Publications

A publication index.

Journal

Cracking the Contact Problem: Fermi-Level Pinning on p-Type GaN

Barrier heights and Fermi level pinning in metal contacts on p-type GaN

Sumaiya Wahid, Nadim Chowdhury, Md. Kawsar Alam, Tomás Palacios

Applied Physics Letters · 10.1063/5.0010699

Benchmarked five metal contacts (Ni, Ir, Ru, Mo, W/Au) on p-GaN using a single, uniform epitaxial platform
Found strong Fermi-level pinning across all metals (pinning factor ~0.15), explaining persistently high contact resistance
Identified Ru/Au as the standout performer, with an ultra-low contact resistivity of 3.45 × 10⁻⁶ Ω·cm²

↗

Current–voltage characteristics of five bilayer metal contacts on p-GaN used to extract Fermi-level pinning and contact resistivity.

Conference

Switching GaN with Light: A New Gate Stack for Optical Triggering

Gate Stack Engineering and Carrier Dynamics of Optically Triggered GaN Transistors on 650V GaN-on-Si Power Platform

Rafid Hassan Palash, Jung-Han Hsia, Soumik Saha, Nittya Ananda Biswas, Qingyun Xie, Victor Moroz, Tomás Palacios, Nadim Chowdhury

IEDM · 10.1109/IEDM50572.2025.11353658

Enabled optical triggering at longer wavelengths (≥395 nm) for the first time, overcoming the limits of conventional UV-triggered GaN switches
Proposed a novel p-InGaN/p-GaN/AlGaN/GaN gate stack, reaching a responsivity of 6.7 × 10³ A/W
Cut fall time by 5.75× relative to conventional optically triggered transistor designs

↗

Device schematics and TCAD calibration of the lateral p-GaN gate optically triggered HEMT, showing measured vs. simulated I–V, intensity, and transient response.

Journal

Beyond Room Temperature: Hole Transport Physics in p-GaN Heterostructures

Hole transport mechanism at high temperatures in p-GaN/AlGaN/GaN heterostructure

Bejoy Sikder, Toiyob Hossain, Qingyun Xie, John Niroula, Nitul S. Rajput, Koon Hoo Teo, Hiroshi Amano, Tomás Palacios, Nadim Chowdhury

Applied Physics Letters · 10.1063/5.0203344

Combined Schottky-emission and space-charge-limited-current (SCLC) models to explain p-GaN conduction across bias and temperature
Pinpointed trap states in the p-GaN channel as a key factor governing high-temperature current transport
Provided design insight for GaN electronics destined for harsh environments — from downhole drilling to planetary probes

↗

TEM cross-section of the Ru/p-GaN contact after annealing at 500 °C, showing the metal–semiconductor interface at increasing magnification.

Journal

Machine Learning Meets GaN: Inverse-Designing RF Power Transistors

Inverse Design of AlGaN/GaN HEMT RF Device with Source Connected Field Plate

A Das, Saimur Rahman Arnab, Xiaofeng Xiang, Rafid Hassan Palash, Toiyob Hossain, Bejoy Sikder, Eiji Yagyu, Marika Nakamura, Koon Hoo Teo, Nadim Chowdhury

Advanced Theory and Simulations · 10.1002/adts.202401207

Built an ANN model (R² = 99%, <1% error) that predicts HEMT structural parameters directly from target breakdown voltage and leakage specs
Coupled the ANN with a genetic algorithm to identify Pareto-optimal field-plate designs, validated against TCAD (1.67% error)
Introduced a fast, field-based method to predict current collapse — bypassing slow pulsed-DC characterization

↗

Simulated electric-field maps across field-plate variations and the ANN architecture used for inverse design of the AlGaN/GaN HEMT.

Journal

Decoding Hole Traps in p-GaN: A Path to Better GaN CMOS

Role of Mg hole traps in hole transport of p-GaN/UID-GaN/AlGaN/GaN heterostructure

Tanvir Hossain, A. K. M. Anindya Alam, Qingyun Xie, Hiroshi Amano, Tomás Palacios, Nadim Chowdhury

Applied Physics Letters · 10.1063/5.0333494

Identified Mg-related hole traps (110 meV activation energy) as the dominant factor limiting hole transport in bulk p-GaN
Showed that sheet resistance follows a Poole–Frenkel field dependence, explaining why conduction changes with bias
Revealed Schottky barrier lowering via thermionic field emission at the Ru/p-GaN contact — a key input for contact design

↗

Epitaxial schematic of the p-GaN/UID-GaN/AlGaN/GaN heterostructure with Ru source and drain contacts used for temperature-dependent hole transport analysis.

Publications

A publication index.

Journal

Cracking the Contact Problem: Fermi-Level Pinning on p-Type GaN

Barrier heights and Fermi level pinning in metal contacts on p-type GaN

Sumaiya Wahid, Nadim Chowdhury, Md. Kawsar Alam, Tomás Palacios

Applied Physics Letters · 10.1063/5.0010699

Benchmarked five metal contacts (Ni, Ir, Ru, Mo, W/Au) on p-GaN using a single, uniform epitaxial platform
Found strong Fermi-level pinning across all metals (pinning factor ~0.15), explaining persistently high contact resistance
Identified Ru/Au as the standout performer, with an ultra-low contact resistivity of 3.45 × 10⁻⁶ Ω·cm²

↗

Current–voltage characteristics of five bilayer metal contacts on p-GaN used to extract Fermi-level pinning and contact resistivity.

Conference

Switching GaN with Light: A New Gate Stack for Optical Triggering

Gate Stack Engineering and Carrier Dynamics of Optically Triggered GaN Transistors on 650V GaN-on-Si Power Platform

Rafid Hassan Palash, Jung-Han Hsia, Soumik Saha, Nittya Ananda Biswas, Qingyun Xie, Victor Moroz, Tomás Palacios, Nadim Chowdhury

IEDM · 10.1109/IEDM50572.2025.11353658

Enabled optical triggering at longer wavelengths (≥395 nm) for the first time, overcoming the limits of conventional UV-triggered GaN switches
Proposed a novel p-InGaN/p-GaN/AlGaN/GaN gate stack, reaching a responsivity of 6.7 × 10³ A/W
Cut fall time by 5.75× relative to conventional optically triggered transistor designs

↗

Device schematics and TCAD calibration of the lateral p-GaN gate optically triggered HEMT, showing measured vs. simulated I–V, intensity, and transient response.

Journal

Beyond Room Temperature: Hole Transport Physics in p-GaN Heterostructures

Hole transport mechanism at high temperatures in p-GaN/AlGaN/GaN heterostructure

Bejoy Sikder, Toiyob Hossain, Qingyun Xie, John Niroula, Nitul S. Rajput, Koon Hoo Teo, Hiroshi Amano, Tomás Palacios, Nadim Chowdhury

Applied Physics Letters · 10.1063/5.0203344

Combined Schottky-emission and space-charge-limited-current (SCLC) models to explain p-GaN conduction across bias and temperature
Pinpointed trap states in the p-GaN channel as a key factor governing high-temperature current transport
Provided design insight for GaN electronics destined for harsh environments — from downhole drilling to planetary probes

↗

TEM cross-section of the Ru/p-GaN contact after annealing at 500 °C, showing the metal–semiconductor interface at increasing magnification.

Journal

Machine Learning Meets GaN: Inverse-Designing RF Power Transistors

Inverse Design of AlGaN/GaN HEMT RF Device with Source Connected Field Plate

A Das, Saimur Rahman Arnab, Xiaofeng Xiang, Rafid Hassan Palash, Toiyob Hossain, Bejoy Sikder, Eiji Yagyu, Marika Nakamura, Koon Hoo Teo, Nadim Chowdhury

Advanced Theory and Simulations · 10.1002/adts.202401207

Built an ANN model (R² = 99%, <1% error) that predicts HEMT structural parameters directly from target breakdown voltage and leakage specs
Coupled the ANN with a genetic algorithm to identify Pareto-optimal field-plate designs, validated against TCAD (1.67% error)
Introduced a fast, field-based method to predict current collapse — bypassing slow pulsed-DC characterization

↗

Simulated electric-field maps across field-plate variations and the ANN architecture used for inverse design of the AlGaN/GaN HEMT.

Journal

Decoding Hole Traps in p-GaN: A Path to Better GaN CMOS

Role of Mg hole traps in hole transport of p-GaN/UID-GaN/AlGaN/GaN heterostructure

Tanvir Hossain, A. K. M. Anindya Alam, Qingyun Xie, Hiroshi Amano, Tomás Palacios, Nadim Chowdhury

Applied Physics Letters · 10.1063/5.0333494

Identified Mg-related hole traps (110 meV activation energy) as the dominant factor limiting hole transport in bulk p-GaN
Showed that sheet resistance follows a Poole–Frenkel field dependence, explaining why conduction changes with bias
Revealed Schottky barrier lowering via thermionic field emission at the Ru/p-GaN contact — a key input for contact design

↗

Epitaxial schematic of the p-GaN/UID-GaN/AlGaN/GaN heterostructure with Ru source and drain contacts used for temperature-dependent hole transport analysis.