MICROSTRUCTURES OF (IN,GA)P ALLOYS GROWN ON GAAS BY METALORGANIC VAPOR-PHASE EPITAXY

The microstructures of metalorganic vapor-phase epitaxy alloys of (In,Ga)P grown on GaAs substrates were examined using transmission electron microscopy. Alloys examined were grown at 600-775°C on substrates at or near (001) or (113)A using growth rates of 0.69 and 0.17 nm/s. Two common semiconductor alloy phenomenon, ordering and phase separation, were studied over this range of growth conditions. The CuPt-type ordering reflections are sharpest for growth at 675°C and more diffuse at 600 and 725°C due to higher densities of antiphase boundaries. Order can be eliminated by growth at 750°C or above to obtain the highest band gaps and optical emission energies. Detailed investigation of the microstructure for growth at 675°C indicates that ordered domains are platelets consisting of thin (1-2 nm) lamella on (001) planes that alternate between the two {111}B ordering variants, in agreement with a model proposed by others. We have formed "unicompositional" quantum wells with sharply defined ordered layers between disordered barrier layers by changing growth temperature, which demonstrates that ordering is determined to a great degree by the conditions during growth. Phase separation is seen for the entire range of growth parameters, independently of ordering; its contrast shows modulations with a variable spacing ranging from a few nanometers to ∼100 nm. Implications of the coexistence of phase separation and ordering for growth models describing these phenomena are discussed. © 1995 American Institute of Physics.