Light-modulated low-frequency noise spectroscopy for deep-level defect characterization in Al-rich AlGaN heterostructures

Al-rich AlxGaN (x > 0.4) heterostructures are pivotal building blocks for high-voltage power electronic and deep ultraviolet optoelectronic devices, yet deep-level defect characterization in such ultrawide-bandgap semiconductors remains challenging. Here, we demonstrate that light-modulated low-frequency noise (LFN) spectroscopy enables quantitative profiling of both trap density and energy depth. Under intensity-tunable above-bandgap illumination, the dominant 1/f noise from carrier number fluctuations yields a trap state density Nt ∼ 1018 cm−3 eV−1, consistent with literature. A distinct ultralow-frequency generation–recombination noise is suppressed under out-of-band excitation with photon energy >2.3 eV, matching a 2.3 eV cathodoluminescence peak and suggesting the presence of a trap, with a VIII-related deep acceptor as a plausible candidate. Its effective areal trap density is quantified as 1.52 × 1010 cm−2. The technique's validity is further corroborated by reduced Nt in devices with an AlN/GaN interface layer. This work establishes light-modulated LFN as a versatile, device-intrinsic method for deep-trap characterization in ultrawide-bandgap semiconductors, independent of specific device architectures.