The buffer and surface trapping effects on low-frequency (LF) Y-parameters of Fe-doped AlGaN/GaN high-electron mobility transistors (HEMTs) are analyzed through experimental and simulation studies. The drain current transient (DCT) characterization is also carried out to complement the trapping investigation. The Y₂₂ and DCT measurements reveal the presence of an electron trap at 0.45–0.5 eV in the HEMT structure. On the other hand, two electron trap states at 0.2 eV and 0.45 eV are identified from the LF Y₂₁ dispersion properties of the same device. The Y-parameter simulations are performed in Sentaurus TCAD in order to detect the spatial location of the traps. As an effective approach, physics-based TCAD models are calibrated by matching the simulated I-V with the measured DC data. The effect of surface donor energy level and trap density on the two-dimensional electron gas (2DEG) density is examined. The validated Y₂₁ simulation results indicate the existence of both acceptor-like traps at E_C –0.45 eV in the GaN buffer and surface donor states at E_C –0.2 eV in the GaN/nitride interface. Thus, it is shown that LF Y₂₁ characteristics could help in differentiating the defects present in the buffer and surface region, while the DCT and Y₂₂ are mostly sensitive to the buffer traps.

The thermal resistance ( ${R}_{\text {TH}}$ ) of 0.15- and 0.25- $\mu $ m AlGaN/GaN high-electron mobility transistor (HEMT) is computed from the linear portion of simulated change in channel temperature ( $\Delta {T}$ ) versus power dissipation ( ${P}_{D}$ ) plot. The simulated I–V characteristics are validated with measured data using the Sentaurus thermodynamic TCAD model. Subsequently, ${R}_{\text {TH}}$ is estimated for the HEMT with and without a gate field-plate (FP) structure. Three linear ${R}_{\text {TH}}$ regions are observed for HEMT with FP, due to the variation in the hotspot position with the increasing drain voltage, whereas a single ${R}_{\text {TH}}$ is identified for the HEMT without FP, as the hotspot remains at the drain side of the gate edge over a wide range of dissipated power. ${R}_{\text {TH}}$ is also reported for the HEMT with different FP lengths ( ${L}_{\text {FP}}$ ), showing that ${R}_{\text {TH}}$ decreases as ${L}_{\text {FP}}$ increases. ${R}_{\text {TH}}$ is found to decrease with the gate width, which is consistent with the theory as well as the thermoreflectance and pulsed I– V measurements. A slight increase in ${R}_{\text {TH}}$ is observed upon reducing the gate voltage. Furthermore, the change in ${R}_{\text {TH}}$ is evaluated by placing thermal contact at three different locations (substrate bottom, buffer and substrate sidewall, and contacts) in the simulation. Similar observations are detected for 0.25- $\mu $ m AlGaN/GaN HEMTs.

The electron trapping in AlGaN/GaN high-electron mobility transistors (HEMTs) with iron (Fe)-doped buffer is investigated through Drain Current Transient (DCT) measurements and TCAD physics-based 2D device simulations. The DCT characterization reveals two prominent deep-level electron traps E1 (∼0.5 eV) and E2 (∼0.6 eV) in the AlGaN/GaN HEMT. The measured DCT spectrum is analyzed at different trap-filling pulse durations (10 µs–100 ms) to obtain the information of trapping kinetics. As the first step in the simulation, the TCAD physical model parameters are calibrated by matching the simulated DC characteristics with the experimental data. It is shown that the TCAD model incorporating the acceptor-type trap at E_C – 0.5 eV in the GaN buffer quantitatively reproduces the measured DCT spectra over the temperature range of 25–100 °C. To explore the buffer trapping effects, the simulated DCT is inspected by varying the activation energy, capture cross section, and concentration of the buffer trap.

This paper described a comparison between a numerical Finite Element Analysis (FEA) and an analytical approach in order to extract the thermal time constants and the thermal resistances of simple but realistic structures. Understanding the complex contribution of multidimensional thermal spreading, the effect of multiple layers, and the correlation with the heat source length is mandatory due to the severe mismatch of thermal expansion in different epitaxial layers and high operating temperatures. This is especially true on GaN HEMT (High Electron Mobility Transistor) with the continuous decrease of the gate length and the increase of the power density. Moreover, in this paper, we extracted the time constants with a Model Order Reduction (MOR) technique based on the Ritz vector approach with inputs coming from the FE matrices. It was found that the time constants obtained by an analytical solution and a model order extraction from FEA were exactly the same. This result validated the idea that our MOR technique provides the real time constants and resistances for our device structures and in this case unified the analytical world with the numerical one.