Measurement of the Transport Property of 2-DEG in AlGaN/GaN Heterostructures Based on Circular Transmission Line Modeling of Two Concentric-Circle Schottky Contacts

Frequency dispersion of the capacitance (C-f) of GaN-based heterostructure are commonly observed at high frequencies. Analytical solutions are derived for frequency dispersion of the heterostructure's capacitance measured on two concentric-circle Schottky contacts, in form of Bessel function, by modeling a distributed network of heterostructure and solving corresponding circular transmission line functions. Solutions reveal C-f is determined by the R
_s
of 2-D electron gas (2-DEG). So in reverse, the sheet resistance at a certain carrier density can be extracted from the C-f measurement. By fitting experimental C-f data with the model, we obtain a peak mobility of 2044 cm
²
/V · s corresponding to a 2-DEG density of 8.2 × 10
¹²
cm
^-2
and a sheet resistance of 373 Ω/□ on an Al
_0.25
Ga
_0.75
N/GaN heterostructure on silicon substrate. The advantage of two Schottky contacts is that they could be implemented by mercury probes with the same geometry, then achieving nondestructive and instant feedback on carrier transport properties and uniformity of as-grown III-V compound semiconductor wafers.