@article{lee_choi_kirkpatrick_huang_misra_2013, title={Improved high-temperature device transport properties and off-state characteristics of AlGaN/GaN power devices with atomic layer deposition (ALD) HfAlO high-k dielectric}, volume={28}, ISSN={["1361-6641"]}, DOI={10.1088/0268-1242/28/7/074016}, abstractNote={The effect of the atomic layer deposition (ALD) HfAlO high-k dielectric on device transport properties and breakdown characteristics of an AlGaN/GaN metal–oxide–semiconductor hetero-junction field-effect transistor (MOS-HFET) was evaluated based on temperature-dependent measurements. It was found that the MOS-HFET device with a HfAlO gate dielectric shows high-channel mobility greater than the Schottky HFET device for the measured temperature range (25–150 °C). In the case of off-state breakdown characteristics, the MOS-HFET device greatly suppressed gate leakage currents for measured temperatures (25–200 °C) resulting in improvements in off-state breakdown characteristics. In contrast, large gate/drain leakage currents were observed for the Schottky HFET device at high temperature (>100 °C) resulting in about 200 V of breakdown voltage reduction. It was also found that the ALD HfAlO layer reduced surface leakage current by passivating the GaN surface effectively. Therefore, the MOS-HFET structure with the HfAlO gate dielectric is very attractive for GaN-based high-power and high-temperature device applications.}, number={7}, journal={SEMICONDUCTOR SCIENCE AND TECHNOLOGY}, author={Lee, B. and Choi, Y. H. and Kirkpatrick, C. and Huang, A. Q. and Misra, V.}, year={2013}, month={Jul} }
 @article{ramanan_lee_kirkpatrick_suri_misra_2013, title={Properties of atomic layer deposited dielectrics for AlGaN/GaN device passivation}, volume={28}, ISSN={["1361-6641"]}, DOI={10.1088/0268-1242/28/7/074004}, abstractNote={In order to minimize ac–dc dispersion, reduce gate leakage and maximize ac transconductance, there is a critical need to identify optimal interfaces, low-k passivation dielectrics and high-k gate dielectrics. In this paper, an investigation of different atomic layer deposited (ALD) passivation dielectrics on AlGaN/GaN-based hetero-junction field effect transistors (HFETs) was performed. Angle-resolved x-ray photoelectron spectroscopy revealed that HCl/HF and NH4OH cleans resulted in a reduction of native oxide and carbon levels at the GaN surface. The role of high temperature anneals, following the ALD, on the effectiveness of passivation was also explored. Gate-lag measurements on HFETs passivated with a thin ALD high-k Al2O3 or HfAlO layer capped with a thick plasma enhanced chemical vapor deposited (PECVD) low-k SiO2 layer, annealed at 600–700 °C, were found to be as good as or even better than those with conventional PECVD silicon nitride passivation. Further, it was observed that different passivation dielectric stacks required different anneal temperatures for improved gate-lag behavior compared to the as-deposited case.}, number={7}, journal={SEMICONDUCTOR SCIENCE AND TECHNOLOGY}, author={Ramanan, Narayanan and Lee, Bongmook and Kirkpatrick, Casey and Suri, Rahul and Misra, Veena}, year={2013}, month={Jul} }
 @article{kirkpatrick_lee_suri_yang_misra_2012, title={Atomic Layer Deposition of SiO2 for AlGaN/GaN MOS-HFETs}, volume={33}, ISSN={["1558-0563"]}, DOI={10.1109/led.2012.2203782}, abstractNote={This letter investigates the electrical properties of SiO<sub>2</sub> gate dielectric on GaN heterostructures deposited by atomic layer deposition (ALD). ALD SiO<sub>2</sub> has a dielectric constant of 3.9 and a bandgap of 8.8 eV. ALD SiO<sub>2</sub> provides a good interface to GaN and minimizes the interfacial layer growth. The threshold voltage of metal-oxide-semiconductor heterojunction field-effect transistors with ALD SiO<sub>2</sub> dielectric is -1.5 V, owing to a fixed charge concentration of -1.6 × 10<sup>12</sup> cm<sup>-2</sup>. It was also found that devices with ALD SiO<sub>2</sub> dielectric exhibit three orders of magnitude reduction in gate leakage current compared to conventional Schottky gate HFETs.}, number={9}, journal={IEEE ELECTRON DEVICE LETTERS}, author={Kirkpatrick, Casey J. and Lee, Bongmook and Suri, Rahul and Yang, Xiangyu and Misra, Veena}, year={2012}, month={Sep}, pages={1240–1242} }
 @article{lee_kirkpatrick_choi_yang_huang_misra_2012, title={Normally-off AlGaN/GaN MOSHFET using ALD SiO2 tunnel dielectric and ALD HfO2 charge storage layer for power device application}, volume={9}, ISSN={["1862-6351"]}, DOI={10.1002/pssc.201100422}, abstractNote={AbstractIn this work, we have demonstrated a normally‐off AlGaN/GaN metal‐oxide semiconductor heterojunction field effect transistor (MOSHFET) wherein the enhancement mode operation is enabled by charge storage characteristics within a high‐k layer. By combining ALD SiO2 tunnel dielectric and HfO2 charge trapping layer, up to 7 V of threshold voltage (VT) shift depending on the applied gate pulse amplitude (corresponding ∼ 1.2 × 1013 charges/cm2 stored within the charge storage layer) is obtained. Electrical characteristics such as gate leakage current, transconductance, and off‐state breakdown after programming are similar to the initial device. Retention characteristics show about 20% of charge loss after 20000 s. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={3-4}, journal={PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 3-4}, author={Lee, Bongmook and Kirkpatrick, Casey and Choi, Young-hwan and Yang, Xiangyu and Huang, Alex Q. and Misra, Veena}, year={2012}, pages={868–870} }
 @article{kirkpatrick_lee_yang_misra_wetzel_khan_2011, title={Performance improvement of AlGaN/GaN high electron mobility transistors with atomic layer deposition (ALD) of SiO2 and HfAlO dielectrics}, volume={8}, ISSN={["1862-6351"]}, DOI={10.1002/pssc.201001064}, abstractNote={AbstractGaN metal oxide semiconductor heterojunction field effect transistors have been fabricated with SiO2 and HfAlO gate dielectrics deposited via atomic layer deposition. These transistors have threshold voltages more positive than ‐4 V and exhibit 3 orders of magnitude lower gate leakage than Schottky gated heterojunction field effect transistors (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={7-8}, journal={PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 7-8}, author={Kirkpatrick, Casey and Lee, Bongmook and Yang, Xiangyu and Misra, Veena and Wetzel, C and Khan, A}, year={2011} }
 @article{kirkpatrick_lee_choi_huang_misra_2012, title={Threshold voltage stability comparison in AlGaN/GaN FLASH MOS-HFETs utilizing charge trap or floating gate charge storage}, volume={9}, ISSN={["1862-6351"]}, DOI={10.1002/pssc.201100421}, abstractNote={AbstractEnhancement mode operation of AlGaN/GaN devices with breakdown voltage over 700 V is achieved by threshold shifting in a FLASH metal oxide semiconductor heterojunction field effect transistor. Charge stored during a programming step in either a charge trap or metal floating gate charge storage layer is responsible for this shift. Threshold stability for charge trap and floating gate memories is compared with charge trap devices losing <10% of initial threshold voltage shift after 104 seconds. Charge trap and floating gate devices maintain enhancement mode operation after 4 × 104 s. Threshold voltage as a function of drain bias for each storage method is compared. The most stable threshold voltage is observed when utilizing charge trap storage due to the discrete nature of the traps. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)}, number={3-4}, journal={PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 3-4}, author={Kirkpatrick, Casey and Lee, Bongmook and Choi, YoungHwan and Huang, Alex and Misra, Veena}, year={2012}, pages={864–867} }
 @article{suri_kirkpatrick_lichtenwalner_misra_2010, title={Energy-band alignment of Al2O3 and HfAlO gate dielectrics deposited by atomic layer deposition on 4H-SiC}, volume={96}, number={4}, journal={Applied Physics Letters}, author={Suri, R. and Kirkpatrick, C. J. and Lichtenwalner, D. J. and Misra, V.}, year={2010} }
 @inproceedings{lee_kirkpatrick_yang_jayanti_suri_roberts_misra_2010, title={Normally-off AlGaN/GaN-on-Si MOSHFETs with TaN floating gates and ALD SiO2 tunnel dielectrics}, DOI={10.1109/iedm.2010.5703401}, abstractNote={In this work, we have demonstrated a normally-off AlGaN/GaN metal-oxide semiconductor heterojunction field effect transistor (MOSHFET) wherein the enhancement mode operation is enabled by charge storage within a metal floating gate embedded in a dielectric stack and negative charges in the tunnel oxide. By combining ALD SiO2 and TaN floating gate (FG), up to 6V of VT shift after pulse programming (corresponding ∼ 1.2×1013 charges/cm2 stored within the FG) is obtained which results in a normally-off device with low gate leakage and good transconductance.}, booktitle={2010 international electron devices meeting - technical digest}, author={Lee, B. and Kirkpatrick, C. and Yang, X. Y. and Jayanti, S. and Suri, R. and Roberts, J. and Misra, Veena}, year={2010} }