D. Gollub

Explanation of annealing-induced blueshift of the optical transitions in GaInAsN/GaAs quantum wells

This letter aims to describe the effect of rapid thermal annealing on a Ga0.64In0.36As0.99N0.01/GaAs single quantum well grown by molecular-beam epitaxy. This effect was investigated using both photoluminescence and photoreflectance. A blueshift of optical transitions and a change of character of the ground-state transition were observed after annealing. We show that this behavior can be explained by a combination of two annealing-induced effects: A change in the nearest-neighbor configuration of nitrogen atoms and a simultaneous change in the quantum well profile due to atom diffusion across the quantum well interfaces.

1.3 μm continuous-wave GaInNAs/GaAs distributed feedback laser diodes

GaInNAs/GaAs single-quantum-well lasers were grown by solid-source molecular-beam epitaxy using a radio-frequency source for nitrogen activation. Distributed feedback has been realized by a metal grating arranged laterally to the laser ridge. Single-mode emission between 1271 and 1304 nm could be demonstrated. Room-temperature continuous-wave operation has been obtained with a threshold current of 28 mA, an external efficiency of 0.16 W/A per facet, and a side-mode suppression ratio of 44 dB at 90 mA drive current.

1.3 µm GaInAsN Laserdiodes with improved High Temperature Performance

We have grown 1.3 µm GaInAsN/GaAs single-quantum-well (SQW) laser structures by solid source molecular beam epitaxy using an RF plasma source for the generation of active nitrogen. For p-type doping Carbon is used. Ridge waveguide lasers show threshold currents of 21 mA and a slope efficiency of 0.52 W/A. Device operation up to temperatures of 150°C (limited by our set-up for temperature variation) is demonstrated. Between 20 and 80°C we observe for a constant drive current of 90 mA a reduction in output power of less than 2 dB. The threshold current variation with temperature yields a T0 of 158 K for temperatures between 20 and 110°C.

Comparison of GaInNAs laser diodes based on two to five quantum wells

We have investigated GaInNAs-GaAsN multiquantum-well (MQW) lasers with two-QW (DQW), three-QW (TQW), and five-QW (5QW) active regions and emission in the 1.3-/spl mu/m range. A solid-source molecular beam epitaxy system has been used to grow the structures. Operation of a GaInNAs 5QW laser is reported. Low threshold currents of 22 (DQW) to 52 mA (5QWs) and external efficiencies of 0.25 W/A (DQWs) to 0.16 W/A (5QWs) per facet are realized under CW operation. T/sub 0/-values of 121 K are obtained.

Photoreflectance evidence of the N-induced increase of the exciton binding energy in an InxGa1−xAs1−yNy alloy

The binding energy of the heavy-hole ground-state exciton in In0.25Ga0.75As1−yNy/GaAs single quantum wells (y=0, 0.011) was experimentally derived by photoreflectance measurements. We measured a binding energy of 6.6 and 8.5 meV for the N-free and the N-containing sample, respectively. The observed increase of the exciton binding energy can be accounted for by an increase of the exciton reduced mass of about 30% upon N introduction into the InxGa1−xAs lattice, consistently with recent experimental results and in agreement with earlier theoretical predictions.

Tunable GaInNAs lasers with photonic crystal mirrors

We present results of tunable GaInNAs lasers with photonic crystal (PhQ mirrors, fabricated from GaAs-AlGaAs layers with a double GaInNAs quantum well emitting at IR wavelength. The devices are realized as ridge waveguide lasers with two coupled segments and a total length between 240 and 580 pm. PhC blocks with different thicknesses are used for the back and front mirror as well as for the intermediate reflector between the two segments. The lasers have threshold currents around 20 mA and output powers up to 6 mW. Tuning of the laser emission over 30 nm is achieved by a variation of the currents injected into the two segments.

Role of the host matrix in the carrier recombination of InGaAsN alloys

We present an experimental study of the carrier recombination dynamics in high-quality (InGa)(AsN)/GaAs and Ga(AsN)/GaAs quantum-well structures after picosecond excitation. A comparison among samples with and without nitrogen and with different In concentration shows that nonradiative channels originated in the host matrix [i.e., (InGa)As and GaAs] play a dominant role in the recombination dynamics of these heterostructures.

Atomic ordering in (InGa)(AsN) quantum wells: An In K-edge X-ray absorption investigation

Abstract (InGa)(AsN) quantum wells are particularly interesting for applications in fiber optics based communications, since they permit to make lasers with emission at 1.3 and 1.55 μm, with good temperature stability. The aim of this work is to study the local environment of In by means of X-ray absorption fine structure. In particular, the site ordering around In will be investigated in order to understand the structural origin of the non-linear optical and electronic proprieties which characterize this alloy. Despite the low N concentration (⩽5.2%) a significant contribution of In–N bonds to the signal is detected. The data provide evidence of a preferential distribution of N atoms around indium, as recently predicted via Monte Carlo simulations. Hydrogenation further enhances the increase in the number of In–N over In–As bonds.

1.3-μm continuously tunable distributed feedback laser with constant power output based on GaInNAs-GaAs

We have investigated tunable distributed-feedback (DFB) lasers based on GaInNAs quantum wells grown by molecular-beam epitaxy. Three-section tunable DFB lasers were fabricated by patterning laterally gain coupled binary superimposed gratings perpendicular to a ridge waveguide. The discrete tuning range covers 24 nm with sidemode suppression ratios of about 35 dB. The lasers were tuned continuously over a range of over 10 nm with a constant power output of 15 mW per facet.

Photomodulation spectroscopy applied to low-dimensional semiconductor structures

We present here few examples of application of photomodulation techniques, e.g. photoreflectance and phototransmittance, as excellent methods for the investigation of semiconductor device structures. The discussion is narrowed down to low-dimensional structures used as an active part of the infrared optoelectronic devices: from new material (GaInAsN) double quantum wells, good candidate for 1.3 and 1.55 μm telecommunication lasers, through InGaSb/GaSb quantum wells pretending to the application in the infrared gas sensors, to 980 nm InGaAs/GaAs quantum dot laser pump source for EDFA amplifiers.