Ultrafast carrier dynamics in an InAs/InGaAs quantum dots-in-a-well heterostructure.

Ultrafast differential transmission spectroscopy is used to explore temperature-dependent carrier dynamics in an InAs/InGaAs quantum dots-in-a-well heterostructure. Electron-hole pairs are optically injected into the three dimensional GaAs barriers, after which we monitor carrier relaxation into the two dimensional InGaAs quantum wells and the zero dimensional InAs quantum dots by tuning the probe photon energy. We find that carrier capture and relaxation are dominated by Auger carrier-carrier scattering at low temperatures, with thermal emission playing an increasing role with temperature.

n-Type GaAs/AlGaAs heterostructure detector with a 3.2 THz threshold frequency.

Terahertz detection using the free-carrier absorption requires a small internal work function of the order of a few millielectron volts. A threshold frequency of 3.2 THz (93 microm or approximately 13 meV work function) is demonstrated by using a 1 x 10(18) cm(-3) Si-doped GaAs emitter and an undoped Al(0.

Cavity Q, mode volume, and lasing threshold in small diameter AlGaAs microdisks with embedded quantum dots.

The quality factor (Q), mode volume (V(eff)), and room-temperature lasing threshold of microdisk cavities with embedded quantum dots (QDs) are investigated. Finite element method simulations of standing wave modes within the microdisk reveal that Veff can be as small as 2(lambda/n)(3) while maintaining radiation-limited Qs in excess of 10(5). Microdisks of diameter 2 microm are fabricated in an AlGaAs material containing a single layer of InAs QDs with peak emission at lambda = 1317 nm.

[Malignant melanoma--a PO-cell tumor? (author's transl)].

In the connective tissue, diffusely scattered phenoloxidase containing cells (PO-cells) can be found by histochemical methods. The same cells were demonstrated in a recurrent malignant melanoma of the skin and in its lymph node metastases. The theory is proposed that PO-cells are the stem cells of malignant melanoma in contrary to the common view that melanoma derives from the melanocytes of the stratum cyclindricum of the epidermis.