Film growth of high quality microcrystalline germanium by ECR plasma CVD

我们已经沉积了高质量的氢化锗薄膜使用ECR等离子体的氢稀释锗烷产生的微波的一个非常窄的频谱，以便很好地控制电子和离子撞击生长表面的背景压力的顺序为10^<-8>Torr。在微波功率为9-12 W时，沉积在绝缘衬底上的薄膜发生了非晶-微晶相变，此时薄膜的霍尔电压因非晶半导体的霍尔效应反常而改变了符号。一个光电参数etamutau给出了一个最大的相变类似于先前观察到的Ge薄膜沉积在导电基板上。为了研究表面场效应迁移率μ<FE>_H与霍尔迁移率μ_H的差别，我们用淀积Ge膜作为有源层制备了底栅型TFT，但在muc-Ge：H TFT上观察到了栅漏电流，发现这种栅击穿不是由于电子的充电引起的，而是由于电子的充电引起的。 关于我们 离子和离子在SiO_2上的沉积，但由于微波辐射，并通过屏蔽样品从微波沉积过程中防止。在a-Ge：HTFT中，表面迁移率μ_<FE>与etamutau相关，而在muc-G：HTFT中，表面迁移率μ_与etamutau不相关。在SiO_2上刻蚀Ge发现，与a-Ge：H相比，muc-Ge：H沉积使Ge-SiO_2界面显著粗糙化。此外，我们发现muc-Ge：HTFT中的μ_与<FE>Ge-SiO_2界面的表面粗糙度相关，这表明表面粗糙度是muc-Ge：HTFT的μ_的重要因素<FE>。虽然等离子体诊断揭示了电子温度和离子辐照是获得高μ_和etamutau的关键因素<FE>，但在本工作中，我们无法实现具有如此高的μ_值的沉积条件，如<FE><similar or equal>a-Ge：H中的μ_H 0.3cm^2/Vs<similar or equal>和muc-Ge：H中的μ_H 2cm^2/Vs。因此，这一问题留待今后研究。我们还发现在a-Ge：H薄膜中存在两种类型的光退化效应：一种与通常在本征a-Si：H中观察到的相同，另一种在辐照过程中和辐照后分别给出完全相反的光电流和暗电流特征。前者具有较好的光电灵敏度和较小的局域隙态密度。但对这两种薄膜的沉积条件的差异还需进一步研究。少

We have deposited high quality hydrogenated Ge films using the ECR plasma of hydrogen diluted germane generated by microwaves of a very narrow frequency spectrum in order to well control electrons and ions impinging to growing surfaces at the background pressure of the order of 10^<-8> Torr. The films deposited on insulating substrates showed amorphous-microcrystalline phase transition around at the microwave power of 9-12 W,where Hall voltage of the films changed sign due to Hall effect anomaly in amorphous semiconductor. An optoelectronic parameter etamutau gave a maximum at the phase transition similarly as previously observed in the Ge films deposited on conductive substrates. To investigate surface field effect mobility mu_<FE> in contrast with Hall mobility mu_H, we have fabricated bottom-gate type TFT with depositing Ge films as as active layrs, but gate-leak current was observed in particular on muc-Ge : H TFT.This gate breakdown was found not to be due to charging up of electr … More ons and ions on SiO_2 but due to microwave irradiation, and prevented by shielding the samples from the microwaves during deposition. The surface mobility mu_<FE> was correlated with etamutau in a-Ge : H TFT but not in muc-G : H TFT.Etching Ge on SiO_2 revealed that the Ge-SiO_2 interface was significantly roughened by muc-Ge : H deposition in comparison with a-Ge : H.Moreover, we found mu_<FE> to be correlated with surface roughness of Ge-SiO_2 interface in muc-Ge : H TFT, which suggest that the surface roughness is an important factor in mu_<FE> of muc-Ge : H TFT.Though it was revealed by plasma diagnostic that electron temperature and ion irradiation are key factors to obtain high mu_<FE> and etamutau in a-Ge : H TFT,we could not realize the deposition condition to have such high values of mu_<FE> as mu_H<similar or equal>0.3cm^2/Vs in a-Ge : H and mu_H<similar or equal>2cm^2/Vs in muc-Ge : H in the present work. Thus this has been left to the subject for a future study. We also found the existence of two type light degradation effects in a-Ge : H films ; one is the same as that usually observed in intrinsic a-Si : H and the other gives completely opposite feature of photo- and dark current, during and after irradiation, respectively. The former film has slightly better optoelectronic sensitivity and smaller localized gap-states density. However detailed study including the difference of deposition condition for the two type films should be further continued. Less