Photo-assisted Kelvin probe force microscopy investigation of three dimensional GaN structures with various crystal facets, doping types, and wavelengths of illumination

Abstract

Three dimensional GaN structures with different crystal facets and doping types have been investigated employing the surface photo-voltage (SPV) method to monitor illumination-induced surface charge behavior using Kelvin probe force microscopy. Various photon energies near and below the GaN bandgap were used to modify the generation of electron–hole pairs and their motion under the influence of the electric field near the GaN surface. Fast and slow processes for Ga-polar c-planes on both Si-doped n-type as well as Mg-doped p-type GaN truncated pyramid micro-structures were found and their origin is discussed. The immediate positive (for n-type) and negative (for p-type) SPV response dominates at band-to-band and near-bandgap excitation, while only the slow process is present at sub-bandgap excitation. The SPV behavior for the semi-polar facets of the p-type GaN truncated pyramids has a similar characteristic to that on its c-plane, which indicates that it has a comparable band bending and no strong influence of the polarity-induced charges is detectable. The SPV behavior of the non-polar m-facets of the Si-doped n-type part of a transferred GaN column is similar to that of a clean c-plane GaN surface during illumination. However, the SPV is smaller in magnitude, which is attributed to intrinsic surface states of m-plane surfaces and their influence on the band bending. The SPV behavior of the non-polar m-facet of the slightly Mg-doped part of this GaN column is found to behave differently. Compared to c- and r-facets of p-type surfaces of GaN-light–emitting diode micro-structures, the m-plane is more chemically stable.

Boosting the performance of NO2 gas sensors based on n–n type mesoporous ZnO@In2O3 heterojunction nanowires: in situ conducting probe atomic force microscopic elucidation of room temperature local electron transport

“…The difference in the work function of the SKPM probe and the material was calculated using the following equations; e CPD= φ tip − φ sample where e is the charge, φ tip is the work function of the conducting probe and φ sample is the work function of the semiconductor material. 53 The topographic AFM images and the corresponding SKPM images of ZnO nanowires and ZnO@In 2 O 3 heterojunction nanowires before and during NO 2 exposure are shown in Fig. 6 .…”

Imaging photoinduced surface potentials on hybrid perovskites by real-time Scanning Electron Microscopy

“…Extended review papers on photovoltage phenomena and related characterizations "at the crossroads of physics, chemistry and electrical engineering" have been provided e.g by Shapira, 2001, 1999). Among commonly used experimental methods to evaluate the effect we can mention photo-assisted Kelvin probe spectroscopy (Ali Deeb et al, 2017), all-optical pump-probe absorption spectroscopies (Jana et al, 2014) and photoemission electron spectroscopies (Tanaka, 2012).…”

Spatial Surface Charge Engineering for Electrochemical Electrodes

“…The KPFM measurements are performed under illumination to obtain a stable and reproducible signal. In the dark, random fast and slow charging and discharging processes at the surface turn the measurements unreliable 45,46 . Such processes are screened and stabilized under illumination.…”