Influence of an advanced buffer layer on the optical properties of an InGaN/GaN MQW grown on a (111) silicon substrate

We study the influence of a buffer layer on the optical properties of InGaN/GaN multiple quantum wells (MQWs) grown on silicon substrates by using metalorganic vapor phase epitaxy. To overcome the large lattice mismatch and the difference in the thermal expansion coefficients by which a high dislocation density occurs, we grow the MQWs on an advanced buffer structure consisting of low-temperature (LT) AlN and a high-temperature (HT) AlN/AlGaN/GaN stack. The Raman spectra confirm that the biaxial tensile strain is reduced by the insertion of the alternating LT and HT buffer layers. Moreover, we find the room-temperature internal quantum efficiency can be improved. Our results suggest that the enhanced optical performance comes from the reduced number of nonradiative recombination centers brought about by the LT and HT composite buffer layers.