Abstract
This article reports a nonpolar GaN metal–semiconductor–metal (MSM) photodetector (PD) with an ultrahigh responsivity and an ultrafast response speed in the ultraviolet spectral region, which was fabricated on nonpolar (112̅0) GaN stripe arrays with a major improvement in crystal quality grown on patterned (110) silicon substrates by means of using our two-step processes. Our nonpolar GaN MSM-PD exhibits a responsivity of 695.3 A/W at 1 V bias and 12628.3 A/W at 5 V bias, both under 360 nm ultraviolet illumination, which are more than 20 times higher and 4 orders of magnitude higher compared to the current state-of-the-art photodetector, respectively. The nonpolar GaN MSM-PD displays a rise time and a fall time of 66 and 43 μs, respectively, which are 3 orders of magnitude faster compared to the current state-of-the-art photodetector.
Highlights
Developing ultraviolet (UV) photodetectors (PDs) that can find a wide range of applications, such as flame sensors, atmospheric ozone detection, space communications, and biophotonics,[1−7] is a subject facing increasing interest
It is worth highlighting that the crystal quality of nonpolar GaN grown on widely used sapphire substrates or silicon substrates is far from a device requirement, normally showing a very broad full width at half-maximum of ∼0.5−0.6° of its X-ray diffraction (XRD) rocking curve,[9−14] whereas the typical value of standard c-plane GaN on sapphire or silicon is less than 0.1°
In recent decades we have developed a number of costeffective overgrowth approaches to achieve semipolar and nonpolar GaN with a major improvement in crystal quality on sapphire.[24−27] We have further extended these approaches to the growth on silicon substrates
Summary
Developing ultraviolet (UV) photodetectors (PDs) that can find a wide range of applications, such as flame sensors, atmospheric ozone detection, space communications, and biophotonics,[1−7] is a subject facing increasing interest. It is worth highlighting that the crystal quality of nonpolar GaN grown on widely used sapphire substrates or silicon substrates is far from a device requirement, normally showing a very broad full width at half-maximum (fwhm) of ∼0.5−0.6° of its X-ray diffraction (XRD) rocking curve,[9−14] whereas the typical value of standard c-plane GaN on sapphire or silicon is less than 0.1° This indicates a very high density of defects in nonpolar GaN, leading to a slow response of nonpolar PDs with a rise time ranging from 0.046 to 17.5 s and a falltime ranging from 0.075 to 20.5 s, heavily depending on the crystal quality,[15] whereas the rise time and the fall time of cplane GaN are typically 10 and 30−59 ms, respectively.[16,17] Clearly, there exists a great potential for achieving superior performance GaN UV PDs if a step change in the crystal quality of nonpolar GaN can be obtained
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