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MOCVD systems are GO!

 

November 2014

 

Tuesday, 18 November saw the official opening of the two newly installed Metal Organic Chemical Vapour Deposition (MOCVD) systems at the ACT Node by Senator Zed Seselja, Senator for the Australian Capital Territory.

 

The event was attended by about 150 people, including representatives from the Federal Government, Department of Education, US Air Force Office of Scientific Research, US National Institutes of Health and many more. It was fortunate that this event coincided with the ANFF Research Showcase as many of our interstate/international colleagues would otherwise been unlikely to have been able attend this opening. After welcoming all the guests Prof. Chennupati Jagadish, ACT Node Director, introduced ANU Pro Vice-Chancellor (Innovation), Prof. Michael Cardrew-Hall; ANFF Board Chairman, Prof. Chris Fell and ANFF CEO, Rosie Hicks for opening remarks.

 

This was followed by Senator Seselja officially opening the facility saying, “The Metal Chemical Vapour Deposition reactors will give Australia the capacity to keep in touch with the latest trends in advanced manufacturing.

 

“For the everyday Australian, like me, this will mean new areas where Australia can excel, new technologies and new jobs. The benefits are many and will all lead to positioning Australia for the future.

“Research infrastructure, like the reactors, are critical for university and public sector researchers, as well as the broader economy. The Australian Government recognises the importance of creating and maintaining such facilities and over the years has invested more than $113 million in the ANFF.

“The Australian National Fabrication Facility is an outstanding example of how capabilities developed under the National Collaborative Research Infrastructure Strategy can reach across large geographical, institutional and state boundaries, providing integration of research infrastructure at a national scale.”

 

MOCVD, or sometimes known as Metal Organic Vapour Phase Epitaxy (MOVPE), is commonly used for the growth of compound semiconductors. It is currently the dominant epitaxial growth process for III-V semiconductor materials and devices, and the technique of choice for the semiconductor industry. Commonly found devices grown by this technique include LEDs, laser diodes, photodetectors, high frequency and high power transistors, and multi-junction solar cells.

 

Both the new systems are the Closed Coupled Showerhead (CCS) model from Aixtron (see Fig. 1 below). In the CCS configuration, precursors and gases are introduced vertically into the process chamber through an array of very small holes in the reactor ceiling, just like a showerhead. The design of the showerhead, and its close proximity to the heated wafers, ensure the gases are distributed uniformly throughout the whole wafer carrier surface.

 

Aixtron MOCVD

Fig. 1 - The new Aixtron CCS MOCVD system for
growing As- and P-based materials.

Bragg reflector

Fig. 2 - A distributed Bragg reflector showing the uniformity of the layers across a 2-inch wafer.

Both systems are capable of growing 3 x 2-inch wafers in each run and equipped with the LayTech Epi-TT, an optical in-situ metrology tool that allows the user to monitor all essential properties of the growing layers, such as growth rate, film thickness, stoichiometry changes and morphology, and also the precise surface temperature. The benefits of the in-situ process monitoring tool include quick identification of process deviations, optimisation of the film quality, improvement of yield and the fast tracking of new processes.

 

One system is designed for N-based material systems and has been in operation since late April 2014 and the other is for As- and P-based materials, in operation since the end of September 2014. The N-based system is capable of reaching a (surface) temperature of up to 1200°C for the growth of materials such as GaN, InGaN and AlGaN. The As/P system has precursors for the growth of materials such as GaAs, AlGaAs, InP, InGaAs, InGaAsP, GaSb, GaAsSb. Both systems meet the material specifications such as background doping, doping concentration, mobility, thickness and composition uniformities. The thickness and composition uniformities are spectacular, with a value of ≤ 1% across a 2-inch wafer. An example of this is shown in Fig. 2 (above) where a red distributed Bragg reflector was grown using GaAs and AlAs multilayers.

 

GaN quantum well LED

Fig. 3 - Electroluminescence from a processed
InGaN-GaN quantum well LED.

GaN pyramidal array

Fig. 4 - Electron micrograph image of a GaN
pyramidal array grown in the new N-based MOCVD.

As further testament to the quality of material being grown, we designed and grew a blue quantum well LED structure. The wafer was then processed into devices at ANFF ACT Node and blue emission was achieved as shown in Fig. 3 above.

 

Detailed characterisation of the devices is now underway. Novel structures such as nano-pyramid arrays are now being explored for light trapping/extraction to improve the quantum efficiency of optoelectronic devices. An example of such a structure is shown in the SEM image of Fig. 4 above.

 

 

MOCVD details courtesy of Prof. Hoe Tan, Department of Electronic Materials Engineering, ANU