The effect of different dielectric films deposited by different techniques, on the electrical characteristics of InP/InGaAs heterojunction bipolar transistors was investigated. The electrical characteristics vary significantly depending on the type of dielectric film used for passivation. A significant increase in the forward biased base current, which resulted in lower transistor gain as well as an increased reverse leakage current in the base-collector junction, was observed when silicon nitride and silicon dioxide were deposited using plasma enhanced chemical vapour deposition. On the other hand, silicon monoxide and strontium fluoride films deposited using thermal evaporation, resulted in little degradation in the transistor characteristics. The low-temperature deposition was believed to have induced less surface states, resulting in the electrical characteristics being maintained long after deposition.
Minority electron mobilities in GaAs, In 0.53 Ga 0.47 As , and GaAs 0.50 Sb 0.50 calculated within an ensemble Monte Carlo model Monte Carlo is used to model the electric field and temperature dependence of the electron ionization coefficient, ␣, in In 0.53 Ga 0.47 As, using a two-component ionization rate to account for its observed anomalous dependence on the electric field. ␣ is predicted to decrease with temperature at fields above approximately 180 kV/cm, where impact ionization is limited by the high-energy electron population, and to increase with temperature at lower fields, where it is enhanced by the decreasing ionization threshold energy, in agreement with experimental observations.
We observe strong nonlinear absorption in the excitation profile of a single InGaAs quantum dot exciton driven by a rectangular spectrum optical pulse, in a region of detuning where the linear response is weak. Here the exciton is resonant with the temporal side-lobes of the pulse, which drive a damped Rabi oscillation. Good agreement is found between experiment and a two-level atom model. In the nonlinear regime the excitation profile exhibits features from both the rectangular spectrum and the two peaks present in the spectrum of the autocorrelation of the pulse.Coherent properties of quantum dot excitons are of considerable interest for implementation of optically based quantum information protocols in the solid state. Notable landmarks include the demonstration of Rabi oscillations, 1-9 two-pulse quantum interference, 4-6 observation of Ramsey fringes, 10 measurement of nanosecond T 2 times, 11 and demonstration of a controlled rotation gate ͑CROT͒. 12 Recently Chen et al. 13 have highlighted the possibilities of minimizing the impact of decoherence on a quantum operation using optimized pulse shapes. Furthermore, the properties of a gate operation, such as spectral selectivity are sensitive to the pulse shape. To tailor a pulse shape to achieve an experimental goal requires an understanding of how the optical response of a quantum dot is influenced by the pulse shape.This Brief Report presents Rabi oscillations driven by a detuned rectangular spectrum pulse. Our two-level atom is the ground-state neutral exciton of a single InGaAs selfassembled quantum dot embedded in an n-i-Schottky diode structure. Quantitative electrical readout of the exciton population is achieved using a photocurrent technique. 8 Three resonances in the photocurrent spectrum are observed. The central resonance corresponds to zero detuning and exhibits classic Rabi oscillation behavior. Surprisingly for excitation at higher pulse area ͑⌰Ͼ͒, two side resonances emerge close to the step in the rectangular spectrum in a region where there is negligible absorption at lower pulse area. Here the side-lobes of the pulse in the time domain are resonant with the exciton transition, and drive a damped Rabi oscillation. We demonstrate that the excitation profile exhibits features from both the pulse spectrum and the Fourier sine transform of the autocorrelation, an important consideration for the design of gate pulses.The sample has low density ͑33-50 m −2 ͒ InGaAs on GaAs quantum dots, embedded in an n-i-Schottky diode structure grown by molecular beam epitaxy. Details of a similar device are presented in Ref. 14.A mode-locked Ti:sapphire laser acts as a source of 100-fs pulses at a 76-MHz repetition rate . The beam is passed through a pulse-shaping apparatus consisting of two diffraction gratings, and two lenses arranged as a 4-F zerodispersion compensator, 15,16 with a variable slit in the mask plane. To first order, in the absence of the slit the pulse passes through the pulse shaper unaffected. Positioning the slit in the image plane of the b...
Electron multiplication for a series of In0.53Ga0.47As p-i-n diodes and hole multiplication for a n-i-p diode were measured at electric fields of 100–260 kV/cm over a temperature range of 20–300 K. The electron multiplication characteristics consistently showed positive temperature dependence at low electric fields (below ∼200 kV/cm) but exhibited negative temperature dependence at high fields. These observations explain the apparent discrepancies of the temperature dependence of the electron ionization coefficient in In0.53Ga0.47As in literature. In contrast, hole multiplication showed little change with temperature.
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