AVS 53rd International Symposium
    Nano-Manufacturing Topical Conference Tuesday Sessions
       Session NM-TuP

Paper NM-TuP7
Molecular-Beam Epitaxy of InN Quantum Dots on Nitrided Sapphire

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Nano-Manufacturing Poster Session
Presenter: Y.E. Romanyuk, University of California at Berkeley and Lawrence Berkeley National Laboratory
Authors: Y.E. Romanyuk, University of California at Berkeley and Lawrence Berkeley National Laboratory
R.-G. Dengel, University of California at Berkeley and Lawrence Berkeley National Laboratory
S.R. Leone, University of California at Berkeley and Lawrence Berkeley National Laboratory
Correspondent: Click to Email
Recent investigations suggest that the bandgap of InN is approximately 0.7 eV, rather than the previously accepted value of 1.8-2.0 eV, making InN a highly desirable component for potential band-gap-tunable optical applications. In this work, InN quantum dots (QDs) are grown by rf-plasma-assisted molecular beam epitaxy on thin nitride layers produced directly on sapphire substrates. Previous studies obtained InN QD growth on substrates or thick buffer layers of Si, GaN, and AlN. The nanostructures in this work are produced directly on nitrided c-cut sapphire substrates. The nitridation of sapphire for a period of one hour at 950°C results in the formation of a rough AlN surface layer, which acts as a very thin buffer and facilitates the nucleation of the InN QDs. A series of InN QD samples are grown at various substrate temperatures from 420°C to 500°C under slightly nitrogen-rich conditions. Ex situ AFM images reveal that the average InN growth rate is limited by the In flux on the surface, and the QD morphology depends strongly on the substrate temperature. Well-confined InN nanoislands with the greatest height / width ratio of 0.2 can be grown at 460°C. Lower substrate temperatures result in a reduced aspect ratio due to lower diffusion rate of the In adatoms, whereas the thermal decomposition of InN complicates the growth at T>500°C. The densities of separated QDs vary between 1.5x10@super 10@ cm@super -2@ and 3.0x10@super 10@ cm@super -2@ depending on the growth time. Typical island heights are 3-10 nm, and therefore, carrier confinement is expected in vertical direction in a part of the fabricated dots. For the investigation of optical properties, work is in progress to encapsulate the QDs to avoid the formation of surface states that suppress radiative recombination. The demonstration of the intrinsic photoluminescence of InN QDs would give a possibility to use InN nanostructures in photonic devices.