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

We present real-time in situ spectroscopic ellipsometry (SE) measurements o f the pseudodielectric function of low-temperature-grown GaAs as a function of growth temperature T-g, As-2:Ga flux ratio R, and thickness. We show th at the interband critical point E-1 amplitude and sharpness decrease monoto nically with decreasing T-g and/or increasing R for layers thinner than the critical epitaxial thickness h(epi). We used in situ SE to reveal distinct signatures of the onset of polycrystalline or amorphous growth above h(epi ), which depends strongly on T-g. We revealed these systematic trends using in situ SE in conjunction with diffuse reflectance spectroscopy for active feedback temperature control. (C) 2000 American Institute of Physics. [S00 03-6951(00)02028-3].