Features of the Band-Edge Injection Electroluminescence in 4H-SiC pn Structures

Band-edge (hνmax=3.17-3.18 eV at T=293 K) injection electroluminescence (IEL) characteristics of 4H-SiC pn structures as a function of doping, electron irradiation, temperature, and current are presented. The intensity of the UV band increases with temperature in the range 290-800 K (with an activation energy Ea of about 90 meV), which is observed for the first time in a wide range of current densities from 9 A/cm2 up to 2∙104 A/cm2. This effect is a fundamental feature of the band-edge IEL in SiC pn structures. The dependence of the intensity L on the current is of the power-law type, L~Jm; at high currents m≈1 at T=650-800 K. This result is probably the first direct observation of the diffusion current in SiC pn structures. The rise in the intensity of the band-edge IEL with increasing temperature and its decrease upon irradiation are probably due to the corresponding change in the lifetime of nonequilibrium carriers.

Temperature Dependence of the Band-Edge Injection Electroluminescence of 4H-SiC pn Structure

We present the injection electroluminescence spectra in the temperature range 290-800 K of 4H-SiC pn structure, which was formed by implantation of Al+ ions in low-doped n-type conductivity 4H-SiC epitaxial layer. The dominant emission band of injection electroluminescence (IEL) spectrum at room temperature was observed in the blue-green region; as the temperature is raised, the blue-green band is quenched, while UV band (near band-edge) IEL become dominant. The peak parameters of UV band at room temperature are: hmax  3.17 eV, full width at half maximum w  90 meV. The UV peak shifted in the long-wave direction with increasing temperature; the hmax (T) dependence was linear with the slope of -2.3∙10-4 eV/K. Both the IEL intensity of the UV peak at hmax and band width w increased upon heating. The w(T) dependence was linear with the slope of 2.9∙10-4 eV/K; intensity increased with the activation energy of 100-150 meV. The UV IEL band can be considered more probable to the band-band recombination and edge IEL increasing with rising temperature can be explained by the nonequilibrium charge carriers lifetime increasing.

Temperature Dependence of the Band-Edge Injection Electroluminescence of 3C-SiC pn Structure

We present the injection electroluminescence spectra in the temperature range 290-760 K of 3C-SiC pn structure, which was fabricated by sublimation epitaxy in vacuum on 6H-SiC substrate. The dominant emission band of injection electroluminescence (IEL) spectrum was observed in the green region; at room temperature the IEL intensity outside the region of hν ≈ 2.0- 2.5 eV was less than 3% of that of the green peak. The peak parameters at room temperature are: hνmax ≈ 2.32 eV, full width at half maximum w ≈ 100 meV. The green peak shifted in the longwave direction with increasing temperature; the hνmax (T) dependence was linear with the slope of - 1.3x10-4 eV/K. Both the IEL intensity of the green peak at hνmax and band width w increased upon heating. The w(T) dependence was linear with the slope of 4.6x10-4 eV/K; intensity increased with the activation energy of 70 meV. The green IEL band can be considered to be due to the free exciton annihilation or to the band-band recombination and edge IEL increasing with rising temperature can be explained by the nonequilibrium charge carriers lifetime increasing.

6H(n+)/3C(n)/6H(p+) - SiC Structures Grown by Sublimation Epitaxy

Investigation of the multilayer 6H(n+)/3C(n)/6H(p+)-SiC heterostructure grown by sublimation epitaxy show that the injection electroluminescence (IEL) in the green region (hνmax≈2.30-2.35eV) of spectrum is dominant. This band is close to the electroluminescence peak due to defects in 6H-SiC but also can be due to free exciton annihilation in a quantum well in 3C-SiC at the 6H/3C-SiC heterointerface. At high current the IEL peak at hνmax≈2.9 eV is found. This peak (and also two another peaks in blue part of spectra: hνmax≈2.6 eV and hνmax≈2.72 eV) can be attributed to recombination in 6H-SiC. The forward current-voltage characteristics for best structures are close to those for ideal 6H-SiC pn homostructure and characterized by abrupt breakdown. A lot of structures are characterized by barrier type excess current. Structure in the region of evident 3C-SiC inclusion is characterized by high forward and reverse excess currents.