Thermal generation rate in quantum dots ͑QD͒ can be significantly smaller than in quantum wells, rendering a much improved signal to noise ratio. QDs infrared photodetectors were implemented, composed of ten layers of self-assembled InAs dots grown on GaAs substrate. Low temperature spectral response shows two peaks at low bias, and three at a high one, polarized differently. The electronic level structure is determined, based on polarization, bias, and temperature dependence of the transitions. Although absorbance was not observed, a photoconductive signal was recorded. This may be attributed to a large photoconductive gain due to a relatively long lifetime, which indicates, in turn, a reduced generation rate.
A quantum cascade detector in the GaN/AlGaN/AlN material system was implemented. The design takes advantage of the large internal field existing in the nitrides in order to generate the essential saw tooth energy level structure. The device operates in the near IR spectral range with a room temperature responsivity at λ=1.7μm of 10mA∕W (1000V∕W) at zero bias. The spectroscopic measurements are in good agreement with simulations.
The recombination mechanisms in HgCdTe are analyzed. Detailed expressions for the radiative lifetime are presented, taking into account recent measurements of the absorption coefficient. In p-type material, carrier freezeout is shown to increase the lifetime exponentially for the radiative and the Auger processes at low temperatures. The effect of background flux is introduced, taking into account its variation with temperature due to the change in energy gap. Lifetime measurements on p-type samples are in good agreement with combined Auger 7 and radiative mechanisms, where the Auger process is more effective for low x values. Highly compensated materials are dominated by the Shockley-Read recombination. For an samples, the intrinsic region is controlled entirely by the Auger process.
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