Takashi Shinohe

Dependence of acceptor levels and hole mobility on acceptor density and temperature in Al-doped p-type 4H-SiC epilayers

The temperature-dependent hole concentration p(T) and hole mobility μp(T) are obtained in p-type 4H-SiC epilayers with several Al-doping densities. From p(T), the densities and energy levels of acceptors are determined by the graphical peak analysis method (free carrier concentration spectroscopy: FCCS) without any assumptions regarding the acceptor species. In the heavily Al-doped case, the excited states of acceptors affect p(T) because the Fermi level is located between the valence band maximum and the acceptor level (i.e., the ground state level of the acceptor), indicating that a distribution function for acceptors, which includes the influence of excited states of acceptors, should be required. Here, FCCS can determine acceptor densities and acceptor levels using any distribution function (e.g., the Fermi-Dirac distributing function or the distribution function including the influence of excited states). Two types of acceptor species are detected in the lightly Al-doped epilayers, while only one typ...

Impact ionization coefficients of 4H silicon carbide

Anisotropy of the impact ionization coefficients of 4H silicon carbide is investigated by means of the avalanche breakdown behavior of p+n diodes on (0001) and (112¯0) 4H silicon carbide epitaxial wafers. The impact ionization coefficients are extracted from the avalanche breakdown voltages and the multiplication of a reverse leakage current, due to impact ionization of these p+n diodes. The breakdown voltage of a p+n diode on a (112¯0) wafer is 60% of that on a (0001) wafer, and the extracted impact ionization coefficients of 4H silicon carbide show large anisotropy. We have shown that the anisotropy of the impact ionization coefficients is related to the anisotropy of carrier heating and drift velocity, which are due to the highly anisotropic electronic structure of 4H silicon carbide.

Parameters required to simulate electric characteristics of SiC devices for n-type 4H-SiC

In order to obtain some of the parameters required to simulate the electric characteristics of silicon carbide (SiC) power electronic devices in a wide temperature range from startup temperatures (⩽30°C) to steady-operation temperatures (⩾200°C), we discuss the dependence of the two donor levels on the total donor density (ND) as well as the dependence of the electron mobility on the total impurity density (Nimp) and operating temperature (T) in the n-type 4H–SiC. The temperature-dependent electron concentration n(T) and electron mobility μn(T) in the n-type 4H–SiC epilayers with several nitrogen-doping densities are obtained from the Hall-effect measurements. By the graphical peak analysis method (free carrier concentration spectroscopy: FCCS) without any assumptions regarding the donor species, the two types of donor species are detected from n(T). Moreover, the energy level and density of each donor species are determined by the FCCS. Using these results, we obtain the parameters with which the depende...

Development of Ultrahigh-Voltage SiC Devices

Ultrahigh-voltage silicon carbide (SiC) devices [p-i-n diodes and insulated-gate bipolar transistors (IGBTs)] and switching test have been investigated. As a result, we have succeeded in developing a 13-kV p-i-n diode, 15-kV p-channel IGBT, and 16-kV flip-type n-channel implantation and epitaxial IGBT with a low differential specific on-resistance (Rdiff,on). It was revealed that a power module fabricated using a nanotech resin, Si3N4 ceramic substrate, and W base plate was suitable for ultrahigh voltage and high temperature. A switching test was carried out using a clamped inductive load circuit, which indicated that the energy loss of a circuit with ultrahigh-voltage SiC devices is lower than that of Si devices.

Development of key components and technologies for a high repetition rate and high-power excimer laser

Key components and technologies have been developed for an ultrahigh repetition rate XeCl excimer laser of 5 kHz to be used for industrial applications. A compact axial blower having a revolution rate of up to 10 000 min−1 and a maximum pressure of 16.2 kPa in air was made with a canned magnetic coupler to circulate a laser gas at a flow velocity of over 150 m/s in a discharge region. Materials constituting a laser chamber were tested to prevent discharge instability by gas contamination to enable long time operation. The dominant cause of the instability was investigated by a simple simulation. For a preionization, a novel sealed-off x-ray tube was developed to compare the suitability in a high repetition rate operation with that of conventional UV preionization. The gas due to the shock and acoustic waves generated by discharge pulses was measured to design the damper, which enabled the suppression of the gas turbulence by around a tenth. To simplify cumbersome laser maintenance, a new power supply prov...

Measurement of Hall Mobility in 4H-SiC for Improvement of the Accuracy of the Mobility Model in Device Simulation

In order to construct a reliable parameter set for the physic al modeling of 4H-SiC, we are collecting and examining the physical parameters. The results of mobility measurement are presented and compared with the built-in model in the device simulator. The doping depe n nce of the electron mobility is in agreement with the built-in model, whereas that of the hole mobility is different from the built-in model in the higher doping region. Further, the anisotropy of the electron and hole mobility is investigated. The anisotropy of the electron mobility ) 0001 ( / ) 00 1 1 ( > < μ > < μ is about 0.83 and is in agreement with the built-in model. The anisotropy of the hole mobility is observed and it is estimated to be 1.15. To our knowledge, this is the first report of the anisotropy of the hole mobility in 4H-SiC. Introduction Silicon carbide devices have outstanding features, namely higher speed and lower loss than silicon devices. Among the many polytypes of SiC, 4H-SiC has attracted gre at att ntion as a candidate material for the next generation of power semiconductor devices, due t o the excellent physical properties such as the electric breakdown field and mobility. In order to r alize SiC devices that make the best use of the excellent physical properties, device simulati on technology of SiC is indispensable. However, the comprehensive and reliable parameter set for the physic al modeling of 4H-SiC for device simulators has not been reported. As a first step in the construction of a reliabl e par meter set for the physical modeling of 4H-SiC, we are collecting and examini ng the physical parameters systematically by fabricating test chips that consist of the el ments for physical property measurements. This paper is the first report on our ongoing research . The final goal of our research is the release of the comprehensive parameter set. In this paper, we present results of mobility measurement and compare them with the previous results. Experimental Figure 1 shows the top view of a test chip of the first lot. A prec ise patterning of contact, electrode and mesa by the mask process guarantees the precision of the physical property measurements. A test chip consists of elements (Hall bars and the square and clover shaped four terminal pattern) for mobility measurements and pin diodes for the impact ionization coefficient mea surements. Hall bars are tilted to the crystallographic axis every fifteenth degree in order to de ect the anisotropy of the mobility. Test chips were fabricated on 4H-SiC epitaxial wafers. For the measurements of the electron mobility, Materials Science Forum Online: 2003-09-15 ISSN: 1662-9752, Vols. 433-436, pp 443-446 doi:10.4028/www.scientific.net/MSF.433-436.443

Smoothing of Si Trench Sidewall Surface by Chemical Dry Etching and Sacrificial Oxidation

By combining the effects of chemical dry etching (CDE) and sacrificial oxidation, a smooth trench sidewall surface with a root-mean-square (Rms) roughness of less than 1 nm was obtained. The possibility of obtaining a smooth surface such as that of a planar metal-oxide-semiconductor (MOS) by increasing both the CDE etching time and the oxide thickness of sacrificial oxidation appears likely.

Guard ring assisted RESURF: a new termination structure providing stable and high breakdown voltage for SiC power devices

A new junction termination structure named guard ring assisted reduced surface field (GRA-RESURF) is proposed. The structure maintains a stable and high breakdown voltage without being influenced by the deviation of impurity dose in the RESURF layer or by parasitic charge. The GRA-RESURF structure was adopted on 600 V range 4H-SiC Schottky barrier diodes, and achieved high breakdown voltages with a good production yield.

Ultra-high di/dt 2500 V MOS assisted gate-triggered thyristors (MAGTs) for high repetition excimer laser system

A novel MOS assisted gate-triggered thyristor (MAGT) having high di/dt turn-on characteristics is proposed. It is shown that 40 kA/cm/sup 2// mu s of di/dt can be attained for a turn-on from 1500-V anode voltage, 9090-A/cm/sup 2/ peak anode current, and 0.7- mu s pulse width, with an extremely low turn-on power loss. The transient anode voltage, caused by high di/dt, is less than 100 V, even in the case of 9090 A/cm/sup 2/ for the anode current density. It is concluded that MAGT is a very promising device to replace thyratrons in a high-repetition excimer laser system.<<ETX>>

Evaluation of a SiC power module using low-on-resistance IEMOSFET and JBS for high power density power converters

In high-power density power converter designs, power losses of power devices are essential design parameters. Silicon-carbide (SiC) power devices are expected as next generation power devices due to their superior performances compared to conventional silicon (Si) power devices. The power loss performances of a SiC power module using SiC Implantation and Epitaxial MOSFET (SiC-IEMOSFET) and Junction barrier controlled Schottky Diode (SiC-JBS) has been evaluated based on parameters of the junction temperature, current density, and switching frequency. The advantage of the SiC power module compared to a latest Si-IGBT and SiC-diode hybrid-pair module are discussed from the view point of the power loss reduction.