(Color online) Plot illustrating an idealized distribution of H2O desorption energies for a cooled metal surface. Nonpumping, pumping, and filled sites are indicated. The filled sites result from the surface being in a steady state with the background H2O partial pressure before cooling.
(Color online) Partial pressures of mass 12, 14, 18, 28, and 44 as a function of time during the cooling of the TSP reservoir (a) to with LN2 and (b) to with a dry-ice/ethanol slurry. In both cases, the cooling of the reservoir commences at t = 0. The two dips in the mass 28 u and 14 u signals of (a) are a result of the reservoir being filled in two stages. The shroud was maintained at +70 °C, with the Ga and As cells at operating temperature (Ga at 921 °C and As at 345 °C with the As-cracker at ∼1000 °C). The substrate and all other cells were at 300 °C.
(Color online) Partial pressures of mass 18, 28, 44, and 75 as a function of time while the shroud is cooled in steps of 20 °C from +20 °C to the lowest achievable temperature of and then warmed back to +20 °C. The steps in the H2O partial pressure correspond to changes in the shroud temperature. For these experiments, the TSP reservoir was empty and the Ga and As cells were at operating temperature (Ga at 921 °C and As at 345 °C with the As-cracker at ∼1000 °C). The substrate and all other cells were at 300 °C.
(Color online) Mass 18 (H2O) partial pressure as a function of shroud temperature during cool down over a 2 h period. The initial shroud temperature was between +40 °C and +70 °C.
(Color online) Room temperature photoluminescence spectra of AlGaAs layers on GaAs grown with closed-cycle cooling of the shroud. The Al0.49Ga0.51As layer is 550 nm thick and the other layers are ∼920 nm thick. Each spectrum shows emission from the AlGaAs layer and the GaAs buffer. The AlGaAs layer growth temperature is indicated for each spectrum. The PL measurement conditions are the same for all the samples.
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