Selective annealing effects in asymmetric metal-semiconductor-metal algan uv sensors

Asymmetric metal-semiconductor-metal (MSM) AlGaN ultraviolet (UV) sensors with 33 % and 39 % Al composition were fabricated using the selective annealing method. Diodes with lower Al compositions exhibited lower dark current densities and improved UV sensing properties. TEM-EDS analysis showed that the selective annealing caused interdiffusion between the metals; the interface was modified by N penetration into the Ti layer. For UV sensors with Al composition of 33 %, the dark current density and the UV-to-visible rejection ratio (UVRR) after selective annealing were 7.7×10^-10 A/cm² and 135, respectively, which were significant improvements over the values of 1.9×10^-8 A/cm² and 19, respectively, before selective annealing. For UV sensors with Al composition of 39 %, the dark current density and UVRR were 2.3×10^-6 A/cm² and 45, respectively, after selective annealing, which were improved from the values of 6.4×10^-6 A/cm² and 11, respectively, before selective annealing.