The outgassing rates of a vacuum remelted type 316L stainless steel were measured as a function of baking temperatures, baking durations, and air exposure/baking cycles. Long-time baking, as was expected, reduced the outgassing rate of the stainless steel. A subsequent air exposure and short-time baking in vacuum was found to reduce the outgassing rate much more than the preceding long-time baking. The outgassing rate after baking qAB was reduced with the repeated air exposure/baking cycles at a constant baking temperature. After a few air exposure/baking cycles, qAB was not reduced and remained constant with a further air exposure/baking cycle. This indicates that the surface of the stainless steel reached the steady state with respect to the outgassing as a result of the repeated air exposure/baking cycles. For this thoroughly degassed state, the effect of baking temperature was evaluated in the range of 150 to 450 °C. Six-hour baking at 150 °C was sufficient to attain the outgassing rate of 1.3×10−10 Pa m3/s m2. The relation between the outgassing rate after baking q*AB and the maximum baking temperature TBmax was approximately expressed by the equation log q*AB =−1.87 log TBmax−4.51. The Auger electron spectroscopy (AES) analysis showed that the Cr enrichment at the surface became more evident as the maximum baking temperature increased. Further for a given baking temperature, little significant difference in AES spectra was observed between the thoroughly degassed state and the intermediately degassed state.

Oval defects in GaAs layers are serious impediments to GaAs device fabrication. Of particular importance is the relationship between the droplets deposited on the crucible walls and the number of oval defects. These droplets previously believed to be gallium oxides are shown to consist of GaAs shells covering the Ga particles. By increasing the wall temperature of the crucible orifice, and reducing the arsenic beam intensity, the density of droplets is reduced, thus decreasing oval defects. Using a uniform-heated Ga effusion cell and adjusting the cell configuration, the droplets can be reduced substantially and the defect density can be reduced from >104 cm−2 to less than 200 cm−2.

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