Color Centers in Silicon Carbide

Dan Maser

Also known as “carborundum”

Occurs naturally (although very rare) as moissanite

While rare naturally on Earth, common form of stardust

First synthetically created in 1893

Initially used as an abrasive

Background

moissanite

Used as a detector in early radios

1907 - First LED Semiconductor Can be doped n-type with

N, P p-type with Al, B, Ga, Be B substitutes C, while Al

substitutes Si (produce different type semiconductors)

Role in Electronics

SiC monocrystal

250 crystalline forms! Three most common polytypes: (α) 6H-SiC

(hexagonal), (β) 3C-SiC (lone cubic), and 4H-SiC (hexagonal)

α-SiC is the most common Pure SiC is colorless – black color comes

from Fe impurities, rainbow shine is from a passivation layer of SiO2

Structure and Properties

Structure and Properties

(α) 6H-SiC

(β) 3C-SiC

4H-SiC

Electrical and Optical Characterization of

SiCG. Pensl and W. J. Choyke

Comparison of n-type CVD film grown on the C-face of 6H-SiC to p-type CVD film grown on Si-face of 6H-SiC

Both samples show ZPL’s P0, R0, S0 characteristic of N-doped 6H-SiC

Come from recombination radiation of exciton (hole-electron pair) in a four-particle neutral donor complex at three inequivalent donor sites

Luminescence measurements of 6H-SiC

In C-face film, prominent features below ZPL are phonon replicas of P center

Indicates strong N-doping In Si-face spectrum, three features denoted

4A, I, A0

4A – acceptor four-particle neutral complex A0 associated with Ti in 6H-SiC

Luminescence measurements of 6H-SiC

Comparison of photoluminescence spectra (410-434 nm)

In C-face, lines due to two phonon replicas of the P line

Combinations of the P line phonon replicas and a center of the zone TO phonon are seen

In Si-face, ZPL of Ti center, A0, B0, C0, and phonon replicas are marked

Luminescence measurements of 6H-SiC (higher wavelength)

Comparison of photoluminescence spectra (430 nm to 480 nm)

Comparative optical investigations of sintered and monocrystallineblack and green silicon carbide (SiC)

H. Werheit and K.A. Schwetz

Solid-state sintering: making a substance from powder by heating it to just below its melting point

Liquid-phase sintering: uses an additive that will melt before matrix phase

Capillary action pulls liquid into pores, grains rearrange into a better packing arrangement

Atoms preferentially go into solution and precipitate in areas of lower chemical potential – called “contact flattening”

Sintered SiC

S-SiC (solid-state sintered) and LPS-SiC (liquid-phase sintered) ordinarily only seen in black only

New LPS process can create green LPS-SiC Uses α-SiC powder S-SiC: doped with 0.2% B LPS-SiC: doped with 1.2% Al, 0.3% N, 0.1%

O Mixed SiC(Al,N,O) crystal shell, pure SiC

core Green is obtained from removal of free

carbon

Sintered SiC

Green SiC

Black SiC

G. Pensl and W.J. Choyke, “Optical and Electrical Characteristics of SiC”. Physica B, 185, 264-283 (1993).

H. Werheit and K. A. Schwetz, “Comparative optical investigations of sintered and monocrystalline black and green silicon carbide (SiC)”. Journal of Solid State Chemistry, 177, 580-585 (2004).

References