Papers by Author: P. Pirouz

Abstract: pn diodes have recently been fabricated from 3C-SiC material heteroepitaxially grown atop on-axis 4H-SiC mesa substrate arrays [1,2]. Using an optical emission microscope (OEM), we have investigated these diodes under forward bias, particularly including defective 3C-SiC films with in-grown stacking faults (SFs) nucleated on 4H-SiC mesas with steps from screw dislocations. Bright linear features are observed along <110> directions in electroluminescence (EL) images. These features have been further investigated using electron channeling contrast imaging (ECCI) [3]. The general characteristics of the ECCI images—together with the bright to dark contrast reversal with variations of the excitation error—strongly suggest that the bright linear features are partial dislocations bounding triangular SFs in the 3C-SiC films. However, unlike partial dislocations in 4H-SiC diodes whose recombination-enhanced dislocation motion serves to expand SF regions, all the partial dislocations we observed during the electrical stressing were immobile across a wide range of current injection levels (1 to 1000 A/cm2).

Abstract: 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.

Abstract: We investigate the possibility of controlling formation of stacking faults (SFs) at the interface region by implanting the 4H-SiC substrate with low-energy antimony ions (75 keV Sb+) prior to conventional CVD growth of the homoepitaxial layers. This approach is based on the solidsolution hardening concept, according to which interaction of impurity atoms with dislocations makes the motion of the latter more difficult. Photoluminescence imaging spectroscopy is employed to investigate incorporation of Sb+ implants at the buried interface and also to assess its impact on structural degradation. Spectral results are analyzed considering both the onset of n-type doping and irradiation damage. The latter factor was estimated separately from supplementary measurements of high-energy (2.5 MeV H+) proton-irradiated 4H-SiC epilayers. We compare results of optically stimulated SF formation in virgin and Sb implanted regions and provide a comprehensive picture of the defect evolution, including microscopic details of the imminent nucleation sites.

Abstract: In this paper the electrical activity of stacking faults and that of their bounding partial dislocations in degraded PiN diodes has been investigated by the technique of electron beam induced current (EBIC). The recombination behavior of C- and Si-core dislocations is discussed. It is proposed that nonradiative recombination significantly exceeds radiative recombination on both the C- and Si-core partial dislocations. At the same time, predominantly radiative recombination takes place in the faulted planes that presumably act as quantum wells.

Abstract: The effects of hydrogen and proton irradiation on stacking fault formation in 4H-SiC are investigated by an optical pump-probe method of imaging spectroscopy. We report optically stimulated nucleation and expansion of stacking faults (SFs) in 0.6 keV 2H+ implanted n-/n+ and p+/n-/n+ structures. The activation enthalpy for recombination enhanced dislocation glide (REDG) in hydrogenated samples (~0.25 eV) is found to be similar to that in a virgin material. Our results indicate that SFs mainly nucleate at the internal n-/n+ interface, beyond reach of hydrogen, thus justifying minor SF passivation effect. No REDG could be initiated optically in 2.5 MeV proton irradiated samples due to radiation defects providing alternative recombination channels to bypass the REDG mechanism. The radiation damage was verified by DLTS, revealing several new levels below EC in the range 0.4-0.80 eV, and by PL, showing the onset of D-center related luminescence band and concurrent increase of the nonradiative recombination rate.