Photostrictive behavior as the piezo-phototronic effect in InGaN/GaN multiple quantum wells

Electrostatic Contribution to the Photo-Assisted Piezoresponse Force Microscopy by Photo-Induced Surface Charge

“…3b) and no amplitude enhancement can be observed in its PFM image (not shown). Second, as reported in our previous work, the 1.8% enhancement in the slope steepness of GaN sample's amplitude curve falls within the fitting error range (1–2%), hence no observable (if any) photostrictive effect can be found in this sample using our PFM setup (Loo et al, 2021). Due to such photo-induced surface charge, when performing imaging mode using photo-assisted PFM, equation (1) that is used to describe the measured A ω ,3 should be modified to include the term V SP which can then be expressed as .…”

“…In the dark, the amplitude of the GaN sample is on average about 1.45 pm (range between 1.3 to 1.6 pm), while upon light illumination, its amplitude increases abruptly by an average of 0.45 pm registering an improvement of about 31%. Since constant V AC was employed throughout the measurement, adopting equation (1) to interpret this result would suggest that such improved amplitude is contributed by the enhancement of the of GaN sample under light illumination which can be elucidated as the photostrictive effect (Kundys, 2015; Loo et al, 2021). This interpretation, however, is in stark contrast with that provided by its amplitude curve, which was obtained through local spectroscopic measurement, see Figure 2a.…”

“…The advantage of operating in this frequency regime is twofold: (i) improve the PFM signal-to-noise ratio (Harnagea et al, 2003) and (ii) reduce the contribution of lateral (in-plane) signal to the of interest vertical (out-of-plane) signal (Kalinin et al, 2006; Jesse et al, 2006 b ). The resonance enhancement factor introduced was determined in our previous work (Loo et al, 2021). PFM images were acquired using a scan rate of 0.5 Hz with a driving AC voltage V AC of about 0.8 V (an identical V AC was used in the spectroscopic measurement).…”

“…In the case of KPFM measurement, the PeakForce Tapping mode, defined by Bruker, was adopted, operating at a scan rate of 0.5 Hz and a lift scan height of nearly 100 nm. Similar to the experimental configuration used in our previous work (Loo et al, 2021), since the nullifying voltage was applied to the sample, the CPD measured is interpreted as e CPD = where e , , and are the electron's charge, sample's work function, and tip's work function, respectively. The SPV was computed by taking the difference between the CPD measured under illumination CPD light and the CPD measured in the dark CPD dark .…”

“…Photo-assisted PFM, an extension of PFM which measures the change of piezoresponse due to light illumination, can be used to probe the interaction between photons and the polarization of a material. For instance, it has been used to investigate optically induced polarization switching in the organic–inorganic lead halide system (Coll et al, 2015; Kim et al, 2015; Wang et al, 2017), BFO thin films (Yang & Alexe, 2018) and ferroelectric heterostructures (Li et al, 2018), as well as revealing the photostrictive behavior of gallium nitride (GaN)-based semiconductors with multiple quantum wells structure (Loo et al, 2021). Herein, we demonstrated that, owing to the electrostatic contribution to the photo-assisted PFM signal, results obtained through PFM imaging and spectroscopic modes provided conflicting interpretations.…”