Modulation spectroscopy study of a strained layer GaAs/GaAsP multiple quantum well structure

Using contactless electroreflectance (CER) and piezoreflectance at 300 K we have characterized a GaAs/GaAs1-xPx multiple quantum well (MQW) structure, "GaAs" (nominal) and GaAsP epilayers grown by chloride transport chemical vapor deposition on GaAs (001) substrates. From a detailed lineshape fit to the CER data from the epilayers we have determined the energies of the fun damental band gap and hence the phosphorous composition. The nominal "GaAs" epilayers were found to have phosphorous compositions of about 2.5-3.2%, a result of the phosphorous diffusion between growth chambers in the reactor . The GaAs1-xPx epilayer had x = 0.29. For the GaAs0.97P0.03/GaAs0.71P0.29 MQW comparison between the experimentally observed energies of a number of quantum transitions with a theoretical envelope function calculation, inclu ding the effects of strain in the barriers, made it possible to evaluate th e unstrained conduction band offset parameter Q(c) = 0.50 +/- 0.05. Our val ue for this parameter is discussed in relation to other works. Atomic force microscopy was employed to investigate the surface morphology of the 230 A ngstrom GaAsP top layer of the MQW in addition to a 2000 Angstrom GaAsP epi layer. From the absence of any cross-hatch pattern associated with misfit d islocations on the former we concluded that the GaAsP in the MQW is pseudom orphic. On the other hand the 2000 Angstrom epilayer exhibited signs of str ain relaxation.