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The carrier lifetime control over 150 μm thick 4H-SiC epitaxial layers via thermal generation and annihilation of carbon vacancy (VC) related Z1/2 lifetime killer sites is reported. The defect developments upon typical SiC processing steps, such as high- and moderate-temperature anneals in the presence of a carbon cap, are monitored by combining electrical characterization techniques capable of VC depth-profiling, capacitance–voltage (CV) and deep-level transient spectroscopy (DLTS), with a novel all-optical approach of cross-sectional carrier lifetime profiling across 4H-SiC epilayer/substrate based on imaging time-resolved photoluminescence (TRPL) spectroscopy in orthogonal pump-probe geometry, which readily exposes in-depth efficacy of defect reduction and surface recombination effects. The lifetime control is realized by initial high-temperature treatment (1800 °C) to increase VC concentration to ≈1013 cm−3 level followed by a moderate-temperature (1500 °C) post-annealing of variable duration under C-rich thermodynamic equilibrium conditions. The post-annealing carried out for 5 h in effect eliminates VC throughout the entire ultra-thick epilayer. The reduction of VC-related Z1/2 sites is proven by a significant lifetime increase from 0.8 to 2.5 μs. The upper limit of lifetimes in terms of carrier surface leakage and the presence of other nonradiative recombination centers besides Z1/2, possibly related to residual impurities such as boron are discussed., Physica Status Solidi A, 220 (10), ISSN:1862-6300, ISSN:1862-6319, ISSN:0031-8965, ISSN:1521-396X

Semi-transparent pn-heterojunctions were fabricated from pulsed laser deposited (PLD) n-type ZnO and DC magnetron sputtered p-type NiO, working as UV-active solar cells. The complete cell stack has an average transmission of 46% in the visible spectral range and an optical absorption edge at 380 nm. The diodes exhibit high current rectification of up to eight orders of magnitude at ±2 V. Upon illumination with a solar simulator, the devices show photovoltaic activity with open-circuit voltages of up to 520 mV, short-circuit current densities of 0.5 mAcm2, and a maximum external quantum efficiency of 55%. However, we observed rather low fill factors of the current–voltage characteristics of around 40%, resulting in total power conversion efficiencies of around 0.1% and efficiencies in the UV range of 3.1%. To identify possible loss mechanisms, the voltage-dependent efficiency of carrier collection was calculated. The data were fitted using a model that considers recombination losses at the NiO/ZnO interface as well as within the electric field region, yielding a high hole interface recombination velocity of 1×105cm s−1. We conclude that the carrier collection efficiency is strongly deteriorated by recombination losses at the NiO/ZnO interface, causing a strong bending of the jV characteristics under illumination and thereby low fill factors.