Trap analysis of composite 2D-3D channel in AlGaN/GaN/graded-AlGaN: Si/GaN: C multi-heterostructure at different temperatures

The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases (3DEGs) at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional (2D)-three-dimensional (3D) channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure (DH:Si/C). Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure (SH:C). There are fast, medium, and slow trap states in DH:Si/C, while only medium trap states exist in SH:C. The time constant/trap density for medium trap state in SH:C heterostructure are (11 μs-17.7 μs)/(1.1×10¹³ cm^-2·eV^-1-3.9×10¹³ cm^-2·eV^-1) and (8.7 μs-14.1 μs)/(0.7×10¹³ cm^-2·eV^-1-1.9×10¹³ cm^-2·eV^-1) at 300 K and 500 K respectively. The time constant/trap density for fast, medium, and slow trap states in DH:Si/C heterostructure are (4.2 μs-7.7 μs)/(1.5×10¹³ cm^-2·eV^-1-3.2×10¹³ cm^-2·eV^-1), (6.8 μs-11.8 μs)/(0.8×10¹³ cm^-2·eV^-1-2.8×10¹³ cm^-2·eV^-1), (30.1 μs-151 μs)/(7.5×10¹² cm^-2·eV^-1-7.8×10¹² cm^-2·eV^-1) at 300 K and (3.5 μs-6.5 μs)/(0.9×10¹³ cm^-2·eV^-1-1.8×10¹³ cm^-2·eV^-1), (4.9 μs-9.4 μs)/(0.6×10¹³ cm^-2·eV^-1-1.7×10¹³ cm^-2·eV^-1), (20.6 μs-61.9 μs)/(3.2×10¹² cm^-2·eV^-1-3.5×10¹² cm^-2·eV^-1) at 500 K, respectively. The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.