S.J. Rashid

Numerical Parameterization of Chemical-Vapor-Deposited (CVD) Single-Crystal Diamond for Device Simulation and Analysis

High-quality electronic-grade intrinsic chemical- vapor-deposited (CVD) single-crystal diamond layers having exceptionally high carrier mobilities have been reported by Isberg et al. This makes the realization of novel electronic devices in diamond, particularly for high-voltage and high-temperature applications, a viable proposition. As such, material models which can capture the particular features of diamond as a semiconductor are required to analyze, optimize, and quantitatively design new devices. For example, the incomplete ionization of boron in diamond and the transition to metallic conduction in heavily boron-doped layers require accurate carrier freeze-out models to be included in the simulation of diamond devices. Models describing these phenomena are proposed in this paper and include numerical approximation of intrinsic diamond which is necessary to formulate doping- and temperature-dependent mobility models. They enable a concise numerical description of single-crystal diamond which agrees with data obtained from material characterization. The models are verified by application to new Schottky m-i-p+ diode structures in diamond. Simulated forward characteristics show excellent correlation with experimental measurements. In spite of the lack of impact ionization data for single-crystal diamond, approximation of avalanche coefficient parameters from other wide-bandgap semiconductors has also enabled the reverse blocking characteristics of diamond diodes to be simulated. Acceptable agreement with breakdown voltage from experimental devices made with presently available single-crystal CVD diamond is obtained.

Termination Structures for Diamond Schottky Barrier Diodes

A comprehensive study on the off-state performance of synthetic single crystal (SSC) diamond Schottky barrier diodes (SBDs) is the subject of this paper. Three termination structures suitable for unipolar diamond power devices are numerically investigated. Comparisons between the three terminations, based on blocking performance and area consumption are presented. Optimum design parameters derived from simulations are included for each structure. Experimental results of reverse-biased diamond SBDs for the first time with ramp angle termination are also presented

Single crystal diamond M-i-P diodes for power electronics

Its outstanding electronic properties and the recent advances in growing single-crystal chemically vapour-deposited substrates have made diamond a candidate for high-power applications. Diamond Schottky diodes have the potential of being an alternative to silicon p-i-n and SiC Schottky diodes in power electronic circuits. Extensive experimental and theoretical results, for both on- and off-state behaviour of metal-insulator-p-type diamond Schottky structures, are presented here. The temperature dependence of the forward characteristics and electrical performance of a termination structure suitable for unipolar diamond devices are also presented.

Switching Performance of Epitaxially Grown Normally-Off 4H-SiC JFET

Static and dynamic behavior of the epitaxially grown dual gate trench 4H-SiC junction field effect transistor (JFET) is investigated. Typical on-state resistance Ron was 6 – 10mΩcm2 at VGS = 2.5V and the breakdown voltage between the range of 1.5 – 1.8kV was realized at VGS = −5V for normally-off like JFETs. It was found that the turn-on energy delivers the biggest part of the switching losses. The dependence of switching losses from gate resistor is nearly linear, suggesting that changing the gate resistor, a way similar to Si-IGBT technology, can easily control di/dt and dv/dt. Turn-on losses at 200°C are lower compared to those at 25°C, which indicates the influence of the high internal p-type gate layer resistance. Inductive switching numerical analysis suggested the strong influence of channel doping conditions on the turn-on switching performance. The fast switching normally-off JFET devices require heavily doped narrow JFET channel design.

Evaluation of Termination Techniques for 4H-SiC Pin Diodes and Trench JFETs

An investigation concerning suitable termination techniques for 4H-SiC trench JFETs is presented. Field plates, p+ floating rings and junction termination extension techniques are used to terminate 1.2kV class PiN diodes. The fabricated PiN diodes evaluated here have a similar design to trench JFETs. Therefore, the conclusions for PiN diodes can be applied to JFET structures as well. Numerical simulations are also used to illustrate the effect of the terminations on the diodes’ blocking mode behaviour.

Numerical and Experimental Analysis of Single Crystal Diamond Schottky Barrier Diodes

We present our findings on the numerical and experimental analysis of diamond Schottky Barrier diodes (SBDs) comprising of intrinsic single crystal (SC) chemical vapour deposited (CVD) diamond layers grown on highly boron doped substrates also grown by CVD. Good correlation with experimental results has been achieved through numerical modelling that has incorporated previously reported data on transport physics and carrier activation. With our numerical model, we are able to match to within 12 to 15% of the measured forward characteristics of fabricated diamond SBDs up to 2 V in excess of the turn on voltage, for two different Schottky metals.

On-State Behaviour of Diamond M-i-P Structures

Diamond Schottky power diodes are currently subject to extensive research. In this paper, the on-state capability of this type of structures is assessed. Measured forward characteristics for different temperatures are included and the use of gold, nickel and aluminium as Schottky metal is evaluated. A theoretical study regarding the influence of different doping profiles at the drift-substrate interface on the electrical performance of the device is also inserted

SiC junction FETs - a state of the art review

The continuous progress made over the past years in terms of material quality and key technological issues have enabled silicon carbide (SiC) to mature as a material for high power semiconductor industry. These improvements combined with a better understanding of the physics of the devices have placed SiC devices in a position from where they can challenge the present day Silicon (Si) solutions in high power/high temperature applications. Amongst the multitude of SiC switches that have been demonstrated, the Junction Field Effect Transistor (JFET) is the most advanced on and, in fact, already available on the market. This paper reviews the present status of SiC junction-controlled devices and discusses the different approaches one may decide on when considering SiC JFETs for high power, high temperature applications

Numerical and Experimental Investigation on Bipolar Operation of 4H-SIC Normally-on Vertical JFETs

It is well known from the literature published on Si devices that junction field effect transistors (JFETs) can be either operated in a unipolar mode (when the gate junction bias is less than 0.4 V) or in a bipolar mode (when the gate junction inject minority carriers into the channel/drift region to modulate its resistance)- The latter mode of operation is typically used to improve the on-state performance of normally-off JFETs. The aim of this paper is to investigate the bipolar mode of operation of 4H-SiC normally-on vertical JFETs. Both numerical and experimental results will be used to conclude whether the bipolar mode of operation offers any clear advantages to SiC normally-on JFETs. The influence of high temperature operation (up to 300degC) on the on-state characteristics will also be considered

Highly efficient edge terminations for diamond schottky diodes

Two termination structures suitable for diamond Schottky diodes are presented in this paper. A thorough comparison between the two structures, concerning both electrical and geometrical aspects, is included. The study is based on theoretical models and extensive numerical results. High termination efficiencies, up to 93%, are reported