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“Background Al x Ga1 – x N alloys have attracted considerable attention in recent years because of their great potential for applications in UV and deep UV optoelectronic devices with spectral lengths as short as 200 nm

[1]. Both high-quality p-type and n-type AlGaN epilayers are strongly demanded for electrical injection in constructing these short wavelength devices. However, similar to most wide bandgap semiconductors, AlGaN suffers from the ‘asymmetric doping’ limitation [2, 3], i.e., JNK inhibitor price doping AlGaN to form n-type layer is easy, but achieving p-type doping is difficult [4, 5].

Although Mg is the most widely adopted p-type dopant for from AlGaN, its doping efficiency is extremely low, particularly for high Al content Al x Ga1 – x N [6]. The low doping efficiency of Mg is mainly attributed to its limited solubility, high activation energy, and compensation effect with impurities or native donor defects [2, 7]. In spite of the extensive efforts to improve the Mg activation efficiency [5, 6, 8, 9], the bottleneck of low Mg solubility in GaN [10] and AlN [11] materials strongly restricts the overall p-type doping in AlGaN. Regarding the dopant solubility issue, an extremely high carbon dopant concentration was shown to exist on the epitaxial surface of Si system [12]. This high concentration can be attributed to the surface enhancement effect caused by the partial release of atom mismatch strain. As the epitaxy continues, part of this high concentration dopant segregates to the new surface, and the residual components freezes into the host matrix [12] which corresponds to the final dopant concentration. In other words, the growing surface plays a critical role in determining dopant solubility.