Search

We report on a theoretical study of the relationship between interdiffusion and the conduction band optical absorption of In(Ga)As/GaAs quantum dots. Quantum dot geometries are progressively interdiffused based on Fick's model and the quantum dot strain, band structure and optical absorption cross-section are calculated numerically. Quantifying the effects of interdiffusion on quantum dot optical absorption is important for applications that utilize post-growth techniques such as selective area intermixing. [ABSTRACT FROM AUTHOR]

In this work, rapid thermal annealing was performed on InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700 °C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800 °C, in addition to the largely redshifted photoresponse peak of 7.4 μm (compared with the 6.1 μm of the as-grown QDIP), a high energy peak at 5.6 μm (220 meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overall device performance was not affected by low annealing temperature, however, for high annealing temperature, some degradation in device detectivity (but not responsivity) was observed. This is a consequence of increased dark current due to defect formation and increased ground state energy. [ABSTRACT FROM AUTHOR]

We investigate the structure of magnetron-sputtered (MS) amorphous silicon (a-Si) prepared under standard deposition conditions and compare this to pure ion-implanted (II) a-Si. The structure of both films is characterized in their as-prepared and thermally annealed states. Significant differences are observed in short- and medium-range order following thermal annealing. Whereas II a-Si undergoes structural relaxation toward a continuous random network, MS a-Si exhibits little change. Cross-sectional transmission electron microscopy reveals the presence of nanopores in the MS film consistent with reduced mass-density. Therefore, the short- and medium-range order of annealed, MS a-Si is tentatively attributed to these pores. [ABSTRACT FROM AUTHOR]

Guided-mode resonances have been exploited to filter the normal-incidence transmission of mid-infrared wavelengths through a photonic crystal slab. A two-dimensionally periodic structure has been integrated with a quantum dot infrared photodetector to narrow its mid-wavelength infrared photoresponse spectrum. Finite-difference time-domain simulations were employed to extract the filter transmittance, which is dominated by a peak near 6µm. The simulated resonance is linearly tunable with the air-hole radius but it is insensitive to small changes in the incidence angle. To realize this filter, a patterned Ge slab was fabricated on a CaF2 cladding layer, on the InGaAs/GaAs photodetector. Filters fabricated on a plain GaAs substrate were also characterized by Fourier-transform infrared spectroscopy. This transmittance was consistent with the corresponding simulation, however the resonance peak was degraded in comparison to the filtered photodetector and its associated simulations. [ABSTRACT FROM AUTHOR]

The effect of GaP strain compensation layers was investigated on ten-layer InGaAs/GaAs quantum dot infrared photodetectors (QDIPs) grown by metal-organic chemical-vapor deposition. Compared with the normal QDIP structure, the insertion of GaP has led to a narrowed spectral linewidth and slightly improved detector performance. A more significant influence of GaP was observed after the structure was annealed at various temperatures. While a similar amount of wavelength tuning was obtained, the GaP QDIPs exhibited much less degradation in device characteristics with increasing annealing temperature. [ABSTRACT FROM AUTHOR]