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Presents the results of the application of photoresponse techniques to the study of the transport of electrons past an energy barrier. Investigations of electron transport through gallium arsenide/aluminum arsenide heterostructures; Model for the absorption of the light in the structures used; Change in the band gap as compared to the shift in the peak position in the voltage spectrum of the second sample.

We present the results of the application of photoresponse techniques to the study of the transport of electrons past an energy barrier. In this study, the barrier was provided by a thin layer of AlAs sandwiched between GaAs layers. The experiment measured the voltage resulting from the migration of optically excited electrons from one side of the barrier to the other. The voltage is measured as a function of the wavelength of the incident light. We also present the results of calculations which explain the nature of the observed spectra and how they change when the thickness of the top layer (the illuminated side) of GaAs is changed. [ABSTRACT FROM AUTHOR]

We report the first observation of inelastic tunneling in electronic transport perpendicular to a thin AlAs layer sandwiched between two GaAs layers. Temperature dependent I-V, first derivative (dI/dV), and second derivative (d2I/dV2) measurements were made on AlAs/GaAs double heterojunctions for a range of AlAs layer thicknesses and dopings. For p-type AlAs barriers current transport at 4.2 K was due to tunneling, and reproducible structure was seen in the second derivative spectrum. This structure was associated with the inelastic excitation of AlAs optical phonons and with a density-of-states effect caused by optical phonon-electron coupling in the GaAs. A different second derivative spectrum which also exhibited reproducible structure was obtained for n-type AlAs layers. Several possible explanations for these differences are proposed. [ABSTRACT FROM AUTHOR]

We report the first observations of resonant tunneling in electronic transport perpendicular to two AlAs layers separated by a GaAs quantum well in GaAs/AlAs heterostructures grown by metalorganic chemical vapor deposition. Resonant tunneling can be observed as inflections in the 1-V curves at room temperature. These inflections become more pronounced as the temperature is reduced, until negative differential resistance regions become visible for temperatures below 260 K. At low temperatures, the I-V curves not only reveal two large negative resistance regions corresponding to the first energy level in the GaAs quantum well but also a structure which shows evidence of resonant tunneling through the second and possibly the third energy states in the well. Second derivative (d²1/dV²) measurements confirm the existence of the resonances seen in the I-V curves. [ABSTRACT FROM AUTHOR]

Near-field scanning optical microscopy (NSOM) was used to study cleaved edges of GaAs solar cell devices. Using visible light for excitation, the NSOM acquired spatially resolved traces of the photocurrent response across the various layers in the device. For excitation energies well above the band gap, carrier recombination at the cleaved surface had a strong influence on the photocurrent signal. Decreasing the excitation energy, which increased the optical penetration depth, allowed the effects of surface recombination to be separated from collection by the pn junction. Using this approach, the NSOM measurements directly observed the effects of a buried minority carrier reflector/passivation layer. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]