Ilya Zwieback

SUBLIMATION GROWTH OF SIC SINGLE CRYSTALS

The technological potential of silicon carbide (SiC) single crystals for highpower, high-temperature, and high-frequency electronic devices has been recognized for several decades; however, such applications have been greatly hindered by problems related to bulk crystal growth. SiC bulk crystal growth technology has recently achieved drastic improvement and enabled the growth of large high-quality single crystals. This chapter overviews the recent achievements in SiC bulk crystal growth aimed at producing high-quality largediameter crystals, highlighting the improvement of the crystal diameter enlargement process and the reduction of crystallographic defects in SiC crystals.

Advanced PVT Growth of 2 & 3-Inch Diameter 6H SiC Crystals

Abstract. The Wide Bandgap Materials Group of II-VI Inc., develops, manufactures and markets n+ and semi-insulating (SI) 6H SiC crystals, including vanadium-compensated and V-free. The PVT growth process is tuned to produce high-quality semi-insulating 6H SiC boules with micropipe densities below 15 cm (for 2-inch wafers) and below 70 cm (for 3-inch wafers). Room temperature resistivity for 2-inch and 3-inch SI V-doped wafers is greater than 10 Ω·cm and 10 Ω·cm, respectively. A novel synthesis process is used for the production of high-purity polycrystalline SiC source, yielding a material in which most impurities are below their GDMS detection limits. An advanced PVT process (APVT) has been developed for the growth of V-free SI 6H SiC crystals. These APVT SiC crystals contain boron below 6.2·10cm, nitrogen below 4.0·10cm and demonstrate semi-insulating behavior with ρ between 10 and 10 Ω·cm. Photoluminescence and EPR of V-free 6H SiC has been studied and EPR data have been assigned to native point defects (C vacancy, Si antisite and CVAC-CSi pair).

Growth and Characterization of Large Diameter 6H and 4H SiC Single Crystals

Over the past year, II-VI has transitioned from 2” to 3” commercial SiC substrates. Large-diameter semi-insulating 6H-SiC and n-type 4H-SiC single crystals are grown using the Advanced PVT growth process. Expansion of boule diameter from 2 to 3 and up to 4.25 inches has been carried out using a specially designed growth technique. Stable semi-insulating properties in 6H-SiC are achieved by precise vanadium compensation. The technique of compensation is optimized to produce a controlled and spatially uniform distribution of vanadium and high and spatially uniform electrical resistivity reaching 10 10 – 1011 ·cm. N-type 3-inch 4H-SiC crystals are grown using doping with nitrogen, and 3-inch 4H-SiC substrates show uniform resistivity of about 0.018 ·cm. The best quality semiinsulating (SI) 3” 6H-SiC substrates demonstrate micropipe density of 3 cm-2, and n-type 3” 4H-SiC substrates - about 1 cm-2. X-ray rocking curve topography of the produced 3” SiC substrates is used for evaluation of their crystal quality.

Development of High Performance AlGaN/GaN High Electron Mobility Transistors for RF Applications

GaN /AlGaN transistors are being developed for a variety of RF electronic and high temperature elctronics applications that will replace GaAs and Silicon devices and circuits for commercial and military applications. AlGaN/ GaN based HEMT device structure shows significant potential to meet these needs. In this paper, we present a GaN/AlGaN based HEMT design with modeling results, that includes AlN buffer layer followed by AlGaN layers on lattice matched semi-insulating SiC substrates. These devices were grown using RF Plasma Assisted MBE Technique. This approach has demonstrated very uniform epitaxial layers. Key to high quality HEMT structures is the ability to grow high quality AlN Buffer layers. Details of the electrical and optical characteristics of the HEMT layers and devices are presented and a short overview of semi-insulating SiC crystal growth is given.

Characterization and Formation Mechanism of Six Pointed Star-Type Stacking Faults in 4H-SiC

Synchrotron white-beam x-ray topography (SWBXT) studies of defects in 100-mm-diameter 4H-SiC wafers grown using physical vapor transport are presented. SWBXT enables nondestructive examination of thick and large-diameter SiC wafers, and defects can be imaged directly. Analysis of the contrast from these defects enables determination of their configuration, which, in turn, provides insight into their possible formation mechanisms. Apart from the usual defects present in the wafers, including micropipes, threading edge dislocations, threading screw dislocations, and basal plane dislocations, a new stacking fault with a peculiar configuration attracts our interest. This fault has the shape of a six-pointed star, comprising faults with three different fault vectors of Shockley type. Transmission and grazing topography of the fault area are carried out, and detailed contrast analysis reveals that the outline of the star is confined by 30° Shockley partial dislocations. A micropipe, which became the source of dislocations on both the basal plane slip system and the prismatic slip system, is found to be associated with the formation of the star fault. The postulated mechanism involves the reaction of 60° dislocations of a/3 〈

Growth of Undoped (Vanadium-Free) Semi-Insulating 6H-SiC Single Crystals

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Propagation and Density Reduction of Threading Dislocations in SiC Crystals during Sublimation Growth

〉 Burgers vector on basal plane and pure screw dislocations of a/3 〈