研究目的
Investigating the effect of Mg incorporation on dislocation and stress evolution during the growth of GaN thin films, including the interplay between dopant size effect, dislocation bending, and polarity inversion.
研究成果
Mg doping promotes dislocation bending and tensile stress generation in GaN films, similar to Si doping. Compressive stresses from Mg size effects are only observable at low dislocation densities (<5×10^9 cm^-2). Polarity inversion at high Mg concentrations reduces screw dislocation density. The developed kinetic model successfully captures these effects, with good agreement between calculated and measured bending angles. These findings are crucial for optimizing p-type doping and defect control in GaN-based devices.
研究不足
The study is limited to Mg-doped GaN films on Si substrates grown by MOCVD; results may not generalize to other doping methods or substrates. The exact mechanism of Mg-induced dislocation bending is not fully understood, and the model relies on fitting parameters. High dislocation densities in stack A may obscure some effects, and polarity inversion complexities require further investigation.
1：Experimental Design and Method Selection:
The study involved growing Mg-doped GaN films on Si substrates using metal-organic chemical vapor deposition (MOCVD) to investigate dislocation bending and stress evolution. In situ curvature measurements and ex situ transmission electron microscopy (TEM) were employed to monitor stress and dislocation behavior. A kinetic stress evolution model was developed to analyze the effects.
2：Sample Selection and Data Sources:
Two growth stacks (A and B) with different dislocation densities were used. Stack A had higher dislocation density (~10^11 cm^-2), while stack B had lower density (~10^9 cm^-2) due to a step-graded transition layer. Samples were labeled A0-A6 and B0-B4 with varying Mg concentrations.
3：List of Experimental Equipment and Materials:
Equipment included an AIXTRON horizontal flow reactor (AIX 200/4 RF-S), in situ multi-beam optical stress sensor (MOSS) from k-space Associates, Inc., TEM for imaging, and secondary ion mass spectrometry (SIMS) for Mg concentration analysis. Materials included tri-methyl aluminium (TMA), tri-methyl gallium (TMG), cyclopentadienyl magnesium (Cp2Mg), ammonia (NH3), and hydrogen carrier gas.
4：Experimental Procedures and Operational Workflow:
Films were grown at 40 mbar pressure and temperatures up to 1000°C. Stress was monitored in real-time using MOSS. After growth, samples were analyzed using TEM to observe dislocation bending and KOH etching to determine polarity. Mg concentrations were measured via SIMS.
5：Data Analysis Methods:
Stress data were fitted using a kinetic model that incorporates dislocation bending and size effects. Bending angles from TEM images were compared with model predictions. Statistical analysis of dislocation densities and stress values was performed.
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