Hamid Amini Moghadam

The performance and reliability of the state-of-the-art power 4H-SiC metal–oxide–semiconductor field-effect transistors (MOSFETs) are affected by electrically active defects at and near the interface between SiC and the gate dielectric. Specifically, these defects impact the channel-carrier mobility and threshold voltage of SiC MOSFETs, depending on their physical location and energy levels. To characterize these defects, techniques have evolved from those used for Si devices to techniques exclusively designed for the SiC MOS structure and SiC MOSFETs. This paper reviews the electrically active defects at and near the interface between SiC and the gate dielectric in SiC power MOSFETs and MOS capacitors. First, the defects are classified according to their physical locations and energy positions into (1) interface traps, (2) near interface traps with energy levels aligned to the energy gap, and (3) near-interface traps with energy levels aligned to the conduction band of SiC. Then, representative published results are shown and discussed for each class of defect.

This paper proposes a criterion to select the best family of commercial SiC power metal–oxide–semiconductor field-effect transistors (MOSFETs) that provides the highest quality and reliability. Applying a recently published integrated-charge method, a newly proposed figure of merit is correlated to the density of near-interface traps that degrade the quality and reliability of SiC MOSFETs. The applicability of the proposed figure of merit is experimentally demonstrated with the most widely used and commercially available planar and trench MOSFETs from different manufacturers.

This paper presents equations for the electron density of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures in three realistic scenarios: (1) AlGaN/GaN heterostructure with surface exposed to ambient with mobile ions, (2) metal gate deposited on the AlGaN surface, and (3) a thick dielectric passivation layer on the AlGaN surface. To derive the equations, we analyzed these scenarios by applying Gauss’s law. In contrast to the idealistic models, our analysis shows that the 2DEG charge density is proportional to the difference between spontaneous polarization of AlGaN and GaN, whereas surprisingly, it is independent of the piezoelectric polarization.

A balance between static and dynamic losses of a power MOSFET is always desirable for accomplishing the maximum efficiency for a specific power converter. The standard semiconductor theory suggests that a minimum power dissipation in a MOSFET can be achieved by selecting a specific device active area. However, for power circuit designers, the active device area is unknown given that only datasheet parameters are available. Hence, in this paper, we propose a simple method, based on semiconductor theory, to select optimum power MOSFET from a family of MOSFETs using only datasheet parameters. By applying this optimization method to the specific power supply circuit under development, power engineers can select the best transistors to yield lowest power losses for the systems under development.

The device library in the standard circuit simulator (SPICE) lacks a gallium nitride based high-electron-mobility-transistor (GaN-HEMT) model, required for the design and verification of power-electronic circuits. This paper shows that GaN-HEMTs can be modeled by selected equations from the standard MOSFET LEVEL 3 model in SPICE. A method is proposed for the extraction of SPICE parameters in these equations. The selected equations and the proposed parameter-extraction method are verified with measured static and dynamic characteristics of commercial GaN-HEMTs. Furthermore, a double pulse test is performed in LTSpice and compared to its manufacturer model to demonstrate the effectiveness of the MOSFET LEVEL 3 model. The advantage of the proposed approach to use the MOSFET LEVEL 3 model, in comparison to the alternative behavioral-based model provided by some manufacturers, is that users can apply the proposed method to adjust the parameters of the MOSFET LEVEL 3 model for the case of manufacturers who do not provide SPICE models for their HEMTs.

The mobility of current carriers in the channel of FETs usually depends on the applied gate voltage. This paper presents experimental evidence that the electron mobility in the 2-D electron gas under the gate of AlGaN/GaN high-electron-mobility transistors (HEMTs) is actually independent of the gate voltage. This demonstration of the gate-voltage independence of the electron mobility relates to power HEMTs, and it was achieved by introducing a new method for the mobility measurement. The gate-voltage independence of the electron mobility was observed for a wide range of temperature, from 25 °C to 300 °C. Furthermore, it is confirmed that the HEMT mobility decreases with increased temperature according to the power law (T ^-k ) and with a quite high value of the power-law coefficient (k = 2.45).

Measurements of the near-interface oxide traps (NIOTs) aligned to the conduction band of silicon-carbide (SiC) are of particular importance as these active defects are responsible for degradation of the channel-carrier mobility in 4H-SiC MOSFETs. In this brief, a new method for measurement of the active NIOTs with energy levels aligned to the conduction band is proposed. The method utilizes transient-current measurements on 4H-SiC MOS capacitors biased in accumulation. Nitrided oxide and dry oxide are used to illustrate the applicability of the proposed measurement method.