Reduction of the acceptor impurity background in GaAs grown by molecular beam epitaxy

We report very high purity, unintentionally doped n‐type GaAs with the lowest acceptor background of all reported molecular beam epitaxy (MBE) GaAs layers. The residual acceptor concentration is 2.4×10¹³ cm⁻³ and the residual donor concentration is 1.5×10¹⁴ cm⁻³, yielding a compensation ratio of N_a/N_d=0.160. The measured Hall mobility is 163 000 cm²/V s at 77 K with a peak value of 216 000 cm²/V s at 45.9 K. The limitations of the Hall mobility at 77 K as a figure of merit are discussed and more accurate figures of merit are considered. The initial preparation of the MBE system and the growth conditions leading to the reduced incorporation of acceptor impurities are also presented.