Processing of gallium nitride blue light emitting diode chips
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Helsinki University of Technology |
Diplomityö
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Date
2007
Department
Major/Subject
Optoelektroniikka
Mcode
S-104
Degree programme
Language
en
Pages
vii + 55 s. + liitt. 8
Series
Abstract
In this thesis, processing of gallium nitride based blue light emitting diodes (LEDs) from as-grown wafers into LED chips was studied. The LED wafers had been grown using a metal organic chemical vapour deposition (MOCVD) system. The aim of the work was to introduce process variations in the fabrication procedure in order to optimize the light intensity and voltage drop of the fabricated LEDs. The processing steps performed include multiple steps of ultra violet (UV) lithography, electron beam (e-beam) evaporation, inductively coupled plasma reactive ion etching (ICP-RIE) and lift-off. The facilities of Micro and Nanosciences Laboratory at TKK were used for successfully carrying out the fabrication process. After the fabrication, some of the LED chips were subjected to electro-luminescence (EL) measurements to investigate the effects of the process variations on the light output and voltage drop of the LEDs. During the etching of LED mesas tetrachlorosilane (SiCl4) was introduced. This step caused a favorable change in the light output of the fabricated LEDs. Another set of LEDs was fabricated with a platinum (Pt) current spreading layer (CSL) instead of the normal Ni/Au CSL. This gave a better light homogeneity for the fabricated LEDs. Also the chamber pressure and the sample biasing power during etching were varied. Optimal values for the parameter range studied were found. It will be worthwhile to continue in the future by trying out different flows of SiCl4 to see whether the light intensity of LEDs can still be improved. As the PtCSL gave a better light homogeneity, fabricating LEDs each with a varying thickness of the Pt CSL will be a good direction to take.Description
Supervisor
Sopanen, MarkkuThesis advisor
Törmä, PekkaKeywords
light emitting diodes, gallium nitride, compound semiconductor, ternary compouds, photoluminescence, lithography, ICP-RIE, etching, e-beam evaporation, lift-off, electro-luminescence measurement