Improving silicon light emitting devices using Kirchhoff´s law

An analytical relation between the internal- and the external luminescence quantum efficiency of textured silicon wafers is derived using a generalisation of Kirchhoff s law. We show that only a fraction of one third of internally generated photons can escape a textured 450 μm thick silicon wafer even under the idealising assumption of negligible free carrier absorption, the major fraction of photons being reabsorbed by band-band-transitions. Surprisingly high external luminescence quantum efficiencies up to 0.6% at room temperature of silicon light emitting diodes have been published recently. From our theoretical model we can conclude that further significant improvements of the external luminescence quantum efficiency of silicon devices can be achieved by optimising the thickness of the devices, the texturing and the passivation of the surfaces texturing.