Electron overflow of AlGaN deep ultraviolet light emitting diodes

We have studied the design, epitaxy, and performance characteristics of deep ultraviolet (UV) AlGaN light emitting diodes (LEDs). By combining the tunnel junction and polarization-engineered AlGaN electron blocking layer, a maximum external quantum efficiency and wall-plug efficiency of 0.35% and 0.21%, respectively, were measured for devices operating at ∼245 nm, which are over one order of magnitude higher than previously reported tunnel junction devices at this wavelength. Severe efficiency droop, however, was measured at very low current densities (∼0.25 A/cm2), which, together with the transverse magnetic (TM) polarized emission, is identified to be the primary limiting factors for the device performance. Detailed electrical and optical analysis further shows that the observed efficiency droop is largely due to an electrical effect instead of an optical phenomenon. Our studies suggest that AlGaN deep UV LEDs with efficiency comparable to InGaN blue-emitting quantum wells can be potentially achieved if issues related to electron overflow and TM polarized emission are effectively addressed.