Polarization engineered InGaN/GaN visible-light photodiodes featuring high responsivity, bandpass response, and high speed

Abstract

Optoelectronic devices, especially III-nitride quantum-structure devices, are suffering from a series of material problems, such as polarization induced quantum efficiency drop and the lack of a suitable p-type dopant. Herein, dopant-free polarization-induced doping by deposition of a linearly graded AlGaN was utilized to achieve the p-type layer. Benefiting from the polarization doping, p-down structure p–i–n photodiodes based on InGaN/GaN multiple quantum wells (MQWs), in which the polarization field in the InGaN QWs is aligned with the built-in electric field, were fabricated to promote the quantum efficiency. As a result, high responsivity, high speed, and bandpass response were realized via polarization engineering. The photodiodes exhibited a turn-on voltage of ∼2.5 V and a very low dark current below 3.0 × 10⁻¹³ A at 0 to −3 V. Bandpass responses of 420 to 365 nm were observed with a peak responsivity of 0.56 A W⁻¹ at 395 nm, an EQE of 145%, and a light to dark current ratio of ∼10⁴ at 26 μW cm⁻² illumination. In addition to the enhanced field in the QWs, the pure photoconductive gain originating from the polarization-induced energy band incline and carrier escape mechanism in the MQWs also contributes to the improved responsivity. The gain mechanism without involving trap states is supported by the high-speed response with a rising time of ∼41 ns.