Effect of AlGaN Barrier Thickness on Trapping Characteristics in AlGaN/GaN Heterostructures

Aluminum Gallium Nitride (AlGaN) barrier thickness dependent trapping characteristic of AlGaN/GaN heterostructure is investigated by frequency dependent conductance measurement. The conductance measurement in depletion region biases (−4.8 to −3.2 V) shows that the \( {\text{Al}}_{0.3} {\text{Ga}}_{0.7} {\text{N}}\left( {18\;{\text{nm}}} \right)/{\text{GaN}} \) structure suffers from both the surface (metal/AlGaN interface of gate region) and interface (AlGaN/GaN interface of channel region) trapping states, whereas the \( {\text{Al}}_{0.3} {\text{Ga}}_{0.7} {\text{N}} \left( { 25\;{\text{nm}}} \right)/{\text{GaN}} \) structure with thicker AlGaN barrier (25 nm) layer suffers from only interface trap energy states in the depletion bias region (−6.0 to −4.2 V). The calculated surface trap time constants (~2 μs) are found to be very less in \( {\text{Al}}_{0.3} {\text{Ga}}_{0.7} {\text{N}}\left( {18\;{\text{nm}}} \right)/{\text{GaN}} \) structure. This lower time constant is correlated to the electric field induced tunneling process for de-trapping of surface trap states.