Effect of inserted AlN layer on the two-dimensional electron gas in AlxGa1-xN/AlN/GaN

Abstract

This paper investigates the changes of electron transport properties in AlxGa1-xN/GaN with an inserted AlN layer. The polarization charge density and two-dimensional electron gas (2DEG) sheet density in AlxGa1-xN/AlN/GaN double heterojunction high electron mobility transistors (HEMT) affected by the spontaneous polarization and piezoelectric polarization in AlxGa1-xN and AlN barrier are studied. Relations of interface roughness scattering and alloy disorder scattering with the AlN thickness are systematically analyzed. It is found that the alloy disorder scattering is the main scattering mechanism in AlxGa1-xN/GaN heterojunction high-electron-mobility transistors, while the interface roughness scattering is the main scattering mechanism in AlxGa1-xN/AlN/GaN double-heterojunction structure. It is also known that the 2DEG sheet density, interface roughness scattering and alloy disorder scattering are depended on the thickness of the inserted AlN layer. The 2DEG sheet density increases slightly and the mobility increases obviously by inserting an AlN layer about 13 nm. Taking Al mole fraction of 0.3 as an example, if without AlN layer, the 2DEG sheet density is 1.47 1013 cm-2 with the mobility limited by the interface roughness scattering of 1.15 104 cm2V-1-1, and the mobility limited by alloy disorder scattering of 6.07 102cm2V-1-1. After inserting an AlN layer of 1 nm, the 2DEG sheet density increases to 1.66 1013cm-2, and the mobility limited by the interface roughness scattering reduces to 7.88 103cm2V-1-1 while the mobility limited by alloy disorder scattering increases greatly up to 1.42 108 cm2V-1-1.