Direct assessment of p–n junctions in single GaN nanowires by Kelvin probe force microscopy

Abstract

Making use of Kelvin probe force microscopy, in dark and under ultraviolet illumination, we study the characteristics of p-n junctions formed along the axis of self-organized GaN nanowires (NWs).We map the contact potential difference of the single NW p-n junctions to locate the space charge region and directly measure the depletion width and the junction voltage. Simulations indicate a shrinkage of the built-in potential for NWs with small diameter due to surface band bending, in qualitative agreement with the measurements. The photovoltage of the NW/substrate contact is studied by analysing the response of NW segments with p-and n-type doping under illumination. Our results show that the shifts of the Fermi levels, and not the changes in surface band bending, are the most important effects under above band-gap illumination. The quantitative electrical information obtained here is important for the use of NW p-n junctions as photovoltaic or rectifying devices at the nanoscale, and is especially relevant since the technique does not require the formation of ohmic contacts to the NW junction.2

Effect of Bias on the Response of GaN Axial p–n Junction Single-Nanowire Photodetectors

“…Yet, the measured value (DCPD = 410±80 mV) is comparable to measurements performed in p-n junctions contained in GaN nanowires with similar diameter. 44,45 We observe that the CPD signal presents a clear increase in the vicinity of the p-contact. This indicates that the metal is partially depleting the p-doped region.…”

Investigation of the effect of the doping order in GaN nanowire p–n junctions grown by molecular-beam epitaxy

“…Focusing first on the "n-base" p-n junction (figure 1(e)) one can notice a widening of the NWs in their upper part. Such sort of inverse tapering results from an enhancement of the radial growth induced by the Mg incorporation during the growth of the ppart [22,23,27,39]. For its "p-base" counterpart (figure 1(f)), although a mild coalescence can be found in the upper side, which is typical for long dense NWs, the shape of individual NWs has almost no inverse tapering.…”

“…Scanning probe microscopy can also be used to assess doping: e.g. Kelvin probe force microscopy and the electron beam induced current microscopy (EBIC) were successfully applied to assess carrier concentrations in GaN NW p-n junctions [22,39].…”

Probing the Local Electrical Properties of Al(In,Ga)N by Kelvin Probe Force Microscopy

“…For the Bragg reflectors, larger thickness in comparison to HEMTs is required, therefore, it is important to understand the growth of these alloys. In this respect, surface study by scanning probe force microscopy has played a significant role in identifying leakage paths, deep traps, polarity and doping assessment, quantification of state density in III‐nitrides, while being limited mostly to only GaN and InGaN layers and nanostructures . Therefore, it is of high interest to extend this study to much wider band gap III‐nitride family Al(Ga, In)N.…”