Film growth of high quality microcrystalline germanium by ECR plasma CVD

我们使用由非常窄频谱的微波产生的氢稀释锗烷的ECR等离子体沉积了高质量的氢化Ge薄膜，以便在10^<-8>托的背景压力下很好地控制撞击到生长表面的电子和离子。沉积在绝缘基底上的薄膜在微波功率9~12 W左右呈现非晶-微晶相变,其中由于非晶半导体的霍尔效应异常,薄膜的霍尔电压发生了符号变化。光电参数 etamutau 在相变处给出最大值，与之前在沉积在导电基板上的 Ge 薄膜中观察到的类似。为了研究表面场效应迁移率 mu_<FE> 与霍尔迁移率 mu_H 的对比，我们制作了沉积 Ge 薄膜作为有源层的底栅型 TFT，但特别是在 muc-Ge : H TFT 上观察到栅极漏电流。发现这种栅极击穿不是由于 SiO_2 上的电子和离子充电所致，而是由于微波辐射所致，并且通过在沉积过程中屏蔽样品免受微波影响来防止栅极击穿。表面迁移率mu_<FE>与a-Ge : H TFT中的etamutau相关，但与muc-G : H TFT中无关。在SiO_2上蚀刻Ge表明，与a-Ge : H相比，通过muc-Ge : H沉积使Ge-SiO_2界面显着粗糙化。此外，我们发现mu_<FE>与muc-Ge : H TFT中Ge-SiO_2界面的表面粗糙度相关，这表明表面粗糙度是muc-Ge : H TFT mu_<FE>的重要因素。虽然等离子诊断表明电子温度和离子辐照是a-Ge : H TFT获得高mu_<FE>和etamutau的关键因素，但我们无法实现a-Ge : H和mu_H<相似或等于mu_<FE>高值mu_<FE>0.3cm^2/Vs的沉积条件。 muc-Ge 中等于>2cm^2/Vs：当前工作中的H。因此，这已留给该主题以供将来研究。我们还发现a-Ge:H薄膜中存在两种类型的光衰减效应：一种与通常在本征a-Si : H中观察到的相同，另一种在辐照期间和辐照后分别给出完全相反的光电流和暗电流特征。前一种薄膜具有稍好的光电灵敏度和较小的局域能隙态密度。然而，应进一步继续详细研究，包括两种类型薄膜沉积条件的差异。较少的

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