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InP membranes have been bonded oxide mediated onto a patterned and unpatterned Si
substrate. Indentation is shown to allow local testing on patterned areas. Both
responses on patterned and unpatterned are compared and placed in reference to
oxide free bonded membranes. Delamination of the membrane was observed to depend
on the presence of patterns in the Silicon substrate. It occurs when the
indenting load reached 55 mN for an oxide mediated bonded unpatterned structure
and 42 mN for an oxide mediated bonded patterned one. This is in both cases
below the value of 80 mN obtained for an oxide free bonded membrane
(unpatterned). Weibull analysis of these events yielded a modulus m of magnitude
6 to 10, indicating that delamination fracture is relatively predictable with a
weaker resistance obtained in patterned oxide mediated bonding. Delamination of
the membrane is the result of constraint of plastic flow by the InP/Si
interface. Membrane rotation is induced and increases with the indentation load,
until it is sufficient to initiate and propagate an interfacial crack.
Instrumented nanoindentation and STEM have been combined ex situ to study the adhesion of 450 nm thick InP membranes to Si substrates. Three distinct regimes are identified in the deformation of the InP/Si stacks during these experiments: the first is plastic flow of InP at low loads; the second is elastic debonding of the InP membrane, far from the indented zone at medium loads; lastly, the local amorphisation of the underlying Si substrate at high loads. The regime of intermediate loads is shown to be particularly useful in the evaluation of the surface bonding energy of InP to Si.
InP membranes have been bonded both oxide free and oxide mediated onto a Si substrate. The mechanical responses of the obtained thin (0.4 µm) membranes could be tested by nanoindentation and compared. Delamination of the membrane was observed to occur when the indenting load reached 55 mN for an oxide mediated bonded structure and 80 mN for an oxide free bonded one. Weibull analysis of these events yielded a modulus m of magnitude 6 to 10, indicating that delamination fracture is relatively predictable with a stronger interface obtained in oxide free approach. Delamination of the membrane is the result of constraint of plastic flow by the InP/Si interface. Membrane rotation is induced and increases with the indentation load, until it is sufficient to induce and propagate an interfacial crack.
New fabrication routes for hybrid photonic devices are explored. We report on silicon bonding to III-V semi-conducteurs e.g. Si/InP for emission/amplification function. The materials have been bonded to silicon since it can be nanostructured to obtain optical guides. The bonded surfaces are of the order of ∼ 1 cm2. Special attention has been paid to the surface preparation. The obtained structure has been characterized employing XRD while the mechanical response and interface strength have been investigated employing instrumented nanoindentation.
We demonstrate the feasibility of a new approach of Nano Selective Area Growth (Nano-SAG) to precisely localize InAs/InP QDs, by low-pressure Metalorganic Vapour Phase Epitaxy (MOVPE). This approach is based on a partial patterning with a dielectric mask containing nano-openings. The two main advantages of MOVPE are: the important diffusion length of the active species and the inhibition of growth on the dielectric mask. We demonstrate the synthesis of localized nanostructures with high structural properties and the precise control of their dimensions at the nanometer scale. This allows in principle the precise control of the tunability of the emission length.
Decisive advances in the fields of nanosciences and nanotechnologies are intimately related to the development of new instruments and of related writing schemes and methodologies. Therefore we have recently proposed exploitation of the nano-structuring potential of a highly Focused Ion Beam as a tool, to overcome intrinsic limitations of current nano-fabrication techniques and to allow innovative patterning schemes urgently needed in many nanoscience challenges. In this work, we will first detail a very high resolution FIB instrument we have developed specifically to meet these nano-fabrication requirements. Then we will introduce and illustrate some advanced FIB processing schemes. These patterning schemes are (i) Ultra thin membranes as an ideal template for FIB nanoprocessing. (ii) Local defect injection for magnetic thin film direct patterning. (iii) Functionalization of graphite substrates to prepare 2D-organized arrays of clusters. (iv) FIB engineering of the optical properties of microcavities.
The primary challenges in implementing a Si based quantum cascade laser are discussed. Intersubband absorption measurements were carried out on a series of modulation doped multiquantum well structures. The spectra were compared to the predictions of a 6 band k.p model, which confirmed the excellent accuracy of the model, and its ability to predict the bandstructures of more complicated cascade structures. A detailed structural analysis demonstrated excellent growth quality, with an interface roughness of < 0.4 nm. Electroluminescence measurements on cascade structures with doped contacts, processed as finger structures and waveguides of various sizes, enabled a quantitative analysis of the active region performance. The upper state lifetime τnr was ∼ 100 fs, leading to a total active region optical gain of ∼ 2 cm−1, a factor of ∼ 10 lower than the estimated total losses due to free carrier absorption. The total emitted power and the linewidth of the intersubband emission saturate above ∼ 6.5 kA/cm2, probably due to misalignment of the injector levels at high biases. The effect of leak currents and interspersed light hole states on the intersubband emission are considered.
One of the major challenges during recent years was to achieve the compatibility of III-V semiconductor epitaxy on silicon substrates to combine opto-electronics with high speed circuit technology. However, the growth of high quality epitaxial GaAs on Si is not straightforward due to the intrinsic differences in lattice parameters and thermal expansion coefficients of the two materials. Moreover, antiphase boundaries (APBs) appear that are disadvantageous for the fabrication of light emitting devices. Recently the successful fabrication of high quality germanium layers on exact (001) Si by chemical vapor deposition (CVD) was reported. Due to the germanium seed layer the lattice parameter is matched to the one of GaAs providing for excellent conditions for the subsequent GaAs growth. We have studied the material morphology of GaAs grown on Ge/Si PS using atomic layer epitaxy (ALE) at the interface between Ge and GaAs. We present results on the reduction of APBs and dislocation density on (001) Ge/Si PS when ALE is applied. The ALE allows the reduction of the residual dislocation density in the GaAs layers to 105 cm−2 (one order of magnitude as compared to the dislocation density of the Ge/Si PS). The optical properties are improved (ie. increased photoluminescence intensity). Using ALE, light emitting diodes based on strained InGaAs/GaAs quantum well as well as of In(Ga)As quantum dots on an exactly oriented (001) Ge/Si pseudo-substrate were fabricated and characterized.
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