In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N2 gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 1016 and ∼5 × 1017, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.
In the present work, AlGaN/GaN quantum wells and High Electron Mobility Transistors (HEMTs) have been grown by molecular beam epitaxy on Si(111) and GaN on sapphire templates. The optical quality and the electrical properties were studied by low temperature photoluminescence and Hall effect. These measurements attest the quality of these heterostructures and demonstrate the high on-wafer uniformity of the materials grown on 50 mm wafers, and this even for the III-nitrides grown on Silicon.1 Introduction In recent years, the Molecular Beam Epitaxy (MBE) has begun to demonstrate potentialities to realize high quality GaN based heterostructures for electronics as well as optoelectronic applications. Beyond the achievement of high quality GaN based heterostructures, MBE is now dealing with other process considerations such as reproducibility and uniformity on various substrates like sapphire, silicon carbide or silicon. In order to address this latter point, AlGaN/GaN quantum wells (QWs) and HEMT heterostructures have been grown with a Riber MBE reactor designed for the growth of IIINitrides materials. Ammonia was used as nitrogen source, whereas effusion cells supplied group III elements. The growth were performed on 50 mm Si(111) wafers and on 50 mm MOCVD grown GaN on sapphire templates. The layer optical properties were assessed by using low temperature photoluminescence (PL) performed across the wafers, whereas the electrical quality was studied by Hall effect after the realization of van der Pauw cloverleaf and Hall bar devices. The effect of heteroepitaxial growth on the layers quality was studied by comparing results obtained on Silicon with those obtained on the low defect density GaN templates.
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