Improved MBE-grown GaAs using a novel, high-capacity Ga effusion cell

A novel PBN crucible has allowed the design of a new high-capacity Ga source incorporating a unique heat shielding cap. The extra heat shielding at the front of the source allows hot lip operation with considerably lower power than for previous designs, thus completely eliminating Ga droplets without an inordinately high heat load. Compared with another high-capacity, low-flux transient cell (an EPI 125DF), the new source operated with significantly less power and produced lower defect densities. Specifically, defect densities of 22-27 defects/cm² for ∼ 1 μm thick GaAs layers have been obtained with the new source, compared with 88-92 defects/cm² from the 125DF. In addition, an 18.7 μm thick GaAs layer grown with the new cell had only 277 defects/cm². The new source also produced GaAs with low background doping ( < 2 × 10¹³/cm³), low total trap density ( < 2.0 × 10¹²/cm³), and good uniformity over a 3 in diameter wafer (center-to-edge decrease in GaAs thickness of ∼ 2.2%). It also exhibited low flux transients ( < 2%) and low-long term drift.