Abstract
To fully exploit the advantages of GaN for electronic devices, a critical electric field that approaches its theoretical value (3 MV/cm) is desirable but has not yet been achieved. It is necessary to explore a new approach toward the intrinsic limits of GaN electronics from the perspective of epitaxial growth. By using a novel two-dimensional growth mode benefiting from our high-temperature AlN buffer technology, which is different from the classic two-step growth approach, our high-electron-mobility transistors (HEMTs) demonstrate an extremely high breakdown field of 2.5 MV/cm approaching the theoretical limit of GaN and an extremely low off-state buffer leakage of 1 nA/mm at a bias of up to 1000 V. Furthermore, our HEMTs also exhibit an excellent figure-of-merit (Vbr2/Ron,sp) of 5.13 × 108 V2/Ω·cm2.
Highlights
Intrinsic GaN with inherent polarization on c-plane substrates is supposed to exhibit superior electrical properties to almost all of the other existing semiconductors, such as high electron mobility and a very high sheet carrier density of twodimensional electron gas (2DEG) formed in an AlGaN/GaN heterostructure but without using any modulation doping[1,2] and high breakdown voltage.[3,4] Due to its wide band gap, intrinsic GaN is supposed to be at least semi-insulating
A standard growth approach for GaN grown on sapphire is based on the classic two-step method developed by three 2014 Nobel Prize Laureates Akasaki, Amano, and Nakamura by using metal−organic vapor-phase epitaxy (MOVPE) techniques; namely, a thin GaN or AlN nucleation layer is initially prepared at a low temperature (LT) followed by a thick GaN buffer layer grown at a high temperature prior to the growth of any further device structures
We have explored an approach toward the limit of GaN materials by means of using our high-temperature AlN buffer, which was originally designed for the growth of novel III-nitride optoelectronics[18−22] instead of the classic two-step growth method, where a 2D growth mode is employed throughout the whole growth processes
Summary
Intrinsic GaN with inherent polarization on c-plane substrates is supposed to exhibit superior electrical properties to almost all of the other existing semiconductors, such as high electron mobility and a very high sheet carrier density of twodimensional electron gas (2DEG) formed in an AlGaN/GaN heterostructure but without using any modulation doping[1,2] and high breakdown voltage (with the theoretical value of the critical electrical field of ∼3MV/cm).[3,4] Due to its wide band gap, intrinsic GaN is supposed to be at least semi-insulating. In terms of growth modes, this approach is based on the initial formation of small islands on a nanometer scale evolved from the LT nucleation layer due to a subsequent annealing process followed by a gradual coalescence process to obtain a flat surface (i.e., initially a three dimensional (3D) growth mode and a 2D growth mode) This two-step growth approach has resulted in major improvement in the crystal quality of GaN in the last two decades, leading to unprecedented success in the field of III-nitride optoelectronics. Four terminal breakdown measurements were performed to characterize an off-state leakage current for our HEMTs. A 1000 V Keithley 2410 SMU was connected to the drain electrode of the DUT to sweep the bias from 0 to 1000 V with a 5 V step size. The currents flowing through the drain, the source, the gate, and the substrate electrodes were monitored individually via the corresponding SMUs
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