Silicon-based electrically driven microcavity LED

Introduction: The realisation of Si-based, electrically driven light emitters is a key requirement for the implementation of low-cost Si-based optoelectronics [1]. Realising Si-based light sources in a process technology compatible with mainstream microelectronics technology is one of the big challenges of semiconductor technology. Because of its indirect bandgap Si has a low radiative recombination rate, leading to efficiencies of the bandgap electroluminescence (EL) in the range of 10 6 [2, 3]. Recently, different approaches have led to an increase of the power efficiency of the bandgap EL by more than three orders of magnitude up to values of 0.1–1% [4–6]. These approaches are based on pn-diodes, where either the non-radiative lifetime is increased by using high-purity floatzone Si, combined with surface texturing to improve the outcoupling efficiency [5], or where specific defects introduced by ion implantation enhance the radiative recombination rate through carrier confinement effects [4, 6]. However, the spectral width and temporal response of these devices still constrains their practical application. One possible route for a further enhancement of the efficiency of these devices is a photonic confinement of the emitting layer. III–V semiconductor based LEDs gained significantly in performance by incorporation into microcavities (MCs) [7]. Planar MCs enhance the brightness, efficiency and directionality of the emission from a high-index material and lead to more than an order of magnitude increase in the spectral power density [8]. An MC consists of a cavity with i lMC=2n thickness (i integer, lMC resonance wavelength of the MC, n refractive index of the cavity material) embedded between two highly reflecting mirrors. For III–V LEDs molecular epitaxy growth allows the deposition of Bragg mirrors, which act simultaneously as electrical contacts to the active layer. This is a technological problem for Si-based devices, where the Bragg mirrors have to be fabricated from insulating dielectric materials thus inhibiting to electrically drive the active layer. Previously, electrically driven MCs were realised, where the active layer and the Bragg mirror consisted of porous Si [9, 10]. These devices suffered from the low stability of porous Si under highvoltage current injection. Here we present a proof-of-principle of an electrically driven MC based on bulk Si as active layer.