Closed-cycle cooling of cryopanels in molecular beam epitaxy, R.B. Lewis, V. Bahrami-Yekta, M.J. Patel, T. Tiedje, M. Masnadi-Shirazi, J. Vac. Sci. Technol. B 32, 02C102 (2014)

Closed-cycle cooling of the cryoshroud in a molecular beam epitaxy (MBE) system with a dimethyl polysiloxane heat transfer fluid has reduced liquid nitrogen consumption by an order of magnitude, significantly lowering operating costs. The temperature dependence of cryopanel pumping efficacy in the MBE system has been investigated. H₂O, CO, CO₂, and As₄ are all pumped effectively by liquid nitrogen cooled cryopanels ( 196C ) in the MBE. At -78C , the operating temperature of the closed-cycle chiller, H₂O and As₄ are pumped effectively, while CO and CO₂ are not. The pumping speed for H₂O is found to increase exponentially with decreasing temperature. Below ~-40C and -95C , the pumping speeds for As₄ and H₂O saturate, respectively. AlGaAs layers grown with the closed-cycle-cooled shroud show strong photoluminescence, expected room temperature electron mobility, and background doping levels less than 4x10¹⁵ cm^-3.