Control of a‐Si FETs characteristics by impurity‐doping

This paper reports the study on characteristics control of amorphous silicon field‐effect‐transistors (a‐Si FETs). For the application of a‐Si FETs to switching elements in the display panel, it is necessary to have enhancement‐type transistors. To do so, the impurity‐doping method is investigated. First, a numerical analysis considering the localized states was carried out. It was shown that the characteristics control of a‐Si FETs, such as single‐crystal Si MOS FETs, can be achieved by impurity doping. Next, practical a‐Si FETs were fabricated with phosphorus doping or boron‐doping into the channels of transistors. Characteristics of these transistors were investigated and characteristics control was shown. Characteristics of the phosphorus‐doped transistor as well as characteristics of boron‐doped p‐channel transistors showed the same properties as have been predicted by numerical analysis. By contrast, at the boron‐doped transistors, characteristics of n‐channel operation were deteriorated even at a small concentration of boron‐doping. This is due probably to a large variation of the localized state density by boron‐doping.