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

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 (V TH) range from - 0.29 V to - 0.72 V with different gate lengths. The device with 2 μ m gate length shows a - 57.9 mA/mm maximum drain current density (I DSmax) at VGS=-5 V. The on/off ratio is around 9 orders of magnitude, with a subthreshold swing of 130 mV. Effective mobility (μ eff) as high as 195.4 cm²/ V · 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.