III-V Crystals Research Articles

Stability of monodomain III-V crystals and antiphase boundaries over a Si monoatomic step

Here, we compare the stabilities of different III-V crystals configurations on stepped Si substrates, with or without anti-phase boundaries, for abrupt and compensated interfaces, using density functional theory. Thermodynamic stability of the different heterostructures is analyzed with an atomic scale description of charge densities distribution and mechanical strain. We show that the configuration where a III-V crystal adapts to a Si monoatomic step through change of charge compensation at the hetero-interface is much more stable than the configuration in which an antiphase boundary is formed. This study thus demonstrates that antiphase boundaries commonly observed in III-V/Si samples are not originating from Si monoatomic step edges but from inevitable kinetically driven coalescence of monophase 3D III-V islands.

(Invited) Material Porosity

We really like pores in our research group. Big pores, small pores, ordered pores, random pores – they all have a function and as is often found, show behaviour that is not always predicted. I started my research journey trying to put extremely thin films onto near-perfect III-V crystals to control (opto)electronic properties and when the first TEM on our campus showed the image in Fig. 1 almost 21 years ago (1,2), the electrochemical modification of the InP made more sense. In this talk, I will summarise the journey from porous InP that led to studies of other porous semiconductors such as silicon (3-10) and GaN (11-15), periodically ordered photonic crystal porous structures (16-26) and some optical, thermal and electrochemical properties photocatalysis, batteries and related that were modified by the porous structure, leading up to the most recent porous materials (27). References C. O’Dwyer, D. N. Buckley, D. Sutton, M. Serantoni and S. B. Newcomb, J. Electrochem. Soc., 154, H78 (2007).C. O’Dwyer, D. N. Buckley, D. Sutton and S. B. Newcomb, J. Electrochem. Soc., 153, G1039 (2006).C. O'Dwyer, W. McSweeney and G. Collins, ECS J. Solid State Sci. Technol., 5, R3059 (2016).W. McSweeney, C. Glynn, H. Geaney, G. Collins, J. D. Holmes and C. O'Dwyer, Semicond. Sci. Technol., 31, 014003 (2016).W. McSweeney, H. Geaney and C. O'Dwyer, Nano Res., 8, 1395 (2015).W. McSweeney, H. Geaney, C. Glynn, D. McNulty and C. O'Dwyer, ECS Trans., 66, 39 (2015).W. McSweeney, O. Lotty, C. Glynn, H. Geaney, J. D. Holmes and C. O'Dwyer, Electrochim. Acta, 135, 356 (2014).W. McSweeney, O. Lotty, N. V. V. Mogili, C. Glynn, H. Geaney, D. Tanner, J. D. Holmes and C. O'Dwyer, J. Appl. Phys., 114, 034309 (2013).E. Quiroga-González, J. Carstensen, C. Glynn, C. O’Dwyer and H. Föll, Phys. Chem. Chem. Phys., 16, 255 (2014).C. Glynn, K.-M. Jones, V. Mogili, W. McSweeney and C. O'Dwyer, ECS J. Solid State Sci. Technol., 6, N3029 (2017).O. V. Bilousov, J. J. Carvajal, A. Vilalta-Clemente, P. Ruterana, F. Díaz, M. Aguiló and C. O’Dwyer, Chem. Mater., 26, 1243−1249 (2014).O. V. Bilousov, J. J. Carvajal, H. Geaney, V. Z. Zubialevich, P. J. Parbrook, O. Martínez, J. Jiménez, F. Díaz, M. Aguiló and C. O’Dwyer, ACS Appl. Mater. Interface, 6, 17954 (2014).O. V. Bilousov, J. J. Carvajal, H. Geaney, F. Díaz, M. Aguiló and C. O’Dwyer, CrystEngComm, 16, 10255 (2014).O. V. Bilousov, H. Geaney, J. J. Carvajal, V. Z. Zubialevich, P. J. Parbrook, A. Giguère, D. Drouin, F. Díaz, M. Aguiló and C. O’Dwyer, Appl. Phys. Lett., 103, 112103 (2013).O. V. Bilousov, J. J. Carvajal, D. Drouin, X. Mateos, F. Díaz, M. Aguiló and C. O'Dwyer, ACS Appl. Mater. Interfaces, 4, 6927 (2012).S. O'Hanon, D. McNulty, R. Tian, J. Coleman and C. O'Dwyer, J. Electrochem. Soc., 167, 140532 (2020).D. McNulty, H. Geaney, Q. Ramasse and C. O'Dwyer, Adv. Funct. Mater., 30, 2005073 (2020).A. Lonergan, C. Hu and C. O'Dwyer, Phys. Rev. Materials, 4, 065201 (2020).G. Collins, A. Lonergan, D. McNulty, C. Glynn, D. Buckley, C. Hu and C. O’Dwyer, Adv. Mater. Interfaces, 7, 1901805 (2020).D. McNulty, A. Lonergan, S. O'Hanlon and C. O'Dwyer, Solid State Ionics, 314, 195 (2018).D. McNulty, H. Geaney, D. Buckley and C. O'Dwyer, Nano Energy, 43, 11 (2018).A. Lonergan, D. McNulty and C. O'Dwyer, J. Appl. Phys., 124, 095106 (2018).S. O'Hanlon, D. McNulty and C. O'Dwyer, J. Electrochem. Soc., 164, D111 (2017).D. McNulty, E. Carroll and C. O'Dwyer, Adv. Energy Mater., 7, 1602291 (2017).E. Armstrong and C. O'Dwyer, J. Mater. Chem. C, 3, 6109 (2015).E. Armstrong, D. McNulty, H. Geaney and C. O’Dwyer, ACS Appl. Mater. Interfaces, 7, 27006 (2015).A. Lonergan, B. Murphy and C. O'Dwyer, ECS J. Solid State Sci. Technol., 10, 085001 (2021). Figure 1. Bright field TEM of a cross section of an InP electrode after a potential sweep from 0.0 to 0.44 V (SCE) in 5 mol dm-3 KOH at 2.5 mV s-1. The plane of the micrograph is (011). Figure 1

(Invited) Material Porosity

Big pores, small pores, ordered pores, random pores – they all have a function and as is often found, show behaviour in new materials that is not always predicted or obvious at the outset. I started my research journey trying to put extremely thin films onto near-perfect III-V crystals to control (opto)electronic properties and when the first TEM on our campus showed remarkable pore growth and structure in InP almost 21 years ago, the electrochemical modification of the InP made more sense. In this paper, I will summarise a few aspects of research into porous materials and semiconductors, from porous InP that led to studies of other porous semiconductors such as silicon, GaN, ZnO and Indium Tin oxide (ITO), to periodically ordered photonic crystal porous structures and some optical, thermal and electrochemical properties, photocatalysis, studies in batteries and related that were enabled or modified by the porous structure.

(Invited) Challenges in III-V Surface Passivation and Some Potential Solutions

In many applications, III-V surfaces lie at the buried or embedded interface of an insulator/III-V or metal/III-V junction. The chemical and physical properties of these III-V interfaces are typically different from the uniform III-V bulk crystal structures. Thus, it is difficult to predict the interface behavior (e.g. electronic structure and doping efficiency) on the basis of the established bulk-crystal physics and chemistry. III-V device interfaces often have an amorphous structure and extend over several atomic layers, instead of having a monocrystalline and atomically sharp structure. Reasons for that are discussed in this presentation.Therefore, it is not surprising that the III-V interfaces are a weak part of many practical devices (e.g. laser diode, infrared photodiode, micro-LED, HEMT) causing degradation in the current as well as future III-V applications. III-V interfaces include a high density of point defects, as compared to the uniform bulk crystals areas, which cause the electronic defect levels around the band gap at the interfaces, which further cause the electrical and optical losses. Use of III-V crystals is expected to increase in the areas like LED lighting, infrared optoelectronics, and high-speed transistor circuits, where it is not possible to utilize the Si crystals.Thus it is relevant to investigate and develop the III-V interface properties. The surface or interface passivation means a decrease in the defect-level density or/and in the effects of defect levels. It can be expected that the III-V passivation development requires a multistep procedure combining benefits of the different methods.Some commonly used passivation methods (e.g. wet chemistry, hydrogen forming gas, ALD self cleaning) are summarized in this talk. Our group has studied the issue whether it is useful to include ultrahigh-vacuum (UHV) treatments in a large arsenal of different passivation methods. The traditional surface science has been based on UHV technology. Our group has approached the III-V passivation challenge from a surface-science viewpoint. We have investigated in particular the clean surface properties and the surface oxidation in UHV conditions. Our group has addressed the question whether it is beneficial to pre-oxidize III-V surfaces intentionally because it is very difficult to avoid oxidation of III-V device surfaces. Our results support the previous findings that proper oxidation of III-V interfaces is a potential method to improve the devices performance.We have taken a step toward combining the surface science with the electrical characterization of III-V interfaces to find interconnections between electrical properties and surface-science ones. The high-resolution synchrotron x-ray photoelectron spectroscopy (XPS) has been used. Because XPS is a widely used method, we have addressed specific challenges in XPS analysis and that how the XPS analysis can be developed by including theoretical ab initio calculations. In this talk, it is also attempted to make a comparison to the silicon interface passivation.

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Photoreflectance is a contactless type of modulation optical spectroscopy. It is used to study the band structure features of monocrystalline semiconductors, their doping level, the composition of alloys, as well as surface and interface band bending. Using high-quality GaAs as an example, the possibilities of describing the photoreflectance lineshape by one-electron and exciton models are demonstrated. The spectra of ultrapure samples of this material exhibit an oscillating structure well described by excitonic effects. For III-V alloys, a review of photoreflectance results concerning the effect of composition and temperature on the band gap and spin-orbit splitting is carried out. Determination of the position of the Fermi level on the surface (Fermi level pinning) for III-V crystals is considered. The currently developing technique for measuring photoreflectance in the mid-infrared range (photomodulation Fourier transform infrared spectroscopy) is described in detail. It is shown that phase correction plays a decisive role in such measurements. Original results demonstrate the capabilities of this method in a wide wavelength range.

Van Der Waals Growth of III-V Semiconductors on Graphene

Recent discovery of graphene and its unique properties has attracted a great deal of interest in implementing this material in a variety of new devices, targeting applications in ultra-fast electronics, quantum information, carbon-free energy conversion, optoelectronics, and bio-integrated technologies [1,2]. However, graphene lacks a controlled non-zero bandgap, which prevents its large-scale application in electronic and energy conversion devices. To overcome this limitation, we exploit direct integration of III-V semiconductors on graphene through van der Waals epitaxy. Known for their efficient light emission and high charge carrier mobilities, III-V semiconductors are at the core of numerous technologies including high-efficiency solar cells, lasers, light emitting diodes, and ultra-fast transistors, to name a few [3].Due to lack of dangling bonds on graphene’s surface, in epitaxial growth of III-V semiconductors on graphene the crystals follow the order of graphene lattice through van der Waals forces. Initially, two nucleation and growth processes were suggested for such van der Waals epitaxy: (1) nucleation starts at defect sites on graphene [4], and (2) nucleation starts on specific sites on graphene lattice, which are the favorable adsorption sites for III/V adatoms [5]. The latter growth mechanism limits the epitaxial growth of the III-V crystals in four different relative orientations (with different strain values) [5]. Recently, density functional theory calculations followed by homoepitaxial growth of InP, GaP, and GaAs through several layers of graphene suggested another determining factor in van der Waals epitaxial growth: long-range interaction between the III-V substrate under graphene and the III-V structures grown on graphene [6].In this talk, we demonstrate the low-pressure metal-organic vapor phase deposition (MOCVD) of InAs, GaAs, InP, and GaP islands on single layer graphene sheets grown on copper foils and transferred on SiO2/Si (100), as well as graphene sheets directly grown on Ge (100), (110), and (111) substrates. We show that regardless of the nature of the substrate under graphene, III-V crystals grow mostly on graphene defect sites and their morphology can be somewhat controlled through controlling the growth parameters. We then show the effect of long-range forces between Ge and III-V structures on growth morphology, which results in significant coalescence and growth of tens of micron large islands on graphene/Ge as opposed to parasitic crystals grown on graphene/SiO2. In what follows, we provide a brief summary of our observations in both systems.All III-V semiconductors grown on graphene/SiO2/Si showed very similar growth morphology and crystal structure. Plan-view and cross-sectional scanning electron microscopy (SEM), micro-Raman spectroscopy, powder and high-resolution X-ray diffraction (XRD), along with cross-sectional transmission electron microscopy (TEM) and nanoscale cathodoluminescence analysis revealed formation of 1D, 2D, and 3D structures in zinc-blende, wurtzite, and polytypic (mixed zinc-blende/wurtzite) phases. We have recently demonstrated that polytypic InP crystals form a type II homojunction with potential applications in optoelectronic devices [7]. XRD analysis of the growth time evolution of texture, as well as growth rate and crystal size evolution analysis of the crystals using atomic force microscopy (AFM) suggested a growth mechanism similar to selected area MOCVD growth [7], which is widely used to grow nanostructures and devices. This enabled us to have some degree of control over the growth morphology (single crystals, polycrystals, nanowires) through controlling the growth parameters such as growth temperature, rate and time.Similar 1D, 2D, and 3D structure were grown on graphene/Ge (100), (110), (111). However, the size and crystalline quality of the islands have significantly improved for growth on Ge substrates. Moreover, two-step growth (nucleation at low temperature (450 °C) and growth at higher temperature (600 °C)) lead to coalescence of the crystals and formation of tens of microns large islands with smooth surface (roughness ~ 1nm from AFM data) on graphene/Ge, while no significant improvement in growth morphology was observed for growth on graphene/SiO2. These observations suggest a strong sensitivity of the morphology of the deposited films on the nature of the substrate below the graphene monolayers. This provides insight to control the properties of such hybrid systems and will pave the path to engineering a new class of electronic and optoelectronic devices by combining the advantages of semiconductors and graphene.

(Invited) First-Principles Studies of the Defect Formation in III-V FETs Grown by Fin Replacement Method

First-principles investigations are used to study the formation of defects in III-V fins grown using the fin replacement method or aspect ratio trapping technique. We show that, during the growth of the III-V, the formation of intermediate chemical states with the precursors leads to the creation of in-diffused Mg/Zn and Al2O3 sub-oxide. We also show that the poor quality of the III-V crystals could enhance the in-diffusions of Mg/Zn and lead to the deposition of Al- and Mg-oxides at the III-V/SiO2 interface. Our prediction is consistent with experimental observations. These defect formations could be an origin of the degradation of the electrical reliability of III-V fin-shaped field-effect transistors. In order to find a way to prevent these defect-related issues, alternative p-type dopants with a high tolerance to these defect formations have been investigated theoretically. To decrease the difficulties met in the fabrication of III-V fin, it is important to understand the nature of the defects present using ab initio approaches.

Near-resonance acousto-optical interactions in GaAs and InP

Acousto-optical properties of GaAs and InP are thoroughly investigated for photon energies tending to the band gap from below, and the whole set of photoelastic constants is determined as a function of the wavelength λ for λ≤1.06 μm. Figures of merit as high as 1200 times those of silica have been measured. It is shown how one can take advantage of the near-resonance acousto-optical properties of GaAs and InP in device design, in spite of the optical absorption. Such devices could be broadband, fast, compact, and insensitive to light polarization and may involve other direct-gap III-V crystals, adapted to the laser radiation.

Phonons and internal stresses in IV-IV and III-V semiconductors: The planar bond-charge model.

We fit phonon-dispersion relations of IV-IV (Si, Ge, and a-Sn) and III-V (GaAs, AlSb, and GaSb) semiconductor crystals along [100] and [111] directions by means of a planar bond-charge model. Eigenvectors at the X and L high-symmetry points are predicted using the fitted parameters for the III-V crystals. For GaAs, results agree fairly well with ab initio calculations and experimental data. Using the mass approximation we deduce the phonon-dispersion curves of AlAs from those of GaAs, finding good agreement with ab initio calculations

The 30° dislocations in plastically deformed gallium phosphide

Abstract An appreciable number of 30° dislocations could be found in plastically deformed GaP single crystals. The bending experiments were realized at an elevated temperature of 883 K. The 30° dislocations are separated into screw and 60° Shockley partials. During high-temperature deformation, stress relaxation is permitted by nucleation and motion not only of 60° and screw dislocations (both of which are separated into partials) which seems to be characteristic of III-V crystals deformed at a low temperature but also of a considerable number of glissile 30° dislocations.

Analysis of dielectric properties of I–VII, II–VI and III–V crystals with ZnS structure

An analysis of dielectric properties such as polarizabilities, effective charge parameters and dielectric constants is presented for I-VIII (CuCl, CuBr, CuI), II-VI (ZnSe, ZnTe, CdS, CdTe) and III-V (AlSb, GaP, GaAs, GaSb, InP, InAs, InSb) crystals with the zincblende structure. Calculations were performed with and without using full local field corrections. The analysis has been extended to evaluate the volume derivatives of the polarizabilities and effective charge parameters for GaAs, GaP, ZnS and CdS crystals. The transverse optic model Grüneisen parameters and anharmonic contributions to dielectric constants are also calculated for these crystals. The results are discussed and compared with available experimental data.

Synthesis and Crystal Growth of AIIIBV Semiconducting Compounds Under High Pressure of Nitrogen

Nitrogen under high pressure due to its elevated thermodynamic potential can be used for the synthesis of semiconducting compounds. High temperature growth of III-group metal nitrides from metallic solution is discussed and illustrated by the results of crystal growth of GaN. The growth of III-V crystals from the melts under high N2 pressure leads to high concentration of substitutional nitrogen. The results of crystal growth experiments are used in the analysis of mixing properties in III-V-N pseudobinary systems.

Atomic Diffusion With Strain and Injection

ABSTRACTThe inherent complexity of defect processes in III-V's and the consequent difficulties with ab initio and semi-empirical methods are recalled. A potential solution using massive Monte Carlo simulation on microcomputers is suggested. Evidence for the validity of the Ballistic Model, BM, of atomic diffusion in III-V's is noted. According to the BM the effect of strain (in the absence of any electrostatic, population, or recombination effect) is to increase the rate at which a given mobile atom hops where the sample is compressed. For the case of misfit strain at a (100) junction, we note that the anisotropy of the elastic constants implies that some planes running into the bulk will be compressed whichever the sign of the misfit. This implies that misfit strain of either sign should increase the observed rate of interdiffusion, in the absence of other effects. We also recall the importance (demonstrated at low T) of recombination enhancement of atomic diffusion, RED. Devices are processed at temperatures where the thermal rate of recombination is very high and often operated at high levels of injection. The interaction of strain with RED is clearly important and complicated. III-V crystals have the further complication of being piezoelectric. The active piezoelectric axes are <111>, so a pure <100> strain does not produce a field. However, the accommodation a device makes to misfit at (100) junctions can generate a strong field, which may fluctuate with bias voltage.

Mossbauer spectra and the DX-centre complex in AlGaAs

Mossbauer spectra for the 'DX' deep-level defect in AlGaAs alloys are just now being made available-for example, in a recent article by Gibart and co-workers. The interpretation of these spectra has been somewhat clouded by the fact that Mossbauer specialists have generally not considered the anti-site defect among the defect complexes present in III-V crystals near the Mossbauer isotope that affect the various components of the spectra. The author notes that the anti-site defect is well established as a component of, for example, the EL2 deep-level defect, and generally as the most prevalent native point defect in III-V crystals. Furthermore, the spectra reported by Gibart and co-workers are consistent with the model wherein the 'X' of the DX defect complex is the pair composed of a metal-on-As-site anti-site defect plus a Ga vacancy that results from As vacancy nearest-neighbour hopping. In particular, they show that a major fraction of donors remain in an unperturbed state when DX compensates the sample.

Comparison of SiIII-SiV and SiIII-VIII diffusion models in III-V heterostructures lattice matched to GaAs

The diffusion of SiIII-SiV neutral pairs versus the diffusion of SiIII-VIII complexes in III-V crystals is compared in the light of experimental data showing the effect of Si diffusion on self-diffusion of column III and column V lattice atoms. Secondary-ion mass spectroscopy is used to compare the enhanced diffusion of column III or column V atoms in several different Si-diffused heterostructures closely lattice matched to GaAs. Enhancement of the lattice-atom self-diffusion, via impurity diffusion, is found to occur predominantly on the column III lattice. Supporting the SiIII-VIII diffusion model, these data indicate that the main native defects accompanying the Si diffusion are column III vacancies, which diffuse directly on the column III sublattice.

Optical phase conjugation in narrow direct-gap semiconductors

Optical phase conjugation processes via degenerate four-wave mixing mechanisms have been investigated analytically in narrow direct-gap semiconductors duly irradiated by low-power near resonant lasers. The role of linear absorption phenomena is introduced intrinsically into the electromagnetic equations through complex first-order optical susceptibility of the crystal. A coherent radiation-exciton interaction model is employed to obtain the intensity-dependent crystal optical susceptibility. The band-to-band optical transitions into the true continuum above the fundamental absorption edge are considered. We have estimated qualitatively the conversion efficiency η for important III-V crystals like InSb, GaSb, and GaAs. The nature of variation of η with respect to detuning as well as excitation intensity are found to be in very good agreement with the experimental observations in ammonia, and in semiconductors like Si, Ge, and Hg1−xCdxTe. The analyses also reveal that large η can be derived by using submicrometer sized crystals. InSb is established as the most promising III-V semiconductor for optical phase conjugation device technology at very low cw resonant laser irradiation.

Dislocations and the piezoelectric effect in III-V crystals

It is shown that 60° and 90° α and β dislocations give rise to piezoelectrically induced charge distributions and electric fields in the surrounding crystal. The general features of the charge distributions are discussed with special references to the relation between the nature of the distributions and the symmetry of the crystal. Finally, it is shown that the dislocation reaction (a0/2)[101̄]+(a0/2)[011]= (a0/2)[110] is self-consistent as regards electrical properties.

The elastic behaviour of InBi single crystals

Ultrasonic wave velocities have been measured by the pulse echo technique at 15MHz in single crystals of InBi grown by zone-melting. The elastic stiffness constant set has been computed from the velocity data by a least-mean-squares procedure. The elastic behaviour of this metallic compound is quite different in kind from that of the semiconducting III-V crystals; the volume compressibility does not follow Keyes' generalisation for the other III-V compounds. The elastic properties of InBi have been found to show the characteristics of a layer-like crystal with weak interlayer binding; this finding is illustrated by the linear compressibilities and by a compilation of cross-sections of the wave velocity and Young's modulus surfaces. The Debye temperature is 115°K.