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 Al x Ga 1 ―x N layer, the pulsed-growth conditions were cyclically adjusted to reduce the dislocations. This leads to AlGaN templates with an RMS roughness of 9.6 A and (102) off-axis X-ray line-width 550 arcsec. The transmission electron microscope (TEM) analysis shows 4 × 10 7 cm ―2 edge type and 2 × 10 6 cm ―2 screw type of threading dislocation densities at best regions. On the average dislocation density in these films is 4 x 10 8 cm ―2 . A light emitting diode (LED) structure emitting at 280nm 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.