Surface interactions are responsible for many properties of condensed matter, ranging from crystal faceting to the kinetics of phase transitions. Usually, these interactions are polar along the normal to the interface and apolar within the interface. Here we demonstrate that polar in-plane surface interactions of a ferroelectric nematic N_F produce polar monodomains in micron-thin planar cells and stripes of an alternating electric polarization, separated by $${180}^{{{{{{\rm{o}}}}}}}$$180 o domain walls, in thicker slabs. The surface polarity binds together pairs of these walls, yielding a total polarization rotation by $${360}^{{{{{{\rm{o}}}}}}}$$360 o . The polar contribution to the total surface anchoring strength is on the order of 10%. The domain walls involve splay, bend, and twist of the polarization. The structure suggests that the splay elastic constant is larger than the bend modulus. The $${360}^{{{{{{\rm{o}}}}}}}$$360 o pairs resemble domain walls in cosmology models with biased vacuums and ferromagnets in an external magnetic field.

The open-circuit voltage (VOC) in a generic TCO/buffer/absorber/back-contact thin-film solar cell device is a key parameter in the recombination analysis. In particular, VOC is sensitively influenced by the interface recombination at the buffer/absorber front interface and at the absorber/back-contact interface. This paper reports the temperature, excitation light intensity, and wavelength-dependent open-circuit voltage analysis to separate and quantify recombination rates in solar cells at the front and back interfaces, in the depletion regions, and in the quasi-neutral region. The wavelength-dependent VOC analysis is exploited to extract the absorber/back-contact recombination coefficient. The experimentally observed results are verified using SCAPS-1D (one dimensional-a solar cell capacitance simulator) simulation.

We use steady-state capacitance measurement originally intended for capacitance–voltage experiment to observe and characterize the electrical properties of deep defects in β-Ga ₂ O ₃ semiconductors. We detect a deep level located 0.81 eV below the conduction band edge with a concentration of 1.2 × 10 ¹⁶ cm ⁻³ and a capture cross-section of 1.1 × 10 ⁻¹⁴ cm ² , making it potentially influential in determining the performance of β-Ga ₂ O ₃ based power electronic and optoelectronic devices. This deep level may dominate the thermal activation of off-state drain current in β-Ga ₂ O ₃ transistors at high temperatures and, together with another shallower level at 0.13 eV, may substantially lower the breakdown voltage in Schottky diodes.

A study is reported comparing the electrical and optical properties of CdTe solar cells, prepared using CdS and CdSe buffer layers, to investigate defects in the bulk and interface, carrier transport, and recombination. Temperature dependent capacitance–voltage measurement and admittance spectroscopy were used to extract carrier concentration, resistivity, charge carrier mobility, and their temperature dependence. The authors identify the presence of two defect signatures corresponding to carrier freeze-out and the formation of a Schottky back-contact barrier. The back-contact barrier height (≈300 meV) extracted from the temperature dependent current density–voltage (JVT) experiment was confirmed by conventional admittance spectroscopy. The activation energies of mobility (resistivity) are 101.2 ± 2.5 meV (92.6 ± 2.3 meV) and 84.7 ± 2.7 meV (77.6 ± 4.5 meV) for CdS and CdSe buffer layers, respectively. Intensity dependent photoluminescence analysis demonstrates that the CdSe/CdTe device exhibits lower radiative efficiency than the CdS/CdTe device. This confirms the presence of higher defects in the CdSe/CdTe device corroborated by temperature dependent VOC analysis. The comparative electrical and optical analysis provides insight into improving the performance of CdTe solar cell device by selenization.