Study on quaternary AlInGaN/GaN HFETs grown on sapphire substrates

Abstract

We report on AlInGaN/GaN heterostructure field effect transistors (HFETs) and the effect of different barrier material compositions. The analytical model for the interface charge in quaternary nitride heterostructures is described in detail and is applied in the calculation of the expected sheet carrier density. Experimental results from different lattice-matched AlInGaN/GaN heterostructures are presented and compared with the analytical predictions. Three heterostructures with AlInGaN barriers grown on sapphire substrates were processed and have been investigated. Each barrier layer was lattice-matched to GaN and the gallium content was 0.1, 0.15 and 0.2 at a barrier thickness of 13.5, 12.8 and 11.3 nm, respectively. Additionally, from these experiments, the basic trends for quaternary nitride Schottky barrier contacts are discussed. Finally, comprehensive dc characterizations have been performed. All devices had a gate length of 1 μm and exhibited a good transconductance of around 260 mS mm −1 at nearly the same current density level. An increase in threshold voltage as well as a decrease in gate leakage current for increasing GaN content has been observed. The nearly constant electron mobility in the range of 1700 cm 2 V −1 s −1 at room temperature is within the best reported so far for HFETs with InN-containing barriers.

InAlGaN/GaN HEMTs at Cryogenic Temperatures

“…Despite the implementation of an ultrathin AlN spacer to reduce the alloy scattering and enhance the 2DEG confinement [3], the growth of the ternary alloy remains challenging. On the other hand, a quaternary InAlGaN compound is attractive as a barrier layer since it allows easier adjustment of the band gap and strain state with suitable Al/In ratios [4][5][6][7][8][9][10]. Recently, we have reported InAlGaN/AlN/GaN heterostructure HEMTs with a sub-10-nm ultrathin quaternary barrier with a state-of-the-art electron mobility of 1800 cm 2¨V´1¨s´1 and a sheet carrier density of 1.9ˆ10 13 cm´2 at room temperature [11].…”

Surface properties of AlInGaN/GaN heterostructure

“…Thus, alternatively to AlGaN/GaN heterostructure, quaternary alloy of AlGaInN could be used as the barrier layer as it allows independent tuning of lattice constant and the band gap. Additionally, due to stronger polarization constants, for the same lattice strain as in AlGaN/GaN, a higher 2DEG concentration could be achieved [7][8][9][10]. This heterostructure originally developed for high-speed devices, has recently experienced a renewed interest due to its wide and tunable band gap, strong polarization and very high sensitivity of 2DEG concentration to the surface barrier that makes it feasible to be used in reduction based applications [11], solar blind UV detectors [12,13] and molecule detectors [14][15][16] is an interest of scientific research.…”

Polarization-Engineered Enhancement-Mode High-Electron-Mobility Transistors Using Quaternary AlInGaN Barrier Layers

“…3, the bandgap, calculated using a weighted formula from Ref. 1, is plotted as a function of the nominal lattice constant a, calculated by Vegard's law. Here, the bowing parameters are updated by the latest results from the literature: The bowing parameters used here are 0.9 eV for AlGaN, 17 1.65 eV for InGaN, 17 and a quite high and constant value of 5.2 eV for AlInN.…”

“…The total polarization P total is the sum of the spontaneous P spon and piezoelectric polarization P piezo , taking formulas from the literature into account. [1][2][3][4] The investigated sample series are also illustrated in Fig. 3.…”

“…[1][2][3] By changing the composition and hence the spontaneous and piezoelectric polarization in a pseudomorphically grown AlInGaN layer, one can control the polarization difference between the AlInGaN barrier and the GaN buffer. 4,5 Tensilestrained AlInGaN layers with high Al contents and lattice-matched pure AlInN both generate high twodimensional electron gas (2DEG) densities.…”