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The first measurements of the linear and nonlinear anisotropic absorption of light propagating along the plane of a single quantum well are reported and discussed in terms of the structure of the valence band in ultrathin semiconductor layers. Nonlinear optical effects are compared to those of multiple layer structures and to recent theory. [ABSTRACT FROM AUTHOR]

Nonlinear refractive index changes in 299 Å multiple quantum well GaAs were obtained directly by measuring Fabry–Perot transmission peak shifts. These changes crosscheck those obtained by Kramers–Kronig transformations of the nonlinear absorption under identical pumping conditions. High intensities saturate the exciton, so that nonlinear refractive index changes are dominated by nonresonant contributions. Thermal refractive index changes were also measured directly. [ABSTRACT FROM AUTHOR]

The effectiveness of surface recombination in speeding up the relaxation of a GaAs étalon is reported. Various thickness (1.5, 0.5, 0.3, 0.13 μm) bulk GaAs windowless samples were fabricated and tested as optical logic gates. Times for complete recovery of transmission lie between 400 and 30 ps. The response shows a roughly linear increase in speed as the sample thickness decreases, consistent with surface recombination being the dominant relaxation mechanism. A very fast cycle time of 70 ps is demonstrated using a 0.3-μm-thick windowless GaAs étalon as an all-optical logic device. Proton-bombarded samples show slower recovery and poorer contrast, and they require more gating energy. [ABSTRACT FROM AUTHOR]

We report the first parallel operation of GaAs optical logic elements and bistable devices. Arrays up to 2×4 in size were operated using a picosecond pump and probe technique, while in the bistable mode we achieved uniform response in two spots. Crosstalk due to carrier diffusion became noticeable at separations of typically ∼20–30 μm in the bistable devices. Pulsed operation at 82 MHz allowed separations down to ∼10 μm limited only by diffraction. Efficient heat sinking in the pulsed array resulted in negligible heating even when continually operated for many minutes. All experiments were performed at room temperature. [ABSTRACT FROM AUTHOR]

We report the first measurements of perpendicular field electroabsorption (quantum confined Stark effect) in GaAs/AlGaAs quantum wells for light propagating parallel to the plane of the layers. This geometry is well suited for integrated optics. The absorption edge shifts to longer wavelengths with increasing field by as much as 40 meV, giving a modulation depth>10 dB. The strong dichroism present in this geometry is retained even at high fields, making polarization-sensitive electro-optical devices possible. We also demonstrate in the waveguide geometry optical bistability due to the self-electro-optic effect with 20:1 on/off ratio. [ABSTRACT FROM AUTHOR]

We have studied the magnetic field dependence of hot-electron spectra using hot-electron spectroscopy. It is shown that application of a magnetic field normal to the injection direction has a dramatic effect on the spectra whereas a magnetic field applied parallel to the injection direction has no effect. The magnetic field is shown to increase the effective transit region width of the spectrometer enabling us to deduce a scattering rate for hot electrons that is at least four times greater than would be expected considering phonon emission alone. [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]

Various pulsed logic functions (nor, xor, etc.) are performed in a high-finesse nonlinear Fabry–Perot étalon containing GaAs-AlGaAs multiple quantum wells at room temperature. Input pulses with energies less than 3 pJ incident on the device produced contrasts greater than 5 : 1 in the nor gate, and relaxation times of about 5 ns allowed us to operate the gates at 82 MHz. Thermal stability was demonstrated in the nor gate even though the device was poorly heat sunk. [ABSTRACT FROM AUTHOR]

Proton bombardment is shown to shorten the recovery time of the excitonic absorption in GaAs/GaAlAs multiple quantum well saturable absorbers. The response time can be reduced from 30 ns to 150 ps without affecting the absorption characteristics or the saturation energy. [ABSTRACT FROM AUTHOR]

Hyperfine control of the interface structure and composition between GaAs and AlAs films grown by molecular beam epitaxy has been achieved by deposition on vicinal (100) GaAs substrates. This control is demonstrated by producing (GaAs)m-(AlAs)n submonolayer (m and/or n<1) superlattices over a wide temperature range. Analysis of these submonolayer superlattices by transmission electron microscopy shows that the layer growth regime is dominant and that layer nucleation is initiated preferentially at the step edges on the (100) vicinal surface. Potential applications of submonolayer superlattices including the growth of superlattice layers perpendicular to the substrate surface are described. [ABSTRACT FROM AUTHOR]

Electroluminescence has been observed from a GaAlAs/GaAs heterojunction bipolar transistor. The absence of luminescence from the GaAlAs emitter confirms that compositional grading significantly enhances hole confinement. In addition, it is suggested that electroluminescence occurring from the radiative recombination of excess electrons in the base may cause significant cross talk between devices of an integrated circuit. [ABSTRACT FROM AUTHOR]

We report a new type of optoelectronic device, a self-electro-optic effect device (SEED), which uses the same GaAs/GaAlAs multiple quantum well material simultaneously as an optical detector and modulator. Using a series resistor and constant voltage bias supply the SEED shows optical bistabilty (OB) of the recently discovered type which relies on increasing absorption and requires no mirrors. OB is seen at room temperature from ∼850-860 nm, at powers as low as 670 nW or switching times as short as 400 ns (limited only by power restrictions) with ∼1-nJ optical switching energy in a 600-μm-diam device. Total energies per unit area (∼18 fJ/μm2) are substantially lower than any previously reported for OB. [ABSTRACT FROM AUTHOR]

We report the successful operation of the first p-type, modulation-doped field-effect transistor ( p-MODFET). The channel consists of a two-dimensional hole gas at a GaAs/(AlGa)As heterostructure interface. With a gate length of 2 μm and a source-drain distance of 7 μm we achieve transconductances of 28 mS/mm at 77 K and 44 mS/mm at 4.2 K. This work represents the first demonstration of a p-type transistor that is the complement of the conventional n-MODFET. [ABSTRACT FROM AUTHOR]

A correlation has been demonstrated between impurity trapping and the interface structure in GaAs quantum well (QW) superlattices and single quantum well structures grown by molecular beam epitaxy (MBE) on (100) GaAs. Using low-temperature cathodoluminescence, photoluminescence, and transmission electron miscroscopy, we have shown that interface roughness in QW superlattices is related to trapped impurities at interfaces. We have observed that impurities originate from either the substrate or from the GaAlAs MBE layers. A new getter smoothing effect associated with QW structures is shown to produce efficient impurity trapping and yield higher quality GaAs QW with atomically smooth interfaces. [ABSTRACT FROM AUTHOR]

We have investigated electric field heating of high mobility electrons in modulation-doped GaAs-AlGaAs heterostructures by simultaneous measurement of luminescence and mobility. We find that hot electrons have a Fermi-Dirac distribution function for fields up to 750 V/cm and that the high field mobility of electrons can be understood in terms of field-induced electron heating and the temperature dependence of low field mobility. [ABSTRACT FROM AUTHOR]

The temperature dependence of the mobility of two-dimensional hole systems at modulation-doped GaAs-(AlGa)As heterojunctions is determined. Its shape follows closely the equivalent curve for high-purity p-type bulk GaAs. Low-temperature mobilities beyond 4×104 cm2/Vs are found for areal hole densities of 5×1011 cm-2. The equivalent scattering times reach those of the best modulation-doped electron systems. In the temperature range where acoustic mode scattering prevails a T-3/4 dependence was observed. Studies under light illumination could not detect any persistent photoconductive effect in two-dimensional holes. [ABSTRACT FROM AUTHOR]

A new type of high-speed optical modulator is proposed and demonstrated. An electric field is applied perpendicular to GaAs/GaAlAs multiple quantum well layers using a ''p-i-n'' diode doping structure of 4-μm total thickness. The optical absorption edge, which is particularly abrupt because of exciton resonances, shifts to longer wavelengths with increasing field giving almost a factor of 2 reduction in transmission at 857 nm with an 8-V reverse bias. The shifts are ascribed to changes in carrier confinement energies in the wells. The observed switching time of 2.8 ns is attributed to RC time constant and instrumental limitations only, and fundamental limits may be much faster. [ABSTRACT FROM AUTHOR]