Dislocation reduction in high Al‐content AlGaN films for deep ultraviolet light emitting diodes

We report a new approach for growing thicker (>2 µm) low‐defect AlGaN layers over sapphire using pulsed MOCVD procedure. These high content AlGaN layers serve as templates for subsequent n‐AlGaN growth for deep ultraviolet light emitting diodes (DUV LEDs). During the growth of the AlxGa1−xN layer, the pulsed‐growth conditions were cyclically adjusted to reduce the dislocations. This leads to AlGaN templates with an RMS roughness of 9.6 Å and (102) off‐axis X‐ray line‐width 550 arcsec. The transmission electron microscope (TEM) analysis shows 4 × 107 cm−2 edge type and 2 × 106 cm−2 screw type of threading dislocation densities at best regions. On the average dislocation density in these films is 4 × 108 cm−2. A light emitting diode (LED) structure emitting at 280 nm was deposited on these templates. A comparative study showed the EL emission for LEDs on the new low‐defect templates to be more than 1.6 times stronger than our conventional DUV LED structures. In this paper the details of our growth procedure, the epi‐structure X‐ray, atomic force microscopy (AFM), TEM, and other characterizations will be presented. A comparative study of DUV LED structures over conventional and improved templates of this work will be discussed.