Silicon-based electrically driven microcavity LED

Abstract

A silicon pn-diode was embedded into a microcavity composed of a buried metal silicide as bottom reflector and a Si=SiO 2 Bragg mirror as top reflector. Spectral narrowing and an increased intensity of the Si bandgap electroluminescence was observed.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 À6 [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  l MC =2n thickness (i integer, l MC 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.

Efficient light emitting diodes based on nanoscale silicon

“…Within this model we are able to explain the EL dependence on current and temperature [16], as well as an electrical bistability occurring at low temperature [17]. Finally, we have fabricated an electrically driven resonant-cavity LED based on silicon [18].…”

“…The CoSi 2 layer is formed by ion beam synthesis based on Co + implantation into n-doped (100) Si and subsequent annealing [18]. The top crystalline Si layer is overgrown using molecular beam epitaxy to a total thickness of 370 nm, corresponding to a λ-cavity at a wavelength of 1115 nm.…”

Efficient silicon based light emitters

“…4) consists of a buried CoSi 2 layer, which acts as the bottom mirror and the bottom electrical contact, the active layer containing the pn diode, and a top Bragg mirror consisting of 2.5 pairs of Si/SiO 2 . The CoSi 2 layer is formed by ion beam synthesis based on Co C implantation into n-doped (100) Si and subsequent annealing [22]. The top crystalline Si layer is overgrown using molecular beam epitaxy to a total thickness of 370 nm, corresponding to a l-cavity at a wavelength of 1115 nm.…”

“…In our B-implanted structures, the electroluminescence (EL) increases with temperature, resulting in a wall-plug efficiency of 0.1% at room temperature [21]. In addition, we have integrated these LEDs into a microcavity [22].…”

Silicon-on-insulator microcavity light emitting diodes with two Si/SiO2 Bragg reflectors

“…Here we use highly boron doped Si pn junction LEDs, which have been shown to show room-temperature EL at a wavelength of 1150 nm with a reasonably high power efficiency of 40.1% [8,9]. In continuation of our work using a buried CoSi 2 mirror [10], we present here the design and fabrication of a RCLED with two distributed Bragg reflectors (DBR).…”