Molecular beam epitaxy of free-standing bulk wurtzite AlxGa1-xN layers using a highly efficient RF plasma source

Recent developments with group III nitrides suggest AlxGa1-xN based LEDs can be new alternative commer-cially viable deep ultra-violet light sources. Due to a sig-nificant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1-xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE) using a novel RF plasma source. Thick wurtz-ite AlxGa1-xN films were grown by PA-MBE on 2-inch GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1-xN samples. Growth rates of AlxGa1-xN up to 3 μm/h have been demonstrated. Our novel high efficiency RF plasma source allowed us to achieve free-standing bulk AlxGa1-xN layers in a single day’s growth, which makes our MBE bulk growth technique commercially vi-able

High quality GaMnAs films grown with As dimers

We demonstrate that GaMnAs films grown with As2 have excellent structural, electrical and magnetic properties, comparable or better than similar films grown with As4. Using As2, a Curie temperature of 112K has been achieved, which is slightly higher than the best reported to date. More significantly, films showing metallic conduction have been obtained over a much wider range of Mn concentrations (from 1.5% to 8%) than has been reported for films grown with As4. The improved properties of the films grown with As2 are related to the lower concentration of antisite defects at the low growth temperatures employed.Comment: 8 pages, accepted for publication in J. Crystal Growt

Cubic and hexagonal InGaAsN dilute arsenides by unintentional homogeneous incorporation of As into InGaN

Arsenic alloying is observed for epitaxial layers nominally intended to be In0.75Ga0.25N. Voids form beneath their interfaces with GaAs substrates, acting as sources of Ga + As out-diffusion into the growing epilayers. As a result, heteroepitaxial single-phase quaternary InxGa1-xAsyN1-y, films are formed with x similar to 0.55 and 0.05 menor que y menor que 0,10. While an undoped epilayer retains the wurtzite structure, a Mn-doped sample showed randomly spaced dopant segregations, which, together with a slightly higher As concentration, led to a transformation from the hexagonal to the twinned cubic phase

Nanoscale characterisation of MBE-grown GaMnN / (001) GaAs

The growth of cubic (Ga,Mn)N/(001)GaAs heterostructures by plasma assisted molecular beam epitaxy has been appraised as a function of Ga:N ratio, Mn concentration and growth temperature. The combined analytical techniques of EFTEM, EDX, CBED and dark field imaging have been used to appraise the Mn distributions within (Ga,Mn)N epilayers. Improved incorporation efficiency of Mn is associated with growth under N-rich conditions, but Mn incorporation may be enhanced under Ga-rich conditions at reduced growth temperatures. The surfactant behaviour of Mn during the growth of this spintronic system determines the resultant alloy composition

Molecular beam epitaxy of free-standing wurtzite AlxGa1−xN layers

AbstractRecent developments with group III nitrides present AlxGa1−xN based LEDs as realistic devices for new alternative deep ultra-violet light sources. Because there is a significant difference in the lattice parameters of GaN and AlN, AlxGa1−xN substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite AlxGa1−xN bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE). Thick wurtzite AlxGa1−xN films were grown by PA-MBE on 2-in. GaAs (111)B substrates and were removed from the GaAs substrate after growth to provide free standing AlxGa1−xN samples. X-ray microanalysis measurements confirm that the AlN fraction is uniform across the wafer and mass spectroscopy measurements show that the composition is also uniform in depth. We have demonstrated that free-standing wurtzite AlxGa1−xN wafers can be achieved by PA-MBE for a wide range of AlN fractions. In order to develop a commercially viable process for the growth of wurtzite AlxGa1−xN substrates, we have used a novel Riber plasma source and have demonstrated growth rates of GaN up to 1.8µm/h on 2-in. diameter GaAs and sapphire wafers

Doping of free-standing zinc-blende GaN layers grown by molecular beam epitaxy

AbstractCurrently there is high level of interest in developing of vertical device structures based on the group III nitrides. We have studied n- and p-doping of free-standing zinc-blende GaN grown by plasma-assisted molecular beam epitaxy (PA-MBE). Si was used as the n-dopant and Mg as the p-dopant for zinc-blende GaN. Controllable levels of doping with Si and Mg in free-standing zinc-blende GaN have been achieved by PA-MBE. The Si and Mg doping depth uniformity through the zinc-blende GaN layers have been confirmed by secondary ion mass spectrometry (SIMS). Controllable Si and Mg doping makes PA-MBE a promising method for the growth of conducting group III-nitrides bulk crystals

Wurtzite AlxGa1-xN bulk crystals grown by molecular beam epitaxy

We have studied the growth of wurtzite GaN and AlxGa1-xN layers and bulk crystals by molecular beam epitaxy (MBE). MBE is normally regarded as an epitaxial technique for the growth of very thin layers with monolayer control of their thickness. However, we have used the MBE technique for bulk crystal growth and have produced 2 in diameter wurtzite AlxGa1-xN layers up to 10 [mu]m in thickness. Undoped wurtzite AlxGa1-xN films were grown on GaAs (1 1 1)B substrates by a plasma-assisted molecular beam epitaxy (PA-MBE) method and were removed from the GaAs substrate after the growth. The fact that free-standing ternary AlxGa1-xN wafers can be grown is very significant for the potential future production of wurtzite AlxGa1-xN substrates optimized for AlGaN-based device structures