Solution-Processed Cubic GaN for Potential Lighting Applications
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.105
Solution-Processed Cubic GaN for Potential Lighting Applications Aakash Kumar Jain1, Sushma Yadav2,3, Meenal Mehra1,4, Sameer Sapra2, and Madhusudan Singh1
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Department of Electrical Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India 2 Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India. 3 Institute of Physical Chemistry and Electrochemistry, Leibnitz University of Hannover, Germany 4 Momentive Performance Materials India Pvt. Ltd., Bengaluru, India
ABSTRACT: Cubic gallium nitride (GaN) is a wide bandgap semiconductor that exhibits a high crystallographic symmetry resulting in a lower inbuilt polarization which is useful for more efficient phosphor-free green light-emitting diodes. It has been grown using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), which produce highly ordered thin films on compatible substrates. In this work, we report the chemical synthesis of GaN using chemical metathesis reaction in diethyl ether with lithium nitride and anhydrous gallium chloride as precursors, inside a nitrogen glove box at the room temperature. The resulting product was subsequently washed to remove lithium chloride and dried before vacuum annealing in a furnace at 850°C. Powder X-ray diffraction (XRD) scans of the as-prepared and annealed product reveal a mixed phase of GaN along with Ga2O3. Energy dispersive X-ray spectroscopy (EDAX) measurements show a nitrogen-poor product, which correlates well with the nearly black color of the powder. Diffuse reflectance spectroscopy (DRS) measurements were carried out with the obtained product on a barium sulfate substrate in a Perkin-Elmer Lambda 1050-UV-Vis-NIR spectrophotometer showing a strong absorbance below 400 nm. The energy band gap is bounded by values extracted from the Tauc plot and DRS measurements in the range of 3.2-3.5 eV, which is in good agreement with the known excitonic bandgap of cubic GaN (~ 3.3 eV). Initial photoluminescence (PL) measurements using a Perkin-Elmer LS-55 spectrophotometer with an excitation wavelength of 310 nm reveal a weak emission centered around 440 nm corresponding to the known defect centers (D0X) in GaN. Further development of this process to form inks is expected to provide an alternate pathway to producing flexible phosphor-free lighting devices.
INTRODUCTION Gallium Nitride (GaN), a wide-bandgap binary III-V semiconductor, has emerged as an important technological material for its potential applications in power
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electronics [1], and LEDs and lasers [2]. In its latter role, wurtzite GaN is a critical enabler for blue and white lighting. GaN in its cubic phase exhibits a lower bandgap (by ~200 meV), lower effective m
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