Thermal Laser Epitaxy

The established epitaxy technologies mostly date back to the middle of the last century. Many of them have been established and have matured together with specific materials systems, such as Molecular Beam Epitaxy (MBE) with GaAs and compound semiconductors, Pulsed Laser Deposition with high temperature superconductors and complex oxides. They have there limits, though, such as high particle energies for laser ablation and plasma techniques, and background contamination with MOVPE.

We have combined the advantages of the usually adsorption-controlled growth mode known from MBE with the ease, speed and flexibility of using lasers as energy sources. The resulting technique, Thermal Laser Epitaxy (TLE), provides a dramatically broadened scope of process conditions, such as any gas pressure in the reactor from XHV to atmospheric pressure and beyond, and no limits in the temperatures used for evaporating source materials and substrates. It is robust, since the growth reactor basically consists of mechanical holders for substrates and sources and the laser entry windows. It is fast, since the almost unlimited power density of the lasers allow for rapid heating rates, while thermal radiation at high temperatures provides fast cooling. Sources can be exchanged with the same transfer mechanism and in about the same time as the substrates. Without the need for baking, TLE exceeds in purity and crystal quality, since the evaporating surface of the sources and the directly heated substrate are the hottest parts in the chamber, and adsorption-controlled growth modes can be used even at very high substrate temperatures; we have demonstrated melting of MgO at beyond 2800 °C. TLE is particularly suited for the synthesis of complex oxides, since it can work with a very wide range of oxygen chemical potential, while being able to evaporate any element in particular in highly oxidizing atmospheres. I will explain the basic ingredients of the technique, its technological implementation, potential for scaling to industrial production, and present a few examples of initial studies, mostly on oxides and nitrides.