Low-temperature chemical vapour deposited semiconducting nitrides

Recent work in the semiconducting nitrides AlN, GaN, InN and their ternary derivatives includes the low-temperature enhancement of MOCVD growth through a combination of ultraviolet laser photodissociation of metal precursors and microwave-plasma activated nitrogen radicals. These modifications allow the relative simplicity of low-pressure MOCVD to be successfully shifted to the 500-600°C temperature range for GaN, and to room temperature for AlN. Advantages include the availability of short-period multilayers and abrupt heterostructures, free from the cross-diffusion of either ternary constituents or dopants. Thermally fragile substrates now also become available. The binaries grown by this method compare well with conventional MOCVD, room-temperature mobilities up to 400 cm² V^-1 s^-1 are obtained in GaN and as-grown carrier concentrations in the range 10¹⁵-10 ¹⁷ cm^-3 can be controlled via the plasma density. CP₂Mg is used as counterdopant. Composition of AlGaN and InGaN is determined by precursor ratios, the relationship is linear in the former case but not in the latter. AlN with excellent dielectric properties has been deposited on unstable CdHgTe at 50C. We also mention the roles of microcrystallinity and polytypism in the physical properties of our materials as a function of substrate/buffer combination