Maciej Bugajski

Eight-band k·p calculations of the electronic states in InAs/GaSb superlattices

In this paper, we present the absorption edge of (InAs)6ML/(GaSb)n superlattices, which has been determined with the use of the 8-band k·p method. The aim of the work was to develop a numerical tool, which gives the possibility to design InAs/GaSb superlattices for infrared detector structures. Most of works, which were published in this field till now, present the results of electronic states calculations performed with the use of the Empirical Pseudopotential Method (EPM) or Envelope Function Approximation (EFA) method. In this work we report on the results of simulations performed with the use of the 8-band k·p method, in which we have considered strain in a superlattice structure and the effects of heavy and light holes interaction at the interfaces in a superlattice. Calculations have been performed for the structures with asymmetric interfaces (i.e., InSb and GaAs ones). Superlattices grown on GaSb substrates were considered and a temperature of 0K was assumed. Results of simulations are in a good agreement with the results of PL spectra and absorbance measurements, which are presented in the literature. They are also in a good agreement with the results of simulations performed with the use of EPM and EFA methods.

New characterization methods for semiconductor lasers

The implementation of more complex diode laser concepts also increases the demands for improved measurement technology and the need for new analytical tools. In particular concerning the thermal properties of novel high-power devices, there are several established experimental methods. Micro-Raman spectroscopy as well as reflectance techniques, such as photo- and thermo-reflectance measurements, provide information on facet temperatures, whereas emission wavelength shifts enable for the determination of averaged temperatures along the laser axis. Here we report on the successful application of a complementary technique, namely imaging thermography in the 1.5-5 μm wavelength range using a thermocamera, to diode laser analysis. The use of this known technique for the purpose of device analysis became possible due to the enormous technical progress achieved in the field of infrared imaging. We investigate high-power diode lasers and laser arrays by inspecting their front facets. We find raw data to be frequently contaminated by thermal radiation traveling through the substrate, which is transparent for infrared light. Subtraction of this contribution and re-calibration allows for the determination of realistic temperature profiles along laser structures, however, without spatially resolving the facet heating at the surface of the laser waveguide. Furthermore, we show how hot spots at the front facet can be pinpointed. Thus our approach also paves the way for an advanced methodology of device screening.

Design optimization of InGaAlAs/GaAs single and double quantum well lasers emitting at 808 nm

The laser diodes and laser bars with InGaAlAs/GaAs active region are attractive as high power devices operating at around 808 nm. The quaternary InGaAlAs active region seems to have distinctive advantages over the standard GaAs quantum well construction. The most important of them is that quantum wells, required to achieve desired wavelength can be wider, which provides better carrier confinement. Another advantage is better thermal conductivity of InGaAlAs as comparing to GaAs. We have modeled single and double quantum well separate confinement heterostructure lasers with various cavity lengths. The well thickness and indium content in the active region were optimized to obtain 808 nm wavelength with acceptable threshold current density. Numerical simulation based on the selfconsistent solution of drift diffusion equations, Schrödinger equation and photon rate equation has been used to optimize the high power lasers design. In this work we have used commercial simulation package PICS3D developed by Crosslight Soft. Inc.

Three-dimensional comprehensive self-consistent simulation of a room-temperature continuous-wave operation of GaAs-based 1.3-/spl mu/m quantum-dot (InGa)As/GaAs vertical-cavity surface-emitting lasers

The comprehensive self-consistent three-dimensional optical-electrical-gain-thermal self-consistent model of the oxide-confined long-wavelength 1.3-/spl mu/m (InGa)As/GaAs quantum-dot vertical-cavity surface-emitting laser is presented. The model has been used to modify and optimise VCSEL structure to reduce its anticipated room-temperature continuous-wave lasing threshold. Some essential guidelines for designers of laser sources for the second-generation 1.3-/spl mu/m communication systems are given.

InGaAs Resonant Cavity Light Emitting Diodes (RC LEDs)

We have developed resonant-cavity light emitting diodes (RC LED) with very good emission characteristics. RC LEDs proved to be more tolerant to the epitaxial growth parameters and device fabrication procedures. As relatively robust devices they are less sensitive to typical for VCSEL manufacturing challenges and seem to have great potential for applications. Comparing to classical LED the spectrum of RC LED is concentrated into a narrow line with less than 2 nm halfwidth. The RC LED spectrum is determined mainly by the cavity resonance; its width decreases with the increase of the cavity finesse and the intensity increase reflect the on axis cavity enhancement. Additional, favorable RC LED property is its emission characteristic directionality which depends on the tuning between QW emission and cavity resonance. We have optimized the series resistance of diodes. The best results have been obtained for digital alloy graded distributed Bragg reflector (DRB) interfaces. The MBE grown structures were tested extensively prior to the device fabrication by reflectivity and photoluminescence. The assembled diodes were subjected to electrical and optical tests. Generally we have found very good correlation between the results of optical test (PL maps) on as grown wafers and probe tests on final devices.

Power efficiency of diode lasers with asymmetric mirror losses

Threshold current and differential quatnum efficiency of broad contact lasers with optically asymmetric mirrors is discussed with the purpose to reveal factors essential for optimization of the power efficiency of such lasers.

(InGa)As/GaAs quantum-dot diode lasers for 1.3-/spl mu/m optical fibre communication

The self-consistent optical-electrical-thermal-gain model of the oxide-confined edge-emitting diode laser has been used to simulate the room-temperature operation of the long-wavelength 1.3-/spl mu/m quantum-dot (InGa)As/GaAs diode laser. Validity of the model has been verified using some experimental results for comparison. An impact of quantum-dot density on laser operation characteristics as well as temperature dependence of lasing threshold have been discussed.