Search

Self-assembled InP quantum dots, embedded in Ga[SUB0.52]In[SUB0.48]P and grown by solid source molecular-beam epitaxy, exhibit strong structural and optical anisotropy. Photoluminescence measurements reveal that the quantum dots are elongated in [1&1bar;0] crystal direction and the optical transitions of both the dots and the surrounding GaInP material dominate for light polarized along this direction, whereas embedded compressively strained Ga[SUBx]In[SUB1-x]P quantum wells behave isotropically. The comparison of the optical gain of a strained Ga[SUBx]In[SUB1-x]P quantum well laser and a threefold stacked quantum-dot laser in [110] and [1&1bar;0] directions (edge emission) emphasizes this difference. The gain of the quantum-well laser shows no directional dependence. The quantum-dot laser reveals significantly larger gain for light propagating perpendicular to the dot elongation. Thus, particular care has to be taken to align the cavities of InP/GaInP quantum-dot lasers in [110] direction. [ABSTRACT FROM AUTHOR]

We report on investigations concerning the modulation dynamics of InP/GaInP quantum-dot (QD) lasers grown by metalorganic vapor-phase epitaxy. Room-temperature operation of our lasers occurs at threshold current densities (j[sub thr]) around 1.8 kA/cm² and emission wavelengths (λ) between 696 and 710 nm with characteristic temperatures of about 50 K. At -33 °C a differential gain dg/dn ≈1.5 x 10[sup -16] ² is determined. Measurements on GaInP/AlGaInP quantum-well lasers with similar lambda; yield comparable values for dg/dn. The decrease of dg/dn in our QD lasers at elevated temperatures is attributed to a lack of carrier confinement, which foils the benefits expected from the zero-dimensionality of the active medium. A maximum intrinsic modulation bandwidth of 12.7 GHz at -33 °C is determined. [ABSTRACT FROM AUTHOR]

Comments on article 'Tunnel injection In[sub 0.4]Ga[sub 0.6As/GaAs quantum dot lasers with 15 GHz modulation bandwidth at room temperature,' which was published in a 2002 issue of 'Applied Physics Letters.'

We report on threefold-stacked vertically aligned InP/GaInP quantum dot injection lasers emitting in the visible part of the spectrum (690–705 nm) with a low threshold current density of j[sub th]=172 A/cm[sup 2] at 90 K showing a thermally activated increase towards higher temperatures. We derived an activation energy for this behavior, which is found to be just one half of the energetic distance between the dot transition energy and the wetting layer band gap. Thus, we identify thermal evaporation of carriers out of the dots and into the wetting layer states as the process responsible for the increase in the threshold current. The nonradiative carrier lifetime in the wetting layer (τ[sub nr][sup WL]) is estimated to be approximately 250–400 ps. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Red-light-emitting quantum dot injection lasers have been prepared by solid-source molecular beam epitaxy. The separate confinement heterostructure contains densely stacked layers of self-assembled InP quantum dots embedded in Ga[sub 0.51]In[sub 0.49]P waveguide and Si/Be-doped Al[sub 0.53]In[sub 0.47]P cladding layers. Edge-emitting laser diodes are processed, which show quantum dot lasing at 90 K. Thereby, the threshold current density is 172 A/cm2. The energy of the laser line is at 1.757 eV, which is very close to the peak energy of subthreshold electroluminescence. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]