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

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.

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