Real-time pseudodielectric function of low-temperature-grown GaAs

We present the real-time pseudodielectric function <<epsilon>(E)> of low-temperature-grown GaAs (LT-GaAs) thin films during the growth as a function of growth temperature T-g and thickness. We obtained accurate measurements of the real-time <<epsilon>(E)> by using in situ spectroscopic ellipsometry (SE) in conjunction with active feedback control of the substrate temperature using diffuse reflectance spectroscopy. We show that for epitaxial LT-GaAs layers, the peak in the imaginary pseudodielectric function <<epsilon>(2)(E)> decreases in amplitude and sharpness systematically with decreasing T-g. We also revealed an abrupt change in <<epsilon>(E)> near the critical epitaxial thickness h(epi), the value of which decreases with decreasing T-g. Above h(epi), the LT-GaAs grows polycrystalline (amorphous) above (below) T-g similar to 190 degreesC. We also simultaneously monitored the surface roughness and crystallinity by using real-time reflection high-energy electron diffraction (RHEED). These results represent progress in obtaining realtime control over the composition and morphology of LT-GaAs.