We report on a systematic study of the determination of the internal quantum efficiency (IQE) in AlGaN-based multiple-quantum-well (MQW) structures using different optical evaluation methodologies and experimental conditions, in order to derive a standard set of measurement conditions for reliable IQE determination. Several potential sources of error that may distort the IQE obtained by optical measurements are discussed, such as carrier transport effects, excitation conditions failing to fulfill ideal resonance conditions, and morphology issues. A series of nominally identical AlGaN-based MQW structures is grown on an AlGaN layer separated by an AlN interlayer of varying thickness. The MQW structures are studied both by resonant and quasiresonant photoluminescence spectroscopy, and IQEs are determined via different commonly employed methods. The obtained values are shown to be significantly affected by the employed excitation conditions, as well as the evaluation techniques. In addition, growth morphology issues and carrier transport effects need to be considered in the interpretation of the measured data, with the latter being investigated in greater detail. The results emphasize the need for an appropriate choice of both experimental conditions and evaluation methodology in order to extract reliable and comparable IQE values.

Herein, the optical properties of aluminum nitride (AlN) epitaxial layers grown on sapphire substrates by metal‐organic chemical vapor deposition (MOCVD) are reported. The structures investigated in this study are grown at highly different degrees of supersaturation in the MOCVD process. In addition, both pulsed and continuous growth conditions are employed and AlN is deposited on nucleation layers favoring different polarities. The samples are investigated by photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectroscopy and are found to vary significantly in absorption and emission characteristics. Two distinct absorption bands in the UV‐C spectral range are observed and examined in greater detail, with either giving rise to a significant absorption coefficient of around 1000 cm−1. The corresponding defect transitions are identified by PL spectroscopy. Combined with secondary‐ion mass spectrometry (SIMS) measurements, these absorption bands are allocated to the incorporation of carbon and oxygen impurities, depending on the applied growth conditions. Furthermore, similarities with other epitaxial growth techniques serving as basis for UV‐C applications are highlighted. These results are highly relevant for a better understanding of absorption issues in AlN templates grown by various deposition techniques. In addition, consequences for the growth of efficient UV‐C devices by MOCVD on sapphire substrates are outlined.

Carrier dynamics in AlGaN-based single quantum well (QW) structures grown on sapphire are studied by means of time-integrated and time-resolved photoluminescence spectroscopy (PL) in a wide temperature range from 5 K to 350 K. The samples cover a broad compositional range, with aluminum contents ranging between 42% and 60% and QW widths between 1.5 nm and 2.5 nm. All samples reveal the characteristic “S”-shape temperature dependence of the PL emission energy as frequently reported in InGaN-based systems, albeit with significantly larger localization strengths of up to 60 meV. It is shown that in the compositional range investigated, carrier localization is determined primarily by the QW width and, in contrast, exhibits a much weaker dependence on aluminum concentration. By the combination of time-integrated and time-resolved PL measurements, the localization of carriers is demonstrated to have a significant impact on the recombination dynamics of AlGaN/AlN QWs grown on sapphire, heavily affecting the internal quantum efficiency and efficiency droop even in standard LED operation conditions.