Search

Abstract: Substrate temperature rises of over 200°C have been observed for growth of InN and In-rich InGaN on GaAs substrates. We present a model to show that it is not the narrow bandgap that is responsible for the large temperature rises observed during growth of InN, but the large bulk background carrier concentration. We also show how the substrate temperature rise during growth increases as a function of increasing indium composition and the effects of controlling the substrate temperature on film quality. [Copyright &y& Elsevier]

Recent developments with group III nitrides present Al x Ga 1− x N 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, Al x Ga 1− x N substrates would be preferable to either GaN or AlN for ultraviolet device applications. We have studied the growth of free-standing wurtzite Al x Ga 1− x N bulk crystals by plasma-assisted molecular beam epitaxy (PA-MBE). Thick wurtzite Al x Ga 1− x N 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 Al x Ga 1− x N 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 Al x Ga 1− x N 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 Al x Ga 1− x N substrates, we have used a novel Riber plasma source and have demonstrated growth rates of GaN up to 1.8 µm/h on 2-in. diameter GaAs and sapphire wafers. [ABSTRACT FROM AUTHOR]

Abstract: Optical properties of free standing cubic gallium nitride grown by molecular beam epitaxy system are investigated by a polarized infrared (IR) reflectance technique. A strong reststrahlen band, which reveals the bulk-like optical phonon frequencies, is observed. Meanwhile, continuous oscillation fringes, which indicate the sample consists of two homogeneous layers with different dielectric constants, are observed in the non-reststrahlen region. By obtaining the first derivative of polarized IR reflectance spectra measured at higher angles of incidence, extra phonon resonances are identified at the edges of the reststrahlen band. The observations are verified with the theoretical results simulated based on a multi-oscillator model. [Copyright &y& Elsevier]

Abstract: We have studied the growth of zinc-blende GaN and Al x Ga1−x N layers, structures and bulk crystals by molecular beam epitaxy (MBE). MBE is normally regarded as an epitaxial technique for 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 GaN layers up to 100μm in thickness. Thick, undoped, cubic GaN films were grown on semi-insulating GaAs (001) substrates by a modified plasma-assisted molecular beam epitaxy (PA-MBE) method and were removed from the GaAs substrate after the growth. The resulting free-standing GaN wafers may be used as substrates for further epitaxy of cubic GaN-based structures and devices. We have demonstrated that the PA-MBE process, we had developed, also allows us to achieve free-standing zinc-blende Al x Ga1−x N wafers. [Copyright &y& Elsevier]

Abstract: We have studied the growth of wurtzite GaN and Al x Ga1−x N 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 2in diameter wurtzite Al x Ga1−x N layers up to 10μm in thickness. Undoped wurtzite Al x Ga1−x N films were grown on GaAs (111)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 Al x Ga1−x N wafers can be grown is very significant for the potential future production of wurtzite Al x Ga1−x N substrates optimized for AlGaN-based device structures. [Copyright &y& Elsevier]

Abstract: Since c-GaN and ScN have near identical lattice parameters, we have studied the growth of ScN by molecular beam epitaxy, on different surfaces, as a possible buffer layer for improving the quality of c-GaN. Epitaxial growth of ScN on c-GaN(100), GaAs(100) and ScAs(100) surfaces has been demonstrated for the first time. ScN was found to grow in a (100) orientation on ScAs, whereas on c-GaN and GaAs it grew in a (111) orientation. Epitaxy of GaN on ScN(111) results in the hexagonal polytype, while GaN on ScN(100) produces the cubic polytype. AFM studies show smoother surfaces are attained for c-GaN grown on ScN(100), in comparison to conventional c-GaN growth on GaAs(100). This shows that ScN(100) layers offer the potential to improve the quality of c-GaN(100). [Copyright &y& Elsevier]