Tetsuzo Ueda

Gate Injection Transistor (GIT)—A Normally-Off AlGaN/GaN Power Transistor Using Conductivity Modulation

We have developed a normally-off GaN-based transistor using conductivity modulation, which we call a gate injection transistor (GIT). This new device principle utilizes hole-injection from the p-AlGaN to the AlGaN/GaN heterojunction, which simultaneously increases the electron density in the channel, resulting in a dramatic increase of the drain current owing to the conductivity modulation. The fabricated GIT exhibits a threshold voltage of 1.0 V with a maximum drain current of 200 mA/mm, in which a forward gate voltage of up to 6 V can be applied. The obtained specific ON-state resistance (RON . A) and the OFF-state breakdown voltage (BV ds) are 2.6 mOmega . cm2 and 800 V, respectively. The developed GIT is advantageous for power switching applications.

GaN on Si Technologies for Power Switching Devices

This paper reviews the recent activities for normally-off GaN-based gate injection transistors (GITs) on Si substrates and their application to inverters. Epitaxial growth of the AlGaN/GaN heterostructures with good crystallinity over 200-mm Si substrates with eliminated bowing enables low-cost fabrication of GaN devices with high breakdown voltages. A novel normally-off GaN transistor called as GIT is proposed in which hole injection from the p-type AlGaN gate increases the drain current with low on-state resistance by conductivity modulation. The low on-state resistance in GaN-based devices greatly helps to increase the efficiency of power switching systems. A GaN-based three-phase inverter successfully drives a motor with high efficiency of 99.3% at a high output power of 1500 W. The presented GaN-based devices are expected to greatly help saving energy in the future as an indispensable power switching system.

99.3% Efficiency of three-phase inverter for motor drive using GaN-based Gate Injection Transistors

In this paper, we present a successful operation of Gallium Nitride(GaN)-based three-phase inverter with high efficiency of 99.3% for driving motor at 900W under the carrier frequency of 6kHz. This efficiency well exceeds the value by IGBT (Insulated Gate Bipolar Transistor). This demonstrates that GaN has a great potential for power switching application competing with SiC. Fully reduced on-state resistance in a new normally-off GaN transistor called Gate Injection Transistor (GIT) greatly helps to increase the efficiency. In addition, use of the bidirectional operation of the lateral and compact GITs with synchronous gate driving, the inverter is operated free from fly-wheel diodes which have been connected in parallel with IGBTs in a conventional inverter system.

High-Extraction-Efficiency Blue Light-Emitting Diode Using Extended-Pitch Photonic Crystal

We have integrated the surface photonic crystal (PhC) on GaN-based blue light-emitting diodes (LEDs) for the first time in order to enhance the extraction efficiency of the LEDs. With the finite-difference time-domain method, we have calculated 3.6-fold enhancement in light output. The theoretical calculations have revealed that the optimum pitch of the PhC is much longer than the emission wavelength when the distance between the PhC and the active layer of LEDs is short. This design enables PhC formation on chemically stable GaN surfaces. In addition, an indium tin oxide (ITO)-based transparent electrode is formed directly on the surface of PhC to realize light emission from the whole area of the LED. The fabricated PhCs have increased the light output of blue LEDs by 1.5 times compared with the LEDs without PhC. We have demonstrated that PhC will realize highly efficient solid-state lighting with GaN-based LEDs.

8300V Blocking Voltage AlGaN/GaN Power HFET with Thick Poly-AlN Passivation

We report ultra high voltage AlGaN/GaN heterojunction transistors (HFETs) on sapphire with thick poly-AlN passivation. Extremely high blocking voltage of 8300 V is achieved while maintaining relative low specific on-state resistance (Ron*A) of 186 mOmegaldrcm2. Via-holes through sapphire at the drain electrodes enable very efficient layout of the lateral HFET array as well as better heat dissipation.

AlGaN/GaN power HFET on silicon substrate with source-via grounding (SVG) structure

We have developed a high-power AlGaN/GaN HFET fabricated on 4-in conductive Si substrate with a source-via grounding (SVG) structure. The SVG structure enables efficient chip layout and high packing density by the vertical configuration. By establishing a high-quality epitaxial technology on a Si substrate and by significantly reducing the parasitic resistance, a very low specific on-state resistance of 1.9 m/spl Omega//spl middot/cm/sup 2/ is achieved. The breakdown voltage is as high as 350 V, which is attributed to the Si substrate acting as a backside field plate. Because of reduction of the parasitic inductance, very high level of current (2.0 kA/cm/sup 2/) transients, i.e., a turn-on time of 98 ps and a turn-off time of 96 ps, are successfully measured for the first time.

Nonpolar (11-20) plane AlGaN∕GaN heterojunction field effect transistors on (1-102) plane sapphire

GaN-based compound semiconductors have been investigated for use in future power switching devices with high breakdown voltages and low on-state resistances due to their high breakdown field and high saturation electron velocity. To date, conventional AlGaN∕GaN heterojunction field effect transistors (HFETs) are fabricated on c-plane across which the spontaneous and piezoelectric polarization fields produce extraordinarily high sheet carrier concentrations. In this paper, we report on the epitaxial growth and fabrication of AlGaN∕GaN HFETs on (11-20) a-plane which are not affected by the polarization fields. The a-plane’s epitaxial layers are grown on (1-102) r-plane sapphire substrates by metal organic chemical vapor deposition. The sheet carrier concentrations can be controlled by simply doping the AlGaN in the nonpolar devices. The a-plane devices exhibit nearly normally-off characteristics in which the threshold voltage is −0.5V, while that of the conventional c-plane device is −4.0V. The HFET on nonp...

Current-collapse-free operations up to 850 V by GaN-GIT utilizing hole injection from drain

Current collapse at high drain voltage in a GaN-based transistor is successfully suppressed by the introduction of p-GaN region which is placed beside the drain of a Gate Injection Transistor (GIT). The additional p-GaN region enables hole injection which effectively releases trapped electrons at around drain region after the application of high drain voltages. The p-GaN region is electrically connected to the drain electrode so that this is named as Hybrid Drain-embedded GIT (HD-GIT). The fabricated HD-GITs are free from current collapse at 850 V of the drain voltage or over, which significantly helps to achieve stable system operations and is very promising for future switching power supply applications.

GaN monolithic inverter IC using normally-off gate injection transistors with planar isolation on Si substrate

We present a GaN monolithic inverter IC on Si substrate and successful motor-drive by it for the first time. Taking advantages of the bi-directional operation free from the forward voltage off-set [1], the inverter can be operated just by the integrated six GaN-based normally-off gate injection transistors (GITs) without any external fast recovery diodes (FRDs) to flow the fly-wheel current. The IC enables the efficiency as high as 93% at low power operation where so far that of conventional Si-based inverters has remained lower value owing to the forward voltage off-set. The key processing technology is the newly introduced planar isolation using Fe ion implantation which fully isolates the GaN-based lateral devices each other.

GaN-on-Si Power Technology: Devices and Applications

In this paper, we present a comprehensive reviewand discussion of the state-of-the-art device technology and application development of GaN-on-Si power electronics. Several device technologies for realizing normally off operation that is highly desirable for power switching applications are presented. In addition, the examples of circuit applications that can greatly benefit from the superior performance of GaN power devices are demonstrated. Comparisonwith other competingpower device technology, such as Si superjunction-MOSFET and SiC MOSFET, is also presented and analyzed. Critical issues for commercialization of GaN-on-Si power devices are discussed with regard to cost, reliability, and ease of use.