We study how carrier transport, trapping and self-heating govern the performance and stability of Wide-Bandgap Semiconductor Devices, especially High Electron Mobility Transistors (HEMTs). We measure real devices from cryogenic to high temperature, extract physical parameters, and turn them into compact models that circuit designers can use.
How We Work
MeasureDC, pulsed, noise and RF data versus bias and temperature
ValidateCheck extracted parameters on independent bias and temperature data
Compact ModelingSmall-signal circuits and ASM-HEMT compact models in IC-CAP
Research Areas
Carrier Transport from 4 K to High Temperature
We extract low-field mobility, the knee-sharpness parameter (γ) and saturation velocity (vsat) from temperature-dependent output, transfer and transconductance data. Transfer-length (TLM) structures separate sheet and contact resistance, and gate-length scaling separates channel transport from access-resistance and high-field velocity effects.
This lets us follow the transition from impurity-limited to phonon-limited transport, and compare devices with and without an AlGaN back barrier.
Trapping, Current Collapse and Dynamic On-Resistance
Traps at the surface, in the AlGaN barrier and in the buffer make a GaN HEMT's current depend on how it was biased before. We use isothermal current-mode DLTS (I-DLTS) to measure capture and emission kinetics and post-stress recovery across temperature.
High-voltage pulsed I–V lets us vary pulse width, duty cycle and quiescent bias to measure dynamic Ron, threshold-voltage shift and knee walk-out, and to separate self-heating from trapping.
Low-Frequency Noise and Trap Spectroscopy
We measure 1/f and generation–recombination (G–R) noise from 4 K to 600 K. Gate-referred noise, SVG = SID/gm2, separates intrinsic trap fluctuations from the strong temperature dependence of transconductance. Arrhenius analysis of G–R corner frequencies gives trap activation energies.
Gate-current noise and gate–drain noise correlation feed the noise models used for minimum noise figure in low-noise amplifiers.
Gate Leakage and Impact Ionization
By fitting and removing Schottky gate leakage, we isolate the hole current that impact ionization near the drain sends to the gate. Mapping where it appears in bias tells compact gate-current and noise models where they need an impact-ionization term.
Radiation Effects
We irradiate AlGaN/GaN HEMTs with protons at different energies and fluences and measure the change in transport and trap behavior. The goal is to predict device lifetime in space and other high-radiation environments.
InGaAs HEMTs for Cryogenic Electronics
Cryogenic low-noise amplifiers are a key part of superconducting qubit readout and deep-space receivers. We study how InGaAs HEMT transport, noise and parasitics change as devices cool toward 4 K.
RF Characterization and Compact Modeling
We measure calibrated S-parameters up to 67 GHz versus bias and temperature, de-embed pad and fixture parasitics, and extract small-signal equivalent circuits (gm, intrinsic capacitances, Rg, Rd, Rs). In Keysight IC-CAP we fit ASM-HEMT models to DC, pulsed and small-signal data, using the extracted transport parameters as physical constraints and reporting each model's range of validity.