Photoluminescence of Si-Doped Gan Grown by Electron Cyclotron Resonance Molecular Beam Epitaxy

Photoluminescence (PL) properties of Si-doped thin (5-13 nm) GaN layers grown on (0001) sapphire substrates at 760 °C by electron cyclotron resonance molecular beam epitaxy are studied. 12K PL spectrum for the undoped GaN layer shows a broad deep-level emission peak. For the Si-doped layers, the PL intensities for the band-edge peak and the Si donor-related peak are increased with increasing Si concentration, and the deep-level peak disappears for the sample with a Si concentration of about 1 × 10²⁰ cm^-3. The activation energy for the nonradiative recombination is observed to increase with Si concentration, and it is estimated to be 17.7 meV for 4.5 × 10²⁰ cm^-3 Si concentration. Atomic force microscopy measurement also shows the improvement of the surface morphology of grown layers with the increase of Si concentration. The results shows that the Si doping improve the crystal quality of GaN due to the decrease of defects.