Determination of trap energy levels in AlGaN/GaN HEMT

The density of two dimensional electron gas (2DEG) in the channel of AlGaN/GaN HEMT is often altered by trapped charges on the surface or in the bulk of the heterostructure, limiting the device performance at high frequencies. The existing methods, such as photoionization spectroscopy, Deep Level Transient Spectroscopy (DLTS) etc., mainly focus on deep level traps in GaN, providing little information about traps in the AlGaN layer. In this work, we use Inelastic Electron Tunneling Spectroscopy (IETS), in conjunction with the Frenkel-Poole (F-P) trap energy extraction method developed by Yeh at el, to examine electrically active traps in the AlGaN barrier layer. The results indicate that traps exist in the AlGaN bulk, as well as at the AlGaN/GaN interface. The trap energy levels are within a 0.5eV band below the conduction band edge (E_c) of AlGaN in the sample that we studied.