GaAs Substrate Preparation for Oval-Defect Elimination during MBE Growth

We have developed a new method for GaAs substrate preparation which significantly reduces the formation of oval defects during MBE growth of selectively doped n-Al x Ga 1- x As/GaAs heterostructures. The method simply requires treatment in H 2 SO 4 after mechano-chemical polishing in NaOCl solution and generation of a protective surface oxide during In soldering. Routinely a density of oval defects of less than 200 cm -2 is achieved for 2 µm thick heterostructures. The efficiency of the new preparation procedure is demonstrated by 2DEG mobilities in excess of 10 6 cm 2 /(Vs) at 6 K obtained with a spacer width as narrow as 18 nm.