Technological building blocks

Wet thermal selective oxidation of AlGaAs :


Représentation schématique du micro-interféromètre intégrant un réseau d'amplitude et une photodiode. (Encadré : Photographie du dispositif opérationnel constitué d'une photodiode recouverte d'un réseau de période égale à 1 µm.)
 
Oxidation furnace of III-V Al-containing materials, with in situ optical monitoring system.
 
  

Since more than a decade, we have worked on building methodologies and tools enabling the high control of the selective thermal oxidation technology of AlGaAs alloys. This technique being essential in most of photonic devices in the III-V material system, in particular for VCSELs and integrated non-linear optical devices. We hence have realized a specific furnace solving the different constraints imposed by the AlOx technology (flow control and stability, temperature uniformity, etc.. ). The most original demonstration has been to set up in this furnace an optical in-situ monitoring system for a real-time control of the process. These unique developments have led in the past years, to the demonstration of highly accurate control of the oxide aperture sizes, on many different optical active devices, through several internal and external collaborations.
This equipment is currently under industrial transfert in collaboration with the SME AET Technologies.
On the basis of these technological resources, we have led research studies on the kinetic and the structural properties of oxidized structures, gaining a unique expertise on the process AlOx.

Related projects : 
ANR Jeunes Chercheur EELOT, ATIP CNRS Novalox
Related publications :

Surface preparation for MBE regrowth:


 
Validation of the surface preparation process: emission of a GaInAs QW grown at a variable distance (spacer) of a pre-grown GaAs layer (red) and of a substrate (black).
 
  

An ex-situ preparation has been developed at LAAS for GaAs processed surfaces which allow to get rid of their contamination, even if very severe. It consists in an oxidation/decontamination by means of an O2:SF6 micro-wave plasma. We have shown that this treatment is very efficient to eliminate carbon, but also silicon contamination when silicon-containing resists are used (after nano-imprinting or after an Al-rich alloy wet oxidation). For growth on processed surfaces where quantum nanostructures have to be grown close the growth interface (15-25nm), an in-situ low temperature deoxidation process is employed in order to prevent the surface from roughening. H-plasma or Ga-assisted deoxidation, performed at 450°C-500°C, is applied for this purpose. The H-plasma has been observed to be more robust than the Ga-assited process and allows the surface to be deoxidized whatever the nature and thickness of the oxide formed ex situ. On the contrary, in the case of the Ga-asssisted deoxidation, a clean native oxide has to be formed at the surface thanks to an ex situ wet treatment in a HCl solution otherwise a residual roughness is observed. Also, the H-deoxidation has been shown to be efficient without any subsequent baking, while for Ga deoxidation the surface needs to be systematically baked at 600°C to eliminate residual contaminants. With these two deoxidation treatments applied under appropriate conditions, we systematically obtain very flat surfaces after deoxidation (AFM roughness (RMS) = 0.3nm). Moreover SIMS has shown that the contamination level at the regrowth interface is kept very low. Quantum wells grown at 25nm exhibit room temperature emission.