以物理气相传输法自支撑生长氮化铝单晶的表征

Characterization of Freestanding AlN Single Crystals Growth through a Novel Approach Using the PVT Method

摘要:

本文提出了以物理气相传输法自支撑生长氮化铝单晶的新方法，此方法可以在氮化铝烧结体表面一次性获得大量生长的氮化铝单晶。本研究中，在2373–2523 K的温度条件下经过100 h生长的氮化铝单晶，其最大尺寸为7 × 8 × 12 mm3，典型直径为5–7 mm。这些原生晶体的表面形貌及结晶质量分别通过扫描电子显微镜、拉曼光谱和高分辨X射线衍射进行表征分析。其中，拉曼光谱E2峰位的半高全宽为5.7 cm-1，高分辨X射线衍射得到的对称摇摆曲线的半高全宽为93.6角秒。经过选择性化学腐蚀后的晶体，其表面的平均腐蚀坑密度为7.5 × 104 cm-2。逸出气体分析和辉光放电质谱分析结果表明，碳和氧为晶体内部的主要杂质元素，含量分别为28 ppmw和120 ppmw。此方法为高质量氮化铝单晶的获取提供了一个新的途径，这些单晶可以被切成晶片作为后续氮化铝同质外延生长的优良籽晶。使用这些小的籽晶，我们首次成功制备出了直径高达60 mm的氮化铝单晶体/晶圆，并具有良好的深紫外光透过性。

Abstract:

In this paper, a novel approach to grow freestanding AlN single crystals spontaneously using the physical vapor transport method is presented. Dozens of single crystals can be obtained on the surface of a pre-sintered AlN powder source in a single growth run using this approach. In this study, the largest AlN single crystal for 100 h of growth at 2373–2523 K was 7 × 8 × 12 mm3, and the typical diameter was 5–7 mm. The surface morphologies of the as-grown crystals were investigated by scanning electron microscopy, whereas the structural quality of the crystals was characterized by Raman spectroscopy and high-resolution X-ray diffraction. Raman spectroscopy exhibited an E2 (high) full width at half maximum (FWHM) of 5.7 cm-1, whereas the high-resolution X-ray diffraction rocking curve showed a FWHM of 93.6 arcsec for the symmetric reflection. The average etch pit density revealed by preferential chemical etching was 7.5 × 104 cm-2, and the major impurities determined by evolved gas analysis and glow discharge mass spectrometry were carbon at 28 ppmw and oxygen at 120 ppmw. The proposed novel approach provides a new means of obtaining high-quality AlN single crystals, which can be cut into wafers and are ideal as seeds for subsequent homoepitaxial AlN growth. Using these small seeds, crack-free bulk AlN single crystal/wafers that have excellent deep UV transparency and are up to 60 mm in diameter were successfully prepared for the first time.