Growth and Characterization of GaSb-Based Type-Ⅱ InAs/GaSb Superlattice Photodiodes for Mid-Infrared Detection

InAs/GaSb superlattiee （SL） midwave infrared photovoltaic detectors are grown by molecular beam epitaxy on GaSb（001） residud p-type substrates. A thick GaSb layer is grown under the optimized growth condition as a buffer layer. The detectors containing a 320-period 8ML/SML InAs/GaS5 SL active layer are fabricated with a series pixel area using anode sulfide passivation. Corresponding to 50% cutoff wavelengths of 5.0 μm at 77K, the peak directivity of the detectors is 1.6 × 10^10 cm.Hz^1/2 W^-1 at 77K.     

Stimulated Emission at a Wavelength of 2.86 μm from In(Sb,As)/In(Ga,Al)As/GaAs Metamorphic Quantum Wells under Optical Pumping

JETP Letters - Metamorphic laser heterostructures In(Sb, As)/In0.81Ga0.19As/In0.75Al0.25As with InSb/InAs/InGaAs composite quantum wells based on submonolayer InSb insertions in a 10-nm InAs layer...     

Growth and Magnetic Properties of Zincblende CrSb Epilayers on Relaxed and Strained （In, Ga）As Buffers

Zincblende CrSb （zb-CrSb） layers with room-temperature ferromagnetism have been grown on relaxed and strained （In,Ga）As buffer layers epitaxially prepared on （001） GaAs substrates by molecular-beam epitaxy. The structural characterizations of CrSb layers fabricated under the two cases are studied by using synchrotron grazing incidence x-ray diffraction （GID）. The results of GID experiments indicate that no sign of second phase exists in all the zb-CrSb layers. Superconducting quantum interference device measurements demonstrate that the thickness of zb-CrSb layers grown on both relaxed and strained （In,Ga）As buffer layers can be increased to ～12 monolayers （～3.6nm）, compared to ,～3 monolayers （～1 nm） on GaAs directly.     

Effect of coherency strain on the deformation of In x Ga1− x As superlattices under nanoindentation and bending

It has been shown elsewhere that the room temperature yield pressure of In _x Ga_{1? x} As superlattices measured by nanoindentation, decreases from a high value as the volume averaged strain modulation is increased, while at 500°C under uniaxial compression or tension the yield stress increases from a low value with increasing strain modulation. We have used cross-sectional transmission electron microscopy to examine the deformation mechanisms in these two loading regimes. At room temperature both twinning and dislocation flow was found with the proportion of twinning decreasing with increasing strain modulation. The coherency strain of the superlattice is retained in a twin but partially relaxed by dislocation flow. The strain energy released by the loss of coherency assists dislocation flow and weakens the superlattice. Twins are only nucleated when a critical elastic shear of about 7° is achieved at the surface. The plastic zone dimensions under the indent are finite at the yield point, with a width and depth of approximately 1.3?µm and 1.1?µm respectively. Under uniaxial compression and tension at 500°C the superlattices deform by dislocation flow along {111} planes. The most highly strained samples also partially relax through the formation of misfit dislocations.     

Relaxation oscillations and damping factors of 1.3 μm In(Ga)As/GaAs quantum-dot lasers

In(Ga)As/GaAs quantum-dot (QD) lasers with emission wavelength at 1295 nm at room temperature are fabricated. The laser active region contains a threefold stack of QD layers with surface dot density of 4.56 × 10¹⁰ cm^–2. The laser structure is aluminum-free with InGaP as cladding layers. Threshold current density of a narrow stripe laser of 8 m wide and 3.5 mm long is 152.5 A/cm². The highest relaxation oscillation frequency measured at room temperature is 1.8 GHz, corresponding to a modulation bandwidth of 2.8 GHz due to the small damping factor. From the above measurement, the differential gain and gain compression factor were extracted to be 4.3 × 10^–16 cm² and 3.4 × 10 ^–17 cm ³, respectively. Using these parameters, the maximum modulation bandwidth f _{3 dB max} is estimated as 7.9 GHz.     

Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Germanium substrate

We have described Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Ge substrate by MBE. The growth technique includes deposition of a thin germanium buffer layer followed by migration-enhanced epitaxy (MEE) grown GaAs layer at 350°C. The MEE layer was overgrown by a thin low-temperature (475°C) grown GaAs layer with a subsequent deposition of a thick GaAs layer grown at 590°C. The sample was characterized by AFM, cross-sectional TEM and temperature-dependent PL measurements. The AFM shows dense formation of QDs with no undulation in the wetting layer. The XTEM image confirms that the sample is free from structural defects. The 8 K PL emission exhibits a 1051 nm peak, which is similar to the control sample consisting of In(Ga)As/GaAs QDs grown on GaAs substrate, but the observed emission intensity is lower. The similar slopes of Arrhenius plot of the integrated PL intensity for the as-grown QD sample grown on Ge substrate as well as for a reference QD sample grown on GaAs substrate are found to be identical, indicating a similar carrier emission process for both the samples. This in turn indicates coherent formation of QDs on Ge substrate. We presume due to the accumulated strain associated with the self-assembled growth of nanostructures on Ge that nonradiative recombination centers are introduced in the GaAs barrier in between the QD layers, which in turn degrades the overall optical quality of the sample.     

Magnetic properties of GaAs/δ〈Mn〉/GaAs/In x Ga1 − x As/GaAs quantum wells

The field and temperature dependences of the magnetization of GaAs/δ〈Mn〉/GaAs/In _x Ga_{1 ? x} As/GaAs quantum wells with the δ〈Mn〉 layer separated from the well by a 3-nm GaAs spacer have been studied in the temperature range of 3–300 K in a magnetic field up to 6 T. An external magnetic-field-induced phase transition to a ferromagnetic state with a magnetization hysteresis loop shifted from a zero magnetic field has been found to occur at a temperature below 40 K. A theoretical model is proposed that implies the coexistence of ferromagnetically and antiferromagnetically ordered regions within the GaAs layers.     

Growth of Highly Conductive n-Type Al0.7Ga0.3N Film by Using AlN Buffer with Periodical Variation of Ⅴ/Ⅲ Ratio

High quality and highly conductive n-type Al0.7Ga0.3N films are obtained by using AlN multi-step layers （MSL） with periodical variation of Ⅴ/Ⅲ ratios by low-pressure metalorganic chemical vapour deposition （LP-MOCVD）. The full-width at half-maximum （FWHM） of （0002） and （1015） rocking curves of the Si-doped Al0.7Ga0.3N layer are 519 and 625 arcsec, respectively, Room temperature （RT） Hall measurement shows a free electron concentration of 2.9 × 10^19 cm^-3, and mobility of 17.8cm^2V^-1s^-1, corresponding to a resistivity of 0.0121 Ω cm. High conductivity of the Si-doped AlGaN film with such high Al mole fraction is mainly contributed by a remarkable reduction of threading dislocations （TDs） in AlGaN layer. The TD reducing mechanism in AlN MSL growth with periodical variation of Ⅴ/Ⅲ ratio is discussed in detail.     

Optical and structural properties of molecular-beam epitaxially grown Ga0.47In0.53As/Al0.48In0.52As superlattices,emitting at 1.55 μm at room temperature

We have combined photoluminescence and absorption measurements with double crystal x-ray diffraction in order to study the influence of growth conditions on optical and structural properties of Ga_0.47In_0.53As/Al_0.48In_0.52As superlattices of 10.5 nm well width grown by molecular beam epitaxy on InPSn substrates. Superlattices with excellent structural properties can be grown even at low substrate temperatures of 500 °C, as indicated by narrow linewidths of the satellite peaks of the x-ray diffraction pattern of 20 to 25 s of arc (FWHM). However, elevated substrate temperatures are required to increase the intensity of the intrinsic luminescent subband transition at 77 K, to reduce the luminescence linewidth to 12 meV (FWHM), and to sharpen the absorption spectra. In addition to the absorption due to the steplike variation of the two-dimensional density of states, we observe excitonic transitions to the excitonic continuum at the subband edges.     

Materials and device properties of pseudomorphic In x Ga1−x As/Al0.3Ga0.7As/GaAs high electron mobility transistors (0<x<0.5)

Modulation doped Al_0.3Ga_0.7As/In _x Ga_1–x As/GaAs high electron mobility transistor structures for device application have been grown using molecular beam epitaxy. Initially the critical layer thickness for InAs mole fractions up to 0.5 was investigated. For InAs mole fractions up to 0.35 good agreement with theoretical considerations was observed. For higher InAs mole fractions disagreement occurred due to a strong decrease of the critical layer thickness. The carrier concentration for Al_0.3Ga_0.7As/In _x Ga_1–x As/GaAs high electron mobility transistor structures with a constant In _x Ga_1–x As quantum well width was investigated as a function of InAs mole fraction. If the In _x Ga_1–x As quantum well width is grown at the critical layer thickness the maximum carrier concentration is obtained for an InAs mole fraction of 0.37. A considerable higher carrier concentration in comparison to single-sided -doped structures was obtained for the structures with -doping on both sides of the In _x Ga_1–x As quantum well. Al_0.3Ga_0.7As/In _x Ga_1–x As/GaAs high electron mobility transistor structures with InAs mole fractions in the range 0–0.35 were fabricated for device application. For the presented field effect transistors best device performance was obtained for InAs mole fractions in the range 0.25–0.3. For the field effect transistors with an InAs mole fraction of 0.25 and a gate length of 0.15 m a f _T of 115 GHz was measured.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

The effect of metal work function on the barrier height of metal/CdS/SnO2/In–Ga structures

In order to interpret the effect of metal work function on the formation of the barrier height at metal/semiconductor (M/S) interface, the CdS/SnO₂/In–Ga structures with several metals (Ag, Au, Al, Te) have been investigated by using I–V characteristics at room temperature. The main electrical parameters such as ideality factor (n), zero-bias barrier height (Φ_Bo), series resistance (R_s) have been determined and compared with each other. The values of n were found to be 3.00, 2.56, 3.83, and 3.31 for Al, Ag, Te, and Au/CdS/SnO₂/In–Ga structures, respectively. The values of Φ_Bo were also found to be 0.489 eV, 0.490 eV, 0.583 eV, 0.591 eV for Al, Ag, Te, and Au/CdS/SnO₂/In–Ga structures, respectively. The Φ_Bo dependence on the metal work function (Φ_m) was found to vary almost linearly as Φ_Bo = 0.106Φ_m + 0.028. The low value of the slope S (dΦ_B/dΦ_M ? 0.106) shows a weak relationship between Φ_Bo and Φ_m due to serious Fermi-level pinning in the conduction band. In addition, the I–V plots have a rectifying behavior. The rectification ratio, defined by the ratio of forward to reverse current (RR = I_F/I_R) measured at the same absolute bias, was found as 11.96, 20.88, 35.82, and 75.61 for Al, Ag, Te, Au/CdS/SnO₂/In–Ga diodes, respectively. In addition, the values of R_s were determined from Ohm's Law and Norde's method. Analysis of I–V characteristics confirm that using of different metal (Al, Ag, Te, Au) has significant effect on electrical parameters of such devices.     

Band Structure and Optical Gain of InGaAs/GaAsBi Type-Ⅱ Quantum Wells Modeled by the k·p Model

Optical gains of type-Ⅱ In Ga As/Ga As Bi quantum wells(QWs) with W, N, and M shapes are analyzed theoretically for near-infrared laser applications. The bandgap and wave functions are calculated using the self-consistent k·p Hamiltonian, taking into account valence band mixing and the strain effect. Our calculations show that the M-shaped type-Ⅱ QWs are a promising structure for making 1.3 um lasers at room temperature because they can easily be used to obtain 1.3 um for photoluminescence with a proper thickness and have large wave-function overlap for high optical gain.     

Effect of the O2/Ar Pressure Ratio on the Microstructure and Surface Morphology of Epi-MgO/IBAD-MgO Templates for GdBa2Cu3O7？δ Coated Conductors

High-quality epi-MgO buffer layers under different O2/Ar pressure ratios are fabricated by rf magnetron sputtering on textured IBAD-MgO templates. Under the total deposition pressure remaining constant （14 Pa）, the effect of changing the ratio of O2/Ar pressure from 1：4 to 3：2 on the microstructure and surface morphology of epi-MgO films is studied. The microstructure and morphology of epi-MgO are fully characterized by x-ray diffraction, atom force microscope and scanning electron microscope. The best texture quality of epi-MgO with an out-plane Δω value of 1.8° and an in-plane Δ？ value of 5.22° are obtained under the ratio of O2/Ar pressure 3：2. Further, the surface morphology indicates that the surface of epi-MgO is smooth with rms surface roughness about 4.7 nm at O2/Ar pressure ratio 3：2. After that, GdBa2Cu3O7？δ （GBCO） layers are deposited on the CeO2 cap layer buffered epi-MgO/IBAD-MgO templates to assess the efficiency of such a buffer layer stack. The critical current density of GBCO films （thickness of 200 nm） is higher than 3 MA/cm2, indicating that epi-MgO/IBAD-MgO is promising for depositing superconducting layers with a higher critical current density.     

Simulation of dark current suppression in p–i–n InGaAs photodetector with In0.66Ga0.34As/InAs superlattice electron barrier

An InGaAs–based photodetector with different periods of inserting strain–compensated In_0.66Ga_0.34As/InAs superlattice (SL) electron barrier in the In_0.83Ga_0.17As absorption layer has been investigated. The band diagram, electron concentration and electric field intensity of the structure were analyzed with numerical simulation. It was found that the period of SL has a remarkable influence on the properties of the photodetectors. With the decrease of the period of In_0.66Ga_0.34As/InAs SL, the dark current density is suppressed significantly, which is reduced to 2.46 × 10⁻³ A/cm² at 300 K and a reverse bias voltage of 1 V when the period is 2.5 nm.     

Effect of In_xGa_(1-x)As Interlayer on Surface Morphology and Optical Properties of GaSb/InGaAs Type-Ⅱ Quantum Dots Grown on InP (100) Substrates

The effects of indium composition in InGaAs interlayer on morphology of GaSb/InGaAs quantum dots(QDs)and on optical properties of GaSb/fnGaAs QD material system are studied.AFM images show that the change of the indium composition in InGaAs interlayer can alter the GaSb QD morphology.It is found that low indium composition in InGaAs interlayer can promote the formation of QDs,while high indium composition can inhibit the formation of QDs.The photoluminescence(PL) spectra of GaSb/InGaAs QDs at 8K under low excitation power indicate that the third root of the excitation power is linear with the peak position,which provides a direct evidence for their luminescence belonging to type-Ⅱ material optical transition.The PL spectra at 8K under an excitation power of 90 mW show that the optical properties of GaSb/InGaAs QD material system can be affected by the indium composition in the InGaAs interlayer,and the PL peak position is linear with the indium composition.The optical properties of GaSb/InGaAs QDs can be improved by adjusting the indium composition in the InGaAs interlayer.     

Optical and electrical properties of modulation-doped n and p-type Ga x In1-x N y As1-y /GaAs quantum wells for 1.3 μm laser applications

We present a comprehensive study of spectral photoluminescence (PL), photoconductivity and Hall mobility in undoped, n and p-type modulation-doped quantum wells of Ga_1-x In _x N _y As_1-y /GaAs with varying nitrogen concentration. We show that the increasing nitrogen composition red shifts the energy gap and this red shift is accompanied with a reduction of the 2D electron mobility in the quantum wells. True temperature dependence of the band gap, free from errors associated with nitrogen induced exciton trapping effects, is observed because in the modulation doped QW samples PL emission is dominated by band-to-band recombination and the S-shape temperature dependence is eliminated. Excellent fit to semi-experimental Varshni equation is obtained and the temperature dependence of the band gap in the linear regime (dE/dT) is tabulated as a function of nitrogen concentration and the type of dopant.     

Effect of Al and Ga interdiffusion on the electronic states in GaAs/Ga<Subscript>1−x</Subscript>Al<Subscript>x</Subscript>As semiconductor superlattice

The effect of interdiffusion of Al and Ga atoms on the confining potential and band structure of a three-dimensional superlattice, composed of initially spherical GaAs/Ga_1?xAl_xAs quantum dots, is investigated in the framework of the modified Wood-Saxon potential model. It is shown that the interdiffusion leads to the disappearance of the quantum dots’ spherical symmetry and to the broadening of the superlattice energy minibands.     

Calculations of the lattice dynamics and spontaneous polarization for thin ferroelectric films of disordered solid solutions PbB′1/2 B″1/2O3 (B′ = Sc,Ga, In,Lu; B″ = Nb,Ta)

Physics of the Solid State - The lattice dynamics and spontaneous polarization in thin ferroelectric films of disordered solid solutions PbB′1/2 B″1/2 O3 (B′ = Sc, Ga, In, Lu;...