Effect of surface cleaning on spectral response for InGaAs photocathodes

Area of Science:

• Materials Science
• Surface Chemistry
• Photocathode Technology

Background:

• High sensitivity in photocathodes requires atomically clean surfaces.
• Contamination on Indium Gallium Arsenide (InGaAs) photocathode surfaces impedes performance.
• Understanding surface composition is key to optimizing photocathode fabrication.

Purpose of the Study:

• To investigate various surface cleaning methods for InGaAs photocathodes.
• To identify the optimal treatment for removing surface oxides.
• To correlate surface oxide presence with photocathode sensitivity and electron emission.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) and Ar ion sputtering were used to analyze atomic composition.
• Various chemical and thermal treatments were applied to InGaAs surfaces.
• Photocurrent and spectral response curves were measured after Cs/O activation.

Main Results:

• The combination of a 1:1 hydrochloric acid/deionized water solution and thermal annealing at 525°C proved most effective.
• This method resulted in an arsenoxide-free InGaAs surface, though trace amounts of Ga2O3 and In2O3 remained.
• Surface oxides were found to negatively impact low-energy electron escape, leading to reduced photocurrent and spectral response.

Conclusions:

• The optimized surface cleaning protocol significantly reduces detrimental oxides on InGaAs photocathodes.
• Minimizing surface oxides is essential for achieving positive electron affinity and improving photocathode sensitivity.
• The proposed surface model explains the adverse effect of residual oxides on electron emission efficiency.