Effects of impurity and composition profiles on electrical characteristics of GaAsSb/InGaAs hetero-junction vertical tunnel field effect transistors

Abstract

We fabricated and characterized GaAs0.51Sb0.49/In0.53Ga0.47As hetero-junction vertical tunnel field effect transistors (TFETs) on InP substrates in order to examine the effects of the structural characteristics of GaAsSb/InGaAs hetero-structures on the electrical properties of the TFETs. The operation of the fabricated GaAs0.51Sb0.49/In0.53Ga0.47As TFET was confirmed with the ION/IOFF ratio of ∼102 over VG swing of 1.25 V at 297 K. This ION/IOFF ratio was improved up to ∼104 at 20 K, thanks to the suppression of the leakage current in the source junction. The secondary ion mass spectrometry analyses for the present hetero-structures have revealed that the concentration of the p-type dopant (Be) atoms, doped in the GaAsSb source regions, decreases in the InGaAs channel regions at an inverse slope of ∼11 nm/dec. Also, the scanning transmission electron microscope-energy dispersive X-ray spectroscopy has shown that group III and V compositions change abruptly in a region within 10 nm from the interface between the Be-doped GaAsSb source and the undoped InGaAs channel. We performed the 2-dimensional device simulation based on the device structure and the experimentally obtained composition and impurity profiles, and we found that the composition profile had little effect on the S.S. values. The device simulation also revealed that both the optimization of the concentration and the profile of the p-type doping of GaAsSb, and thinning of the effective oxide thickness (EOT) of the gate stacks could effectively improve the inherent S.S. values of the present GaAs0.51Sb0.49/In0.53Ga0.47As hetero-junction vertical TFETs. When 1.0 nm EOT and NA = 1 × 1020 cm−3 are used under the present impurity abruptness, S.S. < 40 mV/dec. can be achieved for the vertical GaAsSb/InGaAs TFETs, which is promising for an ultralow power switching device.