Single domain GaAs layers with satisfactory morphology were grown on (100)-oriented Si substrates by heat treatment of the substrates at above 900°C and subsecquent two-step growth at low temperatures of 450°C or below and by conventional growth temperatures. The grown GaAs layers showed a high mobility of 5200 cm2V-1s-1 at room temperature with a carrier density of 1×1016 cm-3.
We have systematically characterized oxygen (O) and carbon (C) impurities in undoped gallium aluminum arsenide ( Al
x
Ga1-
x
As) epitaxial layers grown by organometallic vapor-phase epitaxy (OMVPE). The concentrations of O and C impurities are evaluated by secondary-ion mass spectroscopy. For x≤0.63 the increase rate of O concentration, [O], with x is nearly proportional to the flow rate of trimethylaluminum (TMA), indicating that the oxygen is contained in the TMA molecules. In contrast, [O] and [C] increase superlinearly with x for x≥0.83, and particularly, [O] exceeds 1018 cm-3. The vibration mode of Al–O bonds is observed at 900–1050 cm-1 for the x=0.83 sample using Fourier-transformation infrared measurements. The superlinear increase of [O] with x is attributed to the increased adsorption of residual O2 or H2O molecules. The mechanism of the superlinear increase is discussed in terms of statistic consideration of the –Al– arrangement on the Al
x
Ga1-
x
As surface. Hall measurements show that the hole concentration markedly decreases for x>0.63 and the Al
x
Ga1-
x
As layer becomes semi-insulating, which was attributed to hole compensation by the O-related deep hole traps. The hole mobility also decreases in the same x range.
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