Surface roughness induced phase-separation in InGaN and LED applications

We report on the phase-separation of InGaN on the rough GaN surface and the fabrication of the light-emitting diode (LED) using a phase-separated InGaN layer as an active layer. Atomic force microscopy (AFM) images of GaN surfaces showed that the roughness of GaN surfaces was increased by supplying trimethyl gallium source during the ramping down time of the temperature. Photoluminescence (PL) spectra and cathodoluminescence (CL) images showed that the phase-separation of InGaN was enhanced on the rough GaN surface due to the difference of surface mobility of Ga and In. An LED was fabricated by inserting the phase-separated InGaN layer between p-type and n-type GaN. The PL spectrum exhibited separated peaks at high and low energy side, but the electroluminescence (EL) spectrum revealed a broad EL peak centered at low energy side at a low injection current. The EL peak was shifted to high energy side with an increase of the input current. These observations were attributed to the different depths of the potential wells of InGaN phases with different indium compositions caused by phase-separation.