Silicon carbide with a poly-type 4H structure (4H-SiC) is an attractive material for power devices. While bipolar devices mainly utilize 4H-SiC p-n junctions, unipolar devices use p-n junctions both within the active region (to control the electric field distribution) and at the edges of the devices (to reduce electric-field crowding) (Baliga, 2005). In a p-type region, very high doping is necessary since common acceptors have deep energy levels (B: 0.3 eV; Al: 0.2 eV) (Heera et al., 2001). Boron is known to exhibit complex diffusion behaviour (Linnarsson et al., 2003), while aluminum has extremely low diffusivity (Heera et al., 2001). Precise modeling of boron diffusion and aluminum-ion implantation is therefore crucial for developing high-performance 4H-SiC power devices. For carbon-doped silicon, a boron diffusion model has been proposed (Cho et al., 2007). Unfortunately, the results cannot be directly applied to boron diffusion in SiC because of the existence of silicon and carbon sublattices. In addition, knowledge of boron segregation in 4H-SiC is lacking, preventing improvement of such novel devices as boron-doped polycrystalline silicon (poly-Si)/nitrogen-doped 4H-SiC heterojunction diodes (Hoshi et al., 2007). Dopant segregation in elementary-semiconductor/compound-semiconductor heterostructures—in which point defects in an elementary semiconductor undergo a configuration change when they enter a compound semiconductor—has yet to be studied. A framework for such analysis needs to be provided. With regards to aluminum distribution, to precisely design p-n junctions in 4H-SiC power devices, as-implanted profiles have to be accurately determined. For that purpose, Monte Carlo simulation using binary collision approximation (BCA) was investigated (Chakarov and Temkin, 2006). However, according to a multiday BCA simulation using a large number of ion trajectories, values of the simulated aluminum concentration do not monotonically decrease when the aluminum concentration becomes comparable to an n-type drift-layerdoping level (in the order of 1015 cm-3). A continuous-function approximation, just like the dual-Pearson approach established for ion implantation into silicon (Tasch et al., 1989), is thus needed. The historic development and basic concepts of boron diffusion in SiC are reviewed as follows. It took 16 years for the vacancy model (Mokhov et al., 1984) to be refuted by the 2
Novel device structures using GaInNP in a thin layer at the base-collector (BC) junction of a heterojunction bipolar transistor (HBT) are described. The proposed devices, blocked hole bipolar transistors (BHBTs) combine the benefits of single and double heterojunction bipolar transistors (DHBTs). In DHBTs there is typically a barrier to electrons at the BC junction. In the BHBT the barrier is eliminated by the incorporation of nitrogen into GaInP. In the new structures the majority of the collector remains GaAs, which yields a device with a higher cutoff frequency than achievable with GaInP collectors. Since the reduction in bandgap energy is primarily in the conduction band from the incorporation of nitrogen, there will remain a substantial valence band discontinuity. This will yield reduced saturation charge storage. The offset voltage will also be reduced by the greater symmetry of the base-emitter (BE) and BC junctions. Additionally, the eliminated barrier at the BC junction will yield devices with a reduced knee voltage. These attributes make the proposed devices very well suited for microwave power amplifiers.
This unique new resource provides a comparative introduction to vertical Gallium Nitride (GaN) and Silicon Carbide (SiC) power devices using real commercial device data, computer, and physical models. This book uses commercial examples from recent years and presents the design features of various GaN and SiC power components and devices. Vertical verses lateral power semiconductor devices are explored, including those based on wide bandgap materials. The abstract concepts of solid state physics as they relate to solid state devices are explained with particular emphasis on power solid state devices. Details about the effects of photon recycling are presented, including an explanation of the phenomenon of the family tree of photon-recycling. This book offers in-depth coverage of bulk crystal growth of GaN, including hydride vapor-phase epitaxial (HVPE) growth, high-pressure nitrogen solution growth, sodium-flux growth, ammonothermal growth, and sublimation growth of SiC. The fabrication process, including ion implantation, diffusion, oxidation, metallization, and passivation is explained. The book provides details about metal-semiconductor contact, unipolar power diodes, and metal-insulator-semiconductor (MIS) capacitors. Bipolar power diodes, power switching devices, and edge terminations are also covered in this resource.
Photon recycling was used to increase ionization of magnesium in GaN p-n diodes by reducing anode radius to 20 μm. On-resistance of GaN p-n diodes (with breakdown voltages of 0.7-0.8 kV) was extremely low (i.e., 0.5 mΩcm 2 at 5 V) in the temperature range of 273-373 K. This temperature-independent extremely low on-resistance is a promising characteristic for power-electronics applications such as fast, high-voltage freewheeling diodes.
Trench-filling epitaxial growth of 4H-SiC by chemical vapor deposition (CVD) with and without HCl was analyzed based on a continuum-diffusion model including the Gibbs–Thomson effect. Qualitative reproduction of the reported observation showed that the effective surface free energy of SiC during CVD can be doubled by the addition of HCl
A 3.3-kV SiC-Si hybrid module, composed of a low-forward-voltage ( V F ) SiC junction-barrier-Schottky (JBS) diode and a low-saturation-voltage V CE(sat) Si trench IGBT was fabricated and demonstrated highly efficient operation.
The collector-emitter offset voltage of GaInP/GaAs collector-up tunnelling-collector heterojunction bipolar transistors (C-up TC-HBTs) was found to be almost zero (10–14 mV) and independent of transistor size and temperature. These findings indicate that GaInP/GaAs C-up TC-HBTs are strong candidates for high-efficiency high-power amplifiers.
