Piezomodulated Electronic Spectra Of Semiconductor Heterostructures: Gaas/Al x ga l_X as Quantum Well Structures

Abstract

Piezomodulated electronic spectra of semiconductorheterostructures: GaAs /AlxGai_xAs quantum well structuresY. R. Lee and A. K. RamdasDepartment of Physics, Purdue University, West Lafayette, Indiana 47907F. A. Chambers and J. M. MeeseAmoco Corporation, Amoco Research Center, Naperville, Illinois 60566andL. R. Ram MohanDepartment of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609AbstractWhen heterostructures of semiconductors are subjected to an alternating strain, thepiezomodulated optical properties, as in the bulk, display signatures characteristic ofelectronic transitions. We have applied the piezomodulation technique to the electronictransitions associated with GaAs /AlxGai_xAs quantum well structures. Our results obtainedat temperatures down to that of liquid helium with single -, double -, and multiple -quantumwells reveal electronic transitions in the wells, the barriers and the buffer layer withexceptional clarity. The effects of coupling in the double and multiple quantum wells areclearly identified. Relative advantages and limitations of the piezomodulation and the nowwell -established photomodulation techniques are discussed on the basis of experimentalresults on identical samples under comparable experimental conditions.IntroductionThe electronic levels associated with quantum wells in semiconductor heterostructures--typically produced by molecular beam epitaxy (MBE) or by metalorganic chemical vapordeposition (MOCVD) --are of special interest in the context of basic physics and deviceapplications. The physical consequences of the confinement of electronic states to struc-tures modulated on a sub -micron scale are interpreted in terms of the electronic bandstructure of the constituents in their bulk form and the matching of their electronic andelastic properties. The electronic levels of GaAs /A1xGa1_xAs heterostructures have beeninvestigated by a variety of spectroscopic techniques e.g. absorption' and photoconduc-tivity,2 photoluminescence and excitation spectroscopy,3 electromodulated or photo -modulated5 reflectivity, and resonance Raman scattering.6 In this report we demonstrate