Enhanced UV detection by non-polar epitaxial GaN films

Shruti Mukundan,Greeshma Chandan,Arjun Shetty,S B Krupanidhi,Lokesh Mohan,Basanta Roul

doi:10.1063/1.4937742

Abstract

Nonpolar a-GaN (11-20) epilayers were grown on r-plane (1-102) sapphire substrates using plasma assisted molecular beam epitaxy. High resolution x-ray diffractometer confirmed the orientation of the grown film. Effect of the Ga/N ratio on the morphology and strain of a-GaN epilayers was compared and the best condition was obtained for the nitrogen flow of 1 sccm. Atomic force microscopy was used to analyze the surface morphology while the strain in the film was quantitatively measured using Raman spectroscopy and qualitatively analyzed by reciprocal space mapping technique. UV photo response of a-GaN film was measured after fabricating a metal-semiconductor-metal structure over the film with gold metal. The external quantum efficiency of the photodetectors fabricated in the (0002) polar and (11-20) nonpolar growth directions were compared in terms of responsivity and nonpolar GaN showed the best sensitivity at the cost of comparatively slow response time.

Highlights

UV photodetectors have wide range application in industrial, environmental and biological fields.1,2 Well established Si-based UV detectors with a band gap of 1.1 eV show some significant drawback because of the ageing due to exposure to radiations of much higher energy, resulting in degradation of device performance and increase in dark current
The external quantum efficiency of the photodetectors fabricated in the (0002) polar and [11,12,13,14,15,16,17,18,19,20] nonpolar growth directions were compared in terms of responsivity and nonpolar GaN showed the best sensitivity at the cost of comparatively slow response time
Effect of nitrogen flux on the surface morphology of the film showed smoother film at a flow rate of 1 sccm which is an indirect evidence for the reduction of defect levels and this condition was chosen as the optimized one

Summary

INTRODUCTION

UV photodetectors have wide range application in industrial, environmental and biological fields. Well established Si-based UV detectors with a band gap of 1.1 eV show some significant drawback because of the ageing due to exposure to radiations of much higher energy, resulting in degradation of device performance and increase in dark current. The large and direct band gap of III-nitride materials are proving very advantageous for UV photodetection and a lot of interest to further improve the performance of photodetectors fabricated on III-nitride material is seen in the past few years.. Heterostructures grown along the c-axis exhibit large internal electric fields that affect the radiative recombination rates as well as the carrier transport of the heterostructure barriers.. Heterostructures grown along the c-axis exhibit large internal electric fields that affect the radiative recombination rates as well as the carrier transport of the heterostructure barriers.7 To overcome this polarization issue, there have been concerted efforts in exploring III-Nitride materials and devices along nonpolar and semipolar crystallographic orientations.. The structure has advantage of very low dark current due to rectifying nature of the contacts, high resistivity of the material, reduced parasitic capacitance, low noise and large internal gain.. The photodetector is fabricated on the best grown film and its performance was compared with photodetector grown on conventional (0 0 0 2) c-plane axis

EXPERIMENTAL

AND DISCUSSION

CONCLUSIONS