Michaela Böberl

Temperature dependent photoresponse from colloidal PbS quantum dot sensitized inorganic/organic hybrid photodiodes

Inorganic/organic hybrid photodiodes, based on a solution-processed ternary blend containing PbS quantum dots (QDs), a fullerene derivative, and a conjugated polymer, have been reported to exhibit external quantum efficiencies in the infrared of up to 51% [T. Rauch et al., Nat. Photonics 3, 332 (2009)]. Temperature dependent experiments reveal the high sensitivity of the photoresponse on the energy level alignment between the QDs and the fullerene derivative, resulting in quenching of the photoresponse at low temperatures for 5.2 nm QDs in size. With smaller QDs the optimum operation temperature is found between room temperature and 72 °C, making these photodiodes promising for various applications.

Quantum dot nanocolumn photodetectors for light detection in the infrared

Colloidal quantum dots absorbing in the infrared are filled into nanoporous alumina membranes to form narrow columns with aspect ratios of 300:1. The columns define the charge carrier path vertical through the ordered pore structure of the membrane. Electrical transport and photocurrent of various quantum dot column photodetectors based on two different nanomaterials, namely, HgTe and PbS quantum dots, with different quantum dot sizes are investigated. Photocurrents up to long wavelengths of 3μm are demonstrated.

IV–VI resonant-cavity enhanced photodetectors for the mid-infrared

A resonant-cavity enhanced detector operating in the mid-infrared at a wavelength around 3.6 µm is demonstrated. The device is based on a narrow-gap lead–salt heterostructure epitaxially grown on a BaF2(111) substrate. Below 140 K, the photovoltage clearly shows a single narrow cavity resonance, with a Δλ/λ ratio of only 2% at 80 K.

Vertical-cavity surface-emitting lasers in the 8-/spl mu/m midinfrared spectral range with continuous-wave and pulsed emission

Continuous-wave (CW) as well as pulsed-laser emission from a midinfrared (/spl lambda/=7.92 /spl mu/m) IV-VI vertical-cavity surface-emitting laser at 1.8 K is presented. The high-finesse microcavity, containing PbSe as an active medium, was optically pumped with a carbon monoxide laser at a wavelength of 5.28 /spl mu/m (1894 cm/sup -1/) in either CW or Q-switched mode. The maximum achieved CW power was 4.8 mW and pulsed peak powers were up to 23 W. Linewidths are considerably narrower than 0.10 cm/sup -1/, corresponding to 0.6 nm.

Molecular Beam Epitaxial Growth and Photoluminescence Characterization of PbTe/CdTe Quantum Wells for Mid-Infrared Optical Devices

This paper describes molecular beam epitaxial growth of PbTe/CdTe quantum wells on (100)-oriented GaAs substrates and characterization of their photoluminescence spectra. Despite of the differences in crystal structure and thermal expansion coefficient between PbTe and CdTe, an intense mid-infrared emission was observed even at higher temperatures than 300K. The energy of the emission peak showed blue shift with decreasing well width and had a positive dependence on temperature in agreement with that of bulk PbTe, indicating that the emission resulted from electron-hole recombination in a type I quantum well. Multiple peaks, however, were found in the PL spectra, and analysis of the temperature dependence of PL peak energy revealed that the thermal mismatch between CdTe and PbTe promoted the peak separation. A PbTe/CdTe double quantum well showed a higher efficiency of the PL emission. These results indicate a promising application of this heterosystem to cleaved-edge cavity laser diodes operating at room temperature.