Reduction of visible defect densities in molecular beam epitaxy grown GaAs using a high-capacity, low flux transient Ga source with novel crucible inserts

A new design of large capacity crucible with novel inserts has been evaluated with respect to visible defect density, layer uniformity, and flux transient. The crucible was tested in a commercially available furnace with two independently controlled heater windings. The inserts were two disks, each having a different set of holes, stacked inside the crucible and permitting no line of sight between the Ga melt and the substrate. The source was tested side-by-side with a similar furnace equipped with a commercially available crucible and conical insert set designed for low shutter transient and low flux drift. Defect densities were measured on epitaxial layer structures having a total of 1 μm of GaAs. The new design showed significantly lower total defect densities than a control growth with the standard cell, producing as few as ∼ 1/3 the defects (43±6 vs 155/cm²). Flux transients were the same with the two sources (<2%). Uniformity was tested by using photoluminescence to measure the thickness of GaAs quantum wells across a 75 mm diameter wafer. While the old design produces a center-to-edge decrease in thickness of ∼2.5%, the new source produces a decrease in thickness of ∼6.5%.