Effect of GaN cap thickness on carrier dynamics in InGaN quantum wells

We have studied optical properties of single In0.1Ga0.9N quantum wells with GaN barriers in close proximity to the wafer surface (<10 nm). We have found that at room temperature a balance of radiative, non-radiative recombination and complex surface states effects results in an optimum cap thickness of 3nm for achieving highest brightness emitters. At low temperature, we observe a behaviour that suggests that some surface states act as trapping centres for carriers rather than as a non-radiative recombination channel. Temperature dependence of the photoluminescence decay curves shows that carrier lifetimes in all the wafers increase at lower temperatures and reach similar maximum value. Main features of the evolution of lifetimes with temperature can be explained satisfactory by a combination of radiative, non-radiative recombination and above mentioned twofold surface effects. Detailed picture of the carrier dynamics is however complex and needs to include the modification of the electrostatic potential in the quantum wells positioned in the surface depletion regions.