Amplified spontaneous emission from a surface-modified GaN film fabricated under pulsed intense UV laser irradiation

We propose a simple method for fabricating random structures directly on Mg-doped GaN thin films. The process is relatively simple, involving only irradiation with strong UV pulses from a fabrication laser on the thin-film surface. After intense UV laser pulses (>400 MW/cm2) are irradiated on the flat GaN film, the surface is roughened and quasi-periodic structures form. When the roughened surface is excited with laser light of intensity about 10 times smaller than the fabrication laser intensity, emission increases around 367 nm, and spectral narrowing and threshold behavior are observed. Because such behaviors are not observed without the application of intense laser irradiation, we conclude that amplified spontaneous emission is induced in the modified GaN surface by the intense UV laser pulse irradiation. This method offers the possibility of easy and direct fabrication of microscale random-laser devices on semiconductor substrates.