High-quality InAs Research Articles

Formation of High Quality InP and InAs Nanocrystals in a Noncoordinating Solvent

High quality InP nanocrystals without any size sorting were synthesized in a noncoordinating solvent by strictly controlling the reaction parameters. This synthetic method is much faster, less expensive, and “greener” than any current methods for the synthesis of high quality InP nanocrystals. Fatty acids with well-defined chain lengths as the ligands, a noncoordinating solvent, and a thorough degassing process are critical factors for the formation of high quality InP nanocrystals. The growth of nearly monodisperse InAs nanocrystals through a similar scheme was also observed.

Growth of InAs quantum dots on focussed ion beam implanted GaAs(100)

The growth of self-assembled InAs quantum dots on implantation doped GaAs was studied. Be and Si ions were implanted in a combined ion implantation/molecular beam epitaxy process to generate p- and n-type GaAs, respectively. The quality of the InAs quantum dots was investigated by photoluminescence spectroscopy and scanning electron microscopy. By employing an in situ annealing step before re-growth it was possible to fabricate high quality InAs quantum dots on ion doped GaAs for Be doses up to 1.4×10 14 cm −2. The sheet resistance of the Be doped GaAs was as low as 1 kΩ at 300 K and 0.6 kΩ at 4.2 K, respectively. Only for rather low Si doses up to 5×10 13 cm −2 acceptable photoluminescence could be detected. The sheet resistance for these doses was 1 kΩ at 300 K and 1.7 kΩ at 4.2K.

Studies on incorporation of As 2 and As 4 in III–V compound semiconductors with two group V elements grown by molecular beam epitaxy

Under the assumption that one incident As 4 molecule produces one active As 2 molecule before incorporating into epitaxial alloys, a novel thermodynamic model is developed to describe the molecular beam epitaxy (MBE) growth of III–V compound semiconductors with two group V elements using As 4 flux. A parameter ε d representing the activation energy of As 4 dissociation process is introduced in the model. High quality InAs y P 1− y materials were grown on InP substrates using our home made all solid source MBE (SSMBE) system with valved cracker cells under different substrate temperatures and arsenic fluxes with different As 2/As 4 ratios. By taking into account the As 2/As 4 ratio, the model is used to calculate the compositions of the grown samples. The calculated results are in good agreement with the experimental data. Both the experiments and the calculations show the lower incorporation efficiency of As 4 than that of As 2.

Temperature dependence of photoluminescence from InAsP/InP strained quantum well structures grown by metalorganic chemical vapor deposition

In this article, we report the growth and characterization of InAsP/InP strained single quantum well (SSQW), strained single quantum well (SSQW) stack, and strained multiple quantum well (SMQW) structures on (1 0 0)-oriented InP substrates grown by metalorganic chemical vapor deposition. Double-crystal X-ray diffraction, photoluminescence (PL) and transmission electron microscope (TEM) are used to characterize the strained quantum wells. The high-quality crystalline InAs y P 1 −y (72Å)/InP SSQW structure with y⩽0.36 exhibits a 9.9 meV full-width at half-maximum (FWHM) of 10 K PL spectra. The peaks in the PL spectra for SSQW stack structure with a well thickness of 8, 14, and 35 Å vanish above 100, 150, and 296 K, respectively, presumably due to the decrease of photons yielded by electron–hole recombination in thinner quantum well regions on increasing the temperature. The PL peak emission energy dependence of well thickness in the InAsP/InP SSQW stack structure is in good agreement with the calculated results. In addition, the variations of the PL peak energy and FWHM in all the InAsP/InP SSQW, SSQW stack, and SMQW structures are described in detail.

Two-step method to grow InAs epilayer on GaAs substrate using a new prelayer

The strain relaxed InAs grown on GaAs(0 0 1) under In-rich condition is investigated by X-ray double-crystal diffraction. It is found that the strain is fully relaxed within 10 nm thick InAs layer grown under this condition, which is much faster than the growth of a similar layer of InAs under As-condition. A new growth method to obtain a high-quality InAs layer is suggested.

High quality InAs grown by liquid phase epitaxy using gadolinium gettering

In this paper, we report the growth of very pure InAs epitaxial layers of high quantum efficiency, by introducing the rare-earth element Gd into the liquid phase during LPE growth. We find that the carrier concentration of InAs layers can be effectively reduced to . Also, the peak photoluminescence (PL) intensity of such layers can be considerably increased by between ten- and 100-fold compared with untreated material. We attribute this behaviour to the gettering of residual impurities and corresponding reduction of non-radiative recombination centres in the presence of Gd. Four intense sharp lines dominated the low temperature (4 K) photoluminescense spectra of Gd-treated InAs layers. The strongest two of these were found to originate from (a) bound excitons, and (b) donor-acceptor recombination, whereas the remaining two, (c) and (d), were associated with defect-related recombination. The linewidth (FWHM) of the exciton peak (a) was reduced to only 3.8 meV, which is narrower than for undoped epitaxial InAs grown by MBE or MOVPE.

Carrier capture in InAs monolayer quantum wells grown on GaAs substrates

In high quality InAs monolayer (ML)/GaAs heterostructures, InAs behaves as a luminescence centre. This centre exchanges carriers with the GaAs layer through trapping and detrapping. Temperature dependence of the ratio between the integrated photoluminescence (PL) intensity from the InAs and the GaAs layers reveals the competition between capture and release of carriers by the InAs layer. It is found that the thermal escape of the carriers in the InAs layer is the dominant quenching mechanism of the InAs PL peak at higher temperatures. A good agreement is obtained between the experiment and the proposed model.

Growth and transport properties of InAs thin films on GaAs

High-quality InAs epitaxial layers have been grown on (1 0 0) oriented semi-insulating GaAs substrates by MBE. The transport properties of largely lattice mismatched InAs/GaAs heterojunctions have been investigated by Hall effect measurements down to 10 K. In spite of a high dislocation density at the heterointerface, very high electron mobilities are obtained in the InAs thin films. By doping Si into the layer far from the InAs/GaAs interface, we found that the doped samples have higher electron mobility than that of the undoped samples with the same thickness. The mobility demonstrates a pronounced minimum around 300 K for the undoped sample. But for Si-doped samples, no pronounced minimum has been found. Such abnormal behaviours are explained by the parallel conduction from the quasi-bulk carriers and interface carriers. These high-mobility InAs thin films are found to be suitable materials for making Hall elements.

Scattering mechanisms in InAs–AlSb quantum wells

High-quality InAs–AlSb quantum wells have been grown by molecular beam epitaxy. The Drude scattering time τ D as well as the quantum scattering times τ Q have been evaluated from low-temperature magnetotransport experiments. While the τ D increases monotonically with carrier density, the quantum scattering time fluctuates as a function of carrier density depending on the cool-down cycle. For high-mobility samples we find that the ratio τ D/ τ Q can be as high as 88 indicating long-range potential fluctuations. If hydrostatic pressure is applied to the sample the carrier density is reduced by about 1×10 11 cm −2 kbar −1 at liquid He temperatures.

InAs nanocrystal growth on Si (100)

We have tried the growth of InAs dots on Si surfaces terminated with hydrogen atoms. It has been confirmed with cross-section transmission electron microscopy (XTEM) and field emission scanning electron microscopy (FESEM) that high quality InAs nanocrystals can be grown with a high density on Si (100) surfaces terminated with hydrogen atoms. The growth of InAs nanocrystals is initiated with formation of In islands followed by diffusion of As atoms into the In dots. The band discontinuity of the InAs/Si interface has been evaluated using the results of synchrotron radiation photoelectron spectroscopy (SRPES). The offsets for valence band and conduction band are estimated to be 0.31 eV and 0.44 eV, respectively. This result indicates that both holes and electrons can be well confined into InAs nanocrystals.

Thermal activation and thermal transfer of localized excitons in InAs self-organized quantum dots

We have investigated the temperature dependence of photoluminescence (PL) properties of a number of InAs/GaAs heterostructures with InAs layer thickness ranging from 0.5 monolayer (ML) to 3 ML. The temperature dependence of the InAs exciton energy and linewidth was found to display a significant difference when the InAs layer thickness is smaller or larger than the critical thickness around 1.7 ML, indicating spontaneous formation of quantum dots (QDs). A model, involving exciton recombination and thermal activation and transfer, is proposed to explain the experimental data. In the PL thermal quenching study, the measured thermal activation energies of different samples demonstrate that the InAs wetting layer may act as a barrier for thermionic emission of carriers in high quality InAs multilayers, while in InAs monolayers and submonolayers the carriers are required to overcome the GaAs barrier to thermally escape from the localized states.

Exchange interaction in InAs nanocrystal quantum dots

The near band-gap level structure in high-quality colloidal InAs nanocrystal quantum dots within the very strong confinement regime is investigated. Size-selective photoluminescence excitation and fluorescence line narrowing measurements reveal a size-dependent splitting between the absorbing and the emitting states. The splitting is assigned to the confinement-enhanced electron–hole exchange interaction. The size dependence of the splitting significantly deviates from the idealized 1/r3scaling law for the exchange splitting. A model incorporating a finite barrier which allows for wavefunction leakage is introduced. The model reproduces the observed 1/r2dependence of the splitting and good agreement with the experimental data is obtained. The smaller barriers for embedded InAs dots grown by molecular-beam epitaxy, are predicted to result in smaller exchange splitting as compared with colloidal dots with a similar number of atoms.

Strain-compensated InAsP/GaInP multiple-quantum-well waveguide modulators and in situ monitored AlGaAs/AlAs mirrors grown by gas-source molecular beam epitaxy

Gas-source molecular beam epitaxy (MBE) is used to grow high-quality strain-compensated InAs x P 1 − x /G y In 1 − y multiple quantum wells on InP substrates for modulator applications at 1.3 μm wavelength. The composition of the InAs x P 1 − x well can be determined in situ by the As-to-In incorporation ratio from As- and In-induced intensity oscillations of reflection high-energy electron diffraction. Tensile Ga y In 1 − y P is used to compensate the compressive strain in the InAsP. A modified doping profile in a waveguide modulator is used to provide a better confinement of the depletion region in the p-i-n structure under reverse bias. An improved quantum-confined Stark effect is obtained. In situ monitoring and controlling reflectivity of the AlGaAs/AlAs quarter-wave mirrors is used for reflection-type modulators on GaAs.

Binding energy of the free exciton in indium arsenide

We report the 0--5 T magnetoabsorption spectra of high-quality InAs epilayers grown by molecular-beam epitaxy on GaAs. Excitonic absorption is observed at all fields, and, from the absolute energy of the magnetoexciton absorption peak, the zero-field exciton binding energy is found to be in excellent agreement with the theoretical prediction of 1.0 meV from calculations which take into account the anisotropy, degeneracy, and spin splitting of the InAs band structure. The energy shift of the magnetoexciton at high fields is found to agree with predicted shifts using the adiabatic method.

Carrier relaxation and thermal activation of localized excitons in self-organized InAs multilayers grown on GaAs substrates.

We have investigated the temperature dependence of photoluminescence (PL) properties of a number of self-organized InAs/GaAs heterostructures with InAs layer thickness ranging from 0.5 to 3 ML. The temperature dependence of InAs exciton emission and linewidth was found to display a significant difference when the InAs layer thickness is smaller or larger than the critical thickness around 1.7 ML. The fast redshift of PL energy and an anomalous decrease of linewidth with increasing temperature were observed and attributed to the efficient relaxation process of carriers in multilayer samples, resulting from the spread and penetration of the carrier wave functions in coupled InAs quantum dots. The measured thermal activation energies of different samples demonstrated that the InAs wetting layer may act as a barrier for the thermionic emission of carriers in high-quality InAs multilayers, while in InAs monolayers and submonolayers the carriers are required to overcome the GaAs barrier to escape thermally from the localized states. \textcopyright{} 1996 The American Physical Society.

Spatial distribution of In during the initial stages of growth of InAs on GaAs(001)-c(4 × 4)

The initial stages in the growth of InAs by molecular beam epitaxy (MBE) on GaAs(001)-c(4 × 4) have been studied by in situ scanning tunnelling microscopy (STM) and reflection high energy electron diffraction (RHEED). Deposition of 0.1 ML at 420°C gives rise to a low number density of two dimensional (2D) islands on top of domains of locally disordered (1 × 3) structures which decorate the step edges. The size of the (1 × 3) domains increase as more InAs is deposited, consistent with the development of a (1 × 3) RHEED pattern. The results show that a 2D growth mode operates with strong evidence for alloying in the surface layer. The spatial distribution of In in the surface layer has also been investigated by varying the substrate temperature for InAs deposition. The implication is that growth at ∼420°C provides the optimal condition for growing high quality InAs monolayers on GaAs(001).

High Quality InAs1–ySby/InAs Multilayers for mid‐IR Detectors

AbstractThe high quality InAsSb multi‐layers have been grown on InAs substrate by Gd‐doped liquid phase epitaxy between 530 and 460°C. Compositional dependence of energy band gap and of lattice constant for epilayers were studied. The material is characterized by surface morphology observation, FTIR transmittance, photoluminescence (PL), spectro‐ellipsometry, and electrical measurements. Surface‐illuminated room temperature p‐n junction photodetectors in 3–5 μm wavelength range have been obtained.

Role of a nucleation layer in suppressing interfacial pitting in

In this work, we investigate the role of a low temperature nucleation layer on the interfacial properties of InAs epilayers grown on (100) semi-insulating InP substrates using a two-step metalorganic chemical vapor deposition method. Cross-sectional and plan-view transmission electron microscopy studies were carried out on InAs films of nearly equal total film thicknesses but for different thicknesses of a nucleation layer of InAs deposited at low temperature on the substrate. Our studies show that thermal etchpits are created at the interface between the InAs film, and the InP substrate for thin nucleation layer thicknesses. This is because the low temperature nucleation layer of InAs does not cover completely the surface of the InP substrate. Hence, when the temperature is raised to deposit the bulk of the InAs film, severe thermal pitting is observed at the interface. These thermal etchpits are sources of threading dislocations. To obtain high quality InAs films and suppress interfacial pitting there is an optimum thickness of the nucleation layer. Also, our studies show that there is a relationship between the density of defects in the film and the thickness of the nucleation layer. This in turn relates to the variation of the electronic properties of the InAs films. We have observed that for all nucleation layer thicknesses, the density of threading dislocations is higher close to the interface than at the free surface of the film.

Molecular beam epitaxial growth of InAs/GaSb double quantum wells for complementary heterojunction field-effect transistors

We report the molecular beam epitaxial growth of InAs/GaSb double quantum wells applied to complementary heterojuntion field-effect transistors. The effect of silicon doping in various positions in the (Al x Ga 1- x )Sb barrier layers on the electrical characteristics of InAs and GaSb quantum wells was investigated. Compensation doping of silicon in the (AlGa)Sb barrier was always found to degrade carrier mobilities of both channels, suggesting substantial diffusion of acceptors in the barrier. A minimum of 150 Å was found to be necessary for the mid-barrier thickness between the channels in order to avoid the carrier transfer. Formation of an InSb-like bond at the InAs/(AlGa)Sb heterointerface by the proper sequential control of molecular beams was suggested by Raman scattering analysis. The proper shutter sequence was confirmed to be useful also in the InAs/GaSb double quantum well structure in order to obtain a high quality InAs channel. Vertically integrated enhancement mode GaSb p-channel heterojunction field-effect transistors (HFETs) and deplition mode InAs n-channel HFETs have been successfully fabricated. It became clear that the increase of compensation doping is not enough to turn the n-HFET into enhancement mode but cause parallel conduction in the barrier. Reduction of native donors will become essential for our goal.

Significance of a Nucleation Layer in Inhibiting Interfacial Pitting in InAs Films Grown by Two-Step MOVCD on (100) Inp Substrates

AbstractIn this paper, we study the significance of a low temperature nucleation layer and its role in inhibiting interfacial pitting vapor deposition. Transmission electron microscopy and scanning electron microscopy studies show that severe interfacial pitting occurs for thin nucleation layers of average thicknesses of 200Å and 400Å. For these average nucleation layer thicknesses we have found that the InAs islands do not cover the entire substrate surface during the low temperature deposition. Hence, when the film is heated to a higher temperature for the growth of the remainder of the film severe pitting at the heterointerface is produced. The thermal etchpits are sources of threading dislocations, which propagate to the surface of the film. For thicker nucleation layers we observe no interfacial pitting. Our studies show that there is an optimum nucleation layer thickness for which high quality InAs films with reduced threading dislocation densities and relatively high electron mobilities are obtained. Both electrical and structural studies suggest that ∼ 800Å is an optimum thickness of the low temperature nucleation layer.