The fact that wide bandgap semiconductors are capable of electronic functionality at much higher temperatures than silicon has partially fueled their development, particularly in the case of SiC. It appears unlikely that wide bandgap semiconductor devices will find much use in low-power transistor applications until the ambient temperature exceeds approximately 300/spl deg/C, as commercially available silicon and silicon-on-insulator technologies are already satisfying requirements for digital and analog VLSI in this temperature range. However practical operation of silicon power devices at ambient temperatures above 200/spl deg/C appears problematic, as self-heating at higher power levels results in high internal junction temperatures and leakages. Thus, most electronic subsystems that simultaneously require high-temperature and high-power operation will necessarily be realized using wide bandgap devices, once they become widely available. Technological challenges impeding the realization of beneficial wide bandgap high ambient temperature electronics, including material growth, contacts, and packaging, are briefly discussed.

High-temperature electronics - a role for wide bandgap semiconductors?

Power semiconductor devices are key components in power conversion systems. Silicon carbide (SiC) has received increasing attention as a wide-bandgap semiconductor suitable for high-voltage and low-loss power devices. Through recent progress in the crystal growth and process technology of SiC, the production of medium-voltage (600?1700 V) SiC Schottky barrier diodes (SBDs) and power metal?oxide?semiconductor field-effect transistors (MOSFETs) has started. However, basic understanding of the material properties, defect electronics, and the reliability of SiC devices is still poor. In this review paper, the features and present status of SiC power devices are briefly described. Then, several important aspects of the material science and device physics of SiC, such as impurity doping, extended and point defects, and the impact of such defects on device performance and reliability, are reviewed. Fundamental issues regarding SiC SBDs and power MOSFETs are also discussed.

https://iopscience.iop.org/article/10.7567/JJAP.54.040103/pdf

Material science and device physics in SiC technology for high-voltage power devices

Semiconductor Power Devices

SiC electronic device technology has made rapid progress during the past decade In this paper, we review the evolution of SiC power MOSFETs between 1992 and the present, discuss the current status of device development, identify the critical fabrication issues, and assess the prospects for continued progress and eventual commercialization

Status and prospects for SiC power MOSFETs

Epitaxial thin films of inorganic single crystals can be grown on single-crystal substrates with a variety of different solution chemistries. This review emphasizes chemical solution deposition, in which a solution is used to deposit a layer of precursor molecules that decompose to low-density, polycrystalline films during heating. Ways to control film cracking during deposition and heat treatment and why many precursors synthesize metastable crystalline structures are discussed, and the different mechanisms that convert the polycrystalline film into a single crystal are reviewed. Hydrothermal epitaxy, in which single crystal thin films are directly synthesized on templating substrates in an aqueous solution at temperatures <150°C, is also discussed.

https://science.sciencemag.org/content/sci/273/5277/903.full.pdf

Chemical Solution Routes to Single-Crystal Thin Films

Epitaxial p-n diodes in 4H SiC are fabricated showing a good uniformity of avalanche multiplication and breakdown. Peripheral breakdown is overcome using the positive angle beveling technique. Photomultiplication measurements were performed to determine electron and hole ionization rates. For the electric field parallel to the c-axis impact ionization is strongly dominated by holes. A hole to electron ionization coefficient ratio of up to 50 is observed. It is attributed to the discontinuity of the conduction band of 4H SiC for the direction along the c axis. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained.

Ionization rates and critical fields in 4H silicon carbide

Electrical data obtained from deep level transient spectroscopy investigations on deep defect centers in the 3C, 4H, and 6H SiC polytypes are reviewed Emphasis is put on intrinsic defect centers observed in as-grown material and subsequent to ion implantation or electron irradiation as well as on defect centers caused by doping with or implantation of transition metals (vanadium, titanium, chromium, and scandium)

Deep Defect Centers in Silicon Carbide Monitored with Deep Level Transient Spectroscopy

Deep level defects in electron-irradiated 4H SiC epitaxial layers grown by chemical vapor deposition were studied using deep level transient spectroscopy. The measurements performed on electron-irradiated p+n junctions in the temperature range 100–750 K revealed several electron traps and one hole trap with thermal ionization energies ranging from 0.35 to 1.65 eV. Most of these defects were already observed at a dose of irradiation as low as ≈5×1013 cm-2. Dose dependence and annealing behavior of the defects were investigated. For two of these electron traps, the electron capture cross section was measured. From the temperature dependence studies, the capture cross section of these two defects are shown to be temperature independent. © 1997 American Institute of Physics.

Deep level defects in electron-irradiated 4H SiC epitaxial layers

Silicon carbide (SiC) devices have the potential to yield new components with functional capabilities that far exceed components based on silicon devices. Selective doping of SiC by ion implantation is an important fabrication technology that must be completely understood if SiC devices are to achieve their potential. One major problem with ion implantation into SiC is the surface roughening that results from annealing SiC at the high temperatures which are needed to activate implanted acceptor ions, boron or aluminum. This paper examines the causes and possible solutions to surface roughening of implanted and annealed 4H-SiC. Samples consisting of n-type epilayers (5 × 1015 cm−3, 4 µm thick) on 4H-SiC substrates were implanted with B or Al to a total dose of 4 × 1014 cm−2 or 2 × 1015 cm−2, respectively. Roughness measurements were made using atomic force microscopy. From the variation of root mean square (rms) roughness with annealing temperature, apparent activation energies for roughening following implantation with Al and B were 1.1 and 2.2 eV, respectively, when annealed in argon. Time-dependent activation and surface morphology analyses show a sublinear dependence of implant activation on time; activation percentages after a 5 min anneal following boron implantation are about a factor of two less than after a 40 min anneal. The rms surface roughness remained relatively constant with time for anneals in argon at 1750°C. Roughness values at this temperature were approximately 8.0 nm. Annealing experiments performed in different ambients demonstrated the benefits of using silane to maintain good surface morphology. Roughnesses were 1.0 nm (rms) when boron or aluminum implants were annealed in silane at 1700°C, but were about 8 and 11 nm for B and Al, respectively, when annealed in argon at the same temperature.

Surface roughening in ion implanted 4H-silicon carbide

Epitaxial p-n diodes in 4H SiC are fabricated with uniform avalanche multiplication and breakdown. Photomultiplication measurements were performed to determine electron and hole ionization rates. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained. We discuss ionization mechanisms in 4H SiC and make a comparison between silicon carbide and gallium nitride.

Nils Nordell

Papers

Ionization rates and critical fields in 4H silicon carbide

Deep Defect Centers in Silicon Carbide Monitored with Deep Level Transient Spectroscopy

Deep level defects in electron-irradiated 4H SiC epitaxial layers

Surface roughening in ion implanted 4H-silicon carbide

Study of avalanche breakdown and impact ionization in 4H silicon carbide