In-situ laser reflectometry of the epitaxial growth of thin semiconductor films

The usefulness of laser reflectometry as a tool for the real-time monitoring of the epitaxial growth of thin semiconductor films is examined. Laser reflectometry is most suitable for monitoring films having a thickness ≥ λ/4, where λ is the monitoring wavelength: it therefore provides an excellent means of monitoring the growth of Bragg reflectors and an example of such a reflector grown with the aid of laser reflectometry is given. In addition it enables both growth rate and chemical composition of alloy semiconductors to be obtained in real time for films of the above thickness and this is illustrated by reference to the AlGaAs system. By monitoring the growth of AlGaAs/GaAs superlattices it is shown that this relatively simple technique has monolayer sensitivity. Results are presented which demonstrate that laser reflectometry is ideal for the monitoring of Ar+ laser assisted chemical beam epitaxial growth since the reflected signal contains growth information relating exactly to the laser footprint; this “auto-monitoring” is providing valuable insight into the mechanisms involved in the laser assistance.