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Ultraviolet light emitting diodes and laser diodes based on quantum structures of Group-III nitrides

Final Activity Report Summary - EMITUVEGAN (Ultraviolet light emitting diodes and laser diodes based on quantum structures of Group-III nitrides)

The work within the EMITUVEGAN Project during its realisation between 1 September 2006, and 31 August 2008, was concentrated on the following problems:

1. Experiment and technology
a) Improvement of gain in group-III-nitride laser diodes structures grown by metalorganic vapor phase epitaxy and plasma assisted molecular beam epitaxy on bulk GaN substrates.
b) The use of misoriented GaN substrates for research and achieving superior electrical and optical performance of LEDs and LDs grown on misoriented GaN substrates. Achievement of hole carrier concentration above 1x1018 cm-3.
c) successful realisation of GaN/InGaN/AlGaN LEDs and LDs with the active structure consisting single quantum well (optimisation results of both simulation / modelling and growth / device technology).
d) Fabrication of efficient UV-violet-blue light emitting diodes (LEDs) and laser diodes (LDs).

During the realisation of the project our experimental activity was concentrated on fabrication of the efficient light emitting diodes and laser diodes operating in the UV-violet-blue spectral range (375-420 nm). LEDs were designed, fabricated and tested at IHPP. This step was treated as the intermediate one in achieving the main goal of the project, i.e. efficient LDs. One of the important issues was to optimise substrates for increasing the lifetime of laser diodes.

At the beginning of the project realisation, we used GaN bulk crystals grown at IHPP by means of high pressure synthesis. Following the requirements of employing larger GaN substrates, the hydride vapour phase epitaxy (HVPE) growth method was developed in IHPP. Preparation of these substrates (mechano-chemical polishing, etc.) for an epitaxial growth of device structures was carried out intensively and successfully during the period of last two years. Both, LEDs and LDs devices obtained on HVPE free standing GaN substrates were fabricated.

Concerning the progress in LEDs performance improvement, optical powers for the spectral range roughly between 420-390 nm at 20 mA are above 1 mW and above 0.7 mW for 375-390 mW. We achieved more than 4 mW and 2 mW at 100 mA at higher and lower wavelength, respectively. Optical power measurements were carried on with a fibre and without employing special procedures of light extraction.

Laser diodes ( CW and pulse) in the region 385 nm and 415 nm were produced with optical power of 220 mW and 2 W, respectively The latest achievements gave 340 mW of CW lasing at 400 nm.

2. Simulations / modelling of InGaN/AlGaN light emitting diodes and laser diodes
Several selected problems have been studied. The most important covered issues of gain in LDs and a performance of GaN/InGaN/AlGaN LEDs and LDs with the active structure consisting of single quantum well.

The IHPP Unipress is strongly collaborating with its spin-off TOPGAN (SME company) involved in the production of violet-UV laser diodes. It is clear that some results of the performed research will be developed in this spin-off SME.

Important results of the EMITUVEGAN project realisation consist of submission of several research projects: one national project of the Polish Ministry of Science and Higher Education and four EU projects. Results obtained within EMITUVEGAN project were presented at six international conferences. It also includes two invited talks.