Search

Abstract: The heteroepitaxy of In-face InN on Ga-face GaN (0001) by nitrogen RF plasma source molecular beam epitaxy, using a two-step growth process, has been investigated. InN nucleation is enhanced at low substrate temperatures and smooth continuous nucleation layers can be grown at 300–350°C, which provide the necessary template for overgrowing films at a higher temperature near 500°C. Porous columnar InN structures are grown without the low-temperature nucleation layer, exhibiting a multiplied growth rate along the c-axis. The continuous InN/GaN (0001) films are under tensile residual stress at room temperature attributed to the different thermal expansion of InN and GaN. Typical lattice constants are and for a continuous 0.9μm film and and for a columnar 1.6μm epilayer. A difference in the density of misfit dislocations at the InN/GaN (0001) interface between columnar and continuous films was observed, in agreement with measurements of the films’ lattice constants. [Copyright &y& Elsevier]

Abstract: Radiofrequency (RF) nitrogen plasma sources are commonly used for the growth of III-nitrides by plasma-assisted molecular beam epitaxy. Their output mainly consists of a mixture of atomic nitrogen and metastable excited molecules. The relative concentration of these species as a function of RF power and nitrogen gas flow rate has been investigated by plasma optical emission spectroscopy. It is shown that the concentration of excited molecular nitrogen species is monotonically increasing with both parameters while the concentration of nitrogen atoms is almost independent of the nitrogen gas flow rate and increases monotonically with the coupled RF power. As a result of this functional dependence, the plasma source can be tuned to produce mainly excited nitrogen molecules or a mixture of excited molecules and atomic nitrogen. Comparison of the growth rates of gallium nitride films grown under different operating conditions of the RF source with the optical spectroscopy data shows that the metastable excited nitrogen molecules component of the source is the predominant factor contributing in the III-nitrides growth. [Copyright &y& Elsevier]