Effect of n+GaN cap polarization field on Cs-free GaN photocathode characteristics

We report on a Cs-free GaN photocathode structure in which band engineering at the photocathode surface caused by Si delta doping eliminates the need for use of cesium for photocathode activation. The structure is capped with a highly doped n(+)GaN layer. We have identified that n(+)GaN cap thickness plays an important role in limiting the effect of polarization induced charges at the GaN surface on the photocathode emission threshold. Physics based device simulations is used for further analysis of the experimental results. Our findings clearly illustrate the impact of polarization induced surface charges on the device properties including its emission threshold. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3476341]