自支撑GaN厚膜制备及其光学性能研究

采用镀Ti插入层在氢化物外延设备中制备了高质量自支撑GaN厚膜。X射线衍射测试发现(0002)峰摇摆曲线的半高宽为260 arcsec；5 K下样品带边发光峰的半高宽为3 meV，室温下样品的带边发光峰也只有20 meV，并且在室温的PL谱中观察不到黄光带；扫描电子显微镜观察显示，腐蚀后的自支撑GaN厚膜表面有位错延伸形成的六角坑，并估算出样品位错密度约为2.1×l07 cm-2。这些结果说明镀Ti插入层有助于提高GaN外延层的晶体质量。通过Raman和低温荧光分析，可以看出自支撑GaN厚膜表面应力已经完全释放。研究了不同温度下样品的荧光特性，证明得到的无应力自支撑GaN厚膜具有很好的晶体质量和光学质量

Preparation and Optical Performance of Freestanding GaN Thick Films

High-quality freestanding GaN thick films were deposited by hydride vapor phase epitaxy (HVPE) on sapphire wafer with a thin Ti film on the top. The FWHM of (0002) peaks in the X-ray rocking curve profile is 260 arcsec. The FWHM of band edge emission peaks at 5 K and room temperature are 3 meV and 20 meV, respectively. The yellow spectral region is not observed at room temperature. The surface morphology of GaN films was characterized by scanning electron microscope; results show that hexagonal pits from dislocation extension exist on the surface of freestanding GaN thick films after corrosion and their dislocation density is estimated as 2.1×l07 cm-2. All these results prove that the Ti metal interlayer improves the crystalline quality of GaN epitaxial layer. The results of Raman and PL show that the surface stress of the GaN films is released completely. Finally, the temperature-dependent PL was investigated; the result also proves that the stress-free freestanding GaN thick films have high crystalline quality and optical quality