Transport characteristics of AlGaN/GaN/AlGaN double heterostructures with high electron mobility

Abstract

The AlGaN/GaN/AlGaN double heterostructure (DH) with high electron mobility of 1862 cm2/Vs at room temperature and 478 cm2/Vs at 573 K high temperature was obtained by a combination of optimization schemes considering scattering mechanisms. First, a composite buffer layer structure, including GaN and AlGaN layer, was used to improve the crystal quality of the AlGaN/GaN/AlGaN DH. Second, interface roughness scattering was reduced by increasing the channel thickness, thus the two-dimensional electron gas mobility was further improved. Moreover, an ultrathin AlN interlayer was inserted between the GaN channel layer and the AlGaN buffer layer to decrease the alloy disorder scattering. The Hall effect measurements showed that the DH had better transport characteristics at high temperatures, and an electron mobility of 478 cm2/Vs was achieved at 573 K, which is twice larger than that of the conventional single heterostructure (∼200 cm2/Vs at 573 K). Therefore, AlGaN/GaN/AlGaN DH is more suitable for the applications in high temperature electronic devices.

Investigation of Inverse Piezoelectric Effect and Trap Effect in AlGaN/GaN HEMTs Under Reverse-Bias Step Stress at Cryogenic Temperature

“…Up to now, the studies of GaN based devices working at low temperature focus on the following aspects: (1) Enhanced transport properties at low temperature due to the weaker phonon scattering [8], [9]; (2) More excellent DC and RF properties at low temperature [10], [11]; (3) The kink effect associated with impact ionization [12]. Most researches have focused on the characterization of the GaN material and devices at low temperature.…”

Overcoming the poor crystal quality and DC characteristics of AlGaN/GaN/AlGaN double‐heterostructure high electron mobility transistors

“…Noticeably, the excellent value of 1014 mA mm −1 is even comparable to that of the InAlN DH HEMTs . Actually, a much thicker channel layer is unnecessary because both sheet carrier density and electron mobility will not keep increasing when the channel reaches a critical thickness ; meanwhile, a much thinner channel is also inferior because electrons in it will suffer serious scattering from both interfaces .…”

“…In addition, the apparent deterioration of the performance of SH HEMTs at high temperatures has also been observed previously . To improve carrier confinement and alleviate the aforementioned problems, DH (double heterostructure) HEMTs, with a very strong 2DEG (two‐dimensional electron gas) confinement, have been investigated . The superior performances of DH HEMTs including high‐temperature stability , excellent breakdown characteristics , and improved punchthrough characteristics have been presented.…”

Barrier Strain and Carbon Incorporation‐Engineered Performance Improvements for AlGaN/GaN High Electron Mobility Transistors**

“…Ozbay and co‐workers have reported that highly resistive GaN layers can be achieved by the growth of a thick HT AlN (0.5 − 1.0 µm) buffer layer on sapphire substrates, however the breakdown voltage of their device was only 60 V. The low breakdown voltage of AlGaN/GaN HEMTs with HT AlN may be due to residual donors in GaN (such as O and Si) incorporated during high‐temperature growth. Because it is necessary to compensate for the residual n‐type conductive GaN buffer to further improve the breakdown voltage of AlGaN/GaN HEMTs on both sapphire substrates and SiC substrates, AlGaN is also widely used to replace GaN buffers to enhance the breakdown . Since, however, AlGaN has poor thermal conductivity, it is probably difficult to achieve both good performances for HEMTs and very high insulating performance of GaN buffers grown on sapphire substrates.…”