Interdiffusion effect on quantum-well structures grown on GaSb substrate

We have modeled the effect of compositional interdiffusion on the optical properties of GaSb/AlGaSb and InGaAsSb/AlGaAsSb quantum-well structures grown on GaSb substrate. Blue shifts of emission wavelength as large as 270 nm and 700 nm are predicted from a 6 nm wide interdiffused GaSb/AlGaSb quantum-well for a diffusion length of 3 nm, and from a 10 nm wide interdiffused InGaAsSb/AlGaAsSb quantum-well for a diffusion length of 5 nm, respectively. The effects of the as-grown quantum-well width and applied electric field on the emission wavelength and their relationship to the interdiffusion are also investigated.     

InAs/GaSb superlattices fabricated by metalorganic chemical vapor deposition

The possibility of fabricating InAs/GaSb strained-layer superlattices by metalorganic chemical vapor deposition has been experimentally demonstrated. The results of transmission electron microscopy and photoluminescence spectroscopy investigations showed that the obtained structures comprise an InAs?GaSb superlattice on a GaSb substrate consisting of 2-nm-thick InAs and 3.3-nm-thick GaSb layers.

     

Metallorganic chemical vapor deposition of InAs/GaSb superlattices on GaAs substrates using a two-step InAs buffer layer

InAs/GaSb type II superlattices (T2SLs) were grown heteroepitaxially, via metallorganic chemical vapor deposition (MOCVD), on GaAs substrates. The 7% lattice mismatch between the T2SL and GaAs substrate was accommodated through the use of a two-step InAs buffer layer. The periodicity of the grown structures was confirmed by X-ray diffraction (XRD). FTIR measurements of the structures yielded cutoff wavelength values from 4.9 μm to 8.7 μm, which, as expected, scaled with thickness of the InAs in the SL structure. Kronig-Penny modeling of the structures produced the general trend of the experimental data.     

Ab initio study of electronic structures of InAs and GaSb nanowires along various crystallographic orientations

InAs and GaSb nanowires oriented along different crystallographic axes—the [0 0 1], [1 0 1] and [1 1 1] directions of zinc-blende structure—have been studied utilizing a first-principles derived nonlocal screened atomic pseudopotential theory, to investigate the band structure, polarization ratio and effective masses of these semiconductor nanowires and their dependences on the wire lateral size and axis orientation. The band energy dispersion over entire Brillouin zone and orbital energy are determined and found to exhibit different characteristics for three types of wires. There is an explicit dispersion hump in the conduction bands of [0 0 1] nanowires with two larger diameters and [1 0 1] nanowires with the smallest diameter considered. Moreover, the [1 1 1] nanowires are shown to exhibit very different orbital energy for the maximum valence state at the zone-boundary point, compared with [0 0 1] and [1 0 1] nanowires. These differences present significant and detailed insight for experimental determination of the band structure in InAs and GaSb nanowires. Furthermore, we study the polarization ratio of these nanowires for different orientations. Our calculation results indicate that, for the same lateral size, the [1 1 1] nanowires give extraordinarily higher polarization ratio compared to nanowires along the other two directions, and at the same time have larger band-edge photoluminescence transition intensity. Consequently, the [1 1 1] nanowires are predicted to be better suitable for optoelectronic applications. We also significantly find that polarization ratio and transition intensity displays different varying trend of dependence on lateral size of nanowires. Specially, the calculated polarization ratio is shown to increase with the decreasing size, which is opposite to the behavior displayed by the optical transition intensity. The predicted polarization ratios of [1 0 1] and [1 1 1] nanowires for 10.6 Å diameter approach the limit of 100%. In addition, the electron and hole masses for InAs and GaSb nanowires with different crystallographic axes have been calculated. For the [1 0 1] and [1 1 1] oriented nanowires, the hole masses are predicted to be around 0.1–0.2 m₀, which are notably smaller than the values (∼0.5 m₀) along the same direction for their bulk counterparts. Thus, we demonstrates an inspired possibility of obtaining a high hole mobility in nanowires that is not available in bulk. The small hole mobility is interpreted as to be associated with the strong electronic band mixing in nanowires.     

High resolution scanning gate microscopy measurements on InAs/GaSb nanowire Esaki diode devices

Gated transport measurements are the backbone of electrical characterization of nanoscale electronic devices. Scanning gate microscopy （SGM） is one such gating technique that adds crucial spatial information, accessing the localized properties of semiconductor devices. Nanowires represent a central device concept due to the potential to combine very different materials. However, SGM on semiconductor nanowires has been limited to a resolution in the 50-100 nm range. Here, we present a study by SGM of newly developed III-V semiconductor nanowire InAs/GaSb heterojunction Esaki tunnel diode devices under ultra-high vacuum. Sub-5 nm resolution is demonstrated at room temperature via use of quartz resonator atomic force microscopy sensors, with the capability to resolve InAs nanowire facets, the InAs/GaSb tunnel diode transition and nanoscale defects on the device. We demonstrate that such measurements can rapidly give important insight into the device properties via use of a simplified physical model, without the requirement for extensive calculation of the electrostatics of the system. Interestingly, by precise spatial correlation of the device electrical transport properties and surface structure we show the position and existence of a very abrupt （〈10 nm） electrical transition across the InAs/GaSb junction despite the change in material composition occurring only over 30-50 nm. The direct and simultaneous link between nanostructure composition and electrical properties helps set important limits for the precision in structural control needed to achieve desired device performance.     

生长温度对InAs／GaSb超晶格晶体结构和表面形貌的影响

采用分子束外延(MBE)技术,在GaSb(100)衬底上外延生长InAs(4ML)/GaSb(8ML)超晶格(SLs).研究了生长温度(400～440℃)对超晶格晶体结构和表面形貌的影响.结果表明,420℃生长的超晶格结构完整和表面粗糙度最小,其荧光光谱(PL)峰值波长在约2.54μm处,响应光谱50%截止波长在约2.4μm处.通过控制快门顺序形成InSb和混合两种界面,并发现生长温度强烈影响混合界面InAs/GaSb超晶格结构和表面形貌,而对InSb界面超晶格的影响较小.     

Post-growth annealing of type-II GaSb/GaAs quantum dots grown with different V/III ratios

We report the influence of V/III beam-equivalent-pressure ratios and post-growth annealing on the photoluminescence of GaSb quantum dots grown on GaAs(1 0 0) by molecular beam epitaxy. Increasing the V/III beam-equivalent-pressure ratio from 3 to 5 and then to 7 results in decreased photoluminescence intensity and redshifts the photoluminescence wavelength. The post-growth annealing blueshifts the quantum dot photoluminescence emission and decreases the full-width-at-half-maximum of the photoluminescence peak when annealing temperature is increased above 800 °C. The blueshift behavior is found to be independent on the V/III ratios indicating a similar atomic interdiffusion mechanism for all investigated samples regardless of the quantum dot properties. The photoluminescence intensities of the three samples experience an increase after moderate annealing. Whereas the intensity of the sample with the highest V/III ratio further increases, the intensity of the sample with lower V/III ratios decreases again upon higher annealing steps above 900 °C. Furthermore, temperature- and power dependent photoluminescence measurements are performed on as-grown and 870 °C annealed samples with V/III ratios of 3 and 7 in order to study the reduced quantum dot confinement in more detail.     

Optical gain calculation of mid-infrared InAsN/GaSb quantum-well laser for tunable absorption spectroscopy applications

We report on optical gain calculations of a dilute-nitride mid-infrared laser structure designed to be grown on InAs substrate. The active region is composed of several strain-compensated type-II “W”-like InAsN/GaSb/InAsN quantum wells adapted to operate near 3.3 μm at room temperature. For typical injected carrier density σ = 1.1012 cm^− 2, the theoretical laser structure performances reveal a gain value at around 1000 cm^− 1 at 300 K, inducing a modal gain value equal to 50 cm^− 1. Low radiative current densities lower than 100 A/cm² are predicted, indicating that this dilute-nitride structure could operate at 300 K with small threshold current density.     

Electrical characterization of InAs/GaAs quantum dot structures

The electrical properties of InAs quantum dots (QD) in InAs/GaAs structures have been investigated by space charge spectroscopy techniques, current–voltage and capacitance–voltage measurements. Au/GaAs/InAs(QD)/GaAs Schottky barriers as well as ohmic/GaAs/InAs(QD)/GaAs/ohmic structures have been prepared in order to analyze the apparent free carrier concentration profiles across the QD plane, the electronic levels around the QD and the electrical properties of the GaAs/InAs(QD)/GaAs heterojunction. Accumulation and/or depletion of free carriers at the QD plane have been observed by Capacitance–Voltage (C–V) measurements depending on the structure parameters and growth procedures. Similarly, quantum dot levels which exhibit distributions in energy have been detected by Deep Level Transient Spectroscopy (DLTS) and Admittance Spectroscopy (AS) measurements only on particular structures. Finally, the rectification properties of the InAs/GaAs heterojunction have been investigated and the influence of the related capacitance on the measured capacitance has been evidenced.     

InAs/GaAs multiple quantum dot structures grown by LP-MOVPE

Structures with self-organised InAs quantum dots in a GaAs matrix were grown by the low pressure metal–organic vapour phase epitaxy (LP-MOVPE) technique. Photoluminescence and atomic force microscopy were used as the main characterisation methods for the growth optimisation. The properties of multiple-stacked quantum dot structures are influenced by the thickness of the GaAs separation layers (spacers) between quantum dot-containing InAs layers, by the InAs layer thickness, by arsine partial pressure during growth, and by group III precursor flow interruption time.     

Emission characteristics improvement in structures with InAs/GaAsN/InGaAsN superlattices

The influence of some parameters of nitrogen-containing heterostructures InAs/GaAsN/InGaAsN with strain-compensated superlattices (SCSL) on their emission characteristics has been studied. It is established that the net strain in the structure affects the photoluminescence (PL) linewidth, internal quantum efficiency, intensity, and wavelength. The maximum PL intensity and minimum full width at half maximum (FWHM) of the PL line were achieved with small strains (0–0.2%), whereas the maximum wavelengths (∼1.76 μm) observed for large strain (about +1%). By adding multilayer InAs inserts in the active InGaAsN quantum well in combination with using strain-compensated GaAsN/InGaAsN superlattices, it is possible to control the room-temperature emission wavelength in the range of 1.45–1.76 μm without significantly deteriorating the emissiion characteristics.     

Electroluminescence enhancement of SiGe/Si multiple quantum wells through nanowall structures

The enhancement of light extraction from Si(0.5)Ge(0.5)/Si multiple quantum wells (MQWs) with nanowall structures fabricated by electron cyclotron resonance (ECR) plasma etching is presented. It is shown that the ECR plasma treatment does not damage the crystalline quality. At a driving current of 5.5 × 10(6)?A?m(-2), the light output intensity of the MQWs with nanowall structures shows an enhancement of about 50% compared with that of the original MQWs. In addition to the enhanced light extraction, the improved optoelectronic properties are also attributed to the strain relaxation in nanowall structures.     

Capacitance transient analysis of different-sized InAs/GaAs quantum dot structures

The energy states of InAs/GaAs self-assembled quantum dots (QDs) were analyzed by comparing between two QD systems with different QD sizes. The electrical properties of the QD systems were investigated via capacitance-voltage measurements and capacitance transient spectroscopy (also known as deep-level transient spectroscopy) with selective carrier injection and extraction which can be achieved with very small pulse amplitude under bias variation. For the large QDs, several energy states were found with the use of selective carrier injection and extraction. The thermal-activation energies obtained from the capacitance transient spectra of the large QDs were distributed from 70 to 600 meV. This energy distribution was originated from the quantized states of the individual QDs and the size distribution of the QDs. The spectra of the small QDs showed a well-defined energy state of E(c) - 132 meV. From these results, it was estimated that two to four electrons fill a single QD under the proper measurement bias of 0.2 V pulse.     

Limits in growing TlGaAs/GaAs quantum-well structures by low-temperature molecular-beam epitaxy

TlGaAs/GaAs multiple-quantum-well (MQW) structures were grown on GaAs substrates at a substrate temperature of 190 °C by molecular-beam epitaxy. The MQW structures were intended to consist of four identical TlGaAs wells, each of which is sandwiched by GaAs barrier layers. X-ray diffraction was used to investigate the limits to Tl content and thickness of the TlGaAs well layer for forming the MQW structures. Successful growth of TlGaAs/GaAs MQW structures having nominal Tl contents of 6, 8, and 9% was confirmed for the three different well thicknesses of about 15, 10, and 5 nm, respectively, while further increase in Tl content resulted in failure in forming MQW structures. The bounds for forming the MQW structures are discussed in terms of the epitaxial thickness of TlGaAs. The effect of the MQW structures on retarding the formation of Tl droplets is pointed out.     

Lasing in submonolayer InAs/AlGaAs structures without external optical confinement

Structures having a set of planes with submonolayer InAs inclusions in an AlGaAs matrix were fabricated and studied. Lasing was observed as a result of optical excitation. It is shown that lasing takes place via the ground state of excitons localized at InAs islands and may be achieved without external optical confinement of the active region by wide-gap layers of lower refractive index. The low threshold excitation density shows that these structures may be used to develop low-threshold injection lasers in the visible range, exciton waveguides, and self-contained microcavities. Pis’ma Zh. Tekh. Fiz. 24, 58–66 (July 26, 1998)     

Growth of InAs/InP core-shell nanowires with various pure crystal structures

We have studied the epitaxial growth of an InP shell on various pure InAs core nanowire crystal structures by metal-organic vapor phase epitaxy. The InP shell is grown on wurtzite (WZ), zinc-blende (ZB), and {111}- and {110}-type faceted ZB twin-plane superlattice (TSL) structures by tuning the InP shell growth parameters and controlling the shell thickness. The growth results, particularly on the WZ nanowires, show that homogeneous InP shell growth is promoted at relatively high temperatures (～500?°C), but that the InAs nanowires decompose under the applied conditions. In order to protect the InAs core nanowires from decomposition, a short protective InP segment is first grown axially at lower temperatures (420-460?°C), before commencing the radial growth at a higher temperature. Further studies revealed that the InP radial growth rate is significantly higher on the ZB and TSL nanowires compared to WZ counterparts, and shows a strong anisotropy in polar directions. As a result, thin shells were obtained during low temperature InP growth on ZB structures, while a higher temperature was used to obtain uniform thick shells. In addition, a schematic growth model is suggested to explain the basic processes occurring during the shell growth on the TSL crystal structures.     

Electroluminescence and current-voltage characteristics of n-type porous silicon structures

An investigation is made of a set of n-type porous-silicon structures exhibiting high electroluminescence efficiency and low degradation, and results are presented. These results demonstrate that operating voltages corresponding to those of standard ceramic-metal-oxide-semiconductor technology can realistically be achieved. Pis’ma Zh. Tekh. Fiz. 23, 70–76 (June 12, 1997)     

Electroluminescence of new dyed polymer films in sandwich structures

Electroluminescence (EL) from sandwich structures with emitting layers based on poly(N-epoxypropylcarbazole) (PEPC) doped with a boron difluoride organic dye complex was discovered and studied. The EL is implemented in heterostructures with Al-or In-based injecting heterojunctions possessing better technological properties as compared to those of conventional magnesium-silver electrodes. It is established that EL is controlled by the bulk recombination of charge carriers, whereby dye molecules act as the recombination centers. The EL efficiency is maximum in systems with a 50 mass % dye content in a submicron polymer film. The growth in EL quenching with an increase in the polymer film thickness is related to accumulation of the bulk space charge within a short time after the application of electric field.     

Electroluminescence of Si-SiO2-Si3N4 structures

Si-SiO₂-Si₃N₄ heterostructures obtained by depositing silicon nitride onto a silicon substrate oxidized in dry oxygen were studied by measuring electroluminescence (EL) in the electrolyte-insulator-semiconductor system. The EL spectra display the emission bands typical of a silicon oxide layer and an intense band at 2.7 eV characteristic of the radiative relaxation of excited silylene centers. Since these centers are typical of silicon oxynitride layers, it is concluded that such a layer is formed at the boundary.