Influence of surface passivation on electric properties of individual GaAs nanowires studied by current–voltage AFM measurements

Abstract

Current-voltage (I-V) characteristics of vertical p-GaAs nanowires (NWs) covered by different surface passivation materials were experimentally measured by conductive atomic force microscopy (C-AFM). The obtained I-V curves for individual NWs with a diameter of 100 nm covered with AlGaAs, GaN, GaP or InP shell layers were compared to analyse the influence of surface passivation on the density of surface states and choose the most beneficial passivating material for technological applications. We have found the absence of a Schottky barrier between the golden catalytic cap on the top of a NW and the nanowire situated below and covered with an ultrathin GaP passivating layer. It was suggested that passivating material can arrange the heterostructure configuration with the GaAs NW near the Au cap. The latter mechanism was proposed to explain a strong energy barrier found in nanowires covered with InP passivation. AlGaAs passivation affected the forward threshold voltage of nanowires for NWs, which was measured simultaneously with the resistivity of each individual vertical structure from an array by means of AFM in the regime of measuring the I-V curves and onefold calculations. We made an attempt to develop the methodology of measurement and characterization of electric properties of passivated NWs.

Piezoelectric Current Generation in Wurtzite GaAs Nanowires

“…The polarity of the I – V curves in Figure corresponds to the p‐type conductivity of the NWs. The breakdown of the Schottky barrier between the NW and the Au catalytic cap in −4 V confirms the high doping level of the NW, that is N A ≈ 10 18 cm −3 …”

“…The NWs were coated by 7 nm AlGaAs layer after completion of the growth phase. This procedure was performed to passivate the surface of the GaAs NWs and to prevent capturing of charge carriers at the surface states . Figure (a) shows a scanning electron microscopy (SEM) image of the NW array.…”

Opportunities of Scanning Probe Microscopy for Electrical, Mechanical and Electromechanical Research of Semiconductor Nanowires

“…It is noticeable that current through the NW in region of forward bias increases for both of them in comparison with unpassivated reference NWs. We studied these passivating shells in details previously [65,66]. GaP appeared to be the most advantageous passivating material from experimental measurements of GaAs NWs.…”

“…Reason for that is accumulation of electric charge at the shell and its capacitive adverse input blocking the conduction channel of the NW. Moreover, inclination of all curves in regions of linear resistance is equal because it represents the concentration of charge carriers, i.e., same doping level [65,66].…”

I–V curve hysteresis induced by gate-free charging of GaAs nanowires' surface oxide

“…Moreover, it is confirmed by the absence of hysteresis observed by us during the recording of I-V curves on passivated NWs because the surface oxide in them is replaced by passivating shell layers. 14 It is vital to consider that the charge accumulation occurs in regions with the highest voltage drop. For example, in the reverse-bias case, it is the Schottky barrier or the p-n junction area.…”