Reciprocal Space Mapping Analysis of Mg-Doped InGaN/GaN Heterostructure for Bias-Dependent UV Photodetection Behavior

Indium gallium nitride (InGaN) has attracted considerable attention for ultraviolet (UV) optoelectronic applications due to its tunable bandgap and compatibility with GaN-based device platforms. However, the optoelectronic performance of InGaN is strongly influenced by lattice strain, indium distribution, surface morphology, and carrier transport properties. In this work, the UV photoresponse of an Mg-doped InGaN/GaN heterostructure subjected to postgrowth annealing at 600 °C is systematically investigated. Structural properties, including lattice parameters, strain state, degree of relaxation, and indium composition, are examined using high-resolution X-ray diffraction reciprocal-space mapping (HRXRD RSM). The results indicate that the Mg-doped InGaN epilayer is partially relaxed on the GaN layer and exhibits phase separation. The indium composition determined from HRXRD RSM ranges from 4.12% to 8.77%. Atomic force microscopy analysis reveals a step-terrace surface morphology. Optical absorption measurements obtained from ultraviolet-visible spectroscopy show a sharp absorption edge at ∼380-382 nm, corresponding to a bandgap of ∼3.25 eV, indicating suitability for UV photodetection. Hall effect measurements reveal a carrier concentration of ∼10¹⁸ cm^-3 and a mobility of ∼188 cm² V^-1 s^-1. The fabricated photodetector exhibits a responsivity of 0.024 A W^-1 and a rise/fall response time of 0.70 s at a bias of 6 V, demonstrating the potential of Mg-doped InGaN for UV photodetector applications.