Low-Temperature Synthesis of Two-Dimensional Gallium Nitride via Liquid Metal Printing

With rapid technological advancements, the integration of third-generation semiconductor technology with two-dimensional materials is revolutionizing society at an unprecedented rate. These materials, such as gallium nitride (GaN) and silicon carbide (SiC), show exceptional promise in electronics, energy conversion, and communication technologies[1]. Notably, advancements in third-generation semiconductor technology have significantly enhanced the performance and reliability of communication systems. Our research specifically focuses on synthesizing two-dimensional GaN. One notable challenge in the application of 2D GaN is the "Green gap" issue in light-emitting diodes (LEDs), which refers to the inefficiency in emitting light within the yellow-green range of the visible spectrum[2]. This inefficiency is primarily due to spontaneous and piezoelectric polarization effects in the wurtzite GaN structure, leading to the quantum confinement Stark effect and reduced emission efficiency[3]. In contrast, the zinc-blende GaN structure, due to its symmetric nature, lacks spontaneous polarization, making it a promising candidate to address the "Green gap" problem in LEDs. However, the growth of zinc-blende GaN is challenging because of its metastable nature, which makes it less stable compared to the wurtzite GaN structure.<br/>To address this, we employed the liquid metal printing technique to fabricate 2D gallium oxide (Ga₂O₃) films, which were subsequently nitridated to form a zinc-blende GaN structure. Liquid metal printing offers several advantages, including the ability to fabricate wafer-scale 2D metal oxide films that are only a few layers thick, simplicity of the process, and low production costs. These attributes make this method highly suitable for industrial applications and align with the ongoing trend of semiconductor device scaling. To validate our results, we utilized Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy to analyze the GaN structure under varying temperatures and durations during the transformation process, achieving an average film thickness at the nanoscale. Our goal was to determine the optimal parameters for the transformation to zinc-blende GaN. We discovered that 500°C is the minimum temperature at which successful transformation can occur. Based on this finding, we have decided to conduct further research at this temperature. Additionally, we examined the lattice structure of the samples using transmission electron microscopy (TEM).<br/>Based on previous experiments, we used TEM and CL to observed that at a transform temperature of 800 degrees Celsius, the hexagonal crystals showed a reduction or appearance of defects as the time increased from 30 minutes to 90 minutes. In addition, further processes at 850 degrees Celsius and 900 degrees Celsius confirmed better stability of hexagonal structures at higher temperatures. Subsequently, we extended the reaction time, lowered the processing temperature, and conducted nitridation under vacuum conditions. We found GaN of different colors including blue, yellow, green, and brown under various experimental parameters. The transformation degree was assessed by the ratio of Ga-O to Ga-N in XPS, and the relationship between color and crystal structure was investigated using TEM, leading to the identification of zincblende GaN.<br/><br/>Reference<br/>1.Zhao, Chao, et al. "Novel III-V semiconductor epitaxy for optoelectronic devices through two-dimensional materials." <i>Progress in Quantum Electronics</i> 76 (2021): 100313.<br/>2.Lee, Lok Yi. "Cubic zincblende gallium nitride for green-wavelength light-emitting diodes." <i>Materials Science and Technology</i> 33.14 (2017): 1570-1583.<br/>3.Ryou, Jae-Hyun, et al. "Control of quantum-confined stark effect in InGaN-based quantum wells." <i>IEEE Journal of Selected Topics in Quantum Electronics</i> 15.4 (2009): 1080-1091.