Film growth of high quality microcrystalline germanium by ECR plasma CVD

为了很好地控制电子和离子在10^lt；-8 Torr量级的背景压力下撞击生长表面，我们用非常窄频谱的微波产生的氢稀释锗的ECR等离子体沉积了高质量的氢化Ge薄膜。在9-12W的微波功率范围内，沉积在绝缘衬底上的薄膜发生了非晶-微晶相变，薄膜的霍尔电压因非晶态半导体中的霍尔效应反常而发生变化。与以前在导电衬底上沉积的Ge薄膜中观察到的情况类似，光电参数etamutau在相变时出现最大值。为了研究表面场效应迁移率和霍尔迁移率的对比，我们用沉积Ge膜作为有源层的方法制备了底栅型TFT，但在MUC-Ge：HTFT上观察到了栅漏电流，发现这种栅击穿不是由于电子…的充电引起的更多的离子和离子在SiO_2上，但由于微波辐射，并在沉积过程中通过屏蔽样品的微波来防止。在a-Ge：H TFT中，表面迁移率与etamutau相关，而在MUC-G：H TFT中不相关。在SiO_2上刻蚀Ge表明，与a-Ge：H相比，MUC-Ge：H沉积使Ge-SiO_2界面明显粗糙。此外，我们还发现MUC-Ge：H TFT中表面迁移率与Ge-SiO_2界面的表面粗糙度相关，这表明表面粗糙度是影响Mu&G；&GT的一个重要因素；虽然等离子体诊断表明，电子温度和离子辐照是a-Ge：H TFT中获得高Mu&lt；Fe&Gt；和Et的关键因素，但我们不能实现在本工作中a-Ge：H和Mu_H&Lt中的Mu_H&Lt；和Mu_H&Lt；相似或相等&GT；2 cm^2/Vs的沉积条件具有如此高的Mu_H&t；Fe&Gt；因此，这一问题留给了未来的研究。我们还发现在a-Ge：H薄膜中存在两种类型的光退化效应，一种与本征a-Si：H相同，另一种在辐照过程中和辐照后分别呈现出完全相反的光电流和暗电流特性。前者具有稍好的光电灵敏度和较小的局域能隙态密度。然而，包括两种类型薄膜的沉积条件的差异在内的详细研究仍需继续。较少

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