Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai; Swarnav Mukhopadhyay; Michael Elliott; Ryan Gilbert; Jiahao Chen; Rafael A. Choudhury; Kyudong Kim; Yu-Chun Wang; Ahmad E. Islam; Andrew J. Green; Shubhra S. Pasayat; Chirag Gupta

doi:10.48550/arxiv.2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Research paper

Experimental GrowthExperimental Characterization

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Ruixin Bai, Swarnav Mukhopadhyay, Michael Elliott, Ryan Gilbert et al.

2025·10.48550/arxiv.2510.08933·arXiv:2510.08933

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

4 preparations5 characterizations13 properties4 figures

ExperimentalGaNStudied MaterialAl0.35Ga0.65NStudied MaterialAlNStudied MaterialHfO₂Capping Or ContactTiNCapping Or ContactCrCapping Or ContactAuCapping Or ContactTiCapping Or ContactSiO₂Substrate / DielectricAl₂O₃Substrate / DielectricGaNStudied Material

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

4 preparations5 characterizations13 properties4 figures

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

4 preparations5 characterizations13 properties4 figures

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

4 preparations5 characterizations13 properties4 figures

Type	Label	Value	Material	Sample	Source
Fet Sheet Resistance	sheet resistance in recessed region	250 to 320ohm/sq	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Carrier Concentration	drain current density	1.8A/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	on-resistance	0.41ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	contact resistance	0.1ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	peak transconductance	0.75S/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	on/off current ratio	10000000	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	cutoff frequency ft	127GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	maximum oscillation frequency fmax	203GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.15W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	27.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.8W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	26.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	current degradation	15%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—

Type	Label	Value	Material	Sample	Source
Fet Sheet Resistance	sheet resistance in recessed region	250 to 320ohm/sq	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Carrier Concentration	drain current density	1.8A/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	on-resistance	0.41ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	contact resistance	0.1ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	peak transconductance	0.75S/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	on/off current ratio	10000000	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	cutoff frequency ft	127GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	maximum oscillation frequency fmax	203GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.15W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	27.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.8W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	26.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	current degradation	15%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—

Type	Label	Value	Material	Sample	Source
Fet Sheet Resistance	sheet resistance in recessed region	250 to 320ohm/sq	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Carrier Concentration	drain current density	1.8A/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	on-resistance	0.41ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	contact resistance	0.1ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	peak transconductance	0.75S/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	on/off current ratio	10000000	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	cutoff frequency ft	127GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	maximum oscillation frequency fmax	203GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.15W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	27.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.8W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	26.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	current degradation	15%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—

Type	Label	Value	Material	Sample	Source
Fet Sheet Resistance	sheet resistance in recessed region	250 to 320ohm/sq	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Carrier Concentration	drain current density	1.8A/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	on-resistance	0.41ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	contact resistance	0.1ohm*mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	peak transconductance	0.75S/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	on/off current ratio	10000000	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	cutoff frequency ft	127GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Mobility	maximum oscillation frequency fmax	203GHz	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.15W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	27.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet Sheet Resistance	output power density POUT	2.8W/mm	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	power-added efficiency PAE	26.8%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—
Fet On Off Ratio	current degradation	15%	GaN Al0.35Ga0.65N AlN HfO₂ TiN Cr Au Ti SiO₂ Al₂O₃ GaN	Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabri	—

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Passivation-Free Ga-Polar AlGaN/GaN Recessed-Gate HEMTs on Sapphire with 2.8 W/mm POUT and 26.8% PAE at 94 GHz

Samples

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

Materials

Growth

Processing

Characterization

Properties

Why these are connected

Samples

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

Materials

Growth

Processing

Characterization

Properties

Why these are connected

Samples

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

Materials

Growth

Processing

Characterization

Properties

Why these are connected

Samples

Passivation-free Ga-polar recessed-gate AlGaN/GaN HEMT fabricated on sapphire with regrown ohmic regions, recessed gate, HfO₂ gate dielectric, TiN gate foot, Cr/Au T-gate head, and Ti/Au ohmic contacts.

Materials

Growth

Processing

Characterization

Properties

Why these are connected