Boundary effects on the optical properties of InGaN multiple quantum wells

We examine the issues of spontaneous and piezoelectric polarization discontinuity on the optical properties of 3.0-nm-thick indium gallium nitride (InGaN) multiple quantum wells (MQWs). A quench of band-edge emission from the cap GaN layer is observed when the photoexcitation source is changed from a 355- to a 248-nm laser. The interband transitions from the InGaN wells exhibit a linear dependence on the 1) spectral blue shift of ∼8.5×10^-18 meV · cm³ and 2) change of the internal field of ∼3×10^-14 meV · cm² with the injected carrier density up to N_inj∼10¹⁹ cm^-3 at 77 K. These observations are attributed to the redistribution of photogenerated carriers in the InGaN wells due to the polarization discontinuity at the QW interface and the surface band bending effect. By incorporating an additional boundary condition of surface Fermi-level pinning into the Poisson equation and the band-structure analysis, it is shown the emission from the InGaN-GaN MQWs is dominant by the recombination between the high-lying subbands and the screening of internal field effects.