AlInN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) have been fabricated with reactive-ion-sputtered (RIS) Al2O3 as a gate dielectric. Significant reduction in the gate leakage current is achieved upon insertion of RIS-Al2O3. MIS-HEMTs also show better transconductance, drain characteristics, and ION/IOFF ratio. Most interestingly, a positive shift in threshold voltage is observed for MIS-HEMTs indicating the presence of net negative charge at oxide-semiconductor interface. The origin and stability of the negative charge at the interface is discussed in this letter. © 2014 IEEE.

Nandita Dasgupta

Department of Electrical Engineering

Amitava Dasgupta

Gourab Dutta

ALINN/GAN

MIS-HEMT

Negative charge

REACTIVE ION

Threshold voltage shifts

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IIT Madras

Positive Shift in Threshold Voltage for Reactive-Ion- Sputtered Al 2 O 3 /AlInN/GaN MIS-HEMT

IEEE Electron Device Letters

Gate leakage mechanisms in AlInN/GaN and AlGaN/GaN metal insulator semiconductor high-electron-mobility transistors (MIS-HEMTs) with SiNx as gate dielectric have been investigated. It is found that the conduction in the reverse gate bias is due to Poole-Frenkel emission for both MIS-HEMTs. The dominant conduction mechanism in low to medium forward bias is trap-assisted tunneling while it is Fowler-Nordheim tunneling at high forward bias. However, conduction near zero gate bias is dominated by defect-assisted tunneling for both sets of MIS-HEMTs. The gate leakage current is primarily dependent on the properties of the gate dielectric material and dielectric/semiconductor interface rather than the barrier layer. A model is proposed for the gate leakage current in GaN-based MIS-HEMTs, and the method to extract the related model parameters is also presented in this paper. The proposed gate current model matches well with the experimental results for both AlInN/GaN and AlGaN/GaN MIS-HEMTs over a wide range of gate bias and measurement temperature. © 1963-2012 IEEE.

IEEE Transactions on Electron Devices

Gate Leakage Mechanisms in AlInN/GaN and AlGaN/GaN MIS-HEMTs and Its Modeling

Dependence of threshold voltage (VTh) on oxide thickness (tox) for GaN-based metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) using sputter-deposited Al2O3 as gate dielectric is studied in detail. Different III-nitride (III-N) heterostructures (AlGaN/GaN and AlInN/GaN) with/without GaN cap layer were used for fabricating these MIS devices. Interestingly, for all the sets of devices, a positive shift in VTh was observed initially with a increase in tox, followed by a negative shift of the same. A comprehensive analytical model has been proposed to explain the variation of VTh with tox and has been shown to match the experimental data for MIS-HEMTs fabricated on different heterostructures and with different values of tox. This model allows the extraction of different charge components in the oxide or at oxide/III-N interface. Normally OFF AlInN/GaN MIS-HEMTs with VTh of +0.67 V have been demonstrated with the optimized tox of sputtered Al2O3. © 2016 IEEE.

Effect of Sputtered-Al2O3 Layer Thickness on the Threshold Voltage of III-Nitride MIS-HEMTs

A physics-based simple and accurate compact model of drain current for GaN-based high electron mobility transistors (HEMTs) is presented. The model is developed using analytical relations for charges in the 2-D electron gas and barrier layer. For the first time, a simple charge linearization approach has been used for GaN-based HEMTs. The access regions are accurately modeled using transistors. The model is rigorously validated over a wide range of geometries and parameters for AlGaN/GaN and AlInN/GaN HEMTs. The model also passes the DC Gummel symmetry test. © 1963-2012 IEEE.

A Compact Model of Drain Current for GaN HEMTs Based on 2-DEG Charge Linearization

Al2O3 was deposited on n-type 4H-SiC by reactive-ion-sputtering (RIS) at room temperature using aluminum target and oxygen as a reactant gas. Post deposition oxygen annealing was carried out at a temperature of 1100 °C. Metal-oxide-semiconductor (MOS) test structures were fabricated on 4H-SiC using RIS-Al2O3 as gate dielectric. The C-V characteristics reveal a significant reduction in flat band voltage for oxygen annealed RIS-Al2O3 samples (Vfb = 1.95 V) compared to as-deposited Al2O3 samples (Vfb &gt; 10 V), suggesting a reduction in negative oxide charge after oxygen annealing. Oxygen annealed RIS-Al2O3 samples also showed significant improvement in I-V characteristics compared to as-deposited RIS-Al2O3 samples. A systematic analysis was carried out to investigate the leakage current mechanisms present in oxygen annealed RIS-Al2O3 on 4H-SiC at higher gate electric field and at different operating temperature. For measurement temperature (T) &lt; 303 K, Fowler-Nordheim (FN) tunneling was found to be the dominant leakage mechanism and for higher temperature (T ≥ 303 K), a combination of FN tunneling and Poole-Frenkel (PF) emission was confirmed. The improvement in I-V characteristics of oxygen annealed RIS-Al2O3/4H-SiC MOS devices is attributed to large effective barrier height (ΦB = 2.53 eV) at Al2O3/SiC interface, due to the formation of an interfacial SiO2 layer during oxygen annealing, as confirmed from X-ray Photoelectron Spectroscopy results. Further improvement in C-V characteristics for oxygen annealed RIS-Al2O3/4H-SiC MOS devices was observed after forming gas annealing at 400 °C. © 2016 Elsevier B.V. All rights reserved.

Thin Solid Films

Electrical properties of reactive-ion-sputtered Al2O3 on 4H-SiC

The gate leakage mechanisms in AlInN/GaN and AlGaN/GaN high electron mobility transistors (HEMTs) are compared using temperature-dependent gate current-voltage $(I-{\rm G}{-}V-{\rm G})$ characteristics. The reverse bias gate current of AlInN/GaN HEMTs is decomposed into three distinct components, which are thermionic emission (TE), Poole-Frenkel (PF) emission, and Fowler-Nordheim (FN) tunneling. The electric field across the barrier in AlGaN/GaN HEMTs is not sufficient to support FN tunneling. Hence, only TE and PF emission is observed in AlGaN/GaN HEMTs. In both sets of devices, however, an additional trap-assisted tunneling component of current is observed at low reverse bias. A model to describe the experimental $I-{\rm G}{-}V \rm G characteristics is proposed and the procedure to extract the associated parameters is described. The model follows the experimental gate leakage current closely over a wide range of bias and temperature for both AlGaN/GaN and AlInN/GaN HEMTs. © 1963-2012 IEEE.

Gate leakage mechanisms in AlGaN/GaN and AlInN/GaN HEMTs: Comparison and modeling

Applied Physics Letters

Interface charge engineering at atomic layer deposited dielectric/III-nitride interfaces

Three interface state density (Dit) characterization methods to evaluate the oxide-semiconductor interface on metal-oxide-semiconductor capacitors fabricated on GaN are compared and discussed. Capacitance-voltage, conductance-voltage, and constant capacitance deep level transient and optical spectroscopy measurements are used to evaluate Dit at the Al 2O3/GaN interface. The effect of annealing ambient on the Pd/Al2O3/GaN capacitors is also examined. Forming gas annealing reduces Dit; nitrogen annealing increases Dit for the annealing conditions tested. The Dit variation correlates with changes in hydrogen concentration at the Al2O3/GaN interface detected by secondary ion mass spectrometry suggesting that hydrogen plays an important role passivating Al2O3/GaN interfaces. © 2013 AIP Publishing LLC.

Journal	Data powered by TypesetIEEE Electron Device Letters
Publisher	Data powered by TypesetInstitute of Electrical and Electronics Engineers Inc.
ISSN	07413106
Open Access	No