E. M. Sankara Narayanan

GaN-Based Super Heterojunction Field Effect Transistors Using the Polarization Junction Concept

GaN super heterojunction field effect transistors (super HFET) based on the polarization junction concept are demonstrated for the first time. The super HFET has charges of 2-D electron gas and hole gas, respectively induced by positive and negative polarization charges at GaN/AlGaN/GaN heterointerfaces. Analogous to the RESURF concept, these unintentionally doped positive and negative polarization charges compensate each other in the off state condition to enhance the breakdown capability of the super HFET. The super HFETs have been fabricated on sapphire substrates and the electrical measurements show breakdown voltages over 1.1 kV with specific on-resistance of 6.1 mΩ· cm^2.

High Density Two-Dimensional Hole Gas Induced by Negative Polarization at GaN/AlGaN Heterointerface

High density two dimensional hole gas (2DHG) with a charge density of 1.1×1013 cm-2 has been demonstrated for the first time in GaN/AlGaN heterostructures. The 2DHG is induced by negative polarization charges at the GaN/AlGaN interface. The layer structures have been designed based on theoretical simulation results to maximize the 2DHG charge density. The heterostructures have been grown on sapphire substrate by metal organic chemical vapor deposition. Hall mobility of the 2DHG of 16 cm2 V-1 s-1 has been measured at room temperature with sheet resistance of 35 kΩ/sq.

2.4kV GaN Polarization Superjunction Schottky Barrier Diodes on semi-insulating 6H-SiC substrate

This paper reports the performance and electrical characterization results of high voltage Polarization Superjunction (PSJ) GaN Schottky Barrier Diodes (SBD) on semi-insulating 6H-SiC substrate for the first time. Fabricated PSJ SBDs with drift length of 25 μm show low on-set voltage of ~ 0.4V, high reverse blocking voltage (V_BR) of ~ 2400V, specific on-state resistance (R_ON.A) of ~ 14 mΩ.cm² and a Power Device Figure of Merit (PDFOM = V_BR²/R_ON.A) of ~ 400 MW/cm².

GaN-based bidirectional Super HFETs Using polarization junction concept on insulator substrate

GaN based bidirectional Super Heterojunction Field Effect Transistors (BiSHFETs) using the polarization junction (PJ) concept are demonstrated for the first time. The fabricated BiSHFETs are arrayed on an insulator substrate of Sapphire and measured isolation voltage between the devices is more than 2 kV. Measured on-resistances of the fabricated BiSHFETs with MES and PN gate structures are 24 Ωmm and 22 Ωmm in the both directions respectively.

Performance Evaluation of 10-kV SiC Trench Clustered IGBT

The performance of a 10-kV p-channel trench clustered insulated-gate bipolar transistor (IGBT) in silicon carbide evaluated through extensive 2-D numerical simulations is reported here for the first time. Comparison with an equivalent trench IGBT reveals a reduction in the following: 1) on -state voltage by more than 30%; 2) differential specific on-resistance by 20%; and 3) total ( on-state and turnoff) losses by more than 25%.

Performance of a trench pmos gated, planar, 1.2 kV Clustered insulated gate bipolar transistor in NPT technology

The conventional Clustered IGBT is a MOS controlled power device with controlled thyristor action, which has been demonstrated to show lower Vce(sat) compared to IGBT, current saturation characteristics at high gate voltages and short circuit performance. In this paper, we show that, with the incorporation additional PMOS trench gates in a normally planar gate structure, the performance of the device can be enhanced even further to tailor saturation current levels and hence improve short-circuit performance without degrading Vce(sat). This is evaluatated using 1.2kV planar NPT CIGBT through extensive 2D simulations. This is the first paper to demonstrate a simple mechanism to control the saturation current without degrading Vce(sat) and other characteristics.

GaN based Super HFETs over 700V using the polarization junction concept

GaN Super Heterojunction Field Effect Transistors (Super HFETs) based on the polarization junction (PJ) concept are demonstrated on Sapphire substrates. These Super HFETs were fabricated from a GaN/Al<inf>0.23</inf>Ga<inf>0.77</inf>N/GaN hetero structure with 2D hole and electron gas densities of 1.1×10¹³ and 9.7×10¹² cm⁻² at the respective hetero-interfaces. The Super HFETs show breakdown voltage above 700 V with on-resistances of 15 Ω·mm. In addition, the super HFETs have inherent body diodes and its reverse conducting characteristics are demonstrated.

An overview of the recent developments in high-voltage power semiconductor MOS-controlled bipolar devices

An overview of the recent developments in high-voltage power semiconductor MOS-controlled bipolar devices is presented. The Insulated Gate Bipolar Transistor (IGBT) technology is explored up to the latest state-of-the-art developments, in terms of cathode cell technology, drift region technology and anode design. MOS-gated thyristors, which are aimed to replace the IGBT are analysed. It is shown that in spite of the recent cathode cell developments to enhance the plasma distribution within the IGBT, a fully optimised MOS gated thyristor still remains the best approach to achieve enhanced Vce(sat) - Eoff trade-offs and negligible temperature coefficient of Vce(sat).

Comparison of trench gate IGBT and CIGBT devices for 3.3kV high power module applications

Trench gate MOS controlled devices are more desirable in power modules because their reduced Vce(sat) enables increased output power density. However with increased drift region thickness with voltage rating, there is significant increase in conduction loss in Trench gate IGBT (T-IGBT) due to low plasma density from inherent pnp transistor action. On the other hand a well-designed trench gate MOS-controlled thyristor such as the Trench Cluster Insulated Gate Bipolar Transistor (T-CIGBT) is a drop in solution, which can provide thyristor-like on-state loss without compromising ease of control, turnoff loss and SOA. The T-CIGBT device technology employs controlled thyristor to lower on-state and a unique `self-clamping of the cathode cell potential to control the saturation current density. The comparison of T-IGBT and T-CIGBT 3.3kV/800A module simulation results in this paper show that T-CIGBT can reduce hard switching total losses and increase the power density of existing IGBT module footprints.

The world's first high voltage GaN-on-diamond power devices

This paper reports the fabrication method and electrical characterization results of the first-ever demonstrated high voltage AlGaN/GaN HEMTs on CVD diamond substrate. Fabricated circular GaN-on-Diamond HEMTs with gate-to-drain drift length of 17 μm and source field plate length of 3 μm show an off-state breakdown voltage of ~ 1100V. Temperature characterization of Capacitance voltage characteristics provides insight on the temperature dependence of VTH and 2DEG sheet carrier concentration in the fabricated devices.