高温退火对PVT法生长的AlN晶体质量的影响

Effect of High-temperature Annealing on AlN Crystal Grown by PVT Method

在PVT法生长AlN晶体的过程中,很难保持理想的热力学平衡状态,不可避免地会产生晶体缺陷。高温退火技术对提高晶体完整性十分有效,受到了广泛关注。本工作在N2气氛环境下对PVT法生长的AlN晶片进行高温退火研究。为了评价退火前后AlN晶体的质量和结构变化情况,进行了高分辨率X射线衍射(HRXRD)和拉曼光谱分析。通过室温光致发光(PL)和吸收光谱对AlN晶体的光学性质以及与杂质相关的带隙变化情况进行了表征。在1400~1800℃退火后,AlN晶体质量显著提高。1400℃退火后,(10-12)晶面的X射线摇摆曲线的半峰宽(FWHM)从104.04 arcsec减小到79.92 arcsec。随着退火温度升高,吸收性能明显增强,带隙增大,说明高温退火处理有利于提高AlN晶体的质量。二次离子质谱(SIMS)结果表明,退火过程降低了C杂质,增加了AlN晶体的带隙,这与光吸收结果一致。

In the process of PVT growth of AlN crystals,there is difficult to maintain ideal thermodynamic equilibrium conditions,causing crystal defects being inevitably generated.High temperature annealing technology has received much attention due to their effectiveness in improving crystal integrity.In this paper,AlN samples grown by PVT method were annealed at high temperature in N2 atmosphere.In order to evaluate the crystalline quality and structural perfection of AlN before and after thermal annealing,high-resolution X-ray diffraction(HRXRD)and Raman spectrum were carried out.In addition,the impurity related band gap changes in the optical properties of AlN crystals were characterized by room temperature photoluminescence(PL)and absorption spectra.The crystal quality of these AlN crystals was significantly improved after annealing at 1400-1800℃.The full width at half maximum(FWHM)of the(1012)plane X-ray rocking curve decreased from 104.04 to 79.92 arcsec(1 arcsec=0.01592°)after annealing at 1400℃.As the annealing temperature increases,the absorption was significantly enhanced and the band gap became larger,indicating that the annealing process was beneficial to improve the quality of AlN crystals.The results of secondary ion mass spectrometry(SIMS)demonstrate that the annealing process reduces the C impurity,resulting in an increase in band gap of AlN crystal,which is consistent with the results of optical absorption.