Optimization of recessed ohmic contacts for AlGaN/AlN/GaN heterostructures using C(V) characterization of MSHM structures

Recess etching is used to reduce the resistance of ohmic contacts to an AlGaN/AlN/GaN heterostructure. The minimization of the resistance relies on exact etching of the barrier. For this purpose C(V) measurements of the etched contacts, before annealing, are used to characterize the effect of the recess etch. Using the C(V) measurements a Cl2/Ar based ICP/RIE etch recipe with a stabilized etch rate of approximately 3 Å/s is developed. By utilizing the recess etch the contact resistivity is reduced from the non etched 0.9 Ω · mm to 0.3 Ω · mm when approximately 2 nm remains of the barriers, while maintaining a low sheet resistance. The C(V) measurements make it possible to monitor sheet carrier density vs. etch depth. Furthermore, the C(V) measurement gives large‐area average values that is not easily obtained with AFM measurements (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)