Abstract
Recent 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.
Highlights
At present there is great interest in the development of ultraviolet (UV) light sources for solid-state lighting, optical sensors, surface decontamination and water purification
At the first stage we carried out plasma-assisted molecular beam epitaxy (PA-MBE) growth of thin ($ 1 μm) wurtzite AlxGa1ÀxN layers on two-in. diameter (111)B GaAs substrates for AlN fractions ranging from 0 up to 0.5
We have studied the growth of free-standing wurtzite AlxGa1ÀxN bulk crystals by PA-MBE
Summary
At present there is great interest in the development of ultraviolet (UV) light sources for solid-state lighting, optical sensors, surface decontamination and water purification. AlxGa1ÀxN substrates would be preferable to those of either GaN or AlN for deep ultraviolet device applications, that has stimulated an active search for methods to produce bulk AlxGa1ÀxN substrates with variable AlN content. We have recently used MBE for bulk crystal growth and have produced layers of zinc-blende GaN up to 100 μm in thickness [2,3,4]. We have shown that our newly developed PA-MBE process for the growth of bulk zinc-blende GaN layers can be used to achieve free-standing wurtzite AlxGa1ÀxN wafers [5,6]. In this paper we will describe our recent results in development of our PA-MBE approach for the growth of free-standing wurtzite AlxGa1ÀxN bulk crystals
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