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To exploit the promising properties of semiconductor nanowires and ensure the uniformity required to achieve device integration, their position on the growth substrate must be controlled. This work demonstrates the direct patterning of a SiO2/Si substrate using focused ion beam (FIB) patterning to control self-catalyzed GaAsSb nanowire growth in molecular beam epitaxy (MBE). Besides position control, FIB patterning parameters influence nanowire yield, composition and structure. Total ion dose per hole is found to be the most important parameter. Yield of single nanowires ranges from ≈34% to ≈83%, with larger holes dominated by multiple nanowires per hole. Areas exposed to low ion beam doses are selectively etched by routine pre-MBE HF cleaning, enabling patterning and nanowire nucleation with minimal damage to the Si substrate. The optical and electronic properties of nanowires are found to depend on the ion dose used during patterning, indicating the potential for FIB patterning to tune nanowire properties. These findings demonstrate the possibility for a FIB lithography protocol which could provide a rapid and direct patterning process for flexible controlled nanowire growth. [ABSTRACT FROM AUTHOR]

Semiconductor nanowire lasers can produce guided coherent light emission with miniaturized geometry, bringing about new possibilities for a variety of applications including nanophotonic circuits, optical sensing, and on-chip and chip-to-chip optical communications. Here, we report on the realization of single-mode and room-temperature lasing from 890 to 990 nm, utilizing a novel design of single nanowires with GaAsSb-based multiple axial superlattices as a gain medium under optical pumping. The control of lasing wavelength via compositional tuning with excellent room-temperature lasing performance is shown to result from the unique nanowire structure with efficient gain material, which delivers a low lasing threshold of ∼6 kW/cm2 (75 μJ/cm2 per pulse), a lasing quality factor as high as 1250, and a high characteristic temperature of ∼129 K. These results present a major advancement for the design and synthesis of nanowire laser structures, which can pave the way toward future nanoscale integrated optoelectronic systems with superior performance. [ABSTRACT FROM AUTHOR]

Annealing effects on the properties of InGaAsN/GaAsSb type-II quantum well (QW) diodes grown on InP substrates by molecular beam epitaxy (MBE) were studied. It was found that the peak of electroluminescence (EL) shows drastic red-shift and the reverse-biased current of the current-voltage ( I- V) characteristic of the type-II QW diode increases by the annealing. In addition, we found that the electron effective mass of the InGaAsN layer of the type-II InGaAsN/GaAsSb multiple quantum wells (MQWs) estimated by the temperature dependence of the amplitude of the Shubnikov-de Haas (SdH) oscillations decreases by the annealing. The mechanism of the observed annealing effects was discussed. [ABSTRACT FROM AUTHOR]

As an important candidate for novel infrared semiconductor lasers, the optical properties of GaAsSb-based multiple quantum wells (MQWs) are crucial. The temperature- and excitation power-dependent photoluminescence (PL) spectra of the GaAs0.92Sb0.08/Al0.2Ga0.8As MQWs, which were grown by molecular beam epitaxy, were investigated and are detailed in this work. Two competitive peaks were observed from 40 K to 90 K. The peak located at the low-energy shoulder was confirmed to be localized states emission (LE) and the high-energy side peak was confirmed to be free-carrier emission by its temperature-dependent emission peak position. It is observed that the LE peak exhibited a blueshift with the increase of laser excitation power, which can be ascribed to the band filling effect of localized states. Our studies have great significance for application of GaAsSb-based MQWs in infrared semiconductor lasers. [ABSTRACT FROM AUTHOR]

We have successfully mitigated the out-diffusion of Ge during molecular beam epitaxy of InGaAs on Ge by using a GaAsSb barrier layer as evidenced by secondary ion mass spectroscopy. Compared to GaAs, this GaAsSb barrier layer also results in a smoother surface morphology with its root-mean-square roughness of 0.7 nm due to the surfactant effect of Sb. Using a step-graded GaAsSb and AlGaAsSb metamorphic buffer layer, a 200-nm p-type In0.53Ga0.47As layer grown on Ge exhibits a hole mobility of 38 cm2 V−1 s−1 with a hole concentration of 2.6 × 1019 cm−3 at 300 K and 53 cm2 V−1 s−1 with a hole concentration of 1.2 × 1019 cm−3 at 77 K. [ABSTRACT FROM AUTHOR]

Ternary semiconductor nanowire arrays enable scalable fabrication of nano-optoelectronic devices with tunable bandgap. However, the lack of insight into the effects of the incorporation of Vy element results in lack of control on the growth of ternary III-V1-yVy nanowires and hinders the development of high-performance nanowire devices based on such ternaries. Here, we report on the origins of Sb-induced effects affecting the morphology and crystal structure of self-catalyzed GaAsSb nanowire arrays. The nanowire growth by molecular beam epitaxy is changed both kinetically and thermodynamically by the introduction of Sb. An anomalous decrease of the axial growth rate with increased Sb2 flux is found to be due to both the indirect kinetic influence via the Ga adatom diffusion induced catalyst geometry evolution and the direct composition modulation. From the fundamental growth analyses and the crystal phase evolution mechanism proposed in this Letter, the phase transition/stability in catalyst-assisted ternary III-V-V nanowire growth can be well explained. Wavelength tunability with good homogeneity of the optical emission from the self-catalyzed GaAsSb nanowire arrays with high crystal phase purity is demonstrated by only adjusting the Sb2 flux. [ABSTRACT FROM AUTHOR]

Abstract: This work describes a regular solution model that considers the free energy of the surface monolayer to explain the orientation-dependent phase separation in GaAsSb. In the proposed model, only the interaction between the second nearest-neighboring atoms sitting on the same monolayer contributes to the interaction parameter. Consequently, the parameter reduces to Ω/2 and Ω/3 for (111)B GaAsSb and (100) GaAsSb, where Ω denotes the parameter of bulk GaAsSb. By including the strain effect, the proposed model thoroughly elucidates the immiscibility behavior of (111)B GaAsSb and (100) GaAsSb. [Copyright &y& Elsevier]

Abstract: We report the GaAsSb bulk layers and GaAsSb/GaAs quantum wells (QWs) grown on (111)B GaAs substrates by gas source molecular beam epitaxy. We found that Sb composition in the GaAsSb epilayers is very sensitive to the substrate temperature. The composition drops from 0.35 to 0.16 as the substrate temperature increases from 450 to 550°C. The [111]B-oriented GaAsSb epilayers show phase separation when the substrate temperature is lower than 525°C. For a GaAsSb/GaAs multiple quantum wells (MQWs) structure composed of five periods of 5nm GaAs0.73Sb0.27 QW and 30nm GaAs barrier, the room temperature photoluminescence emission is located at 1255, 80nm longer than the [100]-oriented sample with the same Sb composition. The peak wavelength shows significant blue shift as the excitation level increases, which evidences the type-II band alignment in this heterostructure. [Copyright &y& Elsevier]

We have studied the molecular beam epitaxy (MBE) growth of GaAsSb on GaAs substrates. The optical properties and composition of GaAsSb layer strongly depend on the growth temperature, the Ga growth rate, and the As and Sb fluxes and their ratios. We also report on two GaAsSb-GaAs photodiode structures operating at 1.3 μm. The peak quantum efficiency was 54% for the GaAsSb resonant-cavity-enhanced (RCE) p-i-n photodiode and 36% for the RCE GaAsSb avalanche photodiode (APD) with separate absorption, charge, and multiplication regions (SACM). At 90% of the breakdown, the dark current of the SACM APD was 5 nA. The GaAsSb SACM APD also exhibited very low multiplication noise and keff was approximately 0.1, which is the lowest ever reported for APDs operating at 1.3 μm. [ABSTRACT FROM PUBLISHER]

The high optical gain of InGaAs/GaAsSb/InAlAs nano-scale heterostructure has motivated us for its further study under variable temperature and electric field. The presented work is devoted to show the impact of variable temperature and electric field on optical gain characteristics of InGaAs/GaAsSb/InAlAs nano-scale heterostructure which has been assumed to grow on lattice matched GaAs substrate. A six band k.p approach has been utilized to optimize the heterostructure in terms of carrier's wavefunctions, local carriers' density in conduction and valence band and dispersion curves followed by calculating momentum matrix elements and the optical gain spectra. According to the calculation results, the increasing range of temperature (having range of 100–300 K at the interval of 50 K) can control the peak gain significantly (6070 cm−1 to 4470 cm−1) with the red shift in wavelength; while enhanced order of electric field at room temperature can control the gain slightly (4470 cm−1 to ~4150 cm−1) with fine red shift in wavelength. The results achieved in this work will definitely prove the method of controlling the gain characteristics as excellent; and the heterostructure studied will be suitable in design of tunable NIR (near infrared) light sources. • Design of novel QW heterostructure having W-shape structure with type-II nature. • Suitable heterostructure for high peak optical gain. • Broad tuning of gain characteristics with red shifted wavelength on temperature increase. • Fine tuning of the gain characteristics by increasing the field strength with red shifted wavelength. • Suitable for operation with fine tuning between the wavelength region ~1550–1680 nm. [ABSTRACT FROM AUTHOR]

Carrier profiles of MBE grown Ga(As,Sb)/GaAs heterostructures were studied. In low Sb content samples of Ga(As,Sb)/GaAs grown by MBE the experimentally measured carrier profiles exhibit double dips in concentration, whereas a single large dip is ob-tained for higher Sb content with larger lattice-mismatched samples. The capacitance voltage(C-V) carrier profile of a Schottky barrier n- N heterojunction of Au/n-GaAsSb/ N-GaAs has been modeled and double dips occur when nonuniform doping is present which may explain the experimentally observed double dips in a GaAsSb/GaAs specimen. For large lattice mismatch and therefore large heterointerface charge density in the model, the accumulation peak due to ΔE is shown to be overwhelmed by a pro-nounced single dip as observed in higher Sb content samples such as GaAsSb/ GaAs and GaAs/GaAsSb. [ABSTRACT FROM AUTHOR]

A type-II GaAsSb Double Heterojunction Bipolar Transistor (DHBT) with an AlInP emitter, doping-graded GaAsSb base, and InP collector has been grown by molecular beam epitaxy. The 0.38 \mum emitter devices have been fabricated by a triple-mesa wet etch process and demonstrated fT/fMAX=470/540~{\rm GHz} at JC=5.1~mA/\mum^{2} and VCB=0.65~\rm V. This performance is comparable with composition-graded base devices with similar emitter width. [ABSTRACT FROM AUTHOR]

Abstract: Strain-compensated InGaAs/GaAsSb type II multiple quantum wells (MQWs) were grown by molecular beam epitaxy (MBE) and their optical and electrical properties were studied. High-quality strain-compensated type II MQWs were successfully grown, which have longer emission wavelength than that of lattice-matched type II MQWs. PL peak energy at 300K of the strain-compensated type II MQWs, where the InGaAs layer has 0.6% tensile strain and GaAsSb layer has 0.6% compressive strain, shows a red-shift of 43meV, which is 12meV larger than the calculated energy shift of 31meV. In addition, the PL intensity and the electron mobility of the strain-compensated MQWs are comparable to those of the lattice-matched MQWs, suggesting that the crystal quality of the strain-compensated MQWs is good and are very promising for low dark current photodiodes in the 2μm wavelength region. [ABSTRACT FROM AUTHOR]

In this study, the optical properties of InAs quantum dots (QDs) were characterized using photoluminescence (PL) measurements. The QDs, capped with GaAs and GaAs 1−x Sb x (x = 6%) strain-reducing layer (SRL), were grown by Molecular Beam Epitaxy. Temperature-dependent photoluminescence (TDPL) of both ground state (GS) and first excited state (ES) was carried out through the analysis of the PL peak position as well as the integrated PL intensity. The temperature dependence of the integrated PL intensity shows the carrier trapping in the potential barrier at the interface between the capping layer and QDs in both samples at low temperatures for the GS and ES. The Excitation density dependent photoluminescence (EDPL) showed a redshift of the GS and ES PL peak energies with increasing excitation density. We attribute this variation to the bandgap renormalization (BGR) effect. The potential barrier reduction for the GaAsSb-capped QDs increases carrier injection efficiency inside the QDs, giving rise to a larger BGR effect compared to the QDs capped with GaAs. With increasing temperature, BGR redshift varies considerably for the GaAs- capped QDs but less for the Q with GaAsSb SRL. This effect was explained using the population rate of carriers inside the QDs while taking into account the nonradiative recombination process for the two samples. Furthermore, the variation of the integrated intensity with the excitation power density grows superlinearly for the two samples for a temperature range from 10 K to 220 K. This behavior was explained by the random capture of carriers in the dots. The sample with GaAsSb SRL having a smaller potential barrier has reduced superlinear dependence at low temperatures. Losses mechanism has a significant impact on increasing the superlinear dependence at high temperatures. The ES showed a stronger superlinearity compared to the GS. This study helps to understand the optical mechanisms in some devices, such as QD lasers. • Photoluminescence (PL) of InAs quantum dots (QDs) capped by GaAs 0.94 Sb 0.06. • Carrier trapping in the potential barrier between the capping layer and QDs. • Using GaAsSb as a capping layer reduces the potential barrier. • Influence of temperature and excitation density on PL. • Dependence of band gap renormalization effect on temperature. [ABSTRACT FROM AUTHOR]