Indium Mole Fraction Research Articles

The deformation-potential scattering and alloy disorder scattering in donor-acceptor pHEMT heterostructures

The increase in the indium mole fraction in the quantum well of pHEMT heterostructures with donor-acceptor doping causes an increase in the 2DEG concentration from 2.2· 1012 cm-2 to 3.9· 1012 cm-2 and a decrease in mobility from 7900 cm2V-1s-1 to 7500 cm2V-1s-1 at room temperature. The temperature dependencies of 2DEG mobility show that the deformation potential scattering grows at increment of indium mole fraction in quantum well. Absolute values of the deformation potential are approximately two times smaller than the widely used values and increases with increasing of indium mole fraction.

A novel numerical approach for the calculation of refractive index of Wurtzite InxGa1−xN

Accurate values of refractive indices for In[Formula: see text]Ga[Formula: see text]N alloy as a function of indium mole fraction play a vital role in the modeling of In[Formula: see text]Ga[Formula: see text]N-based optoelectronics devices. This work extensively investigated, analyzed and derived a conclusive numerical approach to calculate the refractive index of In[Formula: see text]Ga[Formula: see text]N over a wide wavelength as a function of indium mole fraction based on Vegard’s law. The model is based on the fact that there is a strong correlation between the mole fraction (x) and the refractive index of ternary alloys A[Formula: see text]B[Formula: see text]C. An excellent agreement is observed between the computed values and experimental data which proves the effectiveness of our numerical approach.

Dependence of Strain Distribution on In Content in InGaN/GaN Quantum Wires and Spherical Quantum Dots

The distribution of strain, developed in zero-dimensional quantum spherical dots and one-dimensional cylindrical quantum wires of an InGaN/GaN system is calculated as functions of radius of the structure and indium mole fraction. The strain shows strong dependence on indium mole fraction at small distances from the center. The strain associated with both the structures is found to decrease exponentially with the increase in dot or cylinder radius and increases linearly with indium content.

Theoretical analysis of the mobility of two-dimensional electron gas in the quaternary AlxInyGa1-x-yN/GaN heterojunctions limited by the alloy composition fluctuation

We established the model of the electron mobility limited by the alloy composition fluctuation scattering in the quaternary AlxInyGa1-x-yN/GaN heterojunctions for the first time. The alloy composition fluctuation along the AlxInyGa1-x-yN/GaN heterointerface was considered and characterized by the lateral correlation length L, and the fluctuations of aluminum and indium mole fractions (Δx and Δy) independent to each other. The situation of alloy composition fluctuation is investigated in the following cases. Only x or y fluctuates, and both x and y fluctuate with equal/unequal amplitudes in the same/opposite direction. We find that the scattering with both x and y fluctuating in the same direction is the weakest, while x and y fluctuating in the opposite directions leads to the strongest scattering. This in nature stems from the disparity of the bandgap and polarization in AlInN, AlGaN and GaN. The effects of different parameters, such as x and y, Δx and Δy, L, and the thickness of AlxInyGa1-x-yN barrier layer d on the mobility are also studied. The model will in principle give a universal explanation to the effect of alloy composition fluctuation scattering on the carrier mobility in the GaN-based heterostructures with ternary or quaternary alloy barrier layers.

Carrier localization in InGaN by composition fluctuations: implication to the “green gap”

A simple semi-empirical model for radiative and Auger recombination constants is suggested, accounting for hole localization by composition fluctuations in InGaN alloys. Strengthening of fluctuation with the indium molar fraction in InGaN is found to be largely responsible for decreases in both the radiative and Auger recombination constants with emission wavelength. The model provides good fitting of the experimental spectral dependencies of the recombination constants, thus demonstrating implication of the carrier localization to light-emitting diode efficiency reduction in the “green gap.”

Comparative Study of the Characteristics in Strained Al<sub>x</sub>In<sub>y</sub>Ga<sub>(1-x-y)</sub>N/InGaN and Al<sub>x</sub>In<sub>y</sub>Ga<sub>(1-x-y)</sub>N/GaN Heterostructures

The paper emphasized on different characteristics AlInGaN/InGaN and AlInGaN/GaN heterostructures for enhancing the device performance. Effect of changing mole fraction in bandgap, strain, polarization have been investigated. Amount of sheet charge density created on the heterointerfaces of AlInGaN /InGaN and AlInGaN/GaN heterostructures have been calculated. It has been observed that with the increment of Indium mole fraction and the decrement of Aluminium mole fraction, the total polarization increases hence larger 2DEG and sheet charge density is created.

Investigation of InP/In0.65Ga0.35As metamorphic p-channel doped-channel field-effect transistor

In this article, the device mechanism and characteristics of InP/InGaAs metamorphic p-channel field-effect transistor (FET), which has a high indium mole fraction of InGaAs channel, grown on the GaAs substrate is demonstrated. The device was fabricated on the top of the InxGa1−xP graded metamorphic buffer layer, and the In0.65Ga0.35As pseudomorphic channel was employed to elevate the transistor performance. For the p-type FET, due to the considerably large valence band discontinuity at InP/In0.65Ga0.35As heterojunction and a relatively thin as well as heavily doped pseudomorphic In0.65Ga0.35As channel between two undoped InP layers, a maximum extrinsic transconductance of 27.3 mS/mm and a maximum saturation current density of −54.3 mA/mm are obtained. Consequently, the studied metamorphic FET is suitable for the development in signal amplification, integrated circuits, and low supply-voltage complementary logic inverters.

Impact of indium mole fraction on the quantum transport of ultra-scaled In x Ga1–x As double-gate Schottky MOSFET: tight-binding approach

This paper explores the impact of indium mole fraction on the electrical characteristic of InxGa1–xAs double-gate Schottky MOSFET (SBFET) in nanoscale regime. A 20-band sp3d5s* tight-binding formalism is applied to compute the bandstructure of ultra-thin body structure as a function of indium mole fraction. The injection velocity of carriers is increased as the indium mole fraction approaches to x = 1. Quantum confinement results in an increment of the effective Schottky barrier height especially for the increased values of indium mole fraction. The ultra-scaled InxGa1–xAs SBFET suffers from a low conduction band DOS in the Γ valley that results in serious degradation of the gate capacitance. The electrical characteristic of this device is considered by solving self-consistent 2D Schrődinger–Poisson equations based on non-equilibrium Green’s function formalism. For channel thicknesses where the effect of quantum confinement on the gate capacitance is not dominant, shrinking the channel thickness besides increasing the indium mole fraction improves the electrical characteristic of the device. However, for the ultra-scaled structure, the indium mole fraction enhancement degrades the device performance due to the enhanced value of Schottky barrier height and low DOS.

Bloch wave conditions for continuum states in the InGaAs/GaAs QWIPs

We study the optical transition between bound-to-(quasi)-continuum states in InGaAs/GaAs quantum well infrared photodetectors (QWIPs) by investigating the boundary conditions of the extended states. Comparing running wave function and Bloch wave function with experimental results, it is find out that Bloch wave function is the much more suitable boundary condition for InGaAs/GaAs QWIPs with multiple quantum well (QW) structure. The blueshift of the responding peak is smaller when the Bloch wave boundary conditions apply. By changing the width of the InGaAs QW, we observe the changing of characterizing photocurrent peak corresponding to two boundary conditions respectively. The blueshift of the responding peak is smaller when Bloch wave boundary conditions apply. The detailed dependence of peak response wavelength and device operation mode on the indium mole fraction and InGaAs QW width is also investigated, offering guidance for device designing and optimization.

Two dimensional electron gas in a hybrid GaN/InGaN/ZnO heterostructure with ultrathin InGaN channel layer

We investigated the influence of an ultrathin InGaN channel layer on two-dimensional electron gas (2DEG) properties in a newly proposed hybrid GaN/InxGa1−xN/ZnO heterostructure using numerical methods. We found that 2DEG carriers were confined at InGaN/ZnO and GaN/InGaN interfaces. Our calculations show that the probability densities of 2DEG carriers at these interfaces are highly influenced by the In mole fraction of the InGaN channel layer. Therefore, 2DEG carrier confinement can be adjustable by using the In mole fraction of the InGaN channel layer. The influence of an ultrathin InGaN channel layer on 2DEG carrier mobility is also discussed. Usage of an ultrathin InGaN channel layer with a low indium mole fraction in these heterostructures can help to reduce the short-channel effects by improvements such as providing 2DEG with higher sheet carrier density which is close to the surface and has better carrier confinement.

Emission color-tuned light-emitting diode microarrays of nonpolar In(x)Ga(1-x)N/GaN multishell nanotube heterostructures.

Integration of nanostructure lighting source arrays with well-defined emission wavelengths is of great importance for optoelectronic integrated monolithic circuitry. We report on the fabrication and optical properties of GaN-based p–n junction multishell nanotube microarrays with composition-modulated nonpolar m-plane InxGa1–xN/GaN multiple quantum wells (MQWs) integrated on c-sapphire or Si substrates. The emission wavelengths were controlled in the visible spectral range of green to violet by varying the indium mole fraction of the InxGa1–xN MQWs in the range 0.13 ≤ x ≤ 0.36. Homogeneous emission from the entire area of the nanotube LED arrays was achieved via the formation of MQWs with uniform QW widths and composition by heteroepitaxy on the well-ordered nanotube arrays. Importantly, the wavelength-invariant electroluminescence emission was observed above a turn-on of 3.0 V because both the quantum-confinement Stark effect and band filling were suppressed due to the lack of spontaneous inherent electric field in the m-plane nanotube nonpolar MQWs. The method of fabricating the multishell nanotube LED microarrays with controlled emission colors has potential applications in monolithic nonpolar photonic and optoelectronic devices on commonly used c-sapphire and Si substrates.

Time-resolved photoluminescence studies of InGaN/GaN multi-quantum-wells blue and green light-emitting diodes at room temperature

Time-resolved photoluminescence (TRPL) of the blue and green LEDs, which has the same number of quantum-well (QW) pairs and the different etched depths, has been studied at room temperature. The purpose is to analyze the effect of different indium (In) content and defects density on TRPL. The carrier lifetime of radiative recombination and non-radiative for blue LED (In=0.15) is 625.0ns and 55.6ns, and for green ones (In=0.21), the figure is 363.6ns and 35.0ns. The carrier lifetime is reduced along with the increasing of In-component. As the etched depth deepened of blue LED, the non-radiative recombination lifetime tends to infinity. When it comes to low indium content, the PL spectra present a blue shift. With the increasing of indium mole fraction, the blue shift appeared at first, and then a red shift has been observed. And the spectral shift has disappeared, while etching the LEDs. At last, we clarify the results, through the band bending caused by polarization electric field.

Highly Strained Mid-Infrared Type-I Diode Lasers on GaSb

We describe how growth at low temperatures can enable increased active layer strain in GaSb-based type-I quantum-well diode lasers, with emphasis on extending the emission wavelength. Critical thickness and roughening limitations typically restrict the number of quantum wells that can be grown at a given wavelength, limiting device performance through gain saturation and related parasitic processes. Using growth at a reduced substrate temperature of 350 °C, compressive strains of up to 2.8% have been incorporated into GaInAsSb quantum wells with GaSb barriers; these structures exhibited peak room-temperature photoluminescence out to 3.96 μm. Using this growth method, low-threshold ridge waveguide lasers operating at 20 °C and emitting at 3.4 μm in pulsed mode were demonstrated using 2.45% compressively strained GaInAsSb/GaSb quantum wells. These devices exhibited a characteristic temperature of threshold current of 50 K, one of the highest values reported for type-I quantum-well laser diodes operating in this wavelength range. This temperature stability is attributable to the increased valence band offset afforded by the high strain values, due to the simultaneously high quantum well indium and antimony mole fractions. Exploratory experiments using bismuth both as a surfactant during quantum well growth, as well as in dilute amounts incorporated into the crystal were also studied. Both methods appear to be promising avenues to surmount current strain-related limitations to laser performance and emission wavelength.

Hole transport assisted by the piezoelectric field in In0.4Ga0.6N/GaN quantum wells under electrical injection

The authors observe the significant penetration of electrically injected holes through InGaN/GaN quantum wells (QWs) with an indium mole fraction of 40%. This effect and its current density dependence were analysed by studies on micro-pixel light-emitting diodes, which allowed current densities to be varied over a wide range up to 5 kA/cm2. The systematic changes in electroluminescence spectra are discussed in the light of the piezoelectric field in the high-indium-content QWs and its screening by the carriers. Simulations were also carried out to clarify the unusual hole transport mechanism and the underlying physics in these high-indium QWs.

Temperature Dependence of Efficiency in GaInN/GaN Light‐Emitting Diodes with a GaInN Underlayer

The temperature dependence of the efficiency (i.e., temperature‐mediated efficiency droop) in blue light‐emitting diodes (LEDs) is investigated. A GaInN/GaN LED with a GaInN underlayer having an indium mole fraction of 8% shows less temperature dependence of efficiency, compared to the LED without an underlayer. Better carrier confinement in the active region of the LED with a GaInN underlayer is proposed to reduce carrier leakage from the active region at high temperature. The results indicate that the insertion of an underlayer leads to an improvement of the LED's radiative efficiency and its high‐temperature‐tolerant performance.

Effects of indium mole fraction on the physical characteristics of magnetron sputtered InxAl1−xN films

InxAl1 − xN films with composition 0.25 ≤ x ≤ 0.86 were grown on p-type Si (111) substrates by using reactive magnetron co-sputtering technique in an ambient of argon and nitrogen at 200 °C. X-ray diffraction results at x = 0.25 and x = 0.40 indicated the formation of nanostructured InAlN films along (101) plane with low diffraction intensities. However, by increasing the indium mole fraction ‘x’ from 0.40 to 0.86, crystallinity of the InAlN film was considerably improved along with a change in its preferred orientation towards the c-plane. Surface morphology analysis revealed an under-dense grains structure at x = 0.25, which was changed into a compact structure with increase of the ‘x’ value. Surface roughness of the films exhibited a decreasing trend with increase of the indium contents whereas the Raman spectroscopy analysis specified the existence of A1 (LO) and E2 (high) phonon modes in the films at x = 0.40 and x = 0.86. The Hall measurements indicated n-type nature of InxAl1 − xN film along with a decrease in its electrical resistivity with increase of the indium composition ‘x’. The current–voltage (I–V) characteristics at x = 0.25 displayed Schottky behavior at the metal/film interface which was changed into the ohmic one with increase of indium mole fraction in the film.

Effects of Lattice Relaxation on Composition and Morphology in Strained In x Ga1−x As y Sb1−y Epitaxial Layers

InxGa1−xAsySb1−y is an important semiconductor material for a variety of mid-infrared devices. Its tunable bandgap, adjustable lattice constant, and other material properties make it appealing for developing optoelectronic devices in the 2 μm to 4 μm region. In this work, we report on the mechanisms of strain relaxation in InxGa1−xAsySb1−y epitaxial layers with low arsenic and high indium concentrations grown on GaSb (100) substrates. Samples were grown via solid-source molecular beam epitaxy with indium mole fractions between x = 0.1 (0.7% lattice mismatch) and x = 0.4 (2.5% lattice mismatch), and arsenic mole fractions between y = 0 and y = 0.02. Sample thicknesses between 10 nm and 100 nm were produced in order to observe the progression of structure formation. Samples were monitored in situ via reflection high-energy electron diffraction and ex situ using scanning electron microscopy, energy-dispersive spectroscopy, Rutherford backscattering spectroscopy, backscattering Raman spectroscopy, and atomic force microscopy. Results suggest that strain relaxation occurs preferentially along the [011] direction, although some crosshatching is observed. A compositional gradient in the growth direction is also observed, suggesting preferential incorporation of gallium at strained interfaces in order to minimize strain energy.

Investigation of In0.7Ga0.3As/In0.7Al0.3As metamorphic HEMT- heterostructures by photoluminescence spectroscopy

Low-temperature photoluminescence and photoreflectance have been studied in several metamorphic HEMT- (MHEMT-) heterostructures with the same active regions and different buffer layer designs grown by solid-source molecular beam epitaxy. The indium mole fraction in InAlAs/InGaAs/InAlAs single quantum well (QW) is 0.7. It was found that structures with step-graded metamorphic buffer have better quality. Also it was shown that mismatched superlattices in metamorphic buffer can influence on the half-width of photoluminescence spectra. The possible attribution of photoluminescence and photoreflectance spectral lines and their thermal behaviour are critically discussed.

Analysis of different tunneling mechanisms of InxGa1−xAs/AlGaAs tunnel junction light-emitting transistors

The electrical and optical characteristics of tunnel junction light-emitting transistors (TJLETs) with different indium mole fractions (x = 5% and 2.5%) of the InxGa1−xAs base-collector tunnel junctions have been investigated. Two electron tunneling mechanisms (photon-assisted or direct tunneling) provide additional currents to electrical output and resupply holes back to the base region, resulting in the upward slope of I-V curves and enhanced optical output under forward-active operation. The larger direct tunneling probability and stronger Franz-Keldysh absorption for 5% TJLET lead to higher collector current slope and less optical intensity enhancement when base-collector junction is under reverse-biased.

Growth of tellurium doped ultra-broadband tunnel junction for the next generation 5J solar cell

Tellurium doped Al0.13Ga0.39In0.48P (AlGaInP) is an ideal material for the n side of an ultra-broadband tunnel junction for next generation 5J solar cell structures grown by metal-organic vapor phase epitaxy (MOVPE). Indium mole fraction is selected to reduce the lattice-mismatch and strain caused by the larger atomic size of tellurium when the AlGaInP must be highly doped for the electron states degeneracy. Growth pause at an elevated temperature after AlGaInP growth is employed to provide for a sharp turn-off, avoiding unintended compensation by donors in the subsequent p layer. The turn-on of tellurium is improved using pre-doping process during the temperature ramp before the growth. Electrochemical capacitance–voltage (ECV) result shows that uniform doping level of ~7×1018cm−3 is obtained in the n side of the tunnel junction with sharp edges at the doping interfaces. The tunneling current density of the fabricated tunnel junction is about 7.8A/cm2.