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Description
Efficient p-type doping remains a central challenge in GaN epitaxy and associated devices such as light-emitting diodes, laser diodes, photoelectrochemical cells as well as quantum devices. Plasma-assisted molecular beam epitaxy (PA-MBE) offers a compelling alternative to metal-organic vapor phase epitaxy (MOVPE) due to its intrinsic advantages in Mg incorporation and the absence of post-growth activation—an especially critical benefit for tunnel-junction and polarization-engineered devices. Despite numerous reports of successful Mg doping, a comprehensive understanding of growth-regime-dependent incorporation behavior across III/V ratios and temperature ranges remains incomplete.
In this work, we present a systematic investigation of Mg acceptor incorporation in GaN grown by PA-MBE under both Ga-rich and N-rich conditions spanning low (~580 °C) and high (~740 °C) temperature regimes. The growth temperature boundary near ~650 °C separates two fundamentally distinct kinetic regimes: in the low-temperature Ga-rich regime, a self-regulated Ga bilayer stabilizes the surface, while at higher temperatures excess Ga rapidly desorbs, eliminating bilayer formation. Although Ga-rich growth has traditionally been favored for achieving high crystalline quality, its influence on Mg incorporation efficiency requires further investigation.
A comprehensive growth map was constructed to correlate Mg incorporation, surface morphology, and electrical properties as a function of III/V ratio and temperature. Secondary ion mass spectroscopy (SIMS) reveals significantly enhanced Mg incorporation efficiency (~80%) under N-rich conditions. In contrast, Ga-rich growth produces smoother surfaces with root-mean-square roughness of ~1–2 nm but exhibits reduced Mg incorporation. Room-temperature Hall measurements confirm tunable hole concentrations ranging from ~7 × 10¹⁷ cm⁻³ (Ga-rich) to ~2 × 10¹⁹ cm⁻³ (N-rich) at fixed Mg flux.These results establish a clear trade-off between surface morphology and Mg incorporation efficiency and provide a practical growth-regime guideline for optimizing p-type GaN. The findings are directly relevant to nitride-based light emitters, tunnel diodes, quantum emitters, PEC cells, and other advanced electronic and photonic device architectures.