In situ ellipsometry study of the early stage of ZnO Atomic Layer Deposition on In0.53Ga0.47As

The initial stages of ZnO atomic layer deposition (ALD) on In0.53Ga0.47As (InGaAs) are studied by monitoring the ZnO film thickness in situ with spectroscopic ellipsometry. Using diethylzinc (DEZn) and water, at a substrate temperature equal to 120 degrees C, the presence of two different ZnO growth regimes prior to steady growth is found: a slow ZnO nucleation on InGaAs, 0.005 nm.cy-1 (growth delay), then a substrate-inhibited growth of type II. Increasing the DEZn injection time, the growth delay shortens from 30 cycles down to 3 cycles; concomitantly, the steady growth rate increases from 0.18 to 0.23 nm.cy(-1). The DEZn residence time and pressure increase during the first ALD cycle, allowing to suppress growth delay; instead, no change is observed when performing the same experiment with water. Atomic force microscopy (AFM) images show that the InGaAs surface roughens after the first cycle with a long DEZn pulse and residence time. The rough surface is likely at the origin of the growth delay elimination.