Device Simulation and Design Optimization for Diamond Based Insulated-gate Bipolar Transistors
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0956-J09-17
Device Simulation and Design Optimization for Diamond Based Insulated-gate Bipolar Transistors Haitao Ye1, Niall Tumilty1, David Garner2, and Richard B. Jackman1 1 London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, United Kingdom 2 Cambridge Semiconductors, St. Andrew's House, St. Andrew's Road, Cambridge, CB4 1DL, United Kingdom
ABSTRACT A diamond based insulated gate bipolar transistor is incorporated into a two –dimensional device simulator (MEDICI) to examine the current gain (β) and potential distribution across the device. Initially, work has focused on an important component of IGBT structure, the PNP bipolar transistor, which has been simulated and is reported upon in this paper. Empirical parameters for emitter and collector regions were used. Various carrier concentrations for base region were used to optimize the simulation. It was found that decreasing the thickness of base region leads to an increase in current gain. A buffer layer is needed to prevent the punch-through at low carrier concentration in the base region. Various approaches of increasing the current gain are also discussed in this paper. INTRODUCTION Crystalline diamond, as opposed to other high performance carbon-based materials such as diamond-like carbon (DLC), has a wide band gap (5.5eV), high thermal conductivity, high electric field breakdown strength, high carrier mobilities and high saturated-carrier velocities, in addition to its more familiar optical, physical and chemical properties. The emergence of chemical vapour deposition (CVD) methods for the routine formation of large area diamond films in the late 1980s led many to conclude that semiconducting diamond devices would become commonplace within high performance device applications. In theory diamond should readily outperform other wide band gap materials, such as SiC and GaN, in high power, high frequency and high temperature applications. This can be illustrated by considering a number of ‘figures of merit’ (FOM) for semiconducting materials. Commonly used measures are Johnsons, Keyes and Baligas FOMs, which may be combined to give a measure which accounts for thermal conductivity, breakdown field, mobility, saturated carrier velocity and dielectric constant to enable high frequency and high power potential to be assessed, as shown in table 1 [1]. The advantage that would be offered by diamond over GaN or SiC is strikingly clear. As will be discussed below, power applications increasingly rely upon insulated gate bipolar transistors (IGBTs). Chow and co-workers [2] have calculated a bipolar FOM for SiC and diamond compared to Si, in terms of the power density dissipated; diamond was predicted to be up to 5 times more efficient than SiC. It should also be remembered that with a larger band-gap (5.5 compared to ~3.6eV) and the highest thermal conductivity of any material, diamond devices offer the prospect of the highest temperature operation for power device structures. Diamond is also ‘radiation-hard’ meaning tha
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