Efficient light emission at 1.54 μm from Er in Si excited by hot electron injection through thin suboxide layers

We studied the electroluminescence of Er:O-doped Si pn diodes and unipolar structures with thin SiO_1.6 suboxide barriers, which were deposited by molecular-beam epitaxy. These suboxide layers reveal a barrier height of about 320 meV in the conduction band and therefore raise the average kinetic energy of electrons injected through the barrier into the Er:O doped region. These electrons turn out to be advantageous for impact excitation processes with the erbium ion. Compared to conventional reverse biased pn diodes a ten-times higher στ product for impact excitation (1.2×10^-19 cm² s) can be achieved in pn diodes with a suboxide injector at 10 K. The saturation electroluminescence (EL) intensity is enlarged in reverse bias and suppressed in forward bias compared to a diode without a suboxide layer. These structures exhibit a reduction of the EL intensity by a factor of 3 for increasing temperature from 10 to 300 K and yield a two-times higher EL output at 1.54 μm and 300 K than an optimized reverse biased pn diode without a suboxide layer. At 300 K this results in an absolute output power of 250 nW and an external quantum efficiency of 1.3×10^-4 at 1.54 μm. For the unipolar structure with an integrated suboxide barrier the EL output also depends on the current flow direction: Injecting the electrons hot through the suboxide barrier into the Er:O doped region results in a six times higher EL intensity at 1.54 μm than for the opposite biasing condition. The EL is detectable up to 300 K with a reduction of the intensity by a factor of 8 between 10 and 300 K. Monte Carlo simulations were performed on unipolar structures with an incorporated barrier to provide insight int- o the carrier density and carrier energy distribution after injection through the barrier. © 2002 American Institute of Physics.