Olle Kjebon

Extended modulation bandwidth of DBR and external cavity lasers by utilizing a cavity resonance for equalization

We have investigated the occurrence of a second resonance frequency in distributed Bragg reflector laser diodes and the high modulation bandwidth resulting from it. The influence of different laser parameters has been theoretically investigated. It is also shown that a similar behavior can be obtained in laser diodes with a passive, low-loss, and gratingless external cavity. The possibilities of large-signal digital modulation are also investigated.

Hydride vapor phase epitaxy revisited

The salient features of hydride vapor phase epitaxy (HYPE) process in the fabrication of optoelectronic devices are demonstrated by combining the state of the art results of several groups working in this field.

An investigation on hydride VPE growth and properties of semi-insulating InP:Fe

Growth of highly resistive semi-insulating InP : Fe has been achieved by the Hydride VPE technique in an ambient consisting mostly of nitrogen. After dealing with some thermodynamic considerations pertinent to InP:Fe growth, the experimental growth parameters are described. It is shown that various amounts of iron can be introduced into the InP crystal just by varying the temperature of the iron source. The crystal quality of the grown material is estimated to be good by etch pit density and x-ray diffraction analyses. Current-voltage behaviour and capacitance studies on ann+-SI-n+ structure are explained by invoking the theory of current injection in solids by Lampert and Mark: the experimental current densities at the threshold of each observed regime are compared with the theoretically derived current densities; in the absence of current injection, the measured capacitance is found to be the same as the geometrical capacitance.

Modulation response measurements and evaluation of MQW InGaAsP lasers of various designs

Results from modulation measurements of 40 high-speed multi quantum well (MQW) lasers ((lambda) equals 1.55 micrometer) of various designs are presented. By fitting the careful calibrated measurements, both magnitude and phase, to an analytical transfer function we were able to determine if a certain laser was limited by thermal effects, parasitic-like effects, or nonlinear gain effects. We found that most of the devices in the study were limited by thermal effects and/or contact parasitics. The parasitics were found to be determined by the width of the high-doped contact layer and cladding layers below the metallic contact. It was also found that a high doping of the separate confinement heterostructure (SCH) layers decreases the damping of the relaxation peak since it facilitates the carrier transport. Improved contact design and high doped SCH-layers resulted in modulation bandwidths of around 24 GHz.

1.55 μm buried heterostructure laser via regrowth of semi-insulating InP:Fe around vertical mesas fabricated by reactive ion etching using methane and hydrogen

A GaInAsP/InP Fabry-Perot-type buried-heterostructure quantum well laser operating at 1.55 μm has been realized utilizing iron-doped semi-insulating InP around vertical mesas fabricated by reactive ion etching using methane and hydrogen. A maximum cw output power of 19 mW has been achieved on as-cleaved chips of 300 μm length with a quantum efficiency of 21% per facet. Threshold currents lie between 20 and 25 mA. As low as 2 Ω series resistance has been measured despite an ohmic contact area not exceeding that of the 2-μm-wide mesa. A 3 dB bandwidth of 7.5 GHz at 12 mW output power is obtained from the small-signal frequency modulation measurements.

Importance of metalorganic vapor phase epitaxy growth conditions for the fabrication of GaInAsP strained quantum well lasers

Abstract GaInAsP / GaInAsP multi quantum well (MQW) structures with 1% compressive strain in the wells and a bandgap wavelenght of 1.55 μm have been grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). Photoluminescence (PL) measurements at 300 and 4 K together with X-ray diffraction analysis reveal a strong dependency of the material quality on the MOVPE growth conditions. The photoluminescence intensity could be increased by more than a factor of 3 by optimizing reactor pressure and temperature. Under properly chosen pressure and temperature in the reactor, we found a greatly reduced sensitivity of the material quality to other parameters such as growth interruptions or barrier composition. When utilizing strain-compensating barriers, the number of strained quantum wells could be increased up to 32, without any indication for material degradation due to strain relaxation. Utilizing those findings, distributed feedback (DFB) laser structures employing 8 compressive strained wells with lattice-matched as well as strain-compensating barriers have been grown. The processed lasers showed excellent static and high-frequency characteristics with threshold currents as low as 3.3. mA and a 3dB modulation frequency of 21.7 GHz, which is among the highest values ever reported for DFB lasers.

24-GHz modulation bandwidth and passive alignment of flip-chip mounted DFB laser diodes

High-frequency lasers have been flip-chip mounted on silicon motherboards. Small-signal modulation bandwidths around 24 GHz were obtained. It was shown that the bandwidth was not limited by extrinsic parasitics associated with the mounting scheme. Lasers were passively aligned to single mode fibers in V-grooves with the self-aligning solder bump technique. By passive alignment 50% of maximum coupling efficiency obtained by active alignment was achieved.

Temporally resolved regrowth of InP

Temporally resolved regrowth of InP around reactive ion etched striped mesas without mask is reported. The regrowth was carried out at the growth temperatures of 600, 650, 685 and 700°C in a near equilibrium process, Hydride vapour phase epitaxy (HVPE). The mesa orientations considered were [110] and [110]. The regrowth profiles, initial lateral growth and evolution of certain crystallographic planes are analysed. The regrowth profiles and initial lateral growth rates are dependent on temperature and mesa orientation. The differences are explained by invoking the bonding configurations existing on the mesa walls under the epitaxial growth conditions of excess phosphorus pressure. The facility of lateral growth especially in the [110] mesa case is explained by a more favourable net reduction of dangling bonds. The emerging crystallographic planes are identified as hhl. Initially the planes with lh ≤ 3 are formed but progress towards lh ≥ 3. The implication of a very high lateral growth rate in utilising regrowth for device fabrication is also mentioned.

High-frequency GaInAsP/InP laser mesas in (-110) direction with thick semi-insulating InP:Fe

Growth of thick semi-insulating InP:Fe (Si-InP:Fe) current-blocking layers to reduce parasitic capacitance around (-110) directional laser mesas has been demonstrated for the first time. The regrowth is found to be equivalent to that around the normally used

Design optimization of InGaAsP-InGaAlAs 1.55 /spl mu/m strain-compensated MQW lasers for direct modulation applications

A comprehensive simulation study of InGaAsP (well)/InGaAlAs(barrier) 1.55 /spl mu/m strain-compensated MQW lasers is presented. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and strain of the barriers and p-doping in the active region. Some preliminary results are also presented for the manufactured lasers using these QWs indicating a good material platform.