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We used a wide miniband GaAs/AlAs superlattice (at room temperature) for detection and autocorrelation of picosecond THz radiation pulses (frequency 4.3 THz) from a free-electron laser. The detection was based on a THz-field induced change in conductivity of the superlattice, and the correlation on the nonlinearity of the conductivity change at strong THz-pulse-power. The nonlinear conductivity change was due to two effects, which we attribute to dynamical localization of miniband electrons and to ionization of deep impurity centers. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on a semiconductor superlattice oscillator for generation of millimeter waves (frequency 65 GHz). The main element of the oscillator is a doped short-period GaAs/AlAs superlattice with negative differential conductance. The oscillator is due to current oscillations caused by charge density domains. The oscillator delivered, at an efficiency of 0.2% for the conversion of electrical power to radiation power, a power of 100 μW in a bandwidth of the order of 200 kHz. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

By inserting stacked sheets of nominally 0.7 monolayer CdSe into a ZnSe matrix we create a region with strong resonant excitonic absorption. This leads to an enhancement of the refractive index on the low-energy side of the absorption peak. Efficient waveguiding can thus be achieved without increasing the average refractive index of the active layer with respect to the cladding. Processed high-resolution transmission electron microscopy images show that the CdSe insertions form Cd-rich two-dimensional (Cd, Zn)Se islands with lateral sizes of about 5 nm. The islands act as quantum dots with a three-dimensional confinement for excitons. Zero-phonon gain is observed in the spectral range of excitonic and biexcitonic waveguiding. At high excitation densities excitonic gain is suppressed due to the population of the quantum dots with biexcitons. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A p-i-n resonant tunnel diode is designed and investigated using photoluminescence (PL) spectroscopy. The device is based on an Al[sub 0.4]Ga[sub 0.6]As/GaAs graded-index waveguide heterostructure enhanced by aperiodic-superlattice injectors for simultaneous resonant injection of electrons and heavy holes. The bias-dependent study of photocurrent, electroluminescence (EL) and PL show strong resonance behavior in the optical intensity confirming the field-dependent resonant injection of the excited states in the emission layers. Pronounced voltage-current bistability due to injection efficiency leads to multiple-wavelength EL and lasing action. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

InAs self-organized quantum dots in In[sub 0.53]Ga[sub 0.47]As and In[sub 0.52]Al[sub 0.48]As matrices have been grown on InP substrates by molecular beam epitaxy. The dot size in InGaAs has been found to be 3–4 times larger, but the areal density about an order of magnitude smaller than that in InAlAs. Low-temperature photoluminescence (PL) of the InAs/InGaAs quantum dots is characterized by a narrow (35 meV) PL line as compared to that of InAs/InAlAs quantum dots (170 meV). Quantum dot formation increases the carrier localization energy as compared to quantum well structures with the same InAs thickness in a similar manner for both InAs/InGaAs and InAs/InAlAs structures. The effect of the barrier band gap on the optical transition energy is qualitatively the same for quantum well and quantum dot structures. The results demonstrate a possibility of controlling the quantum dot emission wavelength by varying the matrix composition. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Mie resonances due to scattering or absorption of light in InN-containing clusters of metallic In may have been erroneously interpreted as the infrared band gap absorption in tens of papers. Here we show by direct thermally detected optical absorption measurements that the true band gap of InN is markedly wider than the currently accepted 0.7 eV. Microcathodoluminescence studies complemented by the imaging of metallic In have shown that bright infrared emission at 0.7-0.8 eV arises in a close vicinity of In inclusions and is likely associated with surface states at the metal/InN interfaces.