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Band diagrams of a AlGaN/GaN HEMT showing various charges at the different interfaces and illustrating the formation of a 2DEG with electrons supplied by surface donor states. Two cases with different distributions of the surface donor states in the energy gap are shown: (a) single surface donor level with high density; (b) distributed surface donor states with low density.The shaded box shows the number of electrons per unit area donated by low density surface donor states.
Comparison between the model (curves) and experimental data (symbols) obtained from Ref. 7, for two different Al compositions in the barrier. The density of surface donor states used were no (x = 0.19) = 4.6× 1012 cm−2V−1 and no (x = 0.24) = 6.1 × 1012 cm−2V−1.7
Schematic view of band diagrams of a AlGaN/GaN HEMT showing surface barrier heights versus barrier layer thicknesses (not to the scale). Here, EF is indicated for a relatively thick barrier.
Comparison between the proposed model according to Eq. (4) (low density surface states) and the model given by Ibbetson et al. 2 (high density of surface states where K4 = 1) for dependence of versus barrier layer thickness.
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