Room-temperature electroluminescence from erbium-doped porous silicon composites for infrared LED applications

The nanostructured matrix of porous silicon makes the material an ideal host for erbium because its very large surface area allows easy infiltration of the ions into the matrix and it readily oxidizes obtaining large concentrations of oxygen necessary for erbium emission. Erbium is infiltrated in the pores ( 10(-19) cm(-3)) by cathodic electrochemical migration of the ions followed by high temperature annealing (950-1100 degrees C). Electrochemical doping of porous silicon by erbium is simpler and of lower cost when compared to conventional techniques like ion implantation, epitaxial growth, and chemical vapor deposition used to fabricate erbium-doped c-Si structures. We demonstrate stable room-temperature electroluminescence at 1.54 mu m from erbium-doped porous silicon devices under both forward and reverse bias conditions. The devices exhibit an exponential electroluminescence dependence in both bias conditions as a function of the driving current and driving voltage. In reverse bias, the external quantum efficiency reaches 0.01 %. The devices show a large temperature dependence of the electroluminescence intensity and transport properties. The electroluminescence intensity decreases by a factor of 24 in reverse bias and 2.6 in forward bias when the temperature increases from 240 to 300 K. The devices also show an increase of more than one order of magnitude in the current through the device at a given voltage for the same temperature range. From the differences in temperature, electrical, and electroluminescence characteristics in forward and reverse biases, we believe that different excitation mechanisms are responsible for the electroluminescence.