Sandia's compound semiconductor activity has been at the center of many partnerships, both with universities and with private industry. These partnerships span the entire spectrum, from materials and processes, devices and systems. A large fraction of those partnerships have been in materials and process science and technology, or "science-based manufacturing".
In part, this stems from Sandia's unique position as a lab in which scientists and engineers work side by side, enabling engineers to gain a deeper understanding of their processes and scientists to gain an appreciation for problems that are relevant and important.
Much of Sandia's work in the area of science-based manufacturing has focused on materials. Materials are at the heart of the band-gap engineering that distinguishes the compound semiconductors, and which enable optoelectronic devices spanning wavelengths from the mid and far IR to the visible and UV.
However, while compound semiconductors are powerful, control of the materials manufacturing process can be challenging. This is particularly the case with metal-organic chemical vapor disposition, (MOCVD). MOCVD is a very flexible process, but is also complex, in part because it depends on complex chemistries.
Even a relatively simple system, CVD of silicon from silane, proceeds through a very complex sequence of reactions, and MOCVD of compound semiconductors is even more complex. As a consequence, many tools have been developed over the years to study and understand CVD.
Two advances in particular have had a significant recent impact on compound semiconductor MOCVD.
The first advance was the development of vertical-flow high-speed rotating-disk CVD reactors. Instead of gases flowing horizontally over a susceptor, as in a conventional CVD reactor, in this kind of reactor, gases flow vertically downward onto a susceptor and are spun out to the side by a rotating susceptor.
Because the fluid mechanics of this vertical-flow reactor are partially simpler than the fluid mechanics of a conventional horizontal reactor, it is possible to decouple the fluid mechanics from the chemistry, and hence, from a research point of view, to study the fundamental chemical mechanisms responsible for CVD.
In addition to enabling better chemical process science, this kind of reactor is also very well suited to manufacturing, and is the bases for a family of high-performance MOCVD tools now used widely by industry.
The second advance is in in situ optical monitoring. In this area, Sandia has focused on a robust and simple technique, normal-incidence optical reflectance, combined with a novel "virtual interface" analysis method.
The analysis algorithm is now used routinely in a code we call ADVISOR, or the "analysis of deposition using virtual interfaces and spectroscopic optical reflectance." Now, in a single, less-than-one-hour growth run, an MOCVD tool can be very accurately and quickly calibrated in preparation for a series of device growths.
For example, vertical-cavity surface-emitting lasers (VCSELs) can now be grown with 0.6% reproducibility and with 0.2% uniformity over 3" wafers.
Solid-State Lighting website