Molten-alkali etching has been widely used to reveal dislocations in 4H silicon carbide (4H-SiC), which has promoted the identification and statistics of dislocation density in 4H-SiC single crystals. However, the etching mechanism of 4H-SiC is limited misunderstood. In this letter, we reveal the anisotropic etching mechanism of the Si face and C face of 4H-SiC by combining molten-KOH etching, X-ray photoelectron spectroscopy (XPS) and first-principles investigations. The activation energies for the molten-KOH etching of the C face and Si face of 4H-SiC are calculated to be 25.09 and 35.75 kcal/mol, respectively. The molten-KOH etching rate of the C face is higher than the Si face. Combining XPS analysis and first-principles calculations, we find that the molten-KOH etching of 4H-SiC is proceeded by the cycling of the oxidation of 4H-SiC by the dissolved oxygen and the removal of oxides by molten KOH. The faster etching rate of the C face is caused by the fact that the oxides on the C face are unstable, and easier to be removed with molten alkali, rather than the C face being easier to be oxidized.

Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide (4H-SiC), which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers. In this work, we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations (TSDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) in 4H-SiC. In n-type 4H-SiC, the inclination angles of the etch pits of TSDs, TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°?35°, 8°?15° and 2°?4°, respectively. In semi-insulating 4H-SiC, the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°?34° and 21°?24°, respectively. The inclination angles of dislocation-related etch pits are independent of the etching duration, which facilitates the discrimination and statistic of dislocations in 4H-SiC. More significantly, the inclination angle of a threading mixed dislocations (TMDs) is found to consist of characteristic angles of both TEDs and TSDs. This enables to distinguish TMDs from TSDs in 4H-SiC.Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide (4H-SiC), which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers. In this work, we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations (TSDs), threading edge dislocations (TEDs) and basal plane dislocations (BPDs) in 4H-SiC. In n-type 4H-SiC, the inclination angles of the etch pits of TSDs, TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°?35°, 8°?15° and 2°?4°, respectively. In semi-insulating 4H-SiC, the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°?34° and 21°?24°, respectively. The inclination angles of dislocation-related etch pits are independent of the etching duration, which facilitates the discrimination and statistic of dislocations in 4H-SiC. More significantly, the inclination angle of a threading mixed dislocations (TMDs) is found to consist of characteristic angles of both TEDs and TSDs. This enables to distinguish TMDs from TSDs in 4H-SiC.

In this work, we propose to reveal the subsurface damage (SSD) of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching. Under UV illumination, SSD acts as a photoluminescence-black defect. The selective photo-chemical etching reveals SSD as the ridge-like defect. It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion. The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines, which are typical features of scratches. This means that the underlying scratches under mechanical stress give rise to the formation of SSD in 4H-SiC wafers. SSD is incorporated into 4H-SiC wafers during the lapping, rather than the chemical mechanical polishing (CMP).In this work, we propose to reveal the subsurface damage (SSD) of 4H-SiC wafers by photo-chemical etching and identify the nature of SSD by molten-alkali etching. Under UV illumination, SSD acts as a photoluminescence-black defect. The selective photo-chemical etching reveals SSD as the ridge-like defect. It is found that the ridge-like SSD is still crystalline 4H-SiC with lattice distortion. The molten-KOH etching of the 4H-SiC wafer with ridge-like SSD transforms the ridge-like SSD into groove lines, which are typical features of scratches. This means that the underlying scratches under mechanical stress give rise to the formation of SSD in 4H-SiC wafers. SSD is incorporated into 4H-SiC wafers during the lapping, rather than the chemical mechanical polishing (CMP).

Hyperdoping that introduces impurities with concentrations exceeding their equilibrium solubility has been attracting great interest since the tuning of semiconductor properties increasingly relies on extreme measures. In this review we focus on hyperdoped silicon (Si) by introducing methods used for the hyperdoping of Si such as ion implantation and laser doping, discussing the electrical and optical properties of hyperdoped bulk Si, Si nanocrystals, Si nanowires and Si films, and presenting the use of hyperdoped Si for devices like infrared photodetectors and solar cells. The perspectives of the development of hyperdoped Si are also provided.Hyperdoping that introduces impurities with concentrations exceeding their equilibrium solubility has been attracting great interest since the tuning of semiconductor properties increasingly relies on extreme measures. In this review we focus on hyperdoped silicon (Si) by introducing methods used for the hyperdoping of Si such as ion implantation and laser doping, discussing the electrical and optical properties of hyperdoped bulk Si, Si nanocrystals, Si nanowires and Si films, and presenting the use of hyperdoped Si for devices like infrared photodetectors and solar cells. The perspectives of the development of hyperdoped Si are also provided.