Effect of inserted Al_<i>x</i>Ga_1–<i>x</i>N layer on characteristic of double-channel <i>n</i>-Al_0.3Ga_0.7N/GaN/<i>i</i>-Al_<i>x</i>Ga_1–<i>x</i>N/GaN HEMT

Abstract

<sec>With the demand for high-temperature, high-frequency, and high-power microwave applications increasing, AlGaN/GaN high electron mobility transistors (HEMT) have attracted much attention in recent years. Two-dimensional electron gas (2DEG) induced by spontaneous polarization and piezoelectric polarization caused by the uneven charge distribution on Ga-N bond and the large tensile strain guarantees the high performance of AlGaN/GaN HEMT. Compared with single-channel devices, dual-channel AlGaN/GaN HEMT has great application prospects in enhancing the electronic confinement, current drive and alleviating the current collapse. In order to study the physical characteristics, the carrier state and transportation characterization of <i>n</i>-Al_0.3Ga_0.7N/GaN/i-Al<i>_x</i>Ga_1–<i>x</i>N/GaN multilayer structure are investigated. By calculating the one-dimensional self-consistent Poisson-Schrödinger, the energy band diagram, electric field and charge distribution in the devices are obtained. The 2DEG, alloy disorder and dislocation scattering mechanism in the device are also analyzed by analytical models in which the wave function in finite barriers and Fermi’s rule are used.</sec><sec>With Al<i>_x</i>Ga_1–<i>x</i>N layer thickness increasing from 0 nm to 30 nm and Al content rising from 0.1 to 0.2, the concentration of 2DEG localized in the heterointerface is diminished in the first channel. Simultaneously, mobility limited by alloy disorder scattering increases monotonically with the <i>r</i> composition occupation number and the Al<i>_x</i>Ga_1–<i>x</i>N thickness proportion increasing. Besides, dislocation scattering on carriers is strengthened in the same quantum well, resulting in the lower mobility. In the second channel, 2DEG density gets growing when the variables mentioned above is enlarged. The mobility restricted by alloy disorder scattering shows a reverse trend with the variation of the Al<i>_x</i>Ga_1–<i>x</i>N thickness and Al fraction, which more greatly affect the carriers in the parasitic channel due to the lower barrier height and high permeable carriers. Furthermore, the effect of dislocation scattering on channel electrons is gradually weakened, resulting in an increasing mobility. In general, The dislocation scattering effect in the second channel is intenser than that in the first channel.</sec>