VI Donors Research Articles

CUSTOM RELAXATION INDUCED IMPURITY PHOTOCONDUCTIVITY IN THE UNITED AII BVI and AIII BV

Two types of non-standard relaxation induced impurity photoconductivity (IIP) observed in photoconductors CdS, ZnSe, GaAs and others, depending on the kinetic characteristics of the traps are described. In one case, at the stage of post flashing monotonic decay which is typical for relaxation associated with slow traps (the ratio of the speed of the electron capture to the recombination rate (R > 1): measurement alternating signal (f > 20 Hz) relaxation curves take the form of curves usual impurity photoconductivity. Electronic processes responsible for relaxation of non-standard IIP are analyzed. For example, fast-centers, which include the characteristic A II B VI donor Ag i 0 , for the first time in semiconductors experimentally, investigated the dependence of the cross section of electron capture by traps energy released during localization.

Nonlinear screening of positive and negative point charges in GaAs

We have used a variational approach for approximately solving Resta's nonlinear Thomas-Fermi equation for the potential of (point) charges in GaAs. We have considered the cases of charges (in atomic units) Z = ±0.16, ±1.16, ±0.84. The charges Z = +0.16 and Z = −0.16 are the effective charges due to the partial ionicity of the chemical bonds on a Ga and As site, respectively. The charge Z = +0.84 corresponds to a Column VI donor on an As site, that of Z = +1.16 to a Column IV donor on a Ga site. Similarly, the charge of Z = −1.16 corresponds to a Column IV acceptor on an As site, that of Z = −0.84 to a Column II acceptor on a Ga site. As a result of our calculations, we have obtained site-dependent and charge-dependent spatial dielectric functions that describe the screening of the (point) charges by the valence electrons of (pure) GaAs.

Band anticrossing in dilute nitrides

Alloying III–V compounds with small amounts of nitrogen leads to a dramatic reduction ofthe fundamental band-gap energy in the resulting dilute nitride alloys. The effect originatesfrom an anticrossing interaction between the extended conduction-band states and localizedN states. The interaction splits the conduction band into two non-parabolic subbands. Thedownward shift of the lower conduction subband edge is responsible for the N-inducedreduction of the fundamental band-gap energy. The changes in the conduction bandstructure result in a significant increase in electron effective mass and a decrease in theelectron mobility, and lead to a large enhancement of the maximum doping level inGaInNAs doped with group VI donors. In addition, a striking asymmetry in the electricalactivation of group IV and group VI donors can be attributed to mutual passivationprocess through formation of the nearest neighbour group-IV donor nitrogenpairs.

Effect of group II impurity and group III native defect on disordering Cu–Pt type ordered structures in In0.5(AlxGa1−x)0.5P layers

Cu–Pt ordering is studied with cross-sectional transmission electron microscopy in p-type, n-type, and nominally undoped InAlP and In(AlGa)P layers. These different doping conditions allow us to investigate the effect of acceptor doping with magnesium and donor doping with tellurium on removing Cu–Pt ordering in In(AlGa)P. Even more significant, however, is the ability to investigate the effect of native group III self-diffusion in p-type, n-type, and nominally undoped InAlP and In(AlGa)P layers. Our data indicate that the rapidly diffusing Mg acceptor species is less effective on removing Cu–Pt ordering than the relatively slow diffusing Te donor species. Also, our results indicate that the native group III defects and group III self-diffusion play a more important role in removing Cu–Pt ordering than either group II acceptor diffusion or group VI donor diffusion.

Advanced Processing of GaN for Electronic Devices

This review focuses on understanding and optimization of several key aspects of GaN device processing. A novel rapid thermal processing up to 1500°C, in conjunction with AlN encapsulation, has been developed. The activation processes of implanted Si or Group VI donors, and common acceptors in GaN by using this ultrahigh-temperature annealing, along with its effects on surface degradation, dopant redistribution, and damage removal have been examined. 1400 degrees has proven to be the optimum temperature to achieve high activation efficiency and to repair the ion-induced lattice defects. Ion implantation was also employed to create high-resistivity GaN. Damage-related isolation with sheet resistances of 1012 Ω/square in n-GaN and 1010 Ω/square in p-GaN has been achieved by implant of O and transition metal elements. The effects of surface cleanliness on characteristics of GaN Schottky contacts have been investigated, and the reduction in barrier height was correlated with removing the native oxide that forms an insulating layer on the conventionally cleaned surface. W alloys have been deposited on Si-implanted samples and Mg-doped epilayers to achieve ohmic contacts with low resistance and better thermal stability than the existing non refractory contact schemes. Dry etching damage in GaN has been studied systematically using Schottky diode measurements. Wet chemical etching and thermal annealing processes have been developed to restore the ion-degraded material properties.Based on these technical improvements, attempts have been made to demonstrate GaN-based bipolar transistors. The devices operated in common base mode at current densities up to 3.6 kAcm−2and temperatures up to 300°C. The key issues that currently limit the device performance, such as high base resistance, poor impurity control, and defects resulting from the heteroepitaxial growth, have been addressed. A physically based simulation suggested that GaN bipolar devices may still suffer from small minority-carrier lifetime in the absence of aforementioned processing problems.

A comprehensive thermodynamic analysis of native point defect and dopant solubilities in gallium arsenide

A detailed analysis of the role of charged native point defects in controlling the solubility of electrically active dopants in gallium arsenide is presented. The key roles of (a) positively charged arsenic vacancies (VAs+) in determining the doping range over which the solubility curve is linear and (b) multiply negative charged gallium vacancies (VGam−) determining annealing and diffusion behavior in n+ material are demonstrated. An equilibrium thermodynamic model based on these concepts is shown to accurately describe the doping behavior of Te, Zn, Sn, Ge, Si, and C and the formation and annealing of the deep level denoted EL2 (assumed to be the arsenic antisite defect AsGa) in melt- and solution-grown crystals. The model provides a much more comprehensive and accurate description of dopant solubility than the widely cited Schottky barrier model of bulk nonequilibrium dopant incorporation. It is unambiguously shown that partial autocompensation of donor dopants by the donor–gallium vacancy acceptor complex occurs for both group IV and group VI donor dopants. The deduced concentrations of arsenic vacancies grown into the crystal during melt growth are shown to be in excellent agreement with values determined by titration and by density/lattice parameter measurements. The obtained data are used to plot the Ga–As solidus. Due to the presence of charged native point defect species (notably, VAs+), the free-carrier concentration at high temperatures is greater than the intrinsic concentration. The calculated concentration is shown to be in excellent agreement with published experimental data. The utility of an equilibrium thermodynamic model in seeking an understanding of doping behavior under conditions of high supersaturation, such as occur with organometallic vapor phase epitaxy and molecular beam epitaxy, is demonstrated. Finally, some suggestions are made as to the likely native point defect equilibria in indium phosphide.

Effect of Local Lattice Relaxation on the Electronic Structure of Substitutional Donors in Silicon

The electronic structure of substitutional group V (P, As and Sb) and group VI (S, Se and Te. both neutral and singly ionized) impurities in silicon has been investigated using self-consistent Multiple Scattering Xα (MSXα) method within the framework of the standard muffin-tin potential approximation, incorporating the effect of lattice relaxation surrounding the impurity. A systematic stud y of the effect of local lattice relaxation on the electronic structure of group V (shallow) and group VI (deep) donors in Si is attempted. It is interesting to note that the size difference between the impurity atom and that of the host Si atom seems to be shared almost equally by the impurity atom (either expansion or squeezing) and the nearest neighbours (inward or outward movement). The effect of size difference on charge transfer and the bonding characteristics between the impurity atom and Si atoms are also analyzed.

Coordination chemistry of transition elements with some group V and VI donors

Coordination chemistry of some transition/post-transition elements with ligands of the type: (a) tertiary phosphine/phosphine chalcogenides, (b) 2-pyridinethiol/its N-oxide, (c) organotellurium(II) and (d) triselenoorganophosphonate are described. Novel features include: (i) symmetrization phenomenon exhibited by organomercury(ll), (ii) formation of 7-membered chelate rings, (iii) variation of mercury-sulphur distances with change in ring size, (iv) stabilization of copper(II)-tertiaryphosphine bonding, (v) phenomenon of reverse transmetaUation, (vi) cis-trans isomerism shown by palladium(lI)/ platinum(II) complexes of organophosphonates etc. The complexes have been established using X-ray crystallography, X-band ESR and multinuclear NMR data apart from usual techniques.

A bistable behavior of the Si and Se donors in Al xGa 1− xAs

It is shown that A 1(Γ) and A 1(L) substitutional group IV and group VI donor states transform into each other with the alloy composition in Al x Ga 1− x As. There are no energy barrier for such transformation. The arguments are presented that the DX state of these donors arises from T 2(L) resonant state as a result of spontaneous tetragonal distortion. Such distortion changes the donor - nearest atom distance by about 2%.

Interactions between hydrogen and group VI donors in GaAs and GaAlAs

GaAs and GaAlAs layers doped with different group VI donors (S, Se, Te) have been exposed to hydrogen plasma. By secondary ion mass spectroscopy, it is shown that, as in Si-doped materials, the hydrogen diffusion strongly depends on the AlAs content. Electronic transport measurements indicate that after hydrogen diffusion the electron concentration systematically decreases and their mobility increases, demonstrating clearly the passivation of the group VI donors by hydrogen.

Oxide, Chalcogenide and Related Clusters of Aluminum, Gallium and Indium

Abstract A review of the cluster compounds of the group III metals (aluminum, gallium, and indium) with group VI donor atoms, focusing on recent developments in the author's laboratory, is given. Compounds with oxide, and related hydroxide, alkoxide and siloxide ligands, are discussed with relevance to the Kaminsky co-catalyst (methylalumoxane), and the sol-gel synthesis of group III oxide ceramics, respectively. The sulfide clusters [(tBu)GaS] x undergo a facile topological rearrangement between the different oligomers (i.e., x = 4, 6, 7, and 8), while the cubane cluster [(tBu)GaS]4 provides the first evidence that new metastable phases of binary compounds may be deposited by chemical vapor deposition from a predesigned molecular motif. The structural relevance of the group II/VI clusters to solid state materials is also discussed.

Magnetic resonance studies of group IV and VI donors in Ga1-xAlxAs

The magnetic resonance results for the group IV (Si, Sn) and group VI (S, Se, Te) donors in GaAlAs alloys are reviewed. For the donors Si, S, Se, Te the DX deep donor state has apparently not been observed; the paramagnetic state generated by photoexcitation has been attributed to the X conduction band derived effective-mass (EM) state. On the contrary recent results for Sn, where the central hyperfine interaction could be resolved, demonstrate clearly that for Sn the paramagnetic donor state is not EM-like; it is attributed to the neutral charge state of the DX centre. A comparison of the photoexcitation process and the associated persistent photoconductivity gives a strong indication for a negative-U DX ground state. It is shown that recent deep-level transient spectroscopy results further support this assignment. However, it is unclear why in some cases (Si, S, Se, Te) apparently only the EM states are observed and not the deep donor state, whereas in the case of Sn the situation is reversed.

Donor-related levels in GaAs and AlxGa1-xAs

It is now widely accepted that DX levels in n-type AlxGa1-xAs are ground states of isolated substitutional donors in distorted configurations which are stabilized by trapping two electrons. The leading model is that the distortion occurs when the group IV donor substituted on a group III lattice site, moves along a <111> axis towards an interstitial site. In the case of a group VI donor which substitutes on a group V lattice site, one of the group III neighbours moves toward the interstitial site. Recent work suggests that localized excited states of both donor configurations play an important role in electron transitions between DX levels and the conduction band. The research leading to this view of substitutional donors is reviewed. Some implications of this model for technological applications of AlxGa1-xAs and related alloys are discussed.

Atomic structure of shallow acceptor- and donor-hydrogen complexes in GaAs

The microscopic structures of an interstitial hydrogen atom in p- and n-type GaAs are determined using an ab initio pseudopotential method. For Be impurities substituting Ga ions, hydrogen sitting at the bond-center site more strongly bonds to one of the neighboring As atoms than to the acceptor, while a direct donor-H bond takes place in Si-doped samples. This character of hydrogen bonding of passivated SiH complexes is similar to that of SiH bonds in n-type Si. For group VI donors such as S, hydrogen strongly interacts with the neighboring host Ga breaking a donor-Ga bond.

Atomic structure ofDX centers: Theory

A structural model forDX centers in Al x Ga1-x As alloys which explains their unusual properties in terms of two distinct bonding configurations for donor impurities is proposed. The results of ourab initio self-consistent pseudopotential calculations showDX to be a “negative-U” defect center. It results from a large lattice relaxation which is different for a Group IV than a Group VI donor. The proposed structural model provides a satisfactory explanation of the properties ofDX centers.

LPE growth of InGaAsP:InP high purity layers using rare earth elements

Use of rare earth (RE) elements has allowed the growth of high purity InGaAsP:InP layers in liquid phase epitaxial (LPE) systems. Experiments show that purification of material takes place on account of interaction between the RE and mainly group VI donor impurities.

Optically Detected Magnetic Resonance of Group IV and Group VI Donors in Al0.6Ga0.4As/GaAs Heterostructures

AbstractThe influence of chemically different donor species on the nature of shallow donor states in Al0.6Ga0.4As/GaAs heterostructures has been investigated by optically detected magnetic resonance (ODMR). Previous theoretical work by Morgan predicts a triplet state for group IV donors and a singlet state for group VI donors. ODMR experiments were performed on as-grown and implanted Si-, Se-, and S-doped epitaxial layers of Al0.6Ga0.4As grown on (001) GaAs substrates. The effective-mass states are modified by the heter-oepitaxial strain in these layers. The Si donors are characterized as quasi-independent valley states. The Se and S donors have valley-orbit splitting energies (i.e. chemical shifts) of 19-20 meV . The results indicate that Si, Se, and S donors are on the lattice sites in the metastable state of DX.

Sensitivity of Si diffusion in GaAs to column IV and VI donor species

Secondary ion mass spectroscopy and carrier concentration measurements are used to characterize Si diffusion into GaAs wafers containing two fundamentally different forms of donors, the column IV donors Si or Sn and the column VI donors Se or Te. A decrease in the Si diffusion rate is found in GaAs containing the column VI donors compared to the column IV donors. This trend is consistent with the model in which the Si diffuses as donor-gallium-vacancy complexes. The decrease in the Si diffusion coefficient is attributed to the greater binding energy of column VI donor-gallium-vacancy nearest-neighbor complexes, thus reducing the concentration of free-gallium vacancies available to complex with the Si.

ChemInform Abstract: Ligand Substitution Reactions of Metal and Organometal Carbonyls with Group V and VI Donor Ligands

ChemInformVolume 18, Issue 47 Reviews ChemInform Abstract: Ligand Substitution Reactions of Metal and Organometal Carbonyls with Group V and VI Donor Ligands D. A. EDWARDS, D. A. EDWARDS UKSearch for more papers by this author D. A. EDWARDS, D. A. EDWARDS UKSearch for more papers by this author First published: November 24, 1987 https://doi.org/10.1002/chin.198747386Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume18, Issue47November 24, 1987 RelatedInformation

ChemInform Abstract: Ligand Substitution Reactions of Metal and Organometal Carbonyls with Group V and VI Donor Ligands

ChemInformVolume 18, Issue 7 Reviews ChemInform Abstract: Ligand Substitution Reactions of Metal and Organometal Carbonyls with Group V and VI Donor Ligands D. A. EDWARDS, D. A. EDWARDS UKSearch for more papers by this author D. A. EDWARDS, D. A. EDWARDS UKSearch for more papers by this author First published: February 17, 1987 https://doi.org/10.1002/chin.198707331Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume18, Issue7February 17, 1987 RelatedInformation