Polarization charge screening and indium surface segregation in (In,Ga)N/GaN single and multiple quantum wells

Energies and oscillator strengths of the optical transitions in (In,Ga)N/Ga N quantum-well structures with thin cap layers are investigated theoretical ly. Based on a self-consistent solution of the Schrodinger-Poisson equation s, the internal fields generated by spontaneous surface charges and piezoel ectric interface charges are systematically discussed for different sample configurations under consideration of indium surface segregation We vary ba ckground doping density, thickness of the cap layer, number of quantum well s, indium content, and polarity of the structure. Indium surface segregatio n is shown to result in a blueshift of the transition energy and in a decre ased optical matrix element at the same time. Background doping influences the band-edge alignment not only via screening of the polarization charge a t the material interfaces by quantum-confined carriers, but also via ionize d dopants in depletion layers. This becomes particularly important in case of Ga-face-grown material with n-type doping. We find that the position of the quantum well within the sample severely affects transition energy and o ptical matrix element.