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（ECRPCVD）方法在（c-）Si、c-Ge和玻璃衬底上沉积了氢化微晶锗（μc-Ge：H）薄膜。随着衬底温度（Ts）的升高，在Ts [约等于] 50 ℃时，非晶相开始向微晶相转变。在200 ℃以上，在c-Si和Ge衬底上的结晶体积分数（_<Xc>）超过[约等于] 80%，并观察到μc-Ge：H沿着衬底晶轴择优生长。对于玻璃基板，_<Xc>在[约等于] 155 ℃时达到最大值，高于该温度时，_随T_s的增加而减小。氢从生长表面的脱附可能是抑制微晶形核的原因。PL峰的能量和强度随T_s的增加而降低，但在T_s = 313 ℃时的PL谱仍比c-Ge宽，说明PL来自于晶界的非晶部分。在a-Ge：H中观察到双峰寿命分布。采用半解析解卷积技术，建立了双相位双锁定（DPDL）正交频率分辨光谱（QFRS），并用于ns寿命的测量。结果表明，硫族半导体和四面体半导体（如a-Si：H和a-Ge：H）的PL寿命分布基本上是双峰型的。短寿命组分（ns-μs）和长寿命组分（ms）分别归属于单重态和三重态激子。我们认为控制电子空穴对的自旋态是延长复合寿命和提高太阳电池效率等器件质量的关键。

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.