Polarization-Graded AlGaN Solar-Blind p-i-n Detector With 92% Zero-Bias External Quantum Efficiency

We report on record high zero-bias external quantum efficiency (EQE) of 92% for back-illuminated Al0.40Ga0.60N p-i-n ultra-violet (UV) photodetectors on sapphire. The zero-bias responsivity measured 211 mA/W at 289 nm, which is the highest value reported for solar-blind, p-i-n detectors realized over any epitaxial wide band-gap semiconductor. This is also the first report for a p-i-n detector, where a polarization-graded Mg-doped AlGaN layer is utilized as the p-contact layer. The devices exhibited a ten-orders of magnitude rectification, a low reverse leakage current density of 1 nA/cm(2) at 10 V, a high R(0)A product of 1.3 x 1011 Omega.cm(2) and supported fields exceeding 5 MV/cm. The light-to-dark current ratio and the UV-to-visible rejection ratio for the detectors exceeded six-orders of magnitude and the thermal noise limited detectivity (D*) measured 6.1 x 1014 cmHz(1/2)W(-1). The state-of-the-art performance parameters can be attributed to a high crystalline quality absorbing AlGaN epi-layer resulting from the use of an AlN/AlGaN superlattice buffer and an improved p-contact via polarization grading.