Structural instability of 4H–SiC polytype induced by n-type doping

Abstract

Spontaneous formation of stacking faults in heavily nitrogen-doped 4H-polytype silicon carbide crystals have been observed by transmission electron microscopy (TEM). Faults were present in as-grown boules and additional faults were generated by annealing in argon at 1150 °C. All faults had identical structure consisting of six layers stacked in a cubic sequence as determined by high-resolution TEM, and were interpreted as a result of two Shockley partial dislocations gliding on two neighboring basal planes of SiC. It is argued that the energy of faulted 4H silicon carbide is lower than the energy of perfect heavily doped (n>1×1019 cm−3) crystal at typical processing temperatures, thus providing a driving force for transformation.

Deformation-induced phase transformation in 4H–SiC nanopillars

“…Since the 3C polytype introduces a quantum well (QW) structure in the 4H structure [4,8,37], energy would be gained through electrons entering the QW-related states, which is energetically favourable for the 4H ! 3C phase transformation during high-temperature annealing (>1000°C) [23,38]. The 3C !…”

Photoluminescence study of oxidation-induced faults in 4H-SiC epilayers

“…Figure 4 shows the PL spectrum emitted from the triangle-shaped SFs. These SFs are considered to be double Shockley SFs (2SSFs) 18,19 because of their emission wavelength (500 nm.) 4 Maximenko and Sudarshan 20 also reported triangle-shaped 2SSFs that extend from nucleation sites near the epitaxial layer surface.…”

“…• off-orientation towards [11][12][13][14][15][16][17][18][19][20], and an epilayer thickness of 10 µm were used. A He-Cd laser (λ = 325 nm) was used as the excitation source for PL imaging measurements.…”

Cubic inclusions in 4H-SiC studied with ballistic electron-emission microscopy

“…However their ͑empty-state͒ conduction-band energy and electronic structure can be very different, resulting in band gaps ranging from ϳ2.36 eV for ''cubic'' 3C-SiC to ϳ3.23 eV for the common hexagonal 4H-SiC and ϳ3.33 eV for the rare 2H-SiC polytype. Recently, the long-term stability issue of SiC devices has received much attention after it was discovered that stacking fault ͑SF͒ formation 2 during room-temperature electrical stressing of 4H-and 6H-SiC pn diode structures [3][4][5] or during high-temperature processing of 4H-SiC materials with heavily n-type epilayers 6 or substrates 7,8 caused significant changes to optical and electrical behavior. It was found that basal plane SFs in 4H-SiC host resulted in planar ''cubic inclusions,'' i.e., thin ͑Ͻ1.5 nm͒ sheets with cubic 3C local stacking embedded in the 4H-SiC host ͑in the electrically stressed diodes, all the inclusions observed by TEM were found to be of the ''single-SF'' type 5,9 while those observed in the high-temperatureprocessed material were all ''double-SF'' inclusions 6,8,10 ͒.…”