[Show abstract][Hide abstract] ABSTRACT: The effects of thermal annealing on the interfaces of InGa(N)As/GaAs single quantum wells (SQWs) are investigated by excitation-, temperature-, and magnetic field-dependent photoluminescence (PL). The annealing at 750 °C results in more significant blueshift and narrowing to the PL peak than that at 600 °C. Each of the PL spectra can be reproduced with two PL components: (i) the low-energy component (LE) keeps energetically unchanged, while the high-energy component (HE) moves up with excitation and shows at higher energy for the In0.375Ga0.625As/GaAs but crosses over with the LE at a medium excitation power for the In0.375Ga0.625N0.012As0.988/GaAs SQWs. The HE is broader than the corresponding LE, the annealing at 750 °C narrows the LE and HE and shrinks their energetic separation; (ii) the PL components are excitonic, and the InGaNAs shows slightly enhanced excitonic effects relative to the InGaAs SQW; (iii) no typical S-shape evolution of PL energy with temperature is detectable, and similar blueshift and narrowing are identified for the same annealing. The phenomena are mainly from the interfacial processes. Annealing improves the intralayer quality, enhances the interfacial In-Ga interdiffusion, and reduces the interfacial fluctuation. The interfacial interdiffusion does not change obviously by the small N content and hence similar PL-component narrowing and blueshift are observed for the SQWs after a nominally identical annealing. Comparison with previous studies is made and the PL measurements under different conditions are shown to be effective for probing the interfacial evolution in QWs.
[Show abstract][Hide abstract] ABSTRACT: We report the first successful growth of InGaPBi single crystals on InP substrate with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InGaPBi thin films reveal excellent surface and structural qualities, making it a promising new III–V compound family member for heterostructures. The strain can be tuned between tensile and compressive by adjusting Ga and Bi compositions. The maximum achieved Bi concentration is 2.2 ± 0.4% confirmed by Rutherford backscattering spectroscopy. Room temperature photoluminescence shows strong and broad light emission at energy levels much smaller than the InP bandgap.
[Show abstract][Hide abstract] ABSTRACT: The effect of post-growth rapid thermal annealing on structural and optical properties of InP1−xBix thin films was investigated. InPBi shows good thermal stability up to 500 °C and a modest improvement in photoluminescence (PL) intensity with an unchanged PL spectral feature. Bismuth outdiffusion from InPBi and strain relaxation are observed at about 600 °C. The InPBi sample annealed at 800 °C shows an unexpected PL spectrum with different energy transitions.
[Show abstract][Hide abstract] ABSTRACT: Femtosecond laser drilled holes of GaSbBi were characterized
by the joint measurements of photoconductivity (PC)
spectroscopy and laser-beam-induced current (LBIC) mapping.
The excitation light in PC was focused down to 60 μm
presenting the spectral information of local electronic property
of individual holes. A redshift of energy band edge of
about 6–8 meV was observed by the PC measurement when
the excitation light irradiated on the laser drilled holes. The
spatial resolving of photoelectric property was achieved by
the LBIC mapping which shows “pseudo-holes” with much
larger dimensions than the geometric sizes of the holes. The
reduced LBIC current with the pseudo-holes is associated
with the redshift effect indicating that the electronic property
of the rim areas of the holes is modified by the femtosecond
[Show abstract][Hide abstract] ABSTRACT: We present a novel method to characterize the internal quantum efficiency and internal optical loss of semiconductor lasers. Its basic concept is studying the dependence of the external quantum efficiency on the mirror reflectivity. This method is very different from the conventional one, which focuses on the external quantum efficiency as a function of cavity length. Our method has great advantages, such as the capability of measuring the internal quantum efficiency and optical loss of a single laser diode, which is intrinsically impossible by the conventional method.
[Show abstract][Hide abstract] ABSTRACT: We report on the InAs quantum dot (QD) external cavity laser (ECL) using a digital mirror device (DMD) as the key component for wavelength tuning. The InAs QD laser diode was grown by gas source molecular-beam epitaxy, which had a broad gain profile. Single mode operation was achieved with the side mode suppression ratio of 21 dB when the optical feed back was provided by a mirror pattern consisting of 9 micromirrors. Moreover, two-color lasing was demonstrated with two laser lines having frequency difference in the THz range. The incorporation of DMD in the ECL enables great flexibility and many unique features, such as high tuning speed independent to the tuning step, two-color or multi-color lasing, and adjustable intensity for individual laser lines.
[Show abstract][Hide abstract] ABSTRACT: A novel approach is demonstrated on the synthesis of hollow carbon nanospheres (HCNs) and their applications as color converter for white light-emitting diodes. HCNs were synthesized in a hydrothermal process using hexamethylenetetramine as precursor. The synthesis involves a template-less and one-step aqueous method for the first time, which enables the growth of HCNs with the temperature as low as 160 degrees C. HCNs solutions exhibit strong yellow-green emission under ultraviolet light excitation and possess typical excitation-dependent photoluminescence (PL) behavior as carbon nanoparticles. We also used a facile coating method to coat a blue LED with HCNs layer which plays a role as color-converted phosphor. The LED shows bright white light, and the spectrum involves two main components, one-from the blue LED chip centered at 455 nm and one from HCNs centered at 520 nm.
[Show abstract][Hide abstract] ABSTRACT: InPBi was predicted to be the most robust infrared optoelectronic material but also the most difficult to synthesize within In-VBi (V = P, As and Sb) 25 years ago. We report the first successful growth of InPBi single crystals with Bi concentration far beyond the doping level by gas source molecular beam epitaxy. The InPBi thin films reveal excellent surface, structural and optical qualities making it a promising new III-V compound family member for heterostructures. The Bi concentration is found to be 2.4 ± 0.4% with 94 ± 5% Bi atoms at substitutional sites. Optical absorption indicates a band gap of 1.23 eV at room temperature while photoluminescence shows unexpectedly strong and broad light emission at 1.4-2.7 μm which can't be explained by the existing theory.
[Show abstract][Hide abstract] ABSTRACT: We propose a novel semiconductor compatible path for nano-graphene synthesis using precursors containing C-Br bonding and liquid catalyst. The unique combination of CBr4 as precursor and Ga as catalyst leads to efficient C precipitation at a synthesis temperature of 200°C or lower. The non-wetting nature of liquid Ga on tested substrates limits nano-scale graphene to form on Ga droplets and substrate surfaces at low synthesis temperatures of T ≤ 450°C and at droplet/substrate interfaces by C diffusion via droplet edges when T ≥ 400°C. Good quality interface nano-graphene is demonstrated and the quality can be further improved by optimization of synthesis conditions and proper selection of substrate type and orientation. The proposed method provides a scalable and transfer-free route to synthesize graphene/semiconductor heterostructures, graphene quantum dots as well as patterned graphene nano-structures at a medium temperature range of 400-700°C suitable for most important elementary and compound semiconductors.
[Show abstract][Hide abstract] ABSTRACT: A theoretical investigation on explanation of the composition profile in triangular and hexagonal cross-sections of InGaN/GaN core–shell nanowires is presented by combining the finite elements method (FEM) and method of moving asymptotes (MMA) in the framework of thermodynamics. Our models can account for strain effect on indium composition. In both models, the maximum indium content through segregation arises either at the side length or at the corner of the InGaN shell. The simulated results are found in good agreement with those of experimental data, thus providing a good guidance for the growth of high indium concentration of InGaN/GaN core–shell nanowires.
Solid State Communications 01/2014; 178:1–6. DOI:10.1016/j.ssc.2013.10.011 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report on the growth of InGaP metamorphic layer by gas source molecular-beam epitaxy. After optimization of the growth temperatures of the compositionally graded InGaP layer and the indium content in the top metamorphic InGaP layer, almost fully relaxed metamorphic layer was obtained with surface roughness of only about 2.17 nm. Strong photoluminescence signals were measured from both InGaAs quantum well and InAs quantum dots embedded in the metamorphic layer, indicating that the top metamorphic layer had low density of threading dislocations.
[Show abstract][Hide abstract] ABSTRACT: Photoluminescence (PL) measurements are performed on one GaSb/AlGaSb single-quantum-well (SQW) sample and two dilute-bismuth (Bi) GaSb/AlGaSb SQW samples grown at 360 and 380 °C, at low temperatures and under magnetic fields. Bimodal PL features are identified in the dilute-Bi samples, and to be accompanied by abnormal PL blueshift in the sample grown at 360 °C. The bimodal PL features are found to be from similar origins of band-to-band transition by magneto-PL evolution. Analysis indicates that the phenomenon can be well interpreted by the joint effect of interfacial large-lateral-scale islands and Al/Ga interdiffusion due to Bi incorporation. The interdiffusion introduces about 1-monolayer shrinkage to the effective quantum-well thickness, which is similar to the interfacial islands height, and the both together result in an unusual shallow-terrace-like interface between GaSbBi and AlGaSb. A phenomenological model is established, the Bi content of isoelectronic incorporation and the exciton reduced effective mass are estimated for the GaSbBi sample grown at 380 °C, and a value of about 21 meV/% is suggested for the bandgap bowing rate of GaSbBi. An effective routine is suggested for determining the Bi content and the depth of the shallow-terraces at interface in dilute-Bi SQW structures.
[Show abstract][Hide abstract] ABSTRACT: A first-principles study has been performed to evaluate the electronic structure and thermoelectric properties of Bi-2(Te1-xSex)(3) compound. The transport coefficients are then calculated within the semiclassical Boltzmann theory, and further evaluated as a function of chemical potential assuming a constant relaxation time and an averaged thermal conductivity. Our theoretical calculations show that the ZT value is 1.43 for Bi-2(Te1-xSex)(3) system, and it agrees well with previous experimental data. Crown Copyright
Solid State Communications 02/2013; 155:34–39. DOI:10.1016/j.ssc.2012.10.037 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report recent progresses on growth of dilute nitrides and 1.3 µm lasers on GaAs using molecular beam epitaxy at Chalmers University of Technology, Sweden. Intense long wavelength light emission up to 1.71 µm at room temperature has been achieved by using the N irradiation method and the low growth rate. It is also demonstrated that incorporation of N in relaxed InGaAs buffer grown on GaAs strongly enhances the optical quality of metamorphic InGaAs quantum wells. With the optimized growth conditions and the laser structures, we demonstrate 1.3 µm GaInNAs edge emitting lasers on GaAs with state-of-the-art performances including a low threshold current density, a high-characteristic temperature, a 3 dB bandwidth of 17 GHz and uncooled operation at 10 Gbit/s up to 110 °C. The laser performances are comparable with the best reported data from the InGaAsP lasers on InP and is superior to the InAs quantum dot lasers on GaAs.
[Show abstract][Hide abstract] ABSTRACT: The optical properties of GaInNAs quantum wells (QW) grown by molecular beam epitaxy with and without N-irradiation (i.e. grown by the classical method) were investigated by the contactless electroreflectance (CER), temperature-dependent photoluminescence (PL) and time-resolved PL (TRPL). From CER measurements it was concluded that one type of nitrogen nearest-neighbor environment (In-rich environment) is dominant for GaInNAs QWs grown with N-irradiation whereas various nitrogen environments are present for the reference GaInNAs QW (i.e. the sample obtained by the classical method). PL and TRPL measurements clearly show that the optical properties of GaInNAs QWs are affected mainly by the amount of the incorporated nitride atoms. It was observed that the PL decay time decreased from ~200 to ~40 ps when the nitrogen concentration is increased from 0.8 to 2.2%. In addition, the presence of As flux during N-irradiation reduces the amount of the incorporated nitrogen and simultaneously improves the optical quality of GaInNAs QWs (i.e. it weakens the carrier localization at low temperatures and improves the quantum efficiency of PL).
[Show abstract][Hide abstract] ABSTRACT: We present a novel computational method by combining the finite element method and the method of moving asymptotes to study the dislocation-induced composition profile in alloy semiconductors. Segregated cylindrical nanoscale regions appear around the dislocation core. We find that the dominant driving force of non-uniform composition is strain contribution. Moreover, the method can be applied to the dislocated nanoscale heterostructures which are inaccessible by atomic treatment.
Solid State Communications 08/2010; 150(29-30):1275-1278. DOI:10.1016/j.ssc.2010.05.023 · 1.90 Impact Factor