Low temperature plasma assisted MBE growth for nitride optoelectronic devices
Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
During last decade in a field of the GaN based optoelectronic devices the main achievements were attained by ammonia based metalorganic vapor phase epitaxy (MOVPE) and until very recently molecular beam epitaxy (MBE) was not regarded as a technology of choice. It was believed, based on thermodynamic considerations, that only growth at temperatures close to those used in MOVPE (as high as 1050oC for GaN) will result in device quality structures. Unfortunately, GaN starts to decompose at 800oC at vacuum conditions and MBE growth at temperatures below 800oC for typical nitrogen rich conditions leads to the three-dimensional growth mode and low material quality.
We present recent progress in growth of nitride based semiconductor structures using Plasma Assisted MBE (PAMBE). This technology is ammonia free and nitrogen for growth is activated in RF plasma source from nitrogen molecules. We describe new approach for growth of nitrides by PAMBE at temperatures much below 800oC. The crucial for this technique is to use thin, dynamically stable, metal (In or Ga) layer on (0001) GaN surface during the growth - making PAMBE growth conditions similar to liquid phase epitaxy. This significantly reduces barriers for N adatom diffusion enabling high quality 2D step-flow growth mode at low temperatures. We discuss also in detail the role played by threading dislocations (TDs) on low temperature growth mechanism. The presence of TDs changes growth mechanism, leading to spiral growth and formation of pyramids. The spiral growth is one of the important factors which deteriorates efficiency of nitride optoelectronic devices, e.g. in InGaN it can lead to fluctuation of In composition and quantum well thickness, as well as formation of “V” defects. We show that growth on low TDs density bulk GaN substrates results in high quality of (In, Al, Ga)N layers with parallel atomic steps morphology and flat interfaces required for optoelectronic devices.
The new perspective for PAMBE has been opened recently by a demonstration of continuous wave (cw) blue–violet laser diodes [1, 2], high electron mobility transistor structures , resonant tunneling diodes  and intersubband devices . All these devices were grown on low TDs density high pressure grown GaN bulk substrates. We will discuss also potential of PAMBE for UV and green emitters as well as for intersubband devices operating at 1.5 mm telecommunication wavelengths.
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Presentation: Invited oral at Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth, by Czeslaw Skierbiszewski
See On-line Journal of Joint Fith International Conference on Solid State Crystals & Eighth Polish Conference on Crystal Growth
Submitted: 2007-01-23 15:54 Revised: 2009-06-07 00:44