S.I. Maximenko

Cathodoluminescence study of the properties of stacking faults in 4H-SiC homoepitaxial layers

In-grown stacking faults in n-type 4H-SiC epitaxial layers have been investigated by real-color cathodoluminescence imaging and spectroscopy carried out at room and liquid helium temperatures. Stacking faults with 8H stacking order were observed, as well as double layer and multilayer 3C-SiC structures and a defect with an excitonic band gap at 2.635 eV. It was found that 8H stacking faults and triangular surface defects can be generated from similar nucleation sources. Time-resolved measurements reveal that compared to defect-free regions, the carrier lifetimes are severely reduced by the presence of stacking faults corresponding to triangular surface defects and three-dimensional 3C-SiC inclusions.

Stacking fault nucleation sites in diffused 4H-SiC p‐i‐n diodes.

The nucleation and development of stacking faults formed during the forward high current stress operation of 4H-SiC silicon carbide p‐i‐n diodes were investigated using the electron beam induced current mode of scanning electron microscopy and chemical etching in molten KOH. Two initial sources of stacking fault development were found. In addition to preexisting basal plane dislocations, localized defects in the near surface region, attributed to clusters of impurities, were found to serve as nucleation centers for stacking fault development during forward biasing of the diffused p‐i‐n diodes. Differences were observed in the electrical activity of stacking faults in diodes with the p+ region created by diffusion versus epitaxial growth.

Electron-beam-induced current observed for dislocations in diffused 4H-SiC P–N diodes

The electron-beam-induced current (EBIC) method was employed to investigate the electrical activity of dislocations in silicon carbide Schottky and diffused p–n diodes. Dislocations in Schottky diodes appear as dark spots with the EBIC current signal at the dislocations reduced with respect to the background. However, in p–n diodes, the same dislocations exhibited characteristic bright halos, with the EBIC current higher than that of the background. These bright halos were attributed to a nonuniform impurity distribution around dislocations caused by the high-temperature (∼2000 °C) diffusion process.

Investigation of the electrical activity of partial dislocations in SiC p-i-n diodes

The electron-beam-induced current (EBIC) mode of scanning electron microscopy was employed to investigate the nucleation and development of stacking faults (SFs) during forward high current stress operation of 4H–SiC p-i-n diodes. The EBIC technique is shown to be a valuable tool for the visualization and analysis of mobile and immobile partial dislocations bounding the SFs and their recombination activity. Both Si and C core partial dislocations exhibit similar EBIC contrast. It is shown that threading edge dislocations can be one source of SF generation leading to the degradation of p-i-n diodes.

Effect of threading screw and edge dislocations on transport properties of 4H–SiC homoepitaxial layers

Local recombination properties of threading screw and edge dislocations in 4H–SiC epitaxial layers have been studied using electron beam induced current (EBIC). The minority carrier diffusion length in the vicinity of dislocations was found to vary with dislocation type. Screw dislocations had a more pronounced impact on diffusion length than the edge dislocations, evidencing stronger recombination activity. Temperature dependence of EBIC contrast of dislocations suggests that their recombination activity is controlled by deep energy levels in the vicinity of dislocation cores. This paper shows that the type of dislocation (screw or edge) can be identified from analysis of EBIC contrast.

Differences in emission spectra of Si- and C-core partial dislocations

The spectra for individual Si- and C-core partial dislocations were obtained using optical emission microscopy. Both electroluminescence and photoluminescence revealed similar spectra. The Si-core spectra peaked at 700nm, consistent with the reported spectra from collection of dislocations. For the C core, a dominant IR band starting at 850nm was revealed for injections around 0.1A∕cm2. For an injection at 1A∕cm2, this band saturated and a band at 700nm dominated. This C-core band at 700nm was broader, and its intensity peak was lower than the Si core. Results are discussed along with existing theoretical models of deep levels.

Observation of dislocations in diffused 4H–SiC p-i-n diodes by electron-beam induced current

The electron-beam induced current (EBIC) method was employed to investigate the electrical activity of dislocations in silicon-carbide-diffused p-n diodes. It was observed that EBIC contrast depends on the type of defect (superscrew, screw, and edge dislocation). This dependence was attributed to spatial inhomogeneities in the electrical properties of the material around the dislocations due to different impurity-dislocation interactions during high-temperature (∼1900°C) diffusion. Chemical etching of the sample was used to define the nature of the defects observed by EBIC imaging. It was found that electrical breakdown of the diodes occurs at the location of superscrew dislocations.

Open Core Dislocations and Surface Energy of SiC

More than fifty years ago Frank proposed that a dislocation with a Burgers vector larger than a critical value would have an open core. Since then, there has been controversy as to whether micropipes in SiC are examples of open core screw dislocations. In this work open core dislocations in 4H-SiC material are investigated by AFM. The results are interpreted on the basis of Frank’s theory and the surface energy of SiC is estimated from the critical value of Burgers vector. Finally, the extracted surface energy is compared with the results of other research.

Application of CL/EBIC-SEM Techniques for Characterization of Radiation Effects in Multijunction Solar Cells

We report the results of the characterization of irradiated InGaP2/GaAs/Ge multijunction (MJ) solar cells using the cathodoluminescence (CL) imaging/spectroscopy and electron beam induced current (EBIC) modes of scanning electron microscopy (SEM). These techniques were applied to verify the influence of irradiation damage on the optoelectronic properties of each subcell in the monolithic MJ structure and correlate them with the illuminated (AM0, 1 sun, 25°C) current-voltage (I-V) and quantum efficiency (QE) measurements. Minority carrier lifetime degradation data from CL measurements confirm that the GaAs subcell dominates the overall degradation of the 3J device. Also, a carrier removal mechanism in the GaAs subcell was revealed from the EBIC/CL measurements.

Characterization of high fluence irradiations on advanced triple junction solar cells

Reported is the characterization of irradiated InGaP2/GaAs/Ge multijunction (MJ) solar cells using the cathodoluminescence (CL) imaging/spectroscopy and electron beam induced current (EBIC) modes of scanning electron microscopy (SEM). These techniques were applied to verify the influence of radiation damage on the optoelectronic properties of each subcell in the monolithic triple junction structure and correlate them with the illuminated (AM0, 1 sun, 25°C) current-voltage (IV) and quantum efficiency (QE) characteristics.