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Focuses on a study which examined the luminescence of optically injected carriers in the thin aluminum gallium arsenide layer of single heterostructures. Information on time-resolved luminescence technique; Methodology of the study; Results and discussion.

Presents a study which utilized radio frequency glow discharge hydrogenated amorphous silicon to fabricate detectors in sandwich geometry. Analysis of the shape of the pulses recorded with a sampling head; Examination of the carrier relaxation times and drift mobilities; Conclusions.

We observe the effect of negative absolute mobility for minority holes in n-modulation-doped GaAs quantum wells at low temperatures. Photoinjected minority holes drift towards the positive electrode, which is shown experimentally using a photoluminescence imaging technique. The effect is attributed to ‘‘carrier drag’’ by the high-mobility electron plasma via electron-hole scattering. From a quantitative analysis we are able to determine electron-hole momentum relaxation times. [ABSTRACT FROM AUTHOR]

We report direct measurements of drift velocities of photoexcited minority electrons in p-doped quantum well structures of GaAs/Al0.48Ga0.52As, using picosecond time-of-flight techniques. At low electric fields the electron mobility is strongly reduced by electron-hole scattering. At high fields (>8 kV/cm) negative differential mobility is observed, which we interpret as real-space and valley transfer of hot electrons into the X valley of Al0.48Ga0.52As. From the photoluminescence spectra the carrier temperatures at which the transfer effects occur are determined. [ABSTRACT FROM AUTHOR]

We report the measurements of changes in the reflectivity spectrum of GaAs-AlGaAs modulation-doped field-effect transistors near the band gaps of both materials when a gate voltage is applied to vary the charge density at the interface. The observed changes (up to 0.3% at the band edge of AlGaAs) are attributed to the high external fields (˜10[sup 5] V/cm) which modulate the already existing band bending, leading to changes in the band-edge absorption due to FranzKeldysh effects in the quantum-confined structures. The possibility of using the effect for optical readout of transistor action is discussed. [ABSTRACT FROM AUTHOR]

We have investigated the influence of surface plasmon polaritons (SPP’s) on the reflection spectra of Ag-Al2O2-Al and Al-AL2O2-Al junctions in the visible range. The SPP’s were excited via sinusoidal grating structures. The SPP photon coupling efficiency was optimized as a function of the grating modulation height and dielectric coatings. For optimum coupling conditions a narrowband photoresponse of up to 60 mV/W into a 100-Ω impedance at 632,8 nm was achieved. The narrowband (3–6 nm wide) photosignal is more than an order of magnitude higher than a broadband background signal. The color sensitivity is varied over the whole visible range with different dielectric coatings. [ABSTRACT FROM AUTHOR]

We observe far infrared broadband emission from the hot two-dimensional electron plasma in GaAs/AlGaAs single heterostructures grown by molecular beam epitaxy. The radiation is analyzed in two different frequency regimes (around 35 and 100 cm[sup -1). From the relative dependence of the intensities on the applied longitudinal electric field the hot-electron temperatures are determined. From the absolute emission intensities values of the free-carrier absorption coefficient (down to 10[sup -5] in ultrahigh mobility samples) are measured. [ABSTRACT FROM AUTHOR]

The tunneling and cooling times of photoexcited hot electrons in AlGaAs/GaAs double (one narrow and the other wide) quantum well structures have been measured using photoluminescence excitation correlation spectroscopy. The tunneling time was of the order of 200 ps for a 60 Å barrier. The tunneling is the indirect process assisted by the emission of optical phonons. The relaxation time of electrons as a function of the kinetic energy shows a threshold for cooling via the emission of optical phonons. [ABSTRACT FROM AUTHOR]

The luminescence of photoexcited carriers far above the band gap of Ga0.47In0.53As is studied with subpicosecond time resolution. In undamaged material the luminescence decays with characteristic times of 2–4 ps in the energy range between 1.9 and 1.4 eV, due to the rapid energy relaxation of electrons and holes far above the band edges. In radiation-damaged (He+ bombarded) material, luminescence decay times as short as 0.9 ps are observed. The luminescence spectra give evidence for extreme nonequilibrium distributions of the photoexcited carriers, caused by the ultrafast recombination, which—in radiation-damaged samples—is a faster process than energy relaxation. [ABSTRACT FROM AUTHOR]

Negative photoconductivity caused by ‘‘carrier drag’’ is experimentally verified for the first time. In p-modulation-doped GaAs/AlGaAs quantum wells carrier drag, leading to ‘‘negative absolute mobility’’ of injected minority electrons, results in a decrease of the total in-plane current in the quantum wells. The temperature dependence of the measured differential photoconductivity quantitatively agrees with the expected behavior due to the effect of electron-hole scattering. [ABSTRACT FROM AUTHOR]

In p-modulation-doped quantum wells of GaAs/AlGaAs extremely high negative photoconductivity is observed at low temperatures. The in-plane sheet resistance can be increased by a factor of more than 60 with illumination of less than 1 W/cm2. Spectral analysis shows that the effect is mainly due to hole trapping in the potential minima of AlGaAs and subsequent recombination of minority electrons. [ABSTRACT FROM AUTHOR]

We introduce a new GaAs/AlxGa1-xAs single heterostructure, which allows local optical injection of a one-component confined plasma. The heterojunction is placed in the undoped region of a p-i-n structure, which provides a high built-in electric field for the separation of injected electrons and holes, as well as for the two-dimensional confinement of electrons. A time-of-flight measurement of the majority-electron drift velocity at room temperature is demonstrated. [ABSTRACT FROM AUTHOR]

The in-plane photoconductivity of n-modulation-doped quantum well structures of GaAs/AlGaAs is experimentally studied as a function of the incident photon energy. Negative photoconductivity with surprising dependences on background illumination, temperature, and electric field is observed for photon energies slightly below the band gap of GaAs. The effect may be due to optical filling of ionized deep donors in AlGaAs as well as to an optical backgating effect. High positive photoconductivity is present above the band gaps—in contrast to theoretical expectations from previous optical transport experiments. [ABSTRACT FROM AUTHOR]