Accumulation and removal of Si impurities on $\beta-Ga_2O_3$ arising from ambient air exposure

Here we report that the source of Si impurities commonly observed on (010) $\beta-Ga_2O_3$ is from exposure of the surface to air. Moreover, we find that a 15 minute HF (49%) treatment reduces the Si density by approximately 1 order of magnitude on (010) $\beta-Ga_2O_3$ surfaces. This reduction in Si is critical for the elimination of the often observed parasitic conducting channel, which negatively affects transport properties and lateral transistor performance. After the HF treatment the sample must be immediately put under vacuum, for the Si fully returns within 10 minutes of additional air exposure. Lastly, we demonstrate that performing a 30 minute HF (49%) treatment on the substrate before growth has no deleterious effect on the structure or on the epitaxy surface after subsequent $Ga_2O_3$ growth.