GaInNAs Quantum Dots Research Articles

Design issues of 1.55 µm emitting GaInNAs quantum dots

We present a theoretical study of the optical properties of GaInNAs quantum dot (QD) structures, emitting at 1.55 µm wavelength. The theoretical model is based on a 10 × 10 k · p band-anti-crossing Hamiltonian, incorporating valence, conduction and nitrogen-induced bands. We have investigated the influence of the nitrogen to the conduction band mixing, and piezoelectric field on the ground state optical matrix element. For QDs grown on GaAs substrate with a reduced amount of indium and an increased amount of nitrogen in the QD the e x polarized optical matrix element becomes on the average larger and less sensitive to the variation of both the QD shape and size than is the case of an InNAs QD. For the QD grown on InP substrate the dominant optical dipole matrix element is of the e z light polarization. Our results identify the specific In and N content in the QDs required for optimal long-wavelength emission on both substrates.

Theoretical analysis of [formula omitted] emitting GaInNAs QD's on different substrates

We present a theoretical study which compares the electronic and optical properties of dilute nitrogen GaInNAs quantum dots (QD) on two different substrates, GaAs and InP. The calculations are based on a 10 band k ⋅ p band-anti-crossing (BAC) Hamiltonian, incorporating valence, conduction and nitrogen-induced bands. We show that 1.55 μ m emission can be achieved on both substrates through appropriate tailoring of the QD size. On GaAs, the dominant dipole matrix element is the e ^ x and e ^ y light polarization, whereas on InP substrate, the dominant component is the e ^ z light polarization. Our results also identifiy the different In and N QD compositions required for long-wavelength emission on both substrates.

Comparative analysis of cavity length-dependent temperature sensitivity of GaInNAsquantum dot lasers and quantum well lasers

Self-assembled GaInNAs/GaAsN single-layer quantum dot (QD) lasers, grown using solid sourcemolecular beam epitaxy, have been fabricated and characterized. A high output power of40.76 mW/facet was obtained from a GaInNAs QD laser with dimensions of50 × 700 µm2 at10 °C. Temperature-dependent measurements were carried out on the GaInNAs QDlasers of different cavity lengths. For comparison, temperature-dependentmeasurements were also performed on GaInNAs single quantum well (SQW)and triple QW (TQW) lasers. Unlike the relationship between cavity length andT0 in GaInNAs SQW/TQW lasers, longer-cavity GaInNAs QD lasers(50 × 1700 µm2) showeda lower T0 of 65.1 K, which is believed to be due to non-uniformity of the GaInNAs QD layer.Furthermore, compared to GaInNAs SQW lasers, a significant improvement in temperaturesensitivity was observed in the TQW GaInNAs lasers. This is attributed to a reduction inthe relative contribution of the Auger recombination current and suppression of heavy-holeleakage in the TQW laser structures.

Self-assembled GaInNAs/GaAsN quantum dot lasers: solid source molecular beam epitaxy growth and high-temperature operation

Self-assembled GaInNAs quantum dots (QDs) were grown on GaAs (001) substrate using solid-source molecular-beam epitaxy (SSMBE) equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were extensively investigated using atomic-force microscopy (AFM), photoluminescence (PL), and transmission electron microscopy (TEM) measurements. Self-assembled GaInNAs/GaAsN single layer QD lasers grown using SSMBE have been fabricated and characterized. The laser worked under continuous wave (CW) operation at room temperature (RT) with emission wavelength of 1175.86 nm. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05 kA/cm2from a GaInNAs QD laser (50 × 1,700 µm2) at 10 °C. High-temperature operation up to 65 °C was demonstrated from an unbonded GaInNAs QD laser (50 × 1,060 µm2), with high characteristic temperature of 79.4 K in the temperature range of 10–60 °C.

High-temperature operation of self-assembled GaInNAs∕GaAsN quantum-dot lasers grown by solid-source molecular-beam epitaxy

Self-assembled GaInNAs∕GaAsN single layer quantum-dot (QD) lasers grown using solid-source molecular-beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. The lowest obtained threshold current density in this work is ∼1.05kA∕cm2 from a GaInNAs QD laser (50×1700μm2) at 10°C. High-temperature operation up to 65°C was also demonstrated from an unbonded GaInNAs QD laser (50×1060μm2), with high characteristic temperature of 79.4K in the temperature range of 10–60°C.

Comparison of Lasing Characteristics of GaInNAs Quantum Dot Lasers and GaInNAs Quantum Well Lasers

ABSTRACTSelf-assembled GaInNAs/GaAsN single layer quantum dot (QD) lasers grown using solid source molecular beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. High-temperature operation up to 65°C was demonstrated from an unbonded GaInNAs QD laser (50 × 1060 μm2), with high characteristic temperature (T0) of 79.4 K in the temperature range of 10-60°C. For comparison, temperature-dependent operation has also been studied on the GaInNAs single quantum well (SQW) lasers. Unlike the relation between the cavity length and T0 in GaInNAs SQW lasers, longer-cavity GaInNAs QD laser (50 × 1700 μm2) showed lower T0 of 65.1 K, which is presumably believed due to the nonuniformity of the GaInNAs QD layer.

Growth of self-assembled GaInNAs quantum dots by atomic-H assisted RF molecular beam epitaxy

Self-organized Ga x In 1− x N y As 1− y quantum dots (QDs) were fabricated on GaAs (001) substrates by atomic hydrogen-assisted molecular beam epitaxy with a radio frequency nitrogen plasma source (RF-MBE). We have investigated the effect of N 2 flow rate on growth dynamics and optical properties of GaInNAs QDs. With increasing N 2 flow rate, both the QD size and size fluctuation became significantly larger possibly due to phase separation and non-uniformity of N atom concentration, thereby causing linewidth broadening of PL emission of band-to-band transition. We found that N 2 flow rate during the growth of GaInNAs QDs on GaAs (001) in RF-MBE strongly affects the growth kinetics and optical properties. Further, appropriate post-growth annealing was found to be effective in improving PL emission efficiency of both thin GaInNAs films and QDs. Finally, we obtained high-quality 1.3-μm wavelength PL emission with a narrow linewidth of 98.4 meV at room temperature from optimally annealed GaInNAs QDs.

Room-temperature continuous-wave operation of GaInNAs∕GaAs quantum dot laser with GaAsN barrier grown by solid source molecular beam epitaxy

We present the results of GaInNAs∕GaAs quantum dot structures with GaAsN barrier layers grown by solid source molecular beam epitaxy. Extension of the emission wavelength of GaInNAs quantum dots by ∼170nm was observed in samples with GaAsN barriers in place of GaAs. However, optimization of the GaAsN barrier layer thickness is necessary to avoid degradation in luminescence intensity and structural property of the GaInNAs dots. Lasers with GaInNAs quantum dots as active layer were fabricated and room-temperature continuous-wave lasing was observed. Lasing occurs via the ground state at ∼1.2μm, with threshold current density of 2.1kA∕cm2 and maximum output power of 16mW.

Growth temperature dependence and study of multilayer self-assembled GaInNAs/GaAsN quantum dots grown by solid source molecular beam epitaxy

Self-assembled GaInNAs quantum dots (QD) with inserted GaAsN strain-reducing layer were grown on GaAs (001) substrate by solid source molecular beam epitaxy. The highest room temperature photoluminescence (PL) intensity at wavelength of ∼1.57μm was obtained from the sample grown at 500°C, which has the most uniform QD size observed from atomic force microscopy measurement. A number of samples with different spacer thickness and stacked QD layers were grown to investigate the effect of growth condition for GaIn0.5N0.01As QDs. Multilayer structures with 5QD stacks and spacer layer thickness of 2nm were found to show the optimum result in terms of PL intensity.

Structural and optical properties of GaInNAs/GaAs quantum structures

Structural and optical properties of GaInNAs/GaAs quantum structures grown bymetalorganic vapour phase epitaxy (MOVPE) are studied. The growth of arsenide–nitridesby MOVPE is reviewed and compared to the other major growth technique, molecularbeam epitaxy. Post-growth thermal annealing and laser irradiation are employed and foundto affect GaInNAs quantum wells differently: with laser treatment no undesired blue-shiftof the photoluminescence peak is observed. The critical thickness for misfit dislocationformation of GaAsN on GaAs is found to be about twice as large as the theoreticalprediction. GaAsN epilayers are also found to contain Ga vacancies in defect complexes.The current status of experimental research on GaInNAs quantum dot structures isreviewed. Self-organized and strain-induced GaInNAs quantum dots are grownand their formation and optical properties are studied. The emission wavelengthof InGaAs quantum dots is extended by using InGaAs and GaInNAs barrierlayers.

Growth characteristic and room-temperature lasing in GaInNAs quantum dots grown by solid-source molecular beam epitaxy

Self-assembled Ga1−xInxNyAs1−y quantum dots (QDs) were grown on GaAs by solid source molecular beam epitaxy using a radio-frequency plasma assisted nitrogen source. High GaInNAs QD density (1010–1011cm−2) was obtained for different In and N composition (0.3⩽x⩽0.7,y⩽0.01). The effect of surface coverage on dot density, dot size, and optical property was studied in detail. Adjusting the bandgap confinement by incorporating a GaNAs strain-reduction layer into the GaInNAs dot layer was found to extend the emission wavelength by 180nm. Room-temperature pulsed operation is demonstrated for a Ga0.5In0.5N0.01As0.99 QD laser emitting at ∼1.1μm.

The effect of nitrogen on self‐assembled GaInNAs quantum dots grown on GaAs

AbstractWe investigate the effect of nitrogen on self‐assembled GaInNAs quantum dots (QDs) grown on GaAs (001) substrates by gas‐source molecular beam epitaxy. The dot density of GaInNAs QDs decreases with increasing nitrogen. The reduced strain resulted from nitrogen incorporation decreases dot density of QDs. However, we find that the dot density of Ga0.3In0.7N0.02As0.98 QDs is still significantly lower than that of Ga0.4In0.6As QDs, even though they have comparable nominal strain. This difference can be explained by the composition fluctuation in the wetting layer. The inhomogeneous local strain due to the composition fluctuation decreases the number of dots when the dots begin to form, resulting in lower dot density after QD growth. The dot density difference between GaInNAs QDs and GaInAs QDs becomes smaller with decreasing growth temperature. Therefore, the PL intensity of GaInNAs QDs grown at low temperature (450 °C) improved to be comparable to that of GaInAs QDs, while the PL intensity of the GaInNAs QDs grown at high temperature (520 °C) dramatically decreased with increasing nitrogen composition. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of self-organized GaInNAs quantum dots by atomic H-assisted RF-molecular beam epitaxy

Self-organized Ga x In 1− x N y As 1− y quantum dots (QDs) were fabricated on GaAs (0 0 1) substrates by atomic hydrogen-assisted molecular beam epitaxy with a radio frequency nitrogen plasma source (RF-MBE). By adjusting the amount of lattice mismatch between Ga x In 1− x N y As 1− y and GaAs to be almost the same as that of In 0.4Ga 0.6As and GaAs, we were able to fabricate Ga 0.53In 0.47N 0.02As 0.98 QDs with densities up to ∼1.1×10 11 cm −2 on GaAs (0 0 1) by atomic H-assisted RF-MBE. Further, we have studied the effect of atomic H irradiation on QDs’ growth dynamics and their optical properties. Based on the atomic force microscope and photoluminescence measurements, we found that there exists an optimum range of H 2 flow rates for a uniform and high quality Ga 0.53In 0.47N 0.02As 0.98 QDs formation on GaAs substrates.

Thermal annealing effect on self‐assembled GaInNAs/GaAs quantum dots grown by chemical beam epitaxy

The self-assembled GaInNAs quantum dot (QD) has been proposed as a novel material system for long-wavelength lasers. In this paper, we have investigated the effect of thermal annealing on GaInNAs QDs. The increase of the photoluminescence (PL) intensity and the blue shift of the peak wavelength were observed by thermal annealing. For 600 °C annealing, the PL intensity was increased with increase of annealing time and maximum intensity was obtained at 2 h. On the other hand, the PL intensity was increased after 30 s annealing, then decreased at longer times for 700 °C annealing. A larger blue shift of the peak wavelength compared to the GaInNAs quantum well system was observed. It is considered that the interdiffusion of atoms was enhanced in the QD system due to its large strain and large interface area between the GaAs capping layer.

Thickness effects on properties of GaInNAs quantum dots grown by molecular-beam epitaxy with nitrogen plasma source

Self-assembled GaInNAs quantum dots (QDs) were grown on a GaAs (001) substrate by solid-source molecular-beam epitaxy equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were investigated using atomic-force microscopy (AFM) and photoluminescence (PL) measurements. The growth experiment was conducted using indium and nitrogen compositions of 50% and ∼1%, respectively, at different nominal thicknesses of 3 monolayers (MLs) to 6 MLs. AFM images suggest the onset of QD formation at ∼3 MLs and QD coalescence at ∼6 MLs. The highest PL intensity at low temperature (5 K) was obtained from the sample with nominal thickness of 5 ML, consistent with the highest QD density observed from AFM measurement. Under the present experimental conditions, GaIn0.5N0.01As QDs of 5–6 MLs gave the best optical property in terms of the lowest full width at half maximum and highest PL intensity. The reduced barrier potential of a strain-compensated layer (SCL) of GaNAs inserted between the substrate and GaInNAs QD layer was able to extend the PL emission wavelength by more than 140 nm compared to the sample without the GaNAs SCL.

InNAs and GaInNAs self-assembled quantum dots and lasers grown by solid source molecular beam epitaxy

ABSTRACTSelf-assembled Ga1−xInxNyAs1-y quantum dots were grown on GaAs by solid source molecular beam epitaxy (SSMBE). Introduction of N was achieved by a RF Nitrogen plasma source. Formation of quantum dots by S-K growth mode is confirmed by observation of standard 2D-3D RHEED pattern transition. Atomic force microscopy (AFM) and photoluminescence (PL) measurements were used to characterize the structure and optical properties of GaInNAs quantum dots. High GaInNAs quantum dot density (1010∼1011cm−2) was obtained for different In and N composition (0.3≤ x ≤1, y≤0.01). The effect of surface coverage on dot density, dot size, and optical properties was studied in detail. Adjusting the bandgap confinement by incorporating a GaNAs strain-reduction layer into the GaInNAs dot layer was found to extend the emission wavelength by 170nm. Room temperature pulsed operation is demonstrated for a Ga0.5In0.5N0.01As0.99 quantum dot laser emitting at ∼1.1μm.

Wavelength elongation of GaInNAs lasers beyond 1.3 μm

The applicability of GaInNAs to long wavelength lasers is discussed by fabricating 1.4 µm GaInNAs quantum well (QW) lasers and by formation of self-organised GaInNAs quantum dots (QDs) grown by chemical beam epitaxy (CBE). A broad lasing spectrum at 77 K and a wide wavelength spacing at room temperature were observed for 1.4 µm QW lasers. The lasing spectrum was similar to that of InAs QD lasers and indicates the existence of potential fluctuation in high nitrogen GaInNAs QWs. Self-organised GaInNAs QD is also investigated as a novel long wavelength material. The nitrogen introduction causes an increase in the nucleus of the QD formation. Understanding and control of the influence of nitrogen introduction are important not only to realise high quality QDs but also to improve the compositional fluctuations in QWs. The observed result is valuable for the realisation of high-performance long (>1.3 µm) wavelength GaInNAs lasers to be used in the next generation of optical network systems.

Growth characteristics of GaInNAs/GaAs quantum dots by chemical beam epitaxy

The growth characteristics of GaInNAs quantum dots by chemical beam epitaxy have been investigated to form uniform and high density dot for high nitrogen (N) composition. The dot density and size were strongly affected by the N composition and the growth temperature. The dot density was increased by increase of N up to 1%, while, the dot density was decreased and the size uniformity became worse over 1% of N at growth temperature above 480°C. At 1.5% of N, wire-like islands were observed at 540°C of the growth temperature, on the other hand, the highest dot density of 1.4×10 11 cm −2 was obtained at 450°C. These phenomena are considered due to the change of the migration length. Low growth temperature is essential to form GaInNAs dots for high N composition.

Optical property of self-assembled GaInNAs quantum dots grown by solid source molecular beam epitaxy

Self-assembled GaInNAs/GaAs quantum dots (QDs) are promising structures for extending the emission wavelength of GaInNAs/GaAs quantum wells from 1.3 to 1.55 μm and beyond. We report herein the growth of GaInNAs/GaAs quantum dot samples of different deposited thickness by solid source molecular beam epitaxy using active nitrogen radicals generated by a radio frequency nitrogen plasma source. Images from atomic force spectroscopy reveal the increase of non-uniformity QDs size following the increase in the deposited thickness. Temperature-dependent photoluminescence (PL) measurements show PL line width shrinkage at low temperature suggests the relaxation of carriers into neighboring QD local-energy minimum. The low thermal activation energy of ∼72 meV, estimated from the temperature-dependent integrated PL intensity curve suggests the existence of non-radiative recombination centers that quench the luminescence intensity at higher temperature.

Self-assembled GaInNAs/GaAs quantum dots grown by solid-source molecular beam epitaxy

GaInNAs/GaAs quantum dots (QDs) were grown by solid-source molecular beam epitaxy equipped with a radio frequency nitrogen (N 2) plasma source for the first time. High-density (∼10 10 cm −2) GaInNAs QDs with small sizes (∼30 nm) were achieved. Reflection high-energy electron diffraction observation revealed that the formation of GaInNAs QDs follows the Stranski–Krastanow growth mode. The evolution of GaInNAs QDs was investigated by atomic force microscopy, and the amount of GaInNAs coverage was found to have a significant effect on the dot density, average size and aspect ratio. Low temperature (5 K) photoluminescence measurement on the GaInNAs QDs showed that the incorporation of N into InGaAs effectively reduced the emission energy, and there is an optimal amount of GaInNAs coverage, which will produce QDs with maximum luminescence intensity.