Film growth of high quality microcrystalline germanium by ECR plasma CVD

为了在10^<-8> Torr的背景压力下很好地控制电子和离子撞击生长表面，我们利用极窄频谱微波产生的氢稀释锗的ECR等离子体沉积了高质量的氢化锗膜。在微波功率为9 ~ 12 W时，沉积在绝缘衬底上的薄膜出现了非晶微晶相变，由于非晶半导体中的霍尔效应异常，薄膜的霍尔电压发生了符号变化。光电参数etamutau在相变处给出了最大值，与之前在导电衬底上沉积的Ge薄膜中观察到的相似。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，我们制备了沉积Ge薄膜作为有源层的底栅型TFT，但在多Ge: H TFT上观察到的栅极漏电流尤为明显。发现这种栅击穿不是由于SiO_2上带电的离子和离子引起的，而是由于微波照射引起的，并通过在沉积过程中屏蔽微波来防止样品的发生。在a-Ge: H TFT中，表面迁移率mu_<FE>与etamutu相关，而在much - g: H TFT中则无关。在SiO_2上刻蚀Ge表明，与a-Ge: H沉积相比，多Ge: H沉积使Ge-SiO_2界面显着粗化，并且我们发现mu_<FE>与多Ge: H TFT中Ge-SiO_2界面表面粗糙度相关，表明表面粗糙度是影响多Ge: H TFT中mu_<FE>的重要因素。等离子体诊断结果表明，电子温度和离子辐照是a-Ge: H TFT中获得高mu_<FE>和etamutu的关键因素，但目前尚不能实现a-Ge: H中mu_H<相似或等于>0.3cm^2/Vs和多- ge: H中mu_H<相似或等于>2cm^2/Vs的高mu_<FE>的沉积条件。因此，这将留给未来的研究课题。我们还发现a-Ge: H薄膜存在两种类型的光降解效应；一个与通常在本征a-Si: H中观察到的相同，另一个在辐照期间和辐照后分别给出了完全相反的光电流和暗电流特征。前者具有稍好的光电灵敏度和较小的局域间隙态密度。但两种类型薄膜的沉积条件差异等详细研究还有待进一步深入。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