It has been recognized that Raman scattering spectroscopy is a powerful tool to characterize SiC crystals non-destructively. We review recent significant developments in the use of Raman scattering to study structural and electronic properties of SiC crystals. The areas to be discussed in the first part include polytype identification, evaluation of stacking disorder and ion-implantation damages, and stress evaluation. The Raman scattering by electronic transitions is discussed in the second part of this article. We concentrate on the plasmon LO-phonon coupled modes whose spectral profiles are used to evaluate the carrier concentration and mobility. Anisotropic electronic properties of α-SiC and characteristics of heavily doped crystals are discussed. Semiconductor-to-metal transition and Fano interference effect are also treated.

Raman Investigation of SiC Polytypes

Various embodiments for improved power devices as well as their methods of manufacture, packaging and circuitry incorporating the same for use in a wide variety of power electronic applications are disclosed. One aspect of the invention combines a number of charge balancing techniques and other techniques for reducing parasitic capacitance to arrive at different embodiments for power devices with improved voltage performance, higher switching speed, and lower on-resistance. Another aspect of the invention provides improved termination structures for low, medium and high voltage devices. Improved methods of fabrication for power devices are provided according to other aspects of the invention. Improvements to specific processing steps, such as formation of trenches, formation of dielectric layers inside trenches, formation of mesa structures and processes for reducing substrate thickness, among others, are presented. According to another aspect of the invention, charge balanced power devices incorporate temperature and current sensing elements such as diodes on the same die. Other aspects of the invention improve equivalent series resistance (ESR) for power devices, incorporate additional circuitry on the same chip as the power device and provide improvements to the packaging of charge balanced power devices.

Power semiconductor devices and methods of manufacture

The present invention is a method of forming large device quality single crystals of silicon carbide. The sublimation process is enhanced by maintaining a constant polytype composition in the source materials, selected size distribution in the source materials, by specific preparation of the growth surface and seed crystals, and by controlling the thermal gradient between the source materials and the seed crystal.

Sublimation of silicon carbide to produce large, device quality single crystals of silicon carbide

PURPOSE: To prevent leakage currents even under severe conditions such as a high temperature, large power, etc., by forming a first electrode onto the surface of an silicon carbide semiconductor layer shaped onto one surface of a substrate, a second electrode onto the other surface of the substrate and a third electrode onto the side face of the silicon carbide semiconductor layer. CONSTITUTION: A nickel film formed onto the rear of an silicon substrate 1 is used as a drain electrode 7, and a titanium-aluminum film shaped onto the projecting end face of an silicon carbide growth layer 2 having mesa structure is employed as a source electrode 6. Currents flowing between the source electrode 6 and the drain electrode 7 are controlled by fluctuating voltage applied to gate electrodes 8 and changing the width of depletion layers 9 spreading in the silicon carbide growth layer 2. Accordingly, an silicon carbide semiconductor device, in which leakage currents are not generated even under severe conditions such as a high temperature, large power, etc., and which has excellent characteristics, can be acquired. COPYRIGHT: (C)1989,JPO&Japio

Silicon carbide semiconductor device

The deposition of silicon carbide thin films and the associated technologies of impurity incorporation, etching, surface chemistry, and electrical contacts for fabrication of solid-state devices capable of operation at temperatures to 925 K are addressed. The results of several research programs in the United States, Japan and the Soviet Union, and the remaining challenges related to the development of silicon carbide for microelectronics are presented and discussed. It is concluded that the combination of alpha -SiC on alpha -SiC appears especially viable for device fabrication. In addition, considerable progress in the understanding of the surface science, ohmic and Schottky contacts, and dry etching have recently been made. The combination of these advances has allowed continual improvement in Schottky diode p-n junction, MESFET, MOSFET, HBT, and LED devices. >

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Thin film deposition and microelectronic and optoelectronic device fabrication and characterization in monocrystalline alpha and beta silicon carbide

LO phonon‐overdamped plasmon coupled modes in n‐type epitaxial films of β‐SiC have been measured in the carrier concentration range from 6.9×1016 to 2×1018 cm−3. The carrier concentrations and damping constants are determined by line‐shape fitting of the coupled modes and compared with the values derived from Hall measurements. The concentrations obtained from the two methods agree fairly well. The Faust–Henry coefficient determined from the fitting is 0.35. The line‐shape analysis of the coupled mode has shown that the dominant scattering mechanisms in β‐SiC are deformation‐potential and electro‐optic mechanisms.

Characterization of the free‐carrier concentrations in doped β‐SiC crystals by Raman scattering

Electrical properties of non‐doped and nitrogen‐doped n‐type β‐SiC films grown on Si substrates have been investigated at 70–1000 K. Those of non‐doped films remarkably depend on the Si/C ratio of the source gases. The highest mobilities of non‐doped films are 510 and 1330 cm2 V−1 s−1 at 296 and 71 K, respectively. The carrier concentrations are as low as 6×1016 cm−3 even at 1000 K. Ionization energies of 34 –37 meV for nitrogen donors and 19–25 meV for unknown donors of non‐doped films are obtained. Mobilities of both non‐doped and nitrogen‐doped films are dominated by lattice scattering at high temperatures and by impurity scattering at low temperatures. Nitrogen donors strongly affect the impurity scattering.

Temperature dependence of electrical properties of non‐doped and nitrogen‐doped beta‐SiC single crystals grown by chemical vapor deposition

3C‐SiC p‐n junction diodes are prepared on Si substrates by chemical vapor deposition growth with appropriate impurity doping, and their current‐voltage (I‐V) and capacitance‐voltage (C‐V) characteristics are studied. I‐V curves show good rectifying characteristics with a value of 3.3 for the ideal factor n and a reverse leakage current less than 10 μA at −5 V. The junction area is approximately 0.8 mm2. The built‐in voltage is around 1.4 V by C‐V measurements.

3C‐SiC p‐n junction diodes

A single-crystal substrate of silicon carbide comprising a single-crystal substrate member of a material other than α-SiC, and a single-crystal layer of α-SiC formed over the substrate member with a ground layer provided between the substrate member and the single-crystal layer, the ground layer comprising a single-crystal layer of nitride of AlN, GaN or Al x Ga 1-x N (0<x<1) having a hexagonal crystal structure or a crystal layer of the same structure made of a mixture of SiC and at least one of the nitrides; and a method for fabricating the same.

Mitsuhiro Shigeta

Papers

Silicon carbide semiconductor device

Characterization of the free‐carrier concentrations in doped β‐SiC crystals by Raman scattering

Temperature dependence of electrical properties of non‐doped and nitrogen‐doped beta‐SiC single crystals grown by chemical vapor deposition

3C‐SiC p‐n junction diodes

Method of fabricating single-crystal substrates of silicon carbide