Fabrication and characterization of self-assembled InGaN quantum dots by periodic interrupted growth

Abstract

Self-assembled InGaN quantum dots are fabricated in a two-flow horizontal MOCVD reactor maintained at the pressure of 200torr. The precursors were trimethyl-gallium (TMG) and trimethyl-indium (TMI) and ammonia (NH₃), and the carrier gas was N₂ and H₂. The optimum condition was deduced to fabricate the InGaN quantum dots. GaN nucleation layer was grown at 500°C with thickness of 25nm, and then 2~3 μm thick GaN buffer-layer was deposited at 1050 °C. InGaN quantum dots were grown on GaN buffer layer. Carrier gas was changed with N₂ instead of H₂ in QD growth. In the growth of InGaN quantum dots, NH₃ was supplied in cyclic periodic interrupted mode with the interval of 5 seconds. The influence of number of periodic interrupted NH3 on the structural and optical properties of InGaN quantum dots was investigated by AFM, FE-SEM and photoluminescence (PL). The InGaN quantum dots are grown by 2 periods growth and have 0.4nm in height and 31nm lateral size. The height of quantum dots was increased with increase of growth periods, and the lateral size was decreased after 3 periods and then increased in 4 periods. The density of InGaN quantum dots with 3 periods and 4 periods was measured to be 1.51×10¹¹/cm² and 8.91×10¹⁰/cm². Density of InGaN quantum dots was decreased after 3 periods, and this is attributed to the coalescence. A strong peak at 362.2 nm (3.41eV) and broad emission peak in 532.9~663.9nm (2.33~1.86eV) were evolved in the photoluminescence measurement using Nd-YAG laser with wavelength of 266nm. Addition emission peak was found in the range 433.7nm~462.2nm (2.85eV~2.68eV) in the samples with 3 periods and 4 periods interruption, and this peak was identified as the InGaN quantum dots with low indium concentration.