High gain and high ultraviolet/visible rejection ratio photodetectors using p-GaN/AlGaN/GaN heterostructures grown on Si

We report high performance ultraviolet (UV) photodetectors (PDs) based on p-GaN-gated AlGaN/GaN heterostructures grown on silicon substrates. Benefitting from the high electrical gain resulting from the transistor-like operation of the device, a photocurrent as high as 4.8mA/mm was achieved with UV illumination. Due to the effective depletion of the two-dimensional electron gas at the AlGaN/GaN heterointerface via a p-GaN optical gate, the dark current was suppressed to below 3 10 mA/mm. A high photo-to-dark current ratio over 10 and a high responsivity of 2 10 A/W were demonstrated in the device. Moreover, with a cutoff wavelength of 395 nm, the PDs exhibited an ultrahigh UV-to-visible rejection ratio of over 10. Limited by a persistent photoconductivity effect, the rise time and fall time of the device frequency response were measured to be 12.2ms and 8.9ms, respectively. The results suggest the potential of the proposed PDs for high-sensitivity UV detection. Published under license by AIP Publishing. https://doi.org/10.1063/5.0011685 Ultraviolet (UV) photodetectors (PDs) have been widely employed in many applications such as aerospace engineering, ozone sensing, flame detection, and advanced communications. As a direct wide bandgap semiconductor with excellent thermal and chemical stabilities, GaN has attracted extensive research interest for fabricating visible-blind UV PDs. Various device structures, for instance, p–i–n, metal–semiconductor–metal (MSM), and Schottky diodes, have been explored for GaN UV PDs. In addition to the conventional PD configurations, photoconductors consisting of an AlGaN (or InAlN)/ GaN heterostructure, which is typically used in high electron mobility transistors (HEMTs), have also drawn great attention for UV detection. Because of a high-density two-dimensional electron gas (2DEG) forming a conductive channel at the heterojunction interface, an ultrahigh photoresponsivity and high photocurrent are usually observed in the HEMT-based UV PDs. However, the existence of the 2DEG channel also resulted in high dark currents (at the same order of the photocurrent) in these devices, which decrease the detectivity and increase the power consumption. To suppress the dark current, the 2DEG channel was either depleted by adding a negatively-biased transparent metal gate or floating p-GaN optical gate on the AlGaN barrier, or partial removal of the AlGaN barrier leaving an i-GaN channel in between. Among these approaches, HEMTbased PDs with a p-GaN optical gate have shown great promise. However, all the reported HEMT-based PDs with p-GaN optical gates were demonstrated on sapphire substrates rather than on larger-sizeavailable Si substrates with potentially lower cost. Moreover, the dark currents in the reported devices, affected by the fabrication process and material epitaxy quality, are still not as low as that in HEMTbased PDs with a selectively removed AlGaN barrier structure. In this study, we report high-performance UV PDs based on p-GaN/AlGaN/GaN heterostructures grown on cost-effective silicon substrates. The device exhibits an ultralow dark current of 29 pA/mm and a large photocurrent of 4.8mA/mm under a 365-nm light illumination, leading to an extremely high photo-to-dark current ratio of over 10 and a high responsivity of 2 10 A/W. With a cutoff wavelength of 395nm, a large UV-to-visible rejection of 10 is also achieved in the device. The gain mechanism of the PDs is discussed through the observation of the incident light intensity-controlled phototransistor operations. The time-domain photoresponse of the device is also investigated. The p-GaN/AlGaN/GaN heterostructures used in this work, typically for p-GaN gate high electron mobility transistor application, Appl. Phys. Lett. 117, 071101 (2020); doi: 10.1063/5.0011685 117, 071101-1 Published under license by AIP Publishing Applied Physics Letters ARTICLE scitation.org/journal/apl