Subcell Debye behavior analysis of order-disorder effects in triple-junction InGaP-based photovoltaic solar cells

Analysis was made of the Subcell Debye behavior of the order-disorder effects in triple-junction InGaP-based photovoltaic solar cells fabricated by a metal organic vapor phase epitaxy (MOVPE) system with careful adjustment of the growth conditions. The order-disorder configurations of the InGaP subcells were investigated after post-annealing treatment at various temperatures in a nitrogen atmosphere. Temperature-dependent photoluminescence (PL) measurements over a broad temperature range provided insight into the roles of the thermophysical phenomena connected with the ordering and disordering in the InGaP alloys. The thermally-related spectroscopic observations associated with the ordering effects on the photon-phonon interactions were confirmed by the McCumber-Sturge theory. The variations of both the full width at half-maximum (FWHM) and shift in the peak of PL with temperature were analyzed. According to the width-related PL observations the effective photon-phonon coupling coefficient and the Debye temperature were 0.53 meV and 424 K, respectively; according to shift-related PL observations of the as-grown sample they were 0.3247 eV and 430 K, respectively, for the width-related PL observation they were 0.29 meV and 421 K; and from the shift-related PL observations for the as-grown ordered samples they were 0.3142 eV and 425 K, respectively, implying that the spontaneously disordered InGaP heterostructures met the demand for improvement of photovoltaic devices. Both the effective photon-phonon coupling coefficient and the Debye temperatures were characterized as functions of the annealing temperature. The Debye temperatures obtained for the disordered and ordered top subcells were consistent with the universal Gruneisen-Bloch relation.