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

We present real-time in situ spectroscopic ellipsometry (SE) measurements of the pseudodielectric function of low-temperature-grown GaAs as a function of growth temperature Tg, As2:Ga flux ratio R, and thickness. We show that the interband critical point E1 amplitude and sharpness decrease monotonically with decreasing Tg and/or increasing R for layers thinner than the critical epitaxial thickness hepi. We used in situ SE to reveal distinct signatures of the onset of polycrystalline or amorphous growth above hepi, which depends strongly on Tg. We revealed these systematic trends using in situ SE in conjunction with diffuse reflectance spectroscopy for active feedback temperature control.