ABSTRACT
GaAlAs, GaAsP, InGaAsP, and InGaAlP are IIIb-Vb compound semiconductor materials used for devices in the visible wavelength region. Lattice constants of alloys are determined by their composition and generally vary depending on the composition ratio. Therefore, the lattice constant of ternary alloys such as GaAlAs and GaAsP is determined uniquely by the bandgap energy value. In quaternary alloys such as InGaAsP and InGaAlP, the bandgap energy can be varied without altering the value of the lattice constant. Attainable device structures for light-emitting diodes (LEDs) and semiconductor lasers depend on the method of crystal growth. The problems with the liquid phase epitaxy (LPE) method arise from the difficulty to grow ultra-thin layers and to control the composition of epitaxial layers for some material systems. An attractive technique for Metal-organic chemical vapor deposition (MOCVD) growth of InGaAlP material systems is growth on an off-angle substrate. This process is related to the formation of a natural superlattice.
