Bernard Aspar

Accurate control of the misorientation angles in direct wafer bonding

A direct wafer bonding process has been developed to accurately control both the bonding interface twist and tilt angles between a monocrystalline layer and a bare monocrystalline wafer. This process is based on the bonding of twin surfaces produced by splitting a single wafer, using for instance the Smart Cut® process. A targeted control of ±0.005° is obtained for the twist angle without any crystallographic measurement. Moreover, pure twist-bonded interfaces have been artificially made between two (001) bonded silicon surfaces.

Modal analysis and engineering on InP-based two-dimensional photonic-crystal microlasers on a Si wafer

We report results on hexagonal-shaped microlasers formed from two-dimensional photonic crystals (PCs) using InP-based materials transferred and bonded onto SiO/sub 2// Si wafers. Two types of hexagonal cavities are investigated : single defect (one hole missing) cavities, so-called H1 cavities (1 /spl mu/m in diameter) and two holes missing per side H2 cavities (2 /spl mu/m in diameter). Their optical properties are analyzed using photoluminescence experiments, and plane wave method simulations have been performed for comparison. High Q modes (/spl sim/600/700) have been measured and they have been shown to enable laser effect at room temperature, under pulsed optical pumping (15% duty cycle and 25-ns pulsewidth). The study of these efficient mode characteristics gives guidance for further improvement of the operation conditions of PC lasers, such as the reduction of the threshold pumping power.

Ultra thin silicon films directly bonded onto silicon wafers

Ultra thin film of silicon bonded on 4 in. (001) silicon wafers have been obtained by combining a direct hydrophobic silicon bonded technique with a layer transfer. The twist angle between the ultra thin Si film and the Si substrate was varied from 0 to 15°. X-ray reflectivity measured the thickness and the roughness of the ultra thin films. Complementary results concerning the interface structure were obtained with high resolution transmission electronic microscopy. It is shown that an ultra thin film (a few nm) can be reproductively prepared upon the full 4 in. wafers. Moreover, this process gives very small thickness fluctuations and a small surface roughness. The bonding interface has a low concentration of oxide precipitates and presents two arrays dislocations respectively, due to the twist (screw dislocations) and a residual tilt angle (mixed dislocations) of the crystals. Dissociation of the screw dislocations is also observed on the lowest twist angle sample.

Nanometric patterning with ultrathin twist bonded silicon wafers

Abstract Ultrathin films of silicon bonded on 4-inch (001) silicon wafers have been obtained by combining a direct hydrophobic silicon bonding technique with a layer transfer. The strain field produced by the dislocation network localized at the bonded interface is a good candidate to induce a long-range order growth of nanostructure. To be able to make this new kind of substrate, knowledge of the dislocation strain field extension is essential. Grazing incidence X-ray diffraction allows us to measure its spatial extension through the diffraction peak satellites due to different dislocation networks. The exponential decay of these peaks were measured and compared. We found that the decrease of the strain field extension is almost two times lower for the screw dislocation network than for the ‘mixed’ dislocations one. The film thickness control is then two times more critical for the screw dislocations.

InP based photonic crystal microlasers on silicon wafer

We report on 2D photonic crystal InP membrane micro-lasers transferred onto a silicon wafer. Two types of lasers are investigated: microcavities and defect-free structures, exploiting either conventional defect modes, or DFB-like modes. Room temperature low threshold laser operation has been performed for low sized devices.

Two-dimensional photonic crystal microlasers

The general objective of this presentation is to demonstrate the great potential of two dimensional (2D) Photonic Crystals (PC) based on InP-membranes bonded onto silica on silicon substrates, with a special emphasis on the development of various classes of 2D PC microlasers. The basic building block consists in an InP (and related material) membrane including a 2D PC formed by a lattice of holes : the membrane is bonded onto low index material,e.g. silica on silicon substrate, in the prospect of heterogeneous integration with silicon based microelectronics. Examples of devices will be presented, specifically micro-lasers based on 2D PC micro-cavities as well as on 2D in plane and surface emitting Bloch modes (2D Distributed-Feed-Back micro-laser).

Photonic crystals on InP membranes: Waveguiding and light emission

We fabricated membranes which generally include InAsP/InP quantum wells that emit light around 1.5 /spl mu/m. Depending on the structure studied, it can be used either as an efficient optical gain material (well suited for light emission), or as an active probe to insert light into PC structures (to study optical waveguides). Characterisation is performed by optical pumping the active layer and by analysing the photoluminescence (PL) signal emitted out of plane from the structures.