How much the thickness whcih you evaporate?

It may be very littil to see by eye becaause it is transparent but this happened when the thickness is

In my case, using laser ablation technique, we evaporate the film from a pellet made of stoichiometric powder; the adavantage of this technique is that it keeps the stoichiometry of the pellets in the films too; in fact our fill were yellow and the band gap was that expected (from optical absorption technique, 2.6 eV if I remember well, apart the Urbach tail due to defects). Also, the substrate temperature was a critical factor determining on silicon a different orientation of the films. Probably in your case the film darkness (or brownish appearence) can be due to a high quantity of metallic cadmium and if the vacuum is not so high, also cadmium oxide forming during evaporation; I suggest to made evaporation for the same time but by varying the evaporation temperature, if possible or the substrate temperature in order to better fix the sulfur atom which is more volatile than Cd.I suggest also to perform XPS measurements in order to assess real the cadmium chemical state.

Preparation CdS thin films using thermal evaporation method will be non-stoichiometry because the difference in vapour pressure between Cd and S elements.Thus, this method is not suitable for CdS thin films preparation. However, using flash evaporation or co-evaporation for Cd and S to avoid this problem. About thin films uniformity, the substrate distance, temperature, rotation and chamber vacuum are the most effective parameters on thin films homogeneity.

the CdS is in powder form. the source to substrate distance is 13cm. and i want to grow the CdS film of 1000 to 5000 arm-strong in thickness. using thermal evaporation tech.

ok the parameters can affect on thin films properties substrate temperature, deposition rate and chamber vacuum. If u need to get uniform thin films i think using flash evaporation is suitable for CdS. however, the 100 nm thickness of CdS can get it by using other method like CBD, it's easier and fast as well produce uniform films.

no , i have already the thermal evaporation unit of Rs 600000. and i dont want to go for any technique... so i am trying to grow the CdS film using thermal evaporation only .

try extremely slow evaporation and vary ur base and working pressure and notice the differences and instead of judging the film by eyes if u cannt see the film take it for SEM that can give u a better idea about the film surface and thickness. one other option can be the change of substrate also

can i use the pallets or ingot of CdS cadmium sulfide for thermal evaporation ? i wants to take the film fo 1000 to 5000 arms strong. i had maintain the pressure 10-5 torr. source to substrate distance is 15 cm. and substrate temperature is room temp. but i already try for 50 to 150 degree centigrade.

Hi

Generally in thermal evaporation technique, the quality of the films depend on several processing parameters such as substrate temperature, deposition rate, film thickness, ultimate vacuum, source to substrate distance precursor materials, nature of substrate etc. The study of effect of each processing parameters on the physical properties of the layers is important factor for device fabrication.

The problem with thermal evaporation for depositing the inorganic materials like CdS, ZnS, In2S3 and SnS is due to the higher vapour pressure of sulfur.

In order to get the uniform films, it is better to go for lower deposition rates.

Chemical bath method is suitable technique for depositing uniform and thin CdS films as a buffer layer in solar cell.

In CBD method, the deposited layers are sensitive to the concentration of the starting material, pH of the bath and the bath temperature etc.

If you have taken as glass substrate, first clean it very cearfully with propenol and concentrated nitric acid. It should be kept for half an hour.Then wash it with distill water. Make it dry and then keep it in the oven at 150 degree centigrate for 15 minutes (Substrate cleaning is fundamental work for every thin film preparation with Thermal evaporation method). Then you can use this as substrate. Remember that pressure should be maintantained at the mimimum of 10 power to the 5 Torr. 15 minutes is sufficient for making good quality thin film of thickness 1000 - 4000 A for CdS if you maintain the substrate temperature of 150 degree centigrate under this pressure.-DR. G. C. Wary

Another question, wich evaporation boat should work better for CdS CdSe, CdTe evaporation deposition, molybdenum, Tantalum or Tungsten boat?