InP NWs, we showed that the influence of insulation layers is doping dependent
Summary
Nanowire (NW) solar cells have the potential to reach similar or even higher efficiencies as thin-film solar cells while at the same time only using fractions of the expensive III-V semiconductor materials [1]. Electron beam induced current (EBIC) measurements have been proven to be a successful tool to investigate p–n junctions of both single NWs [17, 19,20,21,22], and processed NW solar cells [23,24,25]. The simulations agree with the experimental data and demonstrate the influence of surface passivation and dopant concentrations on the electrostatic potential of NWs with p–i–n junctions helping to understand the correlation of TRPL and EBIC measurements. Understanding the effect of the use of different oxides on the electrostatic potential of semiconductor NWs is crucial, as many nanowire-based devices, especially NW solar cells with axially defined junctions [17, 29, 30], employ insulation layers to prevent electric short circuits
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