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 (LaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ). The reason for the enhancement mode should be that the electrons in the LaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TH</sub> ) range from - 0.29 V to - 0.72 V with different gate lengths. The device with 2μm gate length shows a - 57.9 mA/mm maximum drain current density (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DSmax</sub> ) at V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> = - 5 V. The on/off ratio is around 9 orders of magnitude, with a subthreshold swing of 130 mV. Effective mobility (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> ) as high as 195.4 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s is obtained from the device. This technique reveals undamaged 2DHG characteristics, uncontaminated interface between LaB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> and aluminum gate metal, and a simple fabrication process, which will promote the development of enhancement diamond FETs.