Temperature‐dependent Kelvin probe studies on GaN from 80 to 600 K

Abstract

In this work, we report on the effect of temperature on near‐surface band bending and surface photovoltage (SPV) in GaN. Band bending and SPV during illumination and after switching the illumination off are calculated for n ‐type and p ‐type GaN by using a thermionic model. The temperature and temporal dependencies are compared with experimental data. We find that the thermionic model describes adequately the SPV values and its dynamics only at high temperatures. At temperatures below room temperature the observed SPV is much higher than predicted from the thermionic model, especially in the case of p ‐type GaN. This fact is explained by a significant shift of the quasi‐Fermi level in p ‐type GaN under illumination. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Barrier Molecules Based on Formamidinium for Low-Dimensional Perovskite Solar Cells

“…For PhACCl, the Fermi level is shifted by 220 mV, whereas for BzmCl, the Fermi level is shifted by 362 mV. Apparently, for BzmCl, the quasi-Fermi level is closer to the valence band than for PhACCl; this suggests that the hole density is higher in perovskite based on BzmCl . This is also supported by Mott–Schottky analysis, which provides the carrier density for BzmCl and PhACCl ( N d = 4.92 × 10 +17 cm –3 for BzmCl compared to N d = 4.72 × 10 +17 cm –3 for PhACCl).…”

“…Apparently, for BzmCl, the quasi-Fermi level is closer to the valence band than for PhACCl; this suggests that the hole density is higher in perovskite based on BzmCl. 39 Further support for different properties when PhACCl is the barrier molecule can be observed from the scanning electron microscope (SEM) top view (Figure S4). The surface of BzmCl has pinholes, in contrast to PhACCl, which has a surface without pinholes.…”

Designing a Robust Kelvin Probe Setup Optimized for Long-Term Surface Photovoltage Acquisition

“…The insets of Diagrams (c) and (d) show the noise bands in the dark and under illumination to be smaller than 1 mV, which is the state-of-the-art for SPV measurements using unmodulated illumination schemes. The subsequent relaxation in the dark can be seen in Diagrams (e) and (f) and was recorded over a time span of about 20 h. In a typical full SPV analysis, comparative datasets of such light-on and light-off transients would be collected for a number of relevant wavelengths under varied light intensity and/or temperature to be processed using one or more mathematical models (see, e.g., [ 27 , 28 , 29 , 30 ], or for a comparative summary, [ 31 ]) to extract a number of material parameters such as capture cross-sections for photons and electrons, activation energies of trap states, or surface/interface band bendings in the dark and under illumination. Prior to the time-consuming acquisition of transients, surface photovoltage spectra, i.e., the SPV as a function of wavelength, are usually recorded in order to select meaningful wavelengths for the recording of transients.…”

Vacancies in InxGa1−xN/GaN multiple quantum wells fabricated onm-plane GaN probed by a monoenergetic positron beam

“…It can be seen that full restoration required almost one day, which is the typical recovery time of band bending after photon illumination for n-type GaN. 16) An inset in Fig. 1 shows a schematic band diagram for an n-type semiconductor under illumination, where E V and E C are the valence band maximum and the conduction band minimum, respectively.…”