Photoluminescence and interface abruptness in InGaAsP/InGaAsP quantum wells

Abstract

Quantum well (QW) structures consisting of InGaAsP wells and InGaAsP barriers grown by gas-source molecular beam epitaxy have been examined by low temperature photoluminescence (PL) in order to evaluate the contributions of compositional fluctuations in the quaternary alloy and of interface roughness to the PL linewidth. The well material was InGaAsP with a bandgap corresponding to a wavelength of 1.3 μm and the barrier material was InGaAsP of 1.15 μm. The theory for QW excitonic linewidths as a function of well thickness Lz due to fluctuations in alloy composition has been extended to include the case of the quaternary InGaAsP barrier. If the interfaces are atomically abrupt, the linewidth is dominated by compositional fluctuations in the well at large Lz and compositional fluctuations in the barrier at small Lz. The theory predicts a weak dependence of the linewidth on Lz since the composition of the well and barrier are similar. For rough heterointerfaces, the theory indicates the usual increase in linewidth with decreasing Lz. Photoluminescence measurements at 13K in arrays of single InGaAsP/InGaAsP QWs with Lz from 1.0 to 6.0 nm show only a weak variation of the full width at half maximum (FWHM) with Lz, in agreement with the theory for smooth interfaces. Furthermore, the lowest measured FWHM of 8.9 meV was found for a narrow well of Lz=1.8 nm, indicating the InGaAsP/InGaAsP interfaces are smooth and that the PL linewidth is dominated by compositional fluctuations.