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MOCVD technology for production of indium nitride based nanophotonic devices

Final Report Summary - INDOT (MOCVD technology for production of indium nitride based nanophotonic devices)

Objectives of the development of new precursors which are suitable for the growth of high quality InN QD and In-rich InGaN layers were to ensure a reliable fabrication process and to guarantee the potential for scale up synthesis and purification procedures to production level.

The first series of compounds developed in the project were alternative N sources to access lower growth temperatures followed by compounds containing both In and N to enhance stoichiometry control and finally improved In compounds to fully optimise the deposition parameters accessible. Having determined the best source combinations for the matrix deposition a range of dopant materials was developed to enable device structures to be targeted. The progress in identification, synthesis, characterisation, purification and supply of samples followed the planned sub task schedule with all milestones and deliverables met in a timely fashion. The experimental processes employed have been refined and proven to yield ultra-high purity materials in a reliable and scaleable fashion. This new combination of precursors is now ready for launch as suitable for InN-based device fabrication to the highest standard.

The objective of the equipment development was to improve the metal-organic chemical vapour deposition (MOCVD) equipment for the low temperature growth of InN and InN-based compounds. The final equipment should allow the growth of InN-based materials under production conditions. Thus, the optimised equipment had to enable stable, reproducible and efficient MOCVD processes. In a first step the R&D MOCVD reactor at CNRS was up-graded accordingly. The main INDOT achievement related to the MOCVD equipment development is the availability MOCVD prototype equipment, for R&D as well as for industry, which can be used for the production of advanced InN or In-rich InGaN based devices. But the new technology is not limited to these materials and can also be used for the deposition of other compound materials requiring low deposition temperatures like chalcogenides (e.g. GeSbTe) which have a huge marked potential as basis for phase change memories.

The objective of gas purification and analysis equipment involved the development of a specific purifying package for InN, InGaN and quantum dots MOCVD growth. SAES has developed and delivered several gas purifying systems for bulk gases. In particular advanced purifiers for H2, Ar and NH3 were installed into the MOCVD system in Montpellier. The purifier package has been tested for the growth of the nitrides thin films and with off-line batch analysis method. The off-line batch analysis method has been developed to measure oxygen containing molecules in gas at single ppb detection limit. The procedure was used to validate the Monotorr nitrogen purifier efficiency at CNRS monitoring the purity upstream and downstream. The test demonstrated both the good efficiency of the purifier and the capability of the off-line batch analysis to monitor low ppb impurities concentration.

Using the new precursors and the optimised equipment CNRS has developed MOCVD processes for the deposition of InN QD and InGaN films at low temperatures. The high temperature encapsulation of InN QD with GaN failed but the alternative approach of using In-rich InGaN grown at moderate temperatures was successful. To achieve this, the reproducible growth process of high quality InGaN, with composition up to 40 % was studied. The use of TMGa was preferred for compositions above 15 %, while TEGa proved more suitable below this limit. The best crystalline quality was obtained by lowering the growth temperature to 500 degrees Celsius, compared to the standard growth temperature of 550 degrees Celsius used before. N-type doping of these alloys with silicon was successfully achieved. For p-type doping, Mg was used, and the incorporation of Mg into InN was calibrated. Annealing procedures for activating the magnesium dopant were established, and the effectiveness of p-type doping was demonstrated by photoluminescence. However parasitic n-type conduction prevented the determination of the p-type doping level in Hall effect experiments. The possibility of parasitic conduction channels at grain boundaries was evidenced, and a breakthrough was made in improving the lateral growth of InN, by using the CBrCl3 precursor developed by SAFC to modify the growth mechanism of InN in MOCVD. Extremely flat surfaces were obtained, which pave the way to strong improvements of the grain structure of InN (seen in all samples worldwide). This should enable CNRS to get rid of the parasitic conduction, but necessitates further studies to be combined with the use of low temperature buffer layers to overcome the lattice mismatch problem.