(Invited) Structural and Optical Properties of InN Quantum Dots Grown by an Alternating Supply of Source Precursors
The two-step growth method consists of one growth cycle for step-1 and two growth cycles in step-2. The duration of one growth cycle is 50 sec, including a 10 s TMIn flow process, a 20 s NH3 process, and two 10 s purge processes intervened in between. The two-step growth included step-1 for high density InN nucleation at 575 oC, and then, the reactor temperature was raised to 650 oC in 5 min increments to decompose the poor material quality InN islands. The aim of the step-1 growth was only to create high density nucleation sites on the GaN buffer layer. The reactor temperature was then reduced to 600oC to enable the growth of InN QDs with high density and high optical property in step-2 of the process. The experimental result show that the high density 1.5×1010 cm−2 truncated hexagonal pyramidal InN QDs can be grown by the two-step growth method. The InN nucleation, InN decomposition and In adatom diffusion in the step-1, annealing and the step-2 process, respectively, determined the density, shape and size distribution of the InN QDs. The bimodal size distribution of the two-step growth InN QDs can be attributed to the high mobility of the incoming adatoms or/and existing islands, which favors coalescence process. The double-peak feature in the photoluminescence (PL) is related to the ground-state emission from the InN QDs with bimodal size-distribution. The low residual carrier concentration (1.8×1018 cm−3), large confinement energy (342 meV) and intense PL emission for 6.1 nm high InN QDs indicated that a two-step growth is suitable for QD device applications.