11 research outputs found
Comparison of dynamic properties of ground- and excited-state emission in p-doped InAs/GaAs quantum-dot lasers
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 104, 181101 (2014) and may be found at https://doi.org/10.1063/1.4875238.The dynamic properties of ground- and excited-state emission in InAs/GaAs quantum-dot lasers operating close to 1.31âÎŒm are studied systematically. Under low bias conditions, such devices emit on the ground state, and switch to emission from the excited state under large drive currents. Modification of one facet reflectivity by deposition of a dichroic mirror yields emission at one of the two quantum-dot states under all bias conditions and enables to properly compare the dynamic properties of lasing from the two different initial states. The larger differential gain of the excited state, which follows from its larger degeneracy, as well as its somewhat smaller nonlinear gain compression results in largely improved modulation capabilities. We demonstrate maximum small-signal bandwidths of 10.51âGHz and 16.25âGHz for the ground and excited state, respectively, and correspondingly, large-signal digital modulation capabilities of 15âGb/s and 22.5âGb/s. For the excited state, the maximum error-free bit rate is 25âGb/s.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
Gain dynamics of quantum dot devices for dual-state operation
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 104, 261108 (2014) and may be found at https://doi.org/10.1063/1.4885383.Ground state gain dynamics of In(Ga)As-quantum dot excited state lasers are investigated via single-color ultrafast pump-probe spectroscopy below and above lasing threshold. Two-color pump-probe experiments are used to localize lasing and non-lasing quantum dots within the inhomogeneously broadened ground state. Single-color results yield similar gain recovery rates of the ground state for lasing and non-lasing quantum dots decreasing from 6 ps to 2 ps with increasing injection current. We find that ground state gain dynamics are influenced solely by the injection current and unaffected by laser operation of the excited state. This independence is promising for dual-state operation schemes in quantum dot based optoelectronic devices.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
The role of abnormal grain growth on solid-state dewetting kinetics
International audienceContinuous thin films of Pt on A-plane 1 1 2 0 Ă Ă sapphire substrates were dewetted to characterize the morphological evolution and dew-etting kinetics at 800 °C using an oxygen partial pressure of 10 Ă20 atm. Hole growth was studied, focusing on partially dewetted samples. Four different low-index orientation relationships were found between the Pt and sapphire substrate by electron backscattered diffraction combined with transmission electron diffraction patterns. Abnormal grains adjacent to the holes with a small deviation from one of the low-index orientation relationships were observed. The difference in the heights of the abnormal grains adjacent to the holes (rim-height) is influenced by the initial position of the hole, and the existence of grains with a low-energy interface orientation relationship, and not only by diffusivity rates dictated by surface orientation as described in existing edge-retraction models. The existence of low-index orientation relationships is seen as the driving force for abnormal grain growth in the vicinity of the holes, and is a dominant factor in controlling the dewetting rate of thin metal films on oxide surfaces
On the relation between electrical and electro-optical properties of tunnelling injection quantum dot lasers
We present a comprehensive study of the temperature dependent electronic and optoelectronic properties of a tunnelling injection quantum dot laser. The optical power-voltage (P
optâV) characteristics are shown to be correlated with the current-voltage (IâV) and capacitance-voltage (CâV) dependencies at low and elevated temperatures. Cryogenic temperature measurements reveal a clear signature of resonant tunnelling manifested in periodic responses of the IâV and P
optâV characteristics, which diminish above 60Â K. The CâV characteristics reveal a hysteresis stemming from charging and de-charging of the quantum dots, as well as negative capacitance. The latter is accompanied by a clear peak that appears at the voltage corresponding to carrier clamping, since the clamping induces a transient-like effect on the carrier density. CâV measurements lead also to a determination of the dot density which is found to be similar to that obtained from atomic force microscopy. CâV measurements enable also to extract the average number of trapped electrons in each quantum dot which is 0.95. As the important parameters of the laser have signatures in the electrical and electro-optical characteristics, the combination serves as a powerful tool to study intricate details of the laser operation
The effect of light irradiation on electrons and holes trapping in nonvolotile memory capacitors employing sub 10 nm SiO2-HfO2 stacks and Au nanocrystals
The role of abnormal grain growth on solid-state dewetting kinetics
International audienceContinuous thin films of Pt on A-plane 1 1 2 0 Ă Ă sapphire substrates were dewetted to characterize the morphological evolution and dew-etting kinetics at 800 °C using an oxygen partial pressure of 10 Ă20 atm. Hole growth was studied, focusing on partially dewetted samples. Four different low-index orientation relationships were found between the Pt and sapphire substrate by electron backscattered diffraction combined with transmission electron diffraction patterns. Abnormal grains adjacent to the holes with a small deviation from one of the low-index orientation relationships were observed. The difference in the heights of the abnormal grains adjacent to the holes (rim-height) is influenced by the initial position of the hole, and the existence of grains with a low-energy interface orientation relationship, and not only by diffusivity rates dictated by surface orientation as described in existing edge-retraction models. The existence of low-index orientation relationships is seen as the driving force for abnormal grain growth in the vicinity of the holes, and is a dominant factor in controlling the dewetting rate of thin metal films on oxide surfaces