An Enhancement-Mode Hydrogen-Terminated Diamond Field-Effect Transistor With Lanthanum Hexaboride Gate Material

Abstract

An enhancement-mode hydrogen-terminated diamond field-effect transistor (FET) is realized by using a low work function gate material, namely, lanthanum hexaboride (LaB6). The reason for the enhancement mode should be that the electrons in the LaB6 layer flow into the two-dimensional hole gas (2DHG) channel and compensate the holes, such that the channel is shut down. The threshold voltages ( ${\mathrm {V}}_{\text {TH}}$ ) range from − 0.29 V to − 0.72 V with different gate lengths. The device with 2 $\mu \text{m}$ gate length shows a − 57.9 mA/mm maximum drain current density ( ${\mathrm {I}}_{\text {DSmax}}$ ) at ${\mathrm {V}}_{\text {GS}} =-$ 5 V. The on/off ratio is around 9 orders of magnitude, with a subthreshold swing of 130 mV. Effective mobility ( $\mu _{\text {eff}}$ ) as high as 195.4 cm2/ $\text{V}\cdot \text{s}$ is obtained from the device. This technique reveals undamaged 2 DHG characteristics, uncontaminated interface between LaB6 and aluminum gate metal, and a simple fabrication process, which will promote the development of enhancement diamond FETs.