Electro Optical Characterisation of Short Wavelength Semiconductor ...

planar shallow ridge deep ridge
2µm LED defect defect
6µm lasing LED LED
10µm LED lasing yellow light
Table 4.6: Unmirrored GaN devices (g0975) measured in this thesis
GaN Devices
Another point to mention is about 10µm deep ridge. Here was a yellow light (instead
of blue) to observe. The spectrum of this light depicted in Fig. 4.15 also proves a weak
yellowish emission. Yellow output light and generally red shift in spectrum is due to
emission of the impurities in the crystalline. Referring to Fig. 4.14 these devices are
coming from the part of the wafer near the margin. Therefore a high defect density is very
good possible. So this type of problem comes from growth and not from technology steps.
Cts/s
600
400
200
0
g0975/deep ridge/10um
spectrum
360 380 400 420 440
Wavelength [nm]
Figure 4.15: Spectrum of the 10µm deep ridge devices. A noticeable red shift is to
observe.
The only devices happened to lase were the 6µm planar structure and the 10µm shallow
ridge. It is to remark that in both cases there were only one device being able to lase. This
could be due to the manual processing steps which cannot guarantee the quality equality
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