| Much progress has been made recently in the-advancement of III-Nitride based UV emitters, in particular light emitting diodes (LED). While high performance LEDs and diode lasers are available to wavelengths of about 360nm, a rather pronounced fall-off in the quantum efficiency occurs in today's devices towards shorter wavelengths. It is generally accepted that the necessity of introducing Al at higher concentrations into the quaternary AlInGaN system presents a significant level of difficulty in the control of defects that affect both the electronic transport and the radiative processes in the constituent layers within the LED structures. The microscopic details of the defect structure and their physical machinery remain still largely opaque, even though the first applications of the new generation of UV LEDs are beginning to emerge.; In this present work, we investigate the performance of AlInGaN-based ultraviolet LEDs (UV LEDs) and compare their properties with the more extensively studied InGaN and low Al-concentration AlGaN systems. Additionally, we employ photoluminescence and time-correlated single photon counting (TCSPC) techniques in an effort to elucidate the defect mechanisms hindering the operation of the devices.; Based upon our results, a model is suggested identifying some of the defects and their intricate interplay, responsible for the problematic electrical transport of carriers within the UV LED structures. This model, though qualitative in nature, may explain why the performance of the UV light emitters has not yet reached the metrics comparable to the LEDs in the blue and violet. |
