Maciej Kuc

Proton implantation for the isolation of AlGaAs/GaAs quantum cascade lasers

The novel fabrication scheme of the mid-infrared (~9.5 μm) Al0.45Ga0.55As/GaAs plasmon-enhanced-waveguide quantum cascade laser (QCL) is reported. The electric isolation was made exclusively by 6.5 μm-deep proton implantation. The applied implantation allowed us to suppress the current spreading and at the same time enabled the laser radiation confinement without any mesa formation. A galvanic gold layer at least 3.5 μm thick covering the top ohmic contact was used as a mask for implantation. This mask was not removed after the implantation, but it served for heat spreading from the laser. A considerable reduction in the necessary technological steps was obtained with the presented novel fabrication scheme, in comparison with the standard mesa-etching-based method.

Numerical investigation of an impact of a top gold metallization on output power of a p-up III-N-based blue-violet edge emitting laser diode

Abstract The effect of modifications in epi-side (top) gold metallization on a thermal performance and on power roll-over of blue-vio- let III-N-based p-up edge-emitting ridge-waveguide laser diode (RW EEL) was explored in this paper. The calculations were carried out using a two-dimensional self-consistent electrical-thermal model combined with a simplified optical model tuned to a RW EEL fabricated in the Institute of High Pressure Physics (Unipress). Our results suggest that with proper modifica- tions in the III-N-based RW EEL, excluding modifications in its inner structure, it is possible to considerably improve the thermal performance and, thus, increase the maximal output power.

Impact of Heat Spreaders on Thermal Performance of III-N-Based Laser Diode

This paper explores the effect on optical output power of modifications to the package assembly of a blue-violet III-N-based p-down edge-emitting ridge-waveguide laser diode grown on bulk GaN crystal. The calculations were carried out using a 3-D self-consistent finite-element model. We focus on thermal analyses of the size and thermal conductivity of the heat spreader (mainly made of natural diamond and chemical vapor deposition diamond) and on the thickness of the solder. The results open the possibility for multiple increases in output power, due to a considerable increase in the power conversion efficiency of the laser diode.

Automated self-consistent approach to modeling of photonic devices

In the talk a new automated and self-consistent approach to modeling photonic devices is presented. Is is based on a new software being developed at Lodz University of Technology and its main idea is automated consideration of mutual interactions between various physical phenomena taking place in photonic devices. The software consists of several solvers that can model temperature distribution within the investigated structure, the electric current flow and carriers diffusion, the optical eigenmodes of the analyzed cavity or waveguide and the light-matter interaction. Results of the modeling performed with one solver are automatically provided as the input state of another one, and the calculations are performed in a user-controlled self-consistent loop. In the talk the basic idea of the approach is presented and it is supported by examples of simulation results of semiconductor lasers.

VCSEL modeling with self-consistent models: From simple approximations to comprehensive numerical analysis

In the talk we show the process of modeling complete physical properties of VCSELs and we present a step-by-step development of its complete multi-physics model, gradually improving its accuracy. Then we introduce high contrast gratings to the VCSEL design, which strongly complicates its optical modeling, making the comprehensive multi-physics VCSEL simulation a challenging task. We show, however, that a proper choice of a self-consistent simulation algorithm can still make such a simulation a feasible one, which is necessary for an efficient optimization of the laser prior to its costly manufacturing.

Concept of the CW GaN-based VECSEL

A concept and numerical study of a continuous-wave (CW) nitride-based vertical-external-cavity surface-emitting laser (VECSEL) with an InGaN/GaN active region is presented. The structure is designed to generate radiation around 450 nm. An array of nitride-based continuous-wave laser diodes is proposed to pump directly the quantum wells in the active region. We expect that it enables CW operation of the presented laser, in contrast to the GaN-based VECSELs demonstrated so far. Moreover, employing in-well pumping instead of barrier pumping reduces pump-laser quantum defect, which contributes to better thermal properties of the device. An external efficiency as high as 26% can be theoretically achieved by using a special multi-pass pump setup.

Metalized monolithic high-contrast grating as a mirror for GaN-based VCSELs

In this paper, we present a novel design of a nitride-based VCSEL emitting at 414 nm and perform numerical analysis of optical, electrical and thermal phenomena. The bottom mirror of the laser is a Al(In)N/GaN DBR (Distributed Bragg Reflector), whereas the top mirror is realized as a semiconductor-metal subwavelength-grating, etched in GaN with silver stripes deposited between the stripes of the semiconductor grating. In this monolithic structure simulations show a uniform active-region current density on the level of 5.5 kA/cm2 for the apertures as large as 10 μm. In the case of a broader apertures, e.g. 40 μm, we showed that, assuming a homogeneous current injection at the level of 5.5 kA/cm2 , the temperature inside the laser should not exceed 360 K, which gives promise to improve thermal management by uniformisation of the current injection.

Optical simulations of blue and green semipolar InGaN/GaN lasers

III-N-based edge-emitting lasers suffer from low refractive index contrast between GaN, AlGaN and InGaN layers, conventionally used in their epitaxial structures. This issue becomes more severe with an increase in wavelength at which those devices operate when tuning from blue-violet to real blue and green light. To overcome this issue and to increase the refractive index contrast other materials must be employed within the epitaxial structures replacing the standard nitride layers with materials with lower refractive index. We demonstrate results of effective-index numerical calculations performed for the state-of-the-art semipolar real blue (471 nm) and green (518 nm) edge-emitting lasers with structural modifications that include ITO, AlInN, plasmonic GaN:Ge and nanoporous GaN layers. Such solutions are extensively investigated for III-N-based EELs operating in blue-violet region but only separately. Using combination of these solutions we managed to increase optical confinement factor over twice in blue- and over 3.5-times in green-EELs.

Al0.45Ga0.55As/GaAs-based single-mode distributed-feedback quantum-cascade lasers with surface gratings

Conditions of fabrication of first order distributed-feedback surface gratings designed for single-mode Al0.45Ga0.55As/GaAs quantum cascades lasers with the emission wavelength of about 10μm are presented. The 1 μm-deep rectangular-shaped gratings with the period of about 1.55 μm and duty cycle in the range of 65-71% made by the standard photolithography are demonstrated. The wavenumber difference of about 7 cm-1 at 77 K is observed for the radiation emitted by lasers fabricated from the same epitaxial structure with ridge widths in the range of 15-25 μm. Moreover, the emission wavelength of the lasers could be tuned with temperature at a rate of 1 nm/K in the temperature range of 77-120 K. The full width at half maximum of the emitted spectra is ~ 0.4 cm-1.

Modeling of multi-mode properties in high-power VCSELs

For many applications of Vertical-Cavity Surface-Emitting Lasers (VCSELs) it is important to obtain high power of emitted light. Due to the laser thermal properties that limit maximum current density in the active region, high power emission requires large laser apertures. This results in appearance of multiple transverse optical modes, which very often are undesirable. In the talk we present important aspects of modeling these modes with advanced self-consistent software and we will also show some propositions of possible measures that can be taken to increase modal selectivity and reduce number of modes. We illustrate these general concepts with examples of modeling gallium-nitride VCSELs.