Turn-off Switching Time Research Articles

GaN p-i-n ultraviolet photodetectors grown on homogenous GaN bulk substrates

Gallium nitride p-i-n ultraviolet (UV) photodetectors (PDs) were fabricated on homogenous bulk substrates. The PDs exhibit high performances at room temperature: 1) The dark current density is as low as 2.11 × 10−9 A/cm2 and the detection rate is as high as 4.71 × 1014 cm⋅Hz1/2⋅W−1; 2) The UV/visible rejection ratio is about 3.1 × 103 and the highest responsivity is about 0.184 A/W; 3) The peak quantum efficiency is about 65.9 % and the average value in the deep UV region is still>40 %; 4) The turn-on and turn-off switching time constants are about 1.25 μs and 2.5 μs, respectively. Nevertheless, at 400 K the peak responsivity and quantum efficiency drop to 0.137 A/W and 50.59 %, respectively. An acceptor-like state model is proposed to explain the degradation, emphasizing that: 1) As the effective generation centers, they release the electron-hole pairs to the conductance and valence band edges, enhancing the photoelectric response in the long-wavelength region; 2) As the non-radiative recombination centers, they compete with the band-edge recombination, decreasing the responsivity and quantum efficiency. Finally, the noise characteristics are briefly discussed, which suggests a dominant Brown noise at reverse biases.

Development of a High-Speed Switching Silicon Carbide Power Module

We developed a silicon carbide (SiC) power module that can switch large currents at high speed. The withstand voltage of this power module is 1200 V, and two SiC MOSFETs are built-in and constitute a circuit for one inverter phase. This power module incorporates a snubber circuit for reducing the surge voltage generated by the SiC MOSFET for high-speed switching. In this study, switching at 270 A (a current density of 1000 A/cm 2 or more for the SiC MOSFET) was performed to evaluate this module. The turn-off switching time tf was ~10 ns, and the maximum dv/dt was 80 kV/us. Furthermore, this research examines the design and performance of the proposed power module.

Development of High Temperature Operation SiC Power Module

We have developed SiC power module which realizes operation at high temperature of 250 °C or higher. The withstand voltage of this power module is 1200 V, and two SiC-MOSFETs are built in and constitute a circuit for one inverter phase. This power module incorporates a snubber circuit for reducing the surge voltage generated by the SiC-MOSFET during switching. Joining of the main parts in the module is done with eutectic solder with a solidus line of 350 °C or higher. It can operate at high temperatures up to 250 °C and ensures reliability at that temperature. We conducted 100 A switching test using this module. High speed switching was realized, and the turn-off switching time tf was about the same about 10 ns from room temperature to 250 °C. In this paper, we describe the design and performance of the developed power module.

Development of High Temperature Operation SiC Power Module

We have developed a Silicon Carbide (SiC) power module that can operate at high temperatures up to 250 °C. Figure 1 shows the overview of the developed power module. The withstand voltage of the power module is 1200 V, two SiC - MOSFETs are built in, and it is a circuit composition of one phase of the power inverter. The two-layer SiC-Active Metal Brazed Copper(AMC) not only reduces the area of the power module but also reduces circuit inductance. In addition, this power module has a built-in snubber circuit that reduces the switching surge voltage of the SiC-MOSFET during high-speed switching. Generally, when the power module is operated at a high temperature, the reliability such as occurrence of lowering of the main bonding strength of the power module is significantly reduced due to thermal deformation. In this power module, the main components of the module are joined using eutectic solder with a solidus line above 350 °C. Copper-tungsten (CuW) was selected as the base plate material. Since the Coefficient of Thermal Expansion (CTE) values of CuW and SiN - AMC are close, it is possible to reduce the stress applied to these joints when the temperature changes. In addition, CuW has excellent thermal conductivity and heat capacity and suppresses heat generation of SiC-MOSFET. To evaluate the performance of this module, a switching test at 100 A was performed at 250 °C. The switching waveform is shown in Fig.2. The turn-off switching time tf was about 10 ns, and the switching surge voltage at that time was about 150 V. The turn-off switching waveform was almost the same from room temperature to 250 °C. As a result, it was shown that this power module can operate at 250 °C and the built-in snubber circuit works effectively at all temperatures. Acknowledgement This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation power electronics / Consistent R&D of next-generation SiC power electronics" (funding agency: NEDO). Figure 1

Long-wavelength multiple-quantum-well voltage-controlled bistable laser diodes

We have investigated static and dynamic characteristics of a multiple-quantum-well (MQW) voltage-controlled bistable laser diode at 1.5 /spl mu/m. Using the quantum confined Stark effect, the absorption coefficient and the absorption band edge of the saturable absorption region are controlled by applied voltage, resulting in easy change of the hysteresis width and the threshold current. Applied voltage from below the current injection regime to the saturable absorption region, typically the reverse bias voltage, allows faster turn-off switching speed due to the carrier sweep-out by the applied electric field, MQW bistable lasers with InGaAs-InP, InGaAs-InGaAsP and InGaAs-InAlAs systems and several kinds of well numbers were fabricated and their threshold current and switching characteristics are compared. A hysteresis width change of about 20 mA was obtained by changing the applied voltage of about 1 V in each case, Less than 100 ps turn-on switching time with injection light of 1-mW peak intensity was obtained. The device can be switched-on by injection light with about 50 nm bandwidth, and the minimum input light switching intensity of less than 10 /spl mu/W is achieved around the absorption peak wavelength of the saturable absorber. The InGaAs-InAIAs system has the advantage of low voltage bias at the saturable absorber, because the absorption edge is sharper than other materials due to its high conduction band offset. It has a turn-off switching time of less than 100 ps at the applied voltage height of 2.0 V. And also, memory operation with the repetition rate of 2 GHz has been achieved using input light and the applied voltage.

Impedance and switching of GaAs p-i-n diodes

The impedance of GaAs p-i-n diodes under forward bias is modeled using the two-dimensional simulation program PISCES. A parallel equivalent circuit gives almost constant resistance and capacitance over a wide range of frequencies. The intrinsic turn-off switching time of the diode, neglecting contact resistance, is determined by the sweep out time of the carriers, not by the carrier lifetime, unless this is very short. The diode current is recombination dominated at low forward bias. At higher applied voltages, this current becomes diffusion dominated if not masked by high injection conditions. >

A novel saturation control in TTL circuits

A novel technique of saturation control in TTL and other saturated logic circuits is described and analyzed. The approach is not only fully compatible with standard bipolar transistor technology, but lends itself to integration. The device parameter tracking on a chip is utilized to suitably bias a feedback saturation control transistor so that the stored charge of a TTL gate output transistor is reduced by typically two orders of magnitude. Thus, the turn-off switching time is significantly decreased without noticeably affecting the turn-on delay time. The performance improvement is close to that achieved by the well-known Schottky diode clamp approach; however, the novel technique offers advantages in noise margin, control of down-level output voltage, and processing. The effectiveness of the proposed technique has been verified theoretically by computer circuit analysis and experimentally by bench setup measurements.