Fabrication of high performance nano-crystalline germanium films using ultra-clean ECR plasma CVD

采用电子回旋共振等离子体化学气相沉积技术在(c-)Si、c-Ge和玻璃衬底上制备了氢化微晶Ge(μc-Ge：H)薄膜。随着衬底温度(Ts)的升高，在ts[约等于]50℃处开始了非晶态到微晶态的相变。在200℃以上，c-Si和Ge衬底上的晶化体积分数(_&lt；xc&gt；)超过80%，观察到μc-Ge：H沿衬底晶轴择优生长。对于玻璃衬底，_&lt；xc&gt；在[约等于]155℃处有一个极大值，在此之后随着T_S的增加而减小。氢从生长表面上的脱附可能是抑制微晶形核的原因。随着T_S的增加，a-Ge：H薄膜的发光峰能量和发光幅值降低，但即使在T_S=313℃时，发光谱线也比c-Ge的发光峰宽，表明发光来自晶界的非晶态部分。在a-Ge：H中观察到了双峰寿命分布。用新设计的半解析反褶积测量ns寿命的双相双锁相正交频率分辨光谱表明，硫属化合物以及a-Si：H和a-Ge：H等四面体半导体中的光致发光寿命分布基本上是双峰分布，短寿命组分(ns-μS)和长寿命组分(Ms)分别属于单态和三态激子。我们提出，控制电子-空穴对的自旋态是延长复合寿命和提高器件质量的关键，例如太阳能电池的效率。

Hydrogenated microcrystalline germanium (μc-Ge : H) films were deposited on crystalline (c-) Si, c-Ge and glass substrates by electron-cyclotron-resonance plasma chemical vapor deposition (ECRPCVD). With increasing substrate temperature (Ts), an amorphous to microcrystalline phase transition started at Ts 【approximately equal】 50 ℃. Above 200 ℃, the crystalline volume fraction (_<Xc>) on the c-Si and Ge substrates exceeded 【approximately equal】 80% and preferential growth of μc-Ge : H along crystallographic axes of the substrates was observed. For the glass substrates, _<Xc> was a maximum at 【approximately equal】 155 ℃, above which it decreased with increasing T_s. Hydrogen desorption from the growth surface is probably responsible for suppressing microciystalline nucleation. The PL peak energy and magnitude decreased with increasing T_s, but PL spectrum even at T_s = 313 ℃ being broad compared with that of c-Ge suggest the PL arises from the amorphous part of the grain boundary.High-quality hydrogenated amorphous germanium (a-Ge : H) films were deposited under the critical condition of the film growth of amorphous-crystalline phase transition. Double-peak lifetime distribution were observed in a-Ge : H. A dual-phase double lock-in (DPDL) quadrature frequency resolved spectroscopy (QFRS) developed to measure ns lifetime with a newly devised semi-analytical deconvolution revealed that the PL lifetime distribution is basically double-peaked in chalcogenide as well as tetrahedral semiconductors such as a-Si : H and a-Ge : H. The short lived (ns-μs) and the long lived (ms) components are attributed singlet and triplet excitons, respectively. We proposed that controlling spin states of electron-hole pairs is a key to prolong the recombination lifetime and improve the device-quality e.g. efficiency of solar cells.