Compact ultraviolet light sources are currently of high interest for applications in solid-state lighting, short-range communication, and bio-chemical detection. Our nitride-based light-emitting diode (LED) includes AlGaN quantum wells with an emission wavelength of approximately 340 nm. In this paper, we analyze internal device physics by three-dimensional (3D) numerical simulation. The simulation incorporated a 3D drift-diffusion model for the carrier transport, the quantum well (QW) energy band-structure including interface polarization charges, the local QW spontaneous emission spectrum, as well as 3D raytracing for photon extraction. The simulation results showed good agreement with measurements. Internal physical mechanisms such as current crowding, carrier leakage, and carrier recombination were investigated. Nanoscale effects exhibited a strong influence on the LED performance.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.