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Articles you may be interested inElectron emission properties of relaxation-induced traps in InAs/GaAs quantum dots and the effect of electronic band structure Combined optical and electrical studies of the effects of annealing on the intrinsic states and deep levels in a self-assembled InAs quantum-dot structure J. Appl. Phys. 100, 043703 (2006); 10.1063/1.2234817Conduction-band offset in a pseudomorphic GaAs/In 0.2 Ga 0.8 As quantum well determined by capacitance-voltage profiling and deep-level transient spectroscopy techniques

We demonstrate normal incidence infrared imaging with quantum dot infrared photodetectors using a raster-scan technique. The device heterostructure, containing multiple layers of InAs/GaAs self-organized quantum dots, were grown by molecular-beam epitaxy. Individual devices have been operated at temperatures as high as 150 K and, at 100 K, are characterized by λpeak=3.72 μm, Jdark=6×10−10 A/cm2 for a bias of 0.1 V, and D*=2.94×109 cm Hz1/2/W at a bias of 0.2 V. Raster-scan images of heated objects and infrared light sources were obtained with a small (13×13) interconnected array of detectors (to increase the photocurrent) at 80 K.

Ultrafast differential transmission spectroscopy with a resonant pump reveals evidence of electronic tunneling among the excited levels of vertically aligned In 0.4 Ga 0.6 As self-organized quantum dots. This evidence of tunneling is observed as a rapid spectral redistribution of electrons within a few hundred femtoseconds of optical excitation. Measurements show that this spectral spread is independent of carrier density and, therefore, indicate that carrier-carrier scattering is not the main mechanism for carrier redistribution. Instead, electronic tunneling is responsible for the interdot coupling; tunneling rate calculations agree reasonably with the experiment, supporting this conclusion.

We report experimental studies on lateral transport in self-organized quantum dots. We find that below 100 K, conduction occurs through interdot hopping and that experimental results are described quite well by a variable-range hopping model. In the hopping regime, the in-plane conductance varies as G = G 0 exp[(−T 0 /T ) 1/3 ], and T 0 is found to be 7100-9400 K. We have also observed a large negative magnetoresistance in this structure.

A microcavity surface-emitting coherent electroluminescent device operating at room temperature under pulsed current injection is described. The microcavity is formed by a single defect in the center of a 2-D photonic crystal consisting of a GaAsbased heterostructure. The gain region consists of two 70-Å compressively strained In 0 15 Ga 0 85 As quantum wells, which exhibit a spontaneous emission peak at 940 nm. The maximum measured output power from a single device is 14.4 W. The near-field image of the output resembles the calculated TE mode distribution in a single defect microcavity. The measured far-field pattern indicates the predicted directionality of a microcavity light source. The lightcurrent characteristics of the device exhibit a gradual turn-on, or a soft threshold, typical of single-or few-mode microcavity devices. Analysis of the characteristics with the carrier and photon rate equations yields a spontaneous emission factor 0 06.

computer simulations are carried out to study impact ionization due to a sinusoidal field present in high-power laser pulses. As an application we study the impact ionization coefficient, ␣, for electrons in silicon as a function of the field frequency, pulse width, and the rms value of the field. In all cases we stay below the frequency values where band-to-band absorption would create electron-hole pairs. As is the case for constant ͑dc͒ fields, log ␣ is found to be linear with field strength. For fields oscillating at frequencies much below the inverse of the carrier scattering rate, the impact ionization coefficient is found to have the same value as in the constant field case with the rms field replacing the dc value. At higher frequencies the impact ionization rate decreases. The dependence of ␣ on field frequency and pulse width is studied.