THEORETICAL INVESTIGATION OF ELECTRICAL CHARACTERISTICS OF ALGAN GAN MODULATION-DOPED FIELD-EFFECT TRANSISTORS/

A theoretical investigation of the electrical characteristics of GaN/A lxGa1-xN (x is the Al mole fraction in AlGaN) modulation doped field-e ffect transistors (MODFETs) is carried out. Using a self-consistent so lution of Schrodinger's equation and Poisson's equation, relations bet ween the concentration of two-dimensional electron gas (2DEG), the Fer mi level in GaN, and the average distance of the electrons from the he terointerface are calculated. A relation between the gate bias and the 2DEG concentration is obtained for a flat quasi Fermi level in AlxGa1 -xN. Based on the relation between the 2DEG concentration and the appl ied gate bias, a model for the drain current and the transconductance of the device is developed. The effects of the n-AlxGa1-xN layer thick ness, the spacer i-AlxGa1-xN layer thickness, the n-AlxGa1-xN doping l evel, the aluminum mole fraction x, and the channel length L on the el ectrical characteristics of MODFETs are presented. Theoretical results are compared with the recent experimental data, which show striking a greement. The 2DEG concentration is found to be as high as 10(13) cm(- 2), and transconductance as high as 1000 mS/mm. Finally, the effect of the difference in the properties of AlN and GaN, and a device structu re that would take advantage of the bending of the quasi Fermi level f or electrons in n-AlxGa1-xN, are discussed. (C) 1996 American Institut e of Physics.