Dear Shah,

that is a very broad topic and related long discussion. I advice you to read:

Article Handbook of Nitride Semiconductors and Devices: Electronic a...

or his paper:

Article Luminescence Properties of Defects in GaN

The paper will give you a very good overview of GaN related features in PL/CL and how you can extract information about defect densities, recombination rate etc.

Hope this is a good start for you!

Dear Shah fahad Yousafzai,

I suggest to build Gaussian fit peaks of the PL spectra. Then, we can compare each peak with that of previous experimental or computational/theoretical results to determine any information about defects, impurities, etc.

Best regards,

S. Muhammady

Dear Shah,

photoluminescence is no way to directly "calculate the band gap" of a material.

The luminescence signal of any material is composed of several different luminescence channels, roughly you can distinguish between defect related emissions (basically low energy in the band gap region; for wurtzite GaN approximately everything below 3eV) and near-band gap emissions (approximately around 3.3-3.5eV, dependent on strain and temperature).

You are not telling us at which temperature your experiment takes place (room temperature, low temperature), which laser you are using for excitation (above band gap laser? which?) at which excitation density you are working (power of laser beam divided by spot size), and so on.

You are further not discussing the questions you are asking to the GaN sample you are looking at! You say it is "quality assurance", this would basically mean you want to make sure that you look at "good material", which is something you'll have to learn by measuring a lot of samples and compare them using your setup and settings. It is definitely possible to use photoluminescence as a tool to compare a lot of samples after growth or processing quickly. If something is very different in the spectrum you likely have some changes in the related process. It is however no good idea to look at a single luminescence spectrum and deduce anything.

When discussing the "band gap" issue further, you should take into account that especially in GaN all near band gap emissions are normally of excitonic character, meaning: by the binding energy red shifted compared to the band gap. Bright features do not always correspond to better material, in contrast, it can mean you have more defects. But not all defects lead to luminescence, and so on.

If you want to learn more about the fundamental technique, I suggest you to study the excellent book by Pelant ansd Valenta:

Book Luminescence Spectroscopy of Semiconductors

which explains a lot of fundamental concepts in great detail. This is no quick reference manual but a book to study with great care. To do proper photoluminescence for scientific purpose is quite complicated - a fact which is often ignored because the experimental part is relatively easy to do.

More details about the luminescence of GaN you can find in the book, Torsten Schwarz did mention. At least there will be some guidance where to look further.

Please do not add to the plethora of really bad photoluminescence works out there in the scientific literature but take your time to learn about the technique first.

Good luck and have fun with your new setup,

Martin.

thanks to all and specially Martin. dear Martin i am using the 325 nm 35 mW He-Cd laser and GaN sample which is grown by MBE method and the experiment was done at room temperature. i characterize many samples grown on MBE technique and change the laser spot on various position of the each sample. i get a very smooth distribution in each case and the peak at 363nm. and one more thing there is any formulation for this technique like PL decay and emission rate etc...