透過液態金屬壓印技術製造出低溫製程的二維氮化鎵

Abstract

隨著科技的迅速發展，第三代半導體技術與二維材料的整合正以前所未有的速度革新社會。這些材料，如氮化鎵（GaN）與碳化矽（SiC），在電子、能量轉換與通訊技術等領域展現出卓越的應用潛力[1]。值得注意的是，第三代半導體技術的進步已大幅提升通訊系統的效能與可靠性。本研究聚焦於二維氮化鎵（2D GaN）的合成。與傳統的三維材料相比，二維材料展現出許多獨特性質。通常會具有高載子遷移率、良好的熱導性以及高透明度[2]，使其成為一些可撓性元件的理想材料。而在氮化鎵的應用中，一項重要的挑戰為發光二極體（LED）中的「綠光缺口」[3]問題，即在可見光譜中黃綠波段的發光效率較低[4]。此效率降低主要源於六方晶（wurtzite）GaN結構中的自發極化與壓電極化效應，這些效應會導致量子侷限史塔克效應（Quantum Confined Stark Effect），進而抑制發光效率[5]。相比之下，閃鋅礦結構（zinc-blende）GaN由於具對稱性結構，不具有自發極化效應，因此被視為解決LED「綠光缺口」問題的有潛力候選材料。由於立方晶氮化鎵為閃鋅礦結構，其相較於六方晶氮化鎵更不穩定，成長難度較高。為了解決此問題，我們採用液態金屬壓印技術[6]製備二維氧化鎵（Ga₂O₃）薄膜，並進一步透過氮化反應轉化為閃鋅礦及纖鋅礦結構氮化鎵。液態金屬轉印具備多項優勢，包括能製備出僅數層厚度且大面積的二維金屬氧化物薄膜、製程簡單，以及成本低廉。這些特點使其非常適合用於工業應用，也符合當前半導體元件持續縮小的趨勢。為了驗證我們的結果，我們運用陰極射線發光光譜 (CL)、X光光電子能譜（XPS）以及原子力顯微鏡（AFM）來分析氮化鎵在不同溫度與時間條件下的轉化過程，並獲得平均為奈米尺度的薄膜。我們的研究目標是找出最佳的轉化參數以生成閃鋅礦以及纖鋅礦結構氮化鎵。研究結果顯示，600 °C 是可以有辦法嘗試控制氮化鎵晶體結構的溫度。我們使用穿透式電子顯微鏡（TEM）觀察樣品的晶格結構，並透過不斷嘗試更改實驗參數來得到穩定的閃鋅礦結構氮化鎵。

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. 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. Compared with traditional three-dimensional materials, two-dimensional materials exhibit many unique properties. They typically possess high carrier mobility, good thermal conductivity, and high transparency [2], making them ideal materials for certain flexible devices. One notable challenge in the application of GaN is the "Green gap"[3] issue in light-emitting diodes (LEDs), which refers to the inefficiency in emitting light within the yellow-green range of the visible spectrum[4]. 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[5]. 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. To address this, we employed the liquid metal printing technique[6] to fabricate 2D gallium oxide (Ga2O3) films, which were subsequently nitridated to form a zinc-blende or wurtzite 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 Cathodoluminescence (CL), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) 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 and wurtzite GaN. The results indicate that 600 °C is a feasible temperature for attempting to control the crystal structure of gallium nitride. We used transmission electron microscopy (TEM) to observe the lattice structure of the samples and continuously adjusted the experimental parameters to obtain a stable zinc-blende phase of gallium nitride.