Double Heterostructure Research Articles

Synthesis, characterization and enhanced visible light photocatalytic activity of Bi2MoO6/Zn–Al layered double hydroxide hierarchical heterostructures

A Bi2MoO6/Zn–Al LDH heterostructure exhibits significantly enhanced photodegradation efficiency for RhB relative to Bi2MoO6 under visible light irradiation.

Temperature dependence of diffusion length, lifetime and minority electron mobility in GaInP

The mobility of electrons in double heterostructures of p-type Ga0.50In0.50P has been determined by measuring minority carrier diffusion length and lifetime. The minority electron mobility increases monotonically from 300 K to 5 K, limited primarily by optical phonon and alloy scattering. Comparison to majority electron mobility over the same temperature range in comparably doped samples shows a significant reduction in ionized impurity scattering at lower temperatures, due to differences in interaction of repulsive versus attractive carriers with ionized dopant sites. These results should be useful in modeling and optimization for multi-junction solar cells and other optoelectronic devices.

The effect of GaN thickness inserted between two AlN layers on the transport properties of a lattice matched AlInN/AlN/GaN/AlN/GaN double channel heterostructure

One AlInN/AlN/GaN single channel heterostructure sample and four AlInN/AlN/GaN/AlN/GaN double channel heterostructure samples with different values of the second GaN layer were studied. The interface profiles, crystalline qualities, surface morphologies, and dislocation densities of the samples were investigated using high resolution transmission electron microscopy, atomic force microscopy, and high-resolution X-ray diffraction. Some of the data provided by these measurements were used as input parameters in the calculation of the scattering mechanisms that govern the transport properties of the studied samples. Experimental transport data were obtained using temperature dependent Hall effect measurements (10–300K) at low (0.5T) and high (8T) magnetic fields to exclude the bulk transport from the two-dimensional one. The effect of the thickness of the second GaN layer inserted between two AlN barrier layers on mobility and carrier concentrations was analyzed and the dominant scattering mechanisms in the low and high temperature regimes were determined. It was found that Hall mobility increases as the thickness of GaN increases until 5nm at a low temperature where interface roughness scattering is observed as one of the dominant scattering mechanisms. When GaN thicknesses exceed 5nm, Hall mobility tends to decrease again due to the population of the second channel in which the interface becomes worse compared to the other one. From these analyses, 5nm GaN layer thicknesses were found to be the optimum thicknesses required for high electron mobility.

Growth, structure, optical and electrical properties of Si/2D Mg2Si/Si(111) double heterostructures and Schottky diodes on their base

AbstractMg2Si layers were grown on silicon by RDE at 150 °C and by SPE at 160 °C, and they were covered by silicon cap grown by MBE at 150‐180 °C. The silicide layers and the silicon cap were investigated by in situ and ex situ methods. The 2D Mg2Si layer continuity and electrical properties were conserved during cap growth. The point defects in the structure are dominated by contamination of the substrate and by diffusion of the not reacted Mg into silicon. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth, steady-state, and time-resolved photoluminescence study of CdTe/MgCdTe double heterostructures on InSb substrates using molecular beam epitaxy

CdTe/MgCdTe double heterostructures (DHs) are grown on InSb substrates using molecular beam epitaxy and reveal strong photoluminescence with over double the intensity of a GaAs/AlGaAs DH with an identical layer structure design grown on GaAs. Time-resolved photoluminescence of the CdTe/MgCdTe DH gives a Shockley-Read-Hall recombination lifetime of 86 ns, which is more than one order of magnitude longer than that of typical polycrystalline CdTe films. These findings indicate that monocrystalline CdTe/MgCdTe DHs effectively reduce surface recombination, have limited nonradiative interface recombination, and are promising for solar cells that could reach power conversion efficiencies similar to that of GaAs.

Electrical Properties of SbSI/Sb_2S_3 Single and Double Heterostructures

The SbSI/Sb2S3 single heterostructures as well as Sb2S3/SbSI/Sb2S3 and SbSI/Sb2S3/SbSI double heterostructures have been produced by applying CO2 laser treatment of p-type SbSI single crystals. The current voltage and transient characteristics of these heterostructures have been measured in temperatures below and above the SbSI single crystal Curie temperature (Tc = 293 K). The results have been tted with appropriate theoretical formulae to determine the following types of the investigated heterojunctions: P p SbSI/Sb2S3, p P p Sb2S3/ SbSI/Sb2S3 and P p P SbSI/Sb2S3/SbSI. In uence of the illumination on electrical properties of SbSI/Sb2S3 single and double heterostructures has been reported. Fabricated new structures may be potentially applicable in electronics and optoelectronics as a new type of metal ferroelectric semiconductor devices.

Low Dislocation Density and High Mobility GaN Layers for DHFET Channels Grown on High-Temperature AlN/AlGaN Buffer Layer by Ammonia MBE

The growth of AlN buffer layer at extremely high temperature (1100-1150oC) in ammonia MBE STE3N2 system is shown to be the key step to obtain high quality GaN layers for DHFET channels. The buffer layer sequence from c-sapphire substrate involved AlN, AlGaN/AlN superlattice and AlGaN transition layers. TEM study showed gradual decrease of threading dislocation density from (2-4)×1010 cm-2 in AlN to (9-10)×108 cm-2 in the top GaN active layer. The improvement of structural quality resulted in substantial increase in electron mobility up to 600-650 сm2/Vs in a 1.5-μm-thick GaN top layer lightly doped with silicon up to n=(3-5)×1016 cm-3. These results correspond to a good quality MOCVD GaN grown on sapphire and several times better than in conventional MBE. Employing such a GaN layer in a double heterostructure (DH) with the cap AlxGa1-xN barrier layer (x=0.25-0.4) allows to change the electron sheet density, mobility and sheet resistance in a two dimensional electron gas in the range of 1300-1700 cm2/V.s, (1.0-1.8)×1013 cm-2 and 230-400 Ω/, respectively. Application of this technology and DH design for growing on SiC substrates enabled one to manufacture a DHFET with a gate length of 0.5 μm for 0.03-4.0 GHz extra-broadband power amplifiers having Pout=2.5 W, gain 17-25 dB and efficiency 30%.

Electric and magnetic field effects on the excitonic properties of elliptic core–multishell quantum wires

The effect of eccentricity distortions of core–multishell quantum wires on their electron, hole and exciton states is theoretically investigated. Within the effective mass approximation, the Schrödinger equation is numerically solved for electrons and holes in systems with single and double radial heterostructures, and the exciton binding energy is calculated by means of a variational approach. We show that the energy spectrum of a core–multishell heterostructure with eccentricity distortions, as well as its magnetic field dependence, are very sensitive to the direction of an externally applied electric field, an effect that can be used to identify the eccentricity of the system. For a double heterostructure, the eccentricities of the inner and outer shells play an important role on the excitonic binding energy, especially in the presence of external magnetic fields, and lead to drastic modifications in the oscillator strength.

SiGeSn growth studies using reduced pressure chemical vapor deposition towards optoelectronic applications

In this contribution, we propose a laser concept based on a double heterostructure consisting of tensile strained Ge as the active medium and SiGeSn ternaries as cladding layers. Electronic band-structure calculations were used to determine the Si and Sn concentrations yielding a type I heterostructure with appropriate band-offsets (50meV) between strained Ge and SiGeSn. Reduced pressure chemical vapor deposition system was employed to study the laser structure growth. Detailed analyses regarding layer composition, crystal quality, surface morphology and elastic strain are presented. A strong temperature dependence of the Si and Sn incorporation has been obtained, ranging from 4 to 19at.% Si and from 4 to 12at.% Sn (growth temperatures between 350°C and 475°C). The high single crystalline quality and low surface roughness of 0.5–0.75nm demonstrate that our layers are suitable for heterostructure laser fabrication.

Properties of ‘bulk’ GaAsSbN/GaAs for multi-junction solar cell application: Reduction of carbon background concentration

GaAsSbN epitaxial films on GaAs substrate grown by metalorganic vapor phase epitaxy (MOVPE) were investigated for integration into multi-junction solar cells. These films are nominally lattice-matched to the GaAs substrate with band gap energies (Eg) in the 1–1.3eV range. The high background carbon concentrations often observed in MOVPE-grown dilute-nitride materials are correlated with poor minority carrier lifetime and hence low photoluminescence (PL) intensity. In the MOVPE growth of dilute-nitride materials, this background hole concentration is quite sensitive to the selection of the gallium and antimony precursor, and the growth temperature. The lowest background carbon concentration is achieved in the dilute-nitride-antimonide alloys when triethyl gallium (TEGa) and Tris-dimethylamino antimony (TrisSb) sources are utilized. Based on GaAsSb/GaAs superlattice (SL) growth, higher-Sb incorporation efficiency occurs when TEGa and TrisSb are utilized compared to films grown using trimethyl gallium (TMGa) and trimethly antimony (TMSb) precursors. The background hole concentration of GaAsSbN (Eg ~1.23eV) grown using TEGa and TrisSb is an order of magnitude lower than that observed when using TMGa and TMSb. Hall measurements indicate a background hole concentration of ~8.5×1017cm−3 (Eg ~1.23eV) from the thermally annealed GaAsSbN films grown at 525°C using TEGa and TrisSb. In addition, higher growth temperature 610°C is utilized for further reducing the background hole concentration (3.2×1017cm−3). Carrier lifetimes of up to ~448psec were obtained from thermally annealed GaAsSbN double hetero (DH) structure samples with energy bandgap ~1.25eV.

Theoretical analysis on optoelectronic performances of long wavelength transistor lasers: base width variation effects

We investigate the base width variation effects on various optical and electrical characteristics of double heterostructure long wavelength transistor laser (DH-LWTL). Considering the device structure, the base region geometry of a LWTL significantly affects its optoelectronic performance. We derive theoretical approximation of optical confinement factor (OCF), where we study the relationship between the base width and the OCF. In order to analyze optoelectronic performance of the LWTL, however, we have to consider the optical loss in base region with intervalence band absorption as the main factor in our calculation approach. We show that both the OCF and the optical loss have opposite trends with base width variation. Transient parameters including resonance peak and frequency are also inspected for their dependence on the base width as well as doping concentration. According to our simulations, we expect a minimum threshold current density of $$4.38\, \hbox {KA/cm}^{2}$$ and a maximum cut-off frequency of 28.22 GHz for 38 nm and 305 nm base widths, respectively. A relatively fast process of “carrier extinction” is also anticipated for narrow enough bases.

Double-heterostructure ridge-waveguide GaAs/AlGaAs phase modulator for 780 nm lasers

Results of a GaAs/AlGaAs-based phase modulator designed for an operating wavelength of 780 nm are presented for the first time. The modulator is based on a P-p-i-n-N double heterostructure and features a waveguide with a vertical W-shaped index profile optimized for low propagation losses and a ridge waveguide for lateral index-guiding. A phase modulation efficiency of 12°/V mm is reported. The propagation losses are determined to about 1.4 dB/cm.

Heterostructures for Optoelectronics: History and Modern Trends

Semiconductor revolution of the 20th century determined not only technological, but also social development of the modern society. The precursors of modern semiconductor electronics were Oleg Losev's discoveries of “crystadine” and “light-emitting diode (LED)” nearly 100 years ago. Creation of the transistor and semiconductor laser and LED based on the homo p-n structure became the most decisive step. Semiconductor optoelectronics was born with the creation of GaAs and GaAsP lasers and “LED.” The possibility to control the type and level of conductivity and injection in p-n junctions was the seed from which semiconductor electronics developed. Heterostructures-“man-made crystals”-solved a more general problem: the necessity to control electron and photon fluxes in crystals. The development of physics and technology for semiconductor heterostructures resulted in drastic changes in our everyday life. It is hardly possible to imagine our recent life without double-heterostructure (DH) laser-based telecommunication systems, without efficient DH LEDs, heterostructure bipolar transistors, and high electron mobility transistors (HEMTs) for high-frequency applications. DH lasers were introduced in every household with CD players. Heterostructure solar cells have been widely used for space and terrestrial applications. The first proposals for heterostructures in semiconductor devices were made as early as in the 1950s, but the most important experimental results were received at the end of the 1960s when the first ideal AlGaAs heterostructures and low threshold room-temperature lasers, efficient heterostructure LEDs, and solar cells were created. Later semiconductor heterostructure became laboratories of low-dimension electron gases. Molecular-beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) technologies were the basis for the development of new structures, including superlattices, and for the industrial production of a large family of heterostructure semiconductor devices. Quantum dot (QD)-based optoelectronics as a modern trend in optoelectronics is the subject of a more detailed consideration.

The Double-Heterostructure Concept: How It Got Started

The double-heterostructure (DH) concept for lasers and light-emitting diodes (LEDs) grew out of the prelaser context of increasing the speed of the early bipolar junction transistors. The 1954 idea was to change the energy gap itself, with a graded-gap base, or a wide-gap emitter. This led to the 1957 more general concept of quasi-electric fields and potentials in structures with a position-dependent energy gap. This paper gives a personal chronological account of the evolution of these concepts toward the 1963 proposal of the DH laser, including some blind alleys and blunders along the way.

Photonic Crystal Cavity With Double Heterostructure in GaN Bulk

In this study, the photonic crystal cavity has been designed, fabricated, and characterized in GaN bulk materials with the double heterostructure, which can provide high Q-factor. The cavity is characterized by optical pumping. The resonant mode is observed at the wavelength of 362 nm. The threshold of excitation power is found to be 0.9 mW, corresponding to the power density of 12.7 kW/ cm2 . The Q-factor of the cavity is measured to be as high as 104.

Van der Waals Epitaxial Double Heterostructure: InAs/Single‐Layer Graphene/InAs

Van der Waals (vdW) epitaxial double heterostructures have been fabricated by vdW epitaxy of InAs nanostructures on both sides of graphene. InAs nanostructures diametrically form on/underneath graphene exclusively along As-polar direction, indicating polarity inversion of the double heterostructures. First-principles and density functional calculations demonstrate how and why InAs easily form to be double heterostructures with polarity inversion.

Electroluminescence from ZnO-nanorod-based double heterostructured light-emitting diodes

Light-emitting diodes (LEDs) with MgZnO/ZnO/MgZnO double heterojunction structure have been fabricated and the room temperature electroluminescence (EL) spectra have been studied. With the help of double heterostructure, LEDs show better visible EL performance than that of LED with ordinary p-i-n structure. By replacing ZnO film with ZnO nanorod arrays in this double heterostructure, strong ultraviolet EL emission around 380 nm was achieved. The ZnO-nanorod-based double heterostructured light-emitting diode exhibits superior stability with an intensity degradation of less than 3% over 8 h. The EL mechanisms were discussed in terms of carrier confinement and carrier transport based on semiconductor heterojunction theory.

GaN-Based Power HEMTs: Parasitic, Reliability and High Field Issues

This paper reviews the main mechanisms responsible for trapping and breakdown in power HEMTs based on gallium nitride. With regard to the trapping mechanisms, we describe the role of carbon and iron buffer doping compensation in determining the dynamic Ron. We also demonstrate how the use of double heterostructure without doping or a single-heterostructure with proper buffer doping compensation can effectively reduce trapping phenomena. In addition, we investigate the breakdown limits of single and double heterostructure (DH) HEMTs, by electrical and electroluminescence characterization. Results indicate that, for the devices adopting double heterostructure without doping or singleheterostructure with proper buffer doping compensation, the breakdown voltage linearly scales with the gate-drain distance, and provides information on the origin of breakdown current components for different bias levels and epitaxial structures.

Features of defect formation during the growth of double heterostructures for injection lasers based on Al x Ga1 − x As y Sb1 − y /GaSb materials

A lack of lattice defects and, in particular, a lack of dislocations in the active layer in complex multilayer heteroepitaxial systems is the basic condition for the efficient and reliable operation of optoelectronic microdevices. Minimum elastic stresses in multilayer heteroepitaxial systems and their lack in the active layer at that elevated temperature that occurs in an efficiently operating electronic device is the second necessary condition for its long-term operation.

The effect of stair case electron injector design on electron overflow in InGaN light emitting diodes

Effect of two-layer (In0.04Ga0.96N and In0.08Ga0.92N) staircase electron injector (SEI) on quantum efficiency of light-emitting-diodes (LEDs) in the context of active regions composed of single and quad 3 nm double heterostructures (DHs) is reported. The experiments were augmented with the first order model calculations of electron overflow percentile. Increasing the two-layer SEI thickness from 4 + 4 nm up to 20 + 20 nm substantially reduced, if not totally eliminated, the electron overflow in single DH LEDs at low injections without degrading the material quality evidenced by the high optical efficiency observed at 15 K and room temperature. The improvement in quad 3 nm DH LEDs with increasing SEI thickness is not so pronounced as the influence of SEI is less for thicker active regions, which in and of themselves necessarily thermalize the carriers.