Impact of Traps on the Adjacent Channel Power Ratios of GaN HEMTs

In this work, the impact of traps on a system level parameter, ACPR (adjacent channel power ratio), of commercial RF AlGaN/GaN HEMTs were studied. ACPR usually depends on the transistor linearity and stability, and in this study it was measured in two different signal duplexing schemes: time division duplexing (TDD) and frequency division duplexing (FDD) after using digital predistortion to minimize static nonlinearities. It is theorized traps lead to time-dependent nonlinearity due to the devices changing operating points, which degrades ACPR. Constant drain current deep level transient spectroscopy (CI
_D
-DLTS) measurements were performed to quantitatively characterize the trap energies and concentration and correlate with the different time sensitivities of the TDD and FDD schemes. Linked by the trap concentration and time constant, the E
_C
-0.57 eV trap was correlated to the FDD ACPR, and the E
_C
-0.72 eV trap was correlated to the TDD ACPR. Finally, it is shown that both traps have been widely reported, suggesting that many GaN systems' ACPR can be potentially improved by reducing the trap concentration.