AlGaN‐based ultraviolet light emitting diodes (UV‐LEDs) on AlN/sapphire template were grown by metal organic chemical vapour deposition. The AlN template was characterized by atomic force microscopy and high resolution X‐ray diffraction. Atomic force microscopy image shows that the AlN surface is very flat, while high resolution X‐ray diffraction results prove the good crystalline quality of the AlN template. A novel structure UV‐LED which has several p‐AlGaN layers with graded composition is compared with a common structure UV‐LED which has a single p‐Al0.5Ga0.5N layer. The forward bias voltage at 20 mA driving current for the novel structure UV‐LED is nearly 3 V higher than that of the common structure UV‐LED, however, the electroluminescence intensity of the former is over two times higher than that of the latter. The total quantum efficiency of the novel structure UV‐LED is more than 50% higher than that of the common structure UV‐LED. The improvement is considered to be the result of better holes injection efficiency in the novel structure UV‐LED. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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Yan et al. (2010) studied this question.