GaN-based power devices: Physics, reliability, and perspectives

Abstract

Over the last decade, gallium nitride has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available on the market, GaN has the widest energy gap, the largest critical field, the highest saturation velocity, thus representing an excellent material for the fabrication of high speed/high voltage components.The presence of spontaneous and piezoelectric polarization allows to create a 2-dimensional electron gas, with high mobility and large channel density, in absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable high frequency operation, with consequent advantages in terms of miniaturization.For high power/high voltage operation, vertical device architectures are being proposed and investigated, and 3-dimensional structuresfin-shaped, trench-structured, nanowire-basedare demonstrating a great potential. Contrary to silicon, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This tutorial paper describes the physics, technology and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main properties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail, to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN, and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight on the most relevant aspects gives the reader a comprehensive overview on present and next-generation GaN electronics. IntroductionOver the past decade, gallium nitride has emerged as an excellent material for the fabrication of power semiconductor devices. Thanks to the unique properties of GaN, diodes and transistors based on this material have excellent performance, compared to their silicon counterparts, and are expected to find wide application in the next-generation power converters. Owing to the flexibility and the energy efficiency of GaN-based power converters, the interest towards this technology is rapidly growing: the aim of this tutorial is to review the most relevant physical properties, the operating principles, the fabrication parameters, and the stability/reliability issues of GaN-based power transistors. For introductory purposes, we start summarizing the physical reasons why GaN transistors achieve a much better performance than the corresponding silicon devices, to help the reader understanding the unique advantages of this technology.The properties of GaN devices allow the fabrication of high-efficiency (near or above 99 %)...

Evolution of Deep Traps in GaN‐Based RF High Electron Mobility Transistors under High Voltage OFF‐State Stress

“…[22] The configuration of traps would be changed via decorating with other point defects like O interstitials or Ga vacancies. [6] Similar traps have also been observed by Arehart et al (0.57 eV, 1 Â 10 À15 cm 2 ), [15] Huang et al (0.762 eV, 3.4 Â 10 À16 cm 2 ), [19] and Jin et al (0.57-1.12 eV). [20] The physical mechanism for the degraded gate leakage current should be related to the tunneling assisted by the traps.…”

“…A. del Alamo, Y. Polyakov, and G. Meneghesso. [ 4–6 ] In their previous works, inverse piezoelectric effect is the major cause for devices’ degradation under 100 V OFF‐state stress, and permanent lattice damage can be observed by optical or electron microscope after wet etching. It is demonstrated that inverse piezoelectric‐induced degradation can be alleviated by reducing Al content in the AlGaN barrier, by optimizing field plate to counterbalance the strain, and even by introducing an AlGaN back barrier.…”

Analysis ofDCandRFperformance of Al0.31Ga0.69N/Al0.1Ga0.9N/β‐Ga2O3double quantum wellHEMTon silicon carbide substrate

“…The breakdown voltage of the HEMT improved by maintaining a large distance between gate and drain (L GD ). On the other hand, the R on of the device will increase with L GD because R on of the HEMT is the sum of 2DEG channel resistance (R channel ) and gate to drain access resistance (R drain ) described by the following Equation 35 : At breakdown condition, . Therefore, From Equation (), the ON‐resistance is strongly depending on the gate length, and breakdown voltage.…”

“…Figure 8A indicates the E‐field distribution of conventional gate HEMT and Figure 8B shows the E‐field distribution of gate field plate HEMT. Impact ionization is the primary source for the breakdown behavior of HEMTs 35 . The high E‐field near the drain side of the gate edge initiates the electron–hole pair generation leads to avalanche multiplication.…”

“…Impact ionization is the primary source for the breakdown behavior of HEMTs. 35 The high E-field near the drain side of the gate edge initiates the electron-hole pair generation leads to avalanche multiplication. The presence of a high E-field near the gate in conventional HEMT as shown in Figure 8A Switching loss of the HEMTs is playing an important role in limiting the efficiency of power converters.…”