Novel high mobility Ga_0.51In_0.49P/GaAs modulation-doped field-effect transistor structures grown using a gas source molecular beam epitaxy

A standard Ga_0.51In_0.49P/GaAs modulation-doped field-effect transistor (MODFET) structure and a novel Ga_0.51In _0.49P/GaAs MODFET structure where the Ga_0.51In _0.49P spacer layer was replaced by an undoped Al_0.3Ga _0.7As layer were grown using a gas source molecular beam epitaxy. The Hall mobility of the novel MODFET's structures are 6600 and 36 400 cm ²/V s at room temperature and 77 K, respectively, which are more than twice as high as that in the ordinary Ga_0.51In_0.49P/GaAs MODFETs structure. The mobility is attributed to better carrier confinement and smoother heterointerface. Furthermore, it is found that both ordinary and novel MODFET's structures have small photo-persistant conductivity effects at low temperatures and that the FETs made in these materials had no threshold voltage shift at low temperatures after illumination.