Veeco’s unique thermal control system features independent heaters for the red and white phosphorus zones, and an air cooling jacket on the white phosphorus reservoir. Both heaters are used for thorough source outgassing. After loading, efficient charge conversion is achieved by heating the red phosphorus zone to evaporation temperatures, while cooling the white phosphorus reservoir to promote condensation of the P4 vapor. During growth, an adjustable temperature gradient is achieved using just a single bulk heater. With the heater in the red phosphorus zone, the crucible can be heated to a red phosphorus temperature of 190°C (sufficiently low to avoid evaporation of red phosphorus during operation) and a white phosphorus temperature of 75-100°C. Air cooling reduces the temperature in the white zone to the desired operating level. This system provides excellent thermal stability, even at white zone temperatures as low as 65°C.
For rapid and reliable flux control, the gas flow is metered from the crucible to the cracking zone with an all-metal needle valve. Efficient conversion of P4 to P2 occurs in the high-conductance cracking zone. A Veeco Phosphorus Valved Cracker Temperature Controller is recommended for use with this source, as well as a Veeco SMC-II Automated Valve Positioner for reliable, automated control of the needle valve.
The Valved Cracker for Phosphorus is a proven effective and safe alternative to the use of phosphine for MBE growth. Valved sources offer the precise Group V flux control needed for demanding quaternary GaInAsP materials, as well as efficient shut-off for the growth of arsenide/phosphide heterostructures with minimal intermixing (1%) between the layers.
The source’s valve mechanism makes it possible to quickly and reproducibly establish whatever beam equivalent pressure (BEP) is required to optimize growth parameters. Closing the valve prevents loss of source material during bakeout. Results from laboratories worldwide using this source demonstrate exceptional material quality and state-of-the-art electronic and optoelectronic devices.
Demonstrated results include: