We report the electrical and optical properties of deep ultraviolet light emitting diodes (LEDs) based on digital alloy structures (DAS) of AlN/Al 0.08Ga0.92N grown by gas source molecular beam epitaxy with ammonia on sapphire substrates and AlGaN/sapphire templates. AlGaN/sapphire templates were grown by recently developed stress controlled hydride vapor phase epitaxy (HVPE). For DAS with effective bandgap of 5.1 eV we obtain room temperature electron concentrations up to 1×1019 cm -3 and hole concentrations of 1×1018 cm -3. Based on these results we prepared double heterostructure (DHS) LEDs operating in the range of 250 to 290 nm. The emission wavelengths were controlled through the effective bandgap of the active region. The possible ways for increase of LED's efficiency are discussed. We observed significant improvement in the room temperature luminescence efficiency (by factor of 100) of AlGaN quantum wells when a transition growth mode is induced by reduced flux of ammonia. We found that active layer grown on HVPE AlGaN/sapphire substrates have higher luminescence efficiency (by factor of 3) than DAS grown on sapphire.