The origin of the high ideality factor in AlGaN-based quantum well ultraviolet light emitting diodes

The ideality factor of AlGaN-based quantum well ultraviolet light emitting diodes (LEDs) is found to be dependent on both material quality and the presence of electron blocking layer (EBL). The ideality factor of the 340 nm LEDs decreases from 6.9 to 4.9 in the low bias regime (1 ≤ V < 2) as the structural dislocation density reduces from 5 × 10 9 to 9 × 10 8 cm -2 . Moreover, the ideality factor of the 310 nm LEDs decreases with increasing thickness of the AlGaN EBL which is placed between the barrier after the QW and the p-type layer. The slope of the I-V characteristics is temperature independent, indicating that the carrier tunneling is the dominant mechanism. The characteristic tunneling energy extracted from the I-V characteristics decreases from the order of 200 to around 100 meV as the dislocation density in the LED is reduced and with the insertion of a 10 nm EBL. This is attributed to the suppression of deep level states assisted electron tunneling into p-type layer.