氢化物气相外延生长高质量GaN膜生长参数优化研究

系统研究了低温成核层生长时间、高温生长时的V/Ⅲ 比以及生长温度对氢化物气相外延生长GaN膜晶体质量的影响. 研究发现合适的低温成核层为后续高温生长提供成核中心, 并能有效降低外延膜与衬底间的界面自由能, 促进成核岛的横向生长; 优化的V/Ⅲ比和最佳生长温度有利于降低晶体缺陷密度, 促进横向生长, 增强外延膜的二维生长. 利用扫描电子显微镜、原子力显微镜、高分辨X射线衍射、 低温光致发光谱和室温拉曼光谱对优化条件下生长的GaN外延膜进行了结构和光电特性表征. 测试结果表明, 膜表面平整光滑, 呈现二维生长模式表面形貌; (002)和(102)面摇摆曲线半高宽分别为317和343 arcsec; 低温光致发光谱中近带边发射峰为3.478 eV附近的中性施主束缚激子发射峰, 存在11 meV的蓝移, 半高宽为10 meV, 并且黄带发光强度很弱;常温拉曼光谱中E₂ (high) 峰发生1.1 cm^-1蓝移.结果表明, 优化条件下生长的GaN外延膜具有良好的晶体质量和光电特性, 但GaN 膜中存在压应力. 关键词： 氮化镓 氢化物气相外延 低温成核层

Optimization of the parameters for growth high-qulity GaN film by hydride vapor phase epitaxy

In this paper, the processing parameters of growing GaN epilayer by hydride vapor phase epitaxy are optimized. The influences of the low-temperature (LT) nucleation layer growth time, V/Ⅲ precursor ratio and the growth temperature on GaN layer are investigated by the high-resolution X-ray diffraction (HRXRD) signature for the asymmetric and symmetric reflections. The investigation finds that the LT-nucleation layer not only supplies the nucleation centers having good crystal quality, but also promotes the lateral growth of the sequent high temperature (HT) growth. The optimal LT nucleation layer growth time, V/Ⅲ precursor ratio and the growth temperature can effectively enhance lateral growth to reduce the crystal defects and are favorable to converting the growth mechanism from three-dimension to two-dimension in HT growth. The structural and optoelectronic properties of the as-grown GaN layer with a thickness of 15 μat the optimal parameters are studied by scanning electron microcopy, atomic force microscopy (AFM), HRXRD, Raman spectra, and photoluminescence (PL) measurements. X-ray rocking curves show that the full widths at half maximum of (002) and (102) are 317 and 343 arcsec, respectively. The surface roughness (rms: root mean square) is 0.334 nm detected using AFM. These characteristics show that the sample has good lattice quality and smooth surface morphology. In PL spectrum, the near band edge emission is dominated by emission from excitons bound to neutral donors (D⁰X) near 3.478 eV with 11 meV blue-shift and the yellow band emission is very weak. The results indicate that the GaN layer has good crystal quality and excellent optoelectronic properties, but a little biaxial in-plane compressive strain also exists in it due to the lattice and thermal mismatch.
Keywords： gallium nitride hydride vapor phase epitaxy low temperature nucleation layer