Interface property of Mg-based dual ion implanted p+-ohmic layers in p-channel pseudomorphic AlGaAs/InGaAs heterostructure FETs

We evaluated pseudomorphtc Al,, Gao,,As/In,~,Ga,sAs/GaAs p-channel heterostructure field effect transistors (pch-HFETs) fabricated by Mg, Mg + P, and Mg + Ar ion implantation, and examined the implanted heterostructures to study the effect of interface characteristics on device properties. It was found that P dual implantation improves device performance by reducing sheet resistance ( p,) and contact resistance CR,), while Ar dual implantation increases p, and R, and, as a result, degrades device performance. Dual implantation has double-edged influence on heterostructures. Interfaces having gradually varying atomic profiles produced by ion implantation usually have low contact resistance because of their lower barrier height. The accompanying radiation damage, however, induces the defects around interfaces that trap carriers. For Mg-based dual ion implanted pch-HFETs, the most gradual interface does not result in the highest device performance, as observed in the Mg + Ar implanted heterostructure that has the most gradual atomic profiles at interfaces, among Mg, Mg + P, and Mg + Ar implanted samples. We showed by the results of electrochemical capacitance-voltage measurement that the carrier density in the Mg + P implanted heterostructure is higher in all layers compared to the Mg implanted sample. This is the reason for the highest performance exhibited by Mg + P implanted pch-HFETs. On the other hand, the Mg + Ar implanted heterostructure has the lowest carrier density in InGaAs layer due to the severe radiation damage induced during Ar dual implantation, which remains even after activation annealing. The different effects of P dual implantation and Ar dual implantation stem from the different mechanisms for Mg activation involved in the processes. We conclude that dual implantation resulting in insignificant radiation damage can be applied to fabricate highly doped ohmic regions in HFETs.