What are the challenges faced by silicon-based power electronic devices?

Currently, power devices that are primarily silicon (Si) based suffer the largest power losses in a power converter.

The constraints on Si devices are

● Maximum attainable switching frequency

● Maximum permissible junction temperature

● Maximum reverse voltage blocking capabilities

● Silicon-insulated-gate bipolar transistors (Si IGBTs) are restricted to lower switching rates than silicon metal-oxide-semiconductor field-effect transistors (Si MOSFETS), despite reports of a high breakdown voltage capability of up to 6.5 kV

● Switch-mode power supply use large-sized inductive and capacitive elements to manage power because of their slower switching speeds

For the reasons stated above, there has been a noticeable decline in the efficiency and performance of current power electronic converters powered by silicon power devices, despite their continued presence in most power electronics.

Wide Band-Gap Semiconductors

The development of power electronics toward more effective, compact, high-voltage, high-frequency functioning requires new developments in power semiconductor devices called wide band-gap semiconductors.

GaN Device Structure

Gallium nitride (GaN) and other wide-bandgap technologies have gained attention as possible candidates for future generations of power semiconductor devices. To develop power electronics circuits, a simulation prototype that can estimate the expected functioning characteristics of the system is needed.

Fig. 1 shows a typical enhancement-mode GaN power HEMT device construction made with Synopsys TCAD Sentaurus.

Fig. 1 GaN device structure constructed in Synopsys TCAD Sentaurus. Source: IEEE Open Journal of Power Electronics

Usually, lateral GaN devices are either in depletion mode or normally on devices. There is a barrier layer and a p-type GaN or AlGaN cap layer made below the gate electrode. This creates an enhancement-mode device structure.

Power electronics don't want the normally-on state because if gate control is lost, the device turns into a short circuit between the drain and source. the processing methods used to deplete the charge carriers in the channel with zero bias. Using the p-type cap layer below the gate link is the most well-known method.

Importance of Modeling Power Semiconductor Devices

Model-based engineering approaches are the foundation of modern multi-objective optimization techniques. These approaches usually rely on device performance, which is estimated using models.

The semiconductor device model is a crucial component of circuit simulations that forecast design performance, offer a structure for design centering and tolerancing, and facilitate troubleshooting. The necessity for a precise, compact model of the GaN power devices that are now on the market serves as the driving force behind this effort.

Modeling of Gallium Nitride-Based Semiconductor Devices

Long before GaN-based power semiconductor devices were made accessible on the market, GaN-based RF high-electron-mobility transistor (HEMT) devices were already in production. RF GaN devices operate at frequencies and operating conditions that differ greatly from those in the power electronics domain.

Consequently, an RF GaN device's modeling methodology, model analysis, and parameter extraction are very different from those of GaN devices employed as power switches. In recent years, a number of GaN-based device models have become available; however, the majority of these models have only been described for depletion-mode RF HEMT devices.

The noteworthy compact models for GaN are

● Angelov Model

● ASM-HEMT model

● MIT GaN model

● SPICE model

Angelov Model

For RF HEMT devices as well as other Si and SiC devices, one of these compact models—the Angelov model—has been employed extensively. A hyperbolic tangent function is used in the model to represent the device's I-V behavior.

For many years, this has served as a commonly used empirical model. The evolution of the device's' shape is often captured by all of the functions included in the model.

This model has a number of empirical parameters, so characterizing it without the use of a computerized optimization tool can be difficult. However, because the model is entirely empirical and has been in widespread use for a long time, it may be implemented on any semiconductor device.

ASM-HEMT Model

The ASM-HEMT model relies on using Schrodinger's and Poisson's equations to formulate the surface potential in the channel. The model can faithfully simulate the behavior of RF GaN HEMT devices.

The usefulness of the model for power electronics applications was confirmed using TCAD simulations, but only for switching at very low voltages (50 V).

This model, however, is particularly ideal for RF GaN applications because it has been successfully proven to have small-signal and large-signal characteristics suitable for RF devices and can be utilized in power electronics as well.

MIT GaN model

Another thorough GaN device model that was just released is the MIT GaN model, also referred to as the MIT virtual source GaN (MVSG) model. This model is being evaluated for an EPC GaN device and for depletion-mode RF devices.

The charge flow in the channel determines the dc I-V and C-V properties. The RF power amplifier works at a very high frequency, and the physics of the model depends on an RF GaN device that can record RF noise and charge-trapping behavior.

This model's capability may be further developed to power GaN devices. Verification was conducted using switching applications with relatively low voltages (200 V).

The model's validity needs to be confirmed for 650 V-rated GaN devices that are sold commercially. However, for depletion-mode RF GaN devices, the model has proven to be durable and has good convergence capabilities.

SPICE Model

For their commercial GaN devices, the majority of semiconductor vendors offer additional SPICE models in addition to the widely known published models.

Researchers have found that these models are mostly based on observations and don't give a way to describe other GaN devices besides the one they were made for.

Also, these models tend to experience convergence problems when evaluated with complicated switching circuits and topologies in SPICE-based simulators such as PSpice and LTspice.

However, considering that most of these models are free and the majority of application engineers are familiar with SPICE-based simulators, these models continue to enjoy considerable popularity.

Summarizing the Key Points

● Wide band-gap semiconductors present a promising solution to the limitations of silicon-based power devices, offering enhanced performance and efficiency in power electronics applications.

● The significance of gallium nitride device structure and the importance of simulation prototypes in estimating the functioning characteristics of power electronics circuits are discussed.

● The article discusses the role of semiconductor device modeling in predicting and optimizing the performance of gallium nitride power devices.

● It highlights advanced models such as ASM-HEMT, MIT GaN, and SPICE models contributing to the advancement of power electronics and semiconductor device technologies.