(CLEO). Conference on Lasers and Electro-Optics, 2005., 2005
We present a dual semiconductor laser system at telecom wavelengths generating pulses below 300fs... more We present a dual semiconductor laser system at telecom wavelengths generating pulses below 300fs. The low-jitter temporal delay of up to 2ns is achieved electrically by a phase shifter enabling pump-probe measurements within short time.
Conference on Lasers and Electro-Optics 2010, 2010
We report near-temperature-insensitive, highly linear oxide-confined directly modulated 850 nm-ra... more We report near-temperature-insensitive, highly linear oxide-confined directly modulated 850 nm-range VCSEL chips and fiber-coupled subassemblies operating up to 40 Gbit/s at < 10 kA/cm2 with a rise-time < 10 ps at up to 100°C.
13th IEEE International Semiconductor Laser Conference
Lightpulses as short as 0.7 ps (FWHM) at 1.3pm are generated by a synchronously pumped laser in a... more Lightpulses as short as 0.7 ps (FWHM) at 1.3pm are generated by a synchronously pumped laser in an external cavity. An absorber is created by ion-bombarding one facet. The measured pulse parameters are theoretically analyzed. So far generation of ultrashort pulses by mode locking at 1.3pm was on:y realized in monolithic devices, which are inherently connected with rep(:
2008 Conference on Lasers and Electro-Optics and 2008 Conference on Quantum Electronics and Laser Science, 2008
The ultrafast population and polarisation dynamics in electrically pumped InGaAs QDs is studied e... more The ultrafast population and polarisation dynamics in electrically pumped InGaAs QDs is studied experimentally and theoretically. Limits for ultrafast pulse train amplification with THz repetition rates at high, electrically-injected, non-equilibrium carrier densities are discussed.
Band Structure Engineering in Semiconductor Microstructures, 1989
The atomic scale crystallographic and chemical properties of interfaces between semiconductors ar... more The atomic scale crystallographic and chemical properties of interfaces between semiconductors are of decisive importance for the performance of novel generations of electronic and photonic devices and are in addition of large fundamental interest. Optical methods like luminescence and absorption have recently emerged to yield quantitative information on these properties, if the corresponding lineshape are carefully analyzed. We emphasize here luminescence. The natural lineshape of luminescence from a quantum well shows Gaussian broadening if its interfaces are not ideally abrupt. A detailed lineshape theory is outlined, allowing for a quantitative determination of the interface roughness distribution function. We find this function to depend in a delicate way on growth rates, temperature, interruption time and chemical compositon of the growth surface. The results of an experimental study of the model quantum well system AlGaAs/GaAs/AlGaAs grown by molecular beam epitaxy with and without interruption of the growth at the interfaces is presented. Roughness reduction upon growth interruption is analyzed in detail. For specific growth conditions and interruptions of 2 min at both interfaces formation of up to 7 µm large interface islands differing by a one monolayer step (2.8 A) are observed. Consequently such quantum wells have a columnar structure, which can be directly visualized using cathodoluminescence imaging. Strong reduction of island size indicating transition from planar growth to three-dimensional growth is observed by CLI upon an increase of growth temperature from Tg = 600° C to 660° C.
ABSTRACT Error-free operation at 25 and 30 Gb/s across 1 km and 500 m of multimode fiber is achie... more ABSTRACT Error-free operation at 25 and 30 Gb/s across 1 km and 500 m of multimode fiber is achieved with 100 and 85 fJ of dissipated energy per bit using narrow spectral-width 850 nm vertical-cavity surface-emitting lasers.
Based on frequency resolved optical gating, a pulse shape and phase characterization of a monolit... more Based on frequency resolved optical gating, a pulse shape and phase characterization of a monolithic-two-section, quantum-dot mode-locked laser (QD-MLL) at 1.3 mum, at a repetition rate of 40 GHz, is presented. The dynamics of the absorber and the gain section are investigated in detail. Increasing the gain current leads to an increase of mostly linear chirp inducing significant pulse broadening.
Charged ͑X + , X − , XX + ͒ and neutral ͑X , XX͒ exciton complexes in single InAs/ GaAs quantum d... more Charged ͑X + , X − , XX + ͒ and neutral ͑X , XX͒ exciton complexes in single InAs/ GaAs quantum dots ͑QDs͒ are investigated by cathodoluminescence spectroscopy. The relative spectral positions of the few-particle transition energies compared to the X transition are shown to be strongly correlated to the QD size. Starting from an unprecedented detailed knowledge about the size, shape, and composition of the investigated quantum dots these energies are calculated using an eight-band k • p theory for the single-particle states and the configuration interaction method for the few-particle states. The observed strong variation of the few-particle energy positions is found to originate from a depletion of the number of excited states in the QDs when they become smaller. Then the degree of correlation is reduced. From a detailed comparison of the numerical results with the experimental data we identify the number of hole states bound in the QD to be the key parameter for size and sign variations of the relative few-particle energies.
We report on the modeling, epitaxial growth, fabrication, and characterization of 830-845 nm vert... more We report on the modeling, epitaxial growth, fabrication, and characterization of 830-845 nm vertical cavity surface emitting lasers (VCSELs) that employ InAs-GaAs quantum dot (QD) gain elements. The GaAs-based VCSELs are essentially conventional in design, grown by solid-source molecular beam epitaxy, and include top and bottom gradedheterointerface AlGaAs distributed Bragg reflectors, a single selectively-oxidized AlAs waveguiding/current funneling aperture layer, and
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1992
ABSTRACT The growth of InGaAs/InP quantum wells (QWs) by low‐pressure metalorganic chemical vapor... more ABSTRACT The growth of InGaAs/InP quantum wells (QWs) by low‐pressure metalorganic chemical vapor deposition on vicinal Si(001) substrate is reported. Despite the fact that the etch pit density is about 2 × 107 cm-2 the low temperature (T=2 K) luminescence efficiency is very high and about the same as for QWs grown at 640 °C on InP substrates. The high efficiency is a result of the large structural perfection of the optically active QW areas. Microtwins (MTs) present a major source of nonradiative recombination in such structures. Transmission electron microscopy cross sections show a reduced growth rate within the MTs. A decrease of the QW width next to the boundaries leads to an increase of the effective band gap of the QW. Thus, local drift fields lead to a depletion of charge carriers close to the defects. The charge carriers in the QW are localized predominantly in defect‐free areas and can efficiently recombine there radiatively. At room‐temperature charge carriers are thermally activated to or remain in the narrower well regions next to the twin boundaries leading to enhanced nonradiative recombination and a comparatively larger drop of the quantum efficiency.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1992
Large differences between the structural and chemical modifications binary AlAs and ternary Al o.... more Large differences between the structural and chemical modifications binary AlAs and ternary Al o. 4 Gllo. 6 As barriers of GaAs quantum wells (QWs) upon undergoing growth interruption are found in an investigation ofluminescence of type I and type II QWs. There are no increased trap incorporation but rapid smoothing and formation of interface islands larger than the diameter of type I excitons but smaller than the diameter of type II excitons is observed on the AlAs surface. Chemical lattice images obtained by high-resolution transmission electron microscopy visualize directly the structure of the interfaces. Areas without monoatomic steps in the interface plane extending more than 0.1 pm are observed at the top surface. The bottom interfaces show structure on the scale of the exciton diameter in agreement with the luminescence results. Superimposed to the in-plane variations of the interface positions is a grading extending over 2-4 monolayers in growth direction.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1987
Abstract Direct images of growth islands differing by 2.8 Å [1 monolayer (ML)] height at GaAs/AlG... more Abstract Direct images of growth islands differing by 2.8 Å [1 monolayer (ML)] height at GaAs/AlGaAs heterointerfaces and of the columnar structure of quantum wells are reported for the first time. The structures are grown by molecular‐beam epitaxy (MBE) with ...
(CLEO). Conference on Lasers and Electro-Optics, 2005., 2005
We present a dual semiconductor laser system at telecom wavelengths generating pulses below 300fs... more We present a dual semiconductor laser system at telecom wavelengths generating pulses below 300fs. The low-jitter temporal delay of up to 2ns is achieved electrically by a phase shifter enabling pump-probe measurements within short time.
Conference on Lasers and Electro-Optics 2010, 2010
We report near-temperature-insensitive, highly linear oxide-confined directly modulated 850 nm-ra... more We report near-temperature-insensitive, highly linear oxide-confined directly modulated 850 nm-range VCSEL chips and fiber-coupled subassemblies operating up to 40 Gbit/s at < 10 kA/cm2 with a rise-time < 10 ps at up to 100°C.
13th IEEE International Semiconductor Laser Conference
Lightpulses as short as 0.7 ps (FWHM) at 1.3pm are generated by a synchronously pumped laser in a... more Lightpulses as short as 0.7 ps (FWHM) at 1.3pm are generated by a synchronously pumped laser in an external cavity. An absorber is created by ion-bombarding one facet. The measured pulse parameters are theoretically analyzed. So far generation of ultrashort pulses by mode locking at 1.3pm was on:y realized in monolithic devices, which are inherently connected with rep(:
2008 Conference on Lasers and Electro-Optics and 2008 Conference on Quantum Electronics and Laser Science, 2008
The ultrafast population and polarisation dynamics in electrically pumped InGaAs QDs is studied e... more The ultrafast population and polarisation dynamics in electrically pumped InGaAs QDs is studied experimentally and theoretically. Limits for ultrafast pulse train amplification with THz repetition rates at high, electrically-injected, non-equilibrium carrier densities are discussed.
Band Structure Engineering in Semiconductor Microstructures, 1989
The atomic scale crystallographic and chemical properties of interfaces between semiconductors ar... more The atomic scale crystallographic and chemical properties of interfaces between semiconductors are of decisive importance for the performance of novel generations of electronic and photonic devices and are in addition of large fundamental interest. Optical methods like luminescence and absorption have recently emerged to yield quantitative information on these properties, if the corresponding lineshape are carefully analyzed. We emphasize here luminescence. The natural lineshape of luminescence from a quantum well shows Gaussian broadening if its interfaces are not ideally abrupt. A detailed lineshape theory is outlined, allowing for a quantitative determination of the interface roughness distribution function. We find this function to depend in a delicate way on growth rates, temperature, interruption time and chemical compositon of the growth surface. The results of an experimental study of the model quantum well system AlGaAs/GaAs/AlGaAs grown by molecular beam epitaxy with and without interruption of the growth at the interfaces is presented. Roughness reduction upon growth interruption is analyzed in detail. For specific growth conditions and interruptions of 2 min at both interfaces formation of up to 7 µm large interface islands differing by a one monolayer step (2.8 A) are observed. Consequently such quantum wells have a columnar structure, which can be directly visualized using cathodoluminescence imaging. Strong reduction of island size indicating transition from planar growth to three-dimensional growth is observed by CLI upon an increase of growth temperature from Tg = 600° C to 660° C.
ABSTRACT Error-free operation at 25 and 30 Gb/s across 1 km and 500 m of multimode fiber is achie... more ABSTRACT Error-free operation at 25 and 30 Gb/s across 1 km and 500 m of multimode fiber is achieved with 100 and 85 fJ of dissipated energy per bit using narrow spectral-width 850 nm vertical-cavity surface-emitting lasers.
Based on frequency resolved optical gating, a pulse shape and phase characterization of a monolit... more Based on frequency resolved optical gating, a pulse shape and phase characterization of a monolithic-two-section, quantum-dot mode-locked laser (QD-MLL) at 1.3 mum, at a repetition rate of 40 GHz, is presented. The dynamics of the absorber and the gain section are investigated in detail. Increasing the gain current leads to an increase of mostly linear chirp inducing significant pulse broadening.
Charged ͑X + , X − , XX + ͒ and neutral ͑X , XX͒ exciton complexes in single InAs/ GaAs quantum d... more Charged ͑X + , X − , XX + ͒ and neutral ͑X , XX͒ exciton complexes in single InAs/ GaAs quantum dots ͑QDs͒ are investigated by cathodoluminescence spectroscopy. The relative spectral positions of the few-particle transition energies compared to the X transition are shown to be strongly correlated to the QD size. Starting from an unprecedented detailed knowledge about the size, shape, and composition of the investigated quantum dots these energies are calculated using an eight-band k • p theory for the single-particle states and the configuration interaction method for the few-particle states. The observed strong variation of the few-particle energy positions is found to originate from a depletion of the number of excited states in the QDs when they become smaller. Then the degree of correlation is reduced. From a detailed comparison of the numerical results with the experimental data we identify the number of hole states bound in the QD to be the key parameter for size and sign variations of the relative few-particle energies.
We report on the modeling, epitaxial growth, fabrication, and characterization of 830-845 nm vert... more We report on the modeling, epitaxial growth, fabrication, and characterization of 830-845 nm vertical cavity surface emitting lasers (VCSELs) that employ InAs-GaAs quantum dot (QD) gain elements. The GaAs-based VCSELs are essentially conventional in design, grown by solid-source molecular beam epitaxy, and include top and bottom gradedheterointerface AlGaAs distributed Bragg reflectors, a single selectively-oxidized AlAs waveguiding/current funneling aperture layer, and
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1992
ABSTRACT The growth of InGaAs/InP quantum wells (QWs) by low‐pressure metalorganic chemical vapor... more ABSTRACT The growth of InGaAs/InP quantum wells (QWs) by low‐pressure metalorganic chemical vapor deposition on vicinal Si(001) substrate is reported. Despite the fact that the etch pit density is about 2 × 107 cm-2 the low temperature (T=2 K) luminescence efficiency is very high and about the same as for QWs grown at 640 °C on InP substrates. The high efficiency is a result of the large structural perfection of the optically active QW areas. Microtwins (MTs) present a major source of nonradiative recombination in such structures. Transmission electron microscopy cross sections show a reduced growth rate within the MTs. A decrease of the QW width next to the boundaries leads to an increase of the effective band gap of the QW. Thus, local drift fields lead to a depletion of charge carriers close to the defects. The charge carriers in the QW are localized predominantly in defect‐free areas and can efficiently recombine there radiatively. At room‐temperature charge carriers are thermally activated to or remain in the narrower well regions next to the twin boundaries leading to enhanced nonradiative recombination and a comparatively larger drop of the quantum efficiency.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1992
Large differences between the structural and chemical modifications binary AlAs and ternary Al o.... more Large differences between the structural and chemical modifications binary AlAs and ternary Al o. 4 Gllo. 6 As barriers of GaAs quantum wells (QWs) upon undergoing growth interruption are found in an investigation ofluminescence of type I and type II QWs. There are no increased trap incorporation but rapid smoothing and formation of interface islands larger than the diameter of type I excitons but smaller than the diameter of type II excitons is observed on the AlAs surface. Chemical lattice images obtained by high-resolution transmission electron microscopy visualize directly the structure of the interfaces. Areas without monoatomic steps in the interface plane extending more than 0.1 pm are observed at the top surface. The bottom interfaces show structure on the scale of the exciton diameter in agreement with the luminescence results. Superimposed to the in-plane variations of the interface positions is a grading extending over 2-4 monolayers in growth direction.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1987
Abstract Direct images of growth islands differing by 2.8 Å [1 monolayer (ML)] height at GaAs/AlG... more Abstract Direct images of growth islands differing by 2.8 Å [1 monolayer (ML)] height at GaAs/AlGaAs heterointerfaces and of the columnar structure of quantum wells are reported for the first time. The structures are grown by molecular‐beam epitaxy (MBE) with ...
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Papers by Dieter Bimberg