Reflectance anisotropy investigation of the metalorganic chemical-vapor deposition of III-V heterojunctions

Using reflectance anisotropy (RA), we investigated in situ the metalorganic chemical-vapor deposition of a number of III-V heterojunctions. Each type of heterojunction exhibits a characteristic RA record as a function of time, depending on the film composition, growth rate, and interface quality, as well as the light wavelength used. Signal changes occurring over different time scales are related to a number of different contributions to the optical anisotropy of the material. Changes during the first 5-10 s are due to the optical anisotropy of both the surface and heterointerface. Over a time scale of several minutes, the signal exhibits damped sinusoidal behavior; a model is proposed to account for these changes, taking into account the interference of light in the growing layer. Finally, the steady-state signal obtained after many minutes is indicative of the difference in surface optical anisotropy between the epilayer and substrate. Practical applications of RA, including heterojunction optimization, superlattice monitoring, and reactor geometry improvements, are also presented.