Closed cycle chiller as a low cost alternative to liquid nitrogen in molecular beam epitaxy, R.B. Lewis, J.A. Mackenzie, T. Tiedje, D.A. Beaton, M. Masnadi-Shirazi, V. Bahrami-Yekta, K.P. Watkins, P.M. Mooney, J. Vac. Sci. Technol. B 31, 03C116 (2013)

The high cost of cooling the cryoshroud in a molecular beam epitaxy system has been greatly reduced by replacing liquid nitrogen (LN2) as a coolant with a silicone polymer heat transfer fluid cooled to as low as -80  C by a closed cycle chiller. Gallium arsenide epitaxial layers have been grown with two different cooling configurations of the shroud: conventional LN2 cooling and cooling to -70  C with the chiller. The partial pressure of water in the chamber is a factor of about 2.5 higher with the closed cycle chiller operating at -70  C than with liquid nitrogen in the shroud. No significant difference is observed in the density of deep levels in the GaAs, as determined by deep level transient spectroscopy.