The effects of crystallographic orientation and strain on the properties of excitonic emissionfrom wurtzite InGaN/GaN quantum wells

Abstract

We have examined in detail crystal orientation effects on the properties of excitonic emission fromwurtzite InxGa1−xN/GaN quantum wells (QWs) with piezoelectric polarization using exciton binding andtransition energy calculations based on a single-band effective-mass theory. Weshow numerical results for the bandgaps, effective heavy-hole masses, piezoelectricpolarizations and fields, exciton wavefunctions, exciton binding and transitionenergies and radiative lifetimes of excitonic emission as a function of the QWcrystallographic growth planes. Band-edge and effective-mass parameters for a continuumof GaN crystallographic orientations, on which InGaN/GaN QWs are grown, wereobtained from In-composition- and strain-dependent calculation for wurtzite InxGa1−xN, using the Hamiltonian in appropriate {hkil} representations. We have performed calculations for a continuum of technologically relevantQW growth planes oriented at various angles θ relative to the (0001) c-plane. The excitonic ground- and first-excited-state energies and wavefunctions were calculatedusing an effective potential method. A strong reduction of average in-plane heavy-holeeffective mass and normal to the plane piezoelectric polarization and field is observed asθ varies fromθ = 0° (i.e. thec-axisdirection) to θ = 49.5°, where the piezoelectric polarization and electric field reverse their orientationwith respect to the plane of the QW. The decrease of the electric field in theInGaN/GaN QW growth direction leads to an increased exciton transitionenergy and oscillator strength, which results in the increase of the excitonbinding energy and decrease of the excitonic radiative lifetime. For anglesθ>49.5° only small variationson the order of ∼10% in the exciton binding and transition energies and excitonic radiative lifetime are observed for narrowIn0.12Ga0.88N/GaN QWs that havewidths less than ∼ 3.5 nm. The average in-plane heavy-hole effective mass reaches its minimum forθ = 90°,i.e. m-plane growth. These results indicate that InGaN/GaN QW structuresgrown on non-(0001)-oriented planes in a wide variety of angles49.5°≤θ≤90° can be used for optimized operation of optoelectronic devices.