Abstract
The inherently complex chemical and crystallographic nature of oxide materials has suppressed the purities achievable in laboratory environments, obscuring the rich physical degrees of freedom these systems host. In this manuscript we provide a systematic approach to defect identification and management in oxide molecular beam epitaxy grown MgZnO/ZnO heterostructures which host two-dimensional electron systems. We achieve samples displaying electron mobilities in excess of 1 × 106 cm2/Vs. This data set for the MgZnO/ZnO system firmly establishes that the crystalline quality has become comparable to traditional semiconductor materials.
Highlights
We begin by addressing some technical aspects of the molecular beam epitaxy (MBE) apparatus which have evolved
This is important as the presence of oxygen simultaneous to high temperatures leads to stringent requirements in apparatus design and handling to avoid increased impurities being expelled
The left column of panels displays the surface morphology measured by atomic force microscopy (AFM) while the right column depicts an optical microscope image
Summary
We address prominent impurity sources within the oxide MBE apparatus and refine the growth conditions, which, in combination with tuning the Mg content, enable reproducible growth of films with μ exceeding 1 × 106 cm2/Vs. While this μ occurs for only a narrow charge density range, significant enhancements in μ are achieved for the full range of n. Previous works using oxygen radical cells[16] found the minimum growth temperature to achieve a smooth sample surface to be roughly Tg ≥ 810 °C under similar Zn flux conditions.
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