超薄氢化非晶锗膜的结构与光电性质

Structural,Eelectronic and Optical Properties of Ultra-thin Hydrogenated Amorphous Germanium Films

通过PECVD制备出了不同厚度的a-Ge∶H膜,采用Raman光谱对样品进行了结构表征,由椭圆偏振光谱仪得到样品的厚度和光学常数,并计算了样品的光学带隙。由变温电导率分析了薄膜的电学输运性质,结果表明,载流子的传输机制为扩展态电导。进而利用变温PL谱研究了薄膜的发光性能,发现其发光峰在1.63μm处;随着膜厚的减小,峰位和峰形都有改变,且强度明显提高。进一步分析发现,随着膜厚的减小非辐射复合跃迁的激活能增大,从而导致辐射复合过程增强。

Ultra-thin hydrogenated amorphous germanium films,with various thickness from 160 nm to 5 nm were grown by plasma enhanced chemical vapor deposition technique.The film structure was characterized by Raman spectroscopy,which exhibited a broad band centered around 280 cm-1 indicating their amorphous nature.The film thickness and optical properties were evaluated by ellipsometer spectroscopy.The measured thickness was well consistent with the pre-designed value and the optical band gap was about 1 eV which slightly increased with the decrease of film thickness.The temperature dependent conductivity of the films was measured.The electronic transport was believed to occur in the extended-states and the corresponding activation energy is about 0.3~0.4 eV.The light emission in infrared region from the films can be detected at low temperature.The sample for 160 nm had a broad luminescence band which can be divided into two sub-bands centered at 0.78 eV and 0.67 eV,respectively.By decreasing the films thickness less than 10 nm,the luminescence band beaome narrower and only a band at 0.8 eV was observed.It may be due to the relatively more hydrogen in the ultrathin films,which passivated the defect states and suppressed the defect-related luminescence.The non-radiative activation energy increased in ultrathin films suggesting the improved efficiency.