Narrow Results

Employing Monte-Carlo simulations we investigate parameters and optimize geometry of IR quantum-dot detectors with diffusion-limited capture into the dots surrounded by potential barriers. Our results show that structures with modulation doping of interdot matrix provide an effective separation of the localized and conducting electron states. In these structures, the capture time is mainly determined by the quantum dot concentration and the height of potential barriers around dots. The capture is not sensitive to the dot positions. It also weakly depends on the electric field up to the characteristic value, at which significant electron heating allows hot electrons to overcome the barriers. Optimizing the carrier capture and transit times, we show that quantum-dot structures have a lot of potentials for increasing the photoconductive gain and for the development of IR room-temperature detectors.

Employing Monte-Carlo simulations we investigate effects of an electric field on electron kinetics and transport in quantum-dot structures with potential barriers created around dots via intentional or unintentional doping. Results of our simulations demonstrate that the photoelectron capture is substantially enhanced in strong electric fields and this process has an exponential character. Detailed analysis shows that effects of the electric field on electron capture in the structures with barriers are not sensitive to the redistribution of electrons between valleys and these effects are not related to an increase of drift velocity. Most data find adequate explanation in the model of hot-electron transport in the potential relief of quantum dots. Electron kinetics controllable by potential barriers and an electric field may provide significant improvements in the photoconductive gain, detectivity, and responsivity of photodetectors.

Higher manganese silicide film (HMS, MnSi_x, x = 1.73–1.75) with addition of Si:B has been prepared on quartz substrate (SiO₂) by magnetron sputtering of MnSi₂ and Si:B (1 at.% B content) targets. It is found that the Si:B-added HMS film has a much lower electrical resistivity (R) but maintains its high Seebeck coefficient (S). As a result, the thermoelectric power factor, P_F = S²/R, is greatly enhanced. It is also found that the metal In together with Ag-paste can be used as ohmic contact materials for measuring the electrical properties of the HMS film. The thermoelectric power factor can reach 1255 μW/m-K² at 733 K for the Si:B-added HMS film, which is about two times higher than that of the pure HMS film.

In this paper, we report a large enhancement in the thermoelectric power factor in CrSi₂ film via Si:B (1 at.% B content) addition. The Si:B-enriched CrSi₂ films are prepared by co-sputtering CrSi₂ and heavily B-doped Si targets. Both X-ray diffraction patterns and Raman spectra confirm the formation of the crystalline phase CrSi₂. Raman spectra also indicate the crystallization of the added Si:B. With the addition of Si:B, the electrical resistivity $(R)$ decreases especially at low temperatures while the Seebeck coefficient $(S)$ increases above 533 K. As a result, the thermoelectric power factor, $\mathrm{\text{PF}}=S^2/R$, is greatly enhanced and can reach $716\times 10^{-6}\mathrm{\text{W/m}}\cdot {\mathrm{\text{K}}}^2$ at 583 K, which is much larger than that of the pure CrSi₂ film.

It is well known that aluminum (Al), boron (B) and copper (Cu) are acceptor impurities with shallow- and deep-energy levels in silicon (Si), respectively. Thus, Al and B impurities with shallow-energy levels in Si are essentially completely ionized at room temperature while Cu impurities with deep-energy levels in Si at higher temperature. In this paper, Al, B and Cu co-doped Si layer is used as a barrier layer while the higher manganese silicide layer (HMS) as a well layer. The Seebeck coefficient (S) of Al and Cu modulation doped film, HMS/Si:(Al + Cu), increases sharply above 583 K, reaches a peak value of 0.300 mV/K at 683 K, and then decreases with further increasing temperature. Concomitance with the great increase in Seebeck coefficient, however, the electrical resistivity (R) is still smaller than that of only Al modulation doped film, HMS/Si:Al. The Cu-induced Seebeck peak, S_max = 0.303 mV/K at 733 K, and reduction in electrical resistivity are also observed in (B + Al + Cu) modulation doped film, Si:(B + Al + Cu)/HMS/Si:(B + Al + Cu), where B is used to reduce the electrical resistivity further. As a result, the thermoelectric power factor (P_F = S²/R) is greatly enhanced and can reach 3.140 × 10^-3 W/m-K² at 733 K, which is larger than that of HMS bulk material.

The growth and characterization of multi-layer 1.3 μm InAs-GaAs quantum dot lasers is reported. It is demonstrated that the growth of the GaAs spacer layer, placed between the InAs quantum dot layers, must be carefully optimized to prevent defect formation. With optimized growth very low room temperature threshold current density (J_th) devices are obtained. Typical cw values are 32.5 and 17 A cm^-2 for as-grown and HR coated facet devices, respectively. Operation above 100°C is possible. Mechanisms contributing to the temperature sensitivity of J_th above room temperature are discussed. By combining the optimized growth with p-type modulation doping of the QDs both low J_th and high temperature stability of J_th are achieved at room temperature.

The introduction of an un-doped silicon layer (spacer) enhances significantly the thermoelectric power factor in modulation-doped Si(Al)-MnSi_1.7-Si(Al) sandwich structure. This un-doped silicon layer is inserted between the MnSi_1.7 (HMS) and Al-doped silicon layers. With a proper spacer thickness, the electrical resistivity decreases sharply and is weakly dependent on temperature from 300 K to 683 K. As a result, the thermoelectric power factor can reach 0.973 × 10^-3 W/m-K² at 683 K, which is about ten times larger than that of an ordinary MnSi_1.7 film without modulation doping.

Employing Monte-Carlo simulations we investigate parameters and optimize geometry of IR quantum-dot detectors with diffusion-limited capture into the dots surrounded by potential barriers. Our results show that structures with modulation doping of interdot matrix provide an effective separation of the localized and conducting electron states. In these structures, the capture time is mainly determined by the quantum dot concentration and the height of potential barriers around dots. The capture is not sensitive to the dot positions. It also weakly depends on the electric field up to the characteristic value, at which significant electron heating allows hot electrons to overcome the barriers. Optimizing the carrier capture and transit times, we show that quantum-dot structures have a lot of potentials for increasing the photoconductive gain and for the development of IR room-temperature detectors.

Employing Monte-Carlo simulations we investigate effects of an electric field on electron kinetics and transport in quantum-dot structures with potential barriers created around dots via intentional or unintentional doping. Results of our simulations demonstrate that the photoelectron capture is substantially enhanced in strong electric fields and this process has an exponential character. Detailed analysis shows that effects of the electric field on electron capture in the structures with barriers are not sensitive to the redistribution of electrons between valleys and these effects are not related to an increase of drift velocity. Most data find adequate explanation in the model of hot-electron transport in the potential relief of quantum dots. Electron kinetics controllable by potential barriers and an electric field may provide significant improvements in the photoconductive gain, detectivity, and responsivity of photodetectors.