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Detailed Program
Paper Number : LD-I01
Time Frame : 10:45~11:10
Presentation Date : Thurseday, 27, November
Session Name : LED and Display Matrials
Session Chair 1# : In-hwan Lee
Session Chair 2# : Motoai Iwaya
New Approach to Fabricate Green, Red and IR Light Sources Based on Nitride Semiconductors by DERI Method
Y. Nanishi
Ritsumeikan University
More than ten years have already passed since narrow band gap energy of InN around 0.7eV was first reported in 2002. This finding opened up new application field of group III nitride optoelectronic semiconductors to green, red and near IR wavelength region. In contrast to such high potential, however, developments of actual optoelectronic devices based on InN and In-rich InGaN were hindered mainly due to relatively poor quality of these material systems.
Main difficulty for preparing high quality material comes from its low dissociation temperature and high equilibrium nitrogen vapor pressure during growth. In droplets which form on the growing surface give another essential problem for high quality InN growth.
We have developed a new RF-MBE growth method called DERI (Droplet Elimination by Radical Beam Irradiation) for growth of these materials. This growth method is consisted of the two series of growth steps with In-rich growth step (MRGP: Metal Rich Growth Process) and consecutive nitrogen radical beam irradiation step (DEP: Droplet Elimination Process). We found that this growth process can be considered as atomic layer level Liquid Phase Epitaxy from in-situ observation by RHEED and optical reflection. This method enabled us to obtain flat and high quality InN reproducibly without precise control of V/III ratio.
As DERI process is carried out under almost thermal equilibrium condition like conventional LPE, InGaN tends to make phase separation under highly metal rich growth condition. Using this phenomenon positively, we have successfully obtained InN/InGaN, InGaN/InGaN MQW structures, which emitted strong PL at IR and green wavelength range, respectively.
In order to realize InGaN LED covering full wave length between GaN to InN on one specific substrate, we should eliminate electrical or optical adverse effects of generated misfit dislocations due to 11% lattice mismatch. For this purpose, we propose a new way to suppress dislocation effect by using this phase separation phenomenon, growing wider band gap material surrounding dislocation cores.
We have also investigated plasma induced defects in InN by RF-MBE changing plasma power during growth. It was found that even from radical source, in which most of ions are supposed to be eliminated, residual ions are supplied to the growing surface and adversely affect quality of InN with increase in carrier concentration and decrease in mobility as we increase plasma power. Positron annihilation experiments revealed that this is due to point defects generated by plasma damage. It was found that DERI method, has advantage to reduce plasma-induced point defects by a few mono-layer of metal coverage on the surface during growth.
Acknowledgements : This work is supported by MEXT through grant-in-Aids for Scientific Research #26600090