Excitonic Behavior in Pseudomorphic InGaAs/(Al)GaAs Quantum Wells Grown by Mbe

Abstract

Pseudomorphic InGaAs quantum well (QW) structures have been the subject of considerable interest for electronic and optoelectronic devices. In order to optimize pseudomorphic QW structures for advanced devices it is necessary to understand the properties of the interfaces with the barrier layers. To this end we have utilized photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy to investigate the optical properties of InGaAs strained single quantum wells (QWs) grown by molecular beam epitaxy with different barrier layers. Samples with 100A In.15Ga.85As layers bounded on top and bottom by either GaAs or Al.15Ga.85As were studied over the temperature range 2-300 K. All four possible barrier combinations were included. The GaAs/InGaAs/GaAs samples exhibited linewidths as small as 1.3 meV at 2 K, which are the narrowest yet observed for these structures grown by conventional techniques. Similar results were observed at 2 K for QWs with AlGaAs barriers below, but the linewidths of samples with AlGaAs on top were substantially broadened. Measurements of the excitation spectra of these samples showed a substantial free exciton component to the luminescence from samples without top AlGaAs barriers. Samples with top AlGaAs barriers, however, showed little free exciton contribution. Investigation of the temperature behavior of the luminescence suggest that the homogeneous broadening in all the samples is similar, but that the inhomogeneous contributions are different for the various structures. In addition, the temperature dependent measurements showed an additional bound exciton component of the samples with top barriers that was ionized at temperatures above 15 K. Samples with lower AlGaAs barriers showed an anomalous increase in linewidth with increasing temperature which is still under investigation.