Superconductivity in covalent semiconductors

This review covers recent advances in superconductivity of diamond, Si, SiC, group III–V and II–IV semiconductors, metal-intercalated graphite and fullerites. The results are critically analyzed and prospects are given for future research directions. In particular, it is argued that the highest transition temperatures of ∼9 K in diamond and 11.5 K in CaC₆ can further be enhanced and that no reliable evidence exists yet for superconductivity in III-V semiconductors.      

Si DX centers in GaAs at large hydrostatic pressures

A number of experimental and theoretical studies indicate that DX centers in GaAs, its alloys and other III–V semiconductors have negative U properties. Using far infrared localized vibrational mode (LVM) spectroscopy of Si donors in GaAs under large hydrostatic pressure in a diamond anvil cell we have discovered an LVM of the Si DX center. From the ratio of the LVM absorption lines of Si_Ga and Si_DX and the compensation in our GaAs samples, we show unambiguously that two electrons are trapped when the ionized shallow Si donors transform into negatively charged DX centers, in full agreement with the negative U model.Dedicated to H.-J. Queisser on the occasion of his 60th birthday     

Relativistic effects on the structural and transport properties of III–V compounds: A first-principles study

We have performed ab initio self-consistent calculations based on the full potential linear augmented plane-wave method (FP-LAPW) with the local density approximation (LDA) and the Generalised Gradient Approximation (GGA) to investigate the relativistic effects, on the structural, and transport properties of III–V compounds. We found that the stabilisation (destabilisation) of s, p^∗(p,d) orbital energies (i) reduces the lattice parameters of III–V compounds, considerably reduces the band gaps of the III–V compounds, (ii) reduces the effective masse, and (iii) induces strong spin orbit splitting of heavier III–V compounds. Furthermore we circumvent the negative gap problem by combining non relativistic and Engel–Vosko approximations. These approaches open the gap of the most III–V compounds, and leads to a realistic band structure.     

Pressure and volume dependence of thelo-to phonons in InAs

The pressure dependence of thelo-to phonons in InAs has been investigated by Raman scattering using the diamond anvil cell. Indium arsenide transforms, presumably to the rock-salt structure at 70±1 kbar. The mode Grüneisen parameters for thelo-to phonons are γ _lo =0.99±0.03, γ _to =1.2±0.03 respectively. The effective charge,e* _T , for InAs decreases slightly with pressure and this trend is in accordance with the behaviour of other III–V zinc blende structured semiconductors: The structural phase transition is discussed in the light of theoretical calculations for phase stability of III–V compounds, as well as recent high pressure x-ray diffraction studies.     

III–V semiconductor interface properties as a knowledge basis for modern heterostructure devices

Some examples of interface studies are reported which show their close link with progress in III–V modern semiconductor device physics and technology. The surface electronic properties investigated in-situ by reflectance anisotropy spectroscopy during InGaP/InP growth (metal-organic vapor-phase epitaxy) are essential for the control of ordering phenomena in these layers, which is relevant for high-performance optoelectronic devices. Studies of electronic interface states at metal/narrow-gap III–V semiconductors are presented, which enabled the successful preparation of semiconductor/superconductor hybrid devices. For group-III nitrides with wurtzite structure the presence of fixed polarization interface charges yields new challenges in order to understand and control Schottky-barrier heights, band offsets and 2D confinement in heterostructure field-effect transistors. Received: 26 April 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002     

Defects in III–V semiconductor surfaces

This work reports the measurement of the nano-scale physical properties of surface vacancies and the extraction of the types and concentrations of dopant atoms and point defects inside compound semiconductors, primarily by cross-sectional scanning tunneling microscopy on cleavage surfaces of III–V semiconductors. The results provide the basis to determine the physical mechanisms governing the interactions, the formation, the electronic properties, and the compensation effects of surface as well as bulk point defects and dopant atoms. Received: 10 May 2001 / Accepted: 23 July 2001 / Published online: 3 April 2002     

The method of increments—a wavefunction-based ab initio correlation method for solids

An overview of wavefunction-based correlation methods generalised for the application to solids is presented. Those methods based on a preceding Hartree–Fock treatment explicitly calculate the many-body wavefunction in contrast to the density-functional theory which relies on the ground-state density of the system. This review focus on the so-called method of increments where the correlation energy of the solid is expanded in terms of localised orbitals or of a group of localised orbitals. The method of increments is applied to a great variety of materials, from covalent semiconductors to ionic insulators, from large band-gap materials like diamond to the half-metal α$\alpha$-tin, from large molecules like fullerenes over polymers, graphite to three-dimensional solids. Rare-gas crystals where the binding is van der Waals like are treated as well as solid mercury, where the metallic binding is entirely due to correlation. Strongly correlated systems are examined and the correlation driven metal–insulator transition is described at an ab initio level.     

Optical properties of III-Mn-V ferromagnetic semiconductors

We review the first decade of extensive optical studies of ferromagnetic, III-Mn-V diluted magnetic semiconductors. Mn introduces holes and local moments to the III–V host, which can result in carrier mediated ferromagnetism in these disordered semiconductors. Spectroscopic experiments provide direct access to the strength and nature of the exchange between holes and local moments; the degree of itineracy of the carriers; and the evolution of the states at the Fermi energy with doping. Taken together, the diversity of optical methods reveal that Mn is an unconventional dopant, in that the metal to insulator transition is governed by the strength of the hybridization between Mn and its p-nictogen neighbor. The interplay between the optical, electronic and magnetic properties of III-Mn-V magnetic semiconductors is of fundamental interest and may enable future spin-optoelectronic devices.     

Microscopic structure of semiconductor surfaces

To study the initial reaction steps of hydrogen, oxygen, and water, on differently prepared single crystal surfaces of silicon, germanium/silicon alloys, indium phosphide and gallium arsenide, we used high-resolution electron energy-loss spectroscopy (HREELS) in combination with low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Very recently, we started a program on the hydrogenation of III–V compound semiconductors, and on the oxidation of Si and III–V compound semiconductors, using alkali metals as a catalyst. This paper summarizes the present stage of our investigations, describing in particular aspects of the microscopic structure of differently prepared semiconductor surfaces.     

Epitaxial ferromagnetic thin films and heterostructures of Mn-based metallic and semiconducting compounds on GaAs

We present two approaches to integrate magnetic materials with III–V semiconductors. One is epitaxial ferromagnetic metallic films and heterostructures on GaAs (0 0 1) substrates. Although crystal structure, lattice constant, chemical bonding and other properties are dissimilar, ferromagnetic hexagonal MnAs thin films and MnAs/NiAs ferromagnet/nonmagnet heterostructures (HSs) are grown on GaAs by molecular beam epitaxy (MBE). Multi-stepped magnetic hysteresis are controllably realized in MnAs/NiAs HSs, making this material promising for the application to multi-level nonvolatile recording on semiconductors. The other approach is to prepare a new class of GaAs based magnetic semiconductor, GaMnAs, by low-temperature molecular beam epitaxy (LT-MBE) on GaAs (0 0 1). New III–V based superlattices consisting of ferromagnetic semiconductor GaMnAs and nonmagnetic semiconductor AlAs are also successfully grown. Structural and magnetic properties of these new heterostructures are presented.     

Three-Dimensional Self-Shaping Nanostructures Based on Free Stressed Heterofilms

The present review examines the formation of three-dimensional nanostructures (nanoshells, nanotubes, nanospirals, nanorings, etc.) from single-crystal heterostructures based on III–V Si/GeSi semiconductors as well as metal and hybrid heterostructures. New results on the formation of various nanostructures with a minimum curvature radius of the order of 1 nm are presented.     

Analysis of semiconductor surfaces and interfaces

Recent development in the experimental and theoretical analysis of semiconductor surfaces is described. Special attention is given to the Secondary Ion Mass Spectroscopy technique and to its use in the ultrasensitive elemental analysis of semiconductors. Applications to III–V compounds are described.     

The thermoelectric power in superlattices of III–V semiconductors with graded structures under strong magnetic quantization

Summary An attempt is made to formulate the thermoelectric power under strong magnetic quantization (TPM) in superlattices (SLS) of III–V semiconductors with graded structures and to compare the same with that of the forming materials. It is found, taking Ga_0.8In_0.14P_0.78Sb_0.22/GaAs SL as an example, that the TPM increases with increasing quantizing magnetic field and decreases with increasing electron concentration respectively in an oscillatory manner. The TPM in SL with graded structures is greater than that of the constituent bulk materials for III–V SL.     

New Approaches to the Creation of Strong Fields by Means of Permanent Magnets and to the Development of Sensor Devices for Their Mapping

New solutions in the field of creating compact strong permanent magnets and magnetometers for mapping of magnetic fields are considered in the present paper. It is demonstrated that the magnetic field induction can be increased up to 4 T. An array of the Hall sensors based on III–V semiconductors is used for mapping of magnetic fields.     

Overcoming limitations in semiconductor alloy design

The phenomenon of giant band gap ‘bowing’ recently observed in several III–V dilute nitride alloys is promising for increasing the flexibility in choice of semiconductor band gaps available for specified lattice constants. However, the poor electrical transport properties that these materials exhibit seriously limit their usefulness. It is proposed that these materials behave as heavily nitrogen-doped semiconductors rather than dilute nitride alloys and that the abnormal or irregular alloy behavior is associated with impurity band formation that manifests itself in the giant bowing and poor transport properties. The potential for regularizing the alloy behavior using isoelectronic co-doping is discussed.     

Neutron-Transmutation Doping and Radiation Modification of Semiconductors: Current Status and Outlook

This review focuses on the development of neutron-transmutation doping (NTD) and radiation modification (RM) technologies for semiconductor materials (Si and III–V compounds) in Russia. The advantages of NTD and RM materials over growth-doped semiconductors are demonstrated. The main tasks and outlook for the development of radiation technologies based on research and commercial RBMK-reactors operated in Russia are discussed.     

III–V based-semiconductor photonic crystals

Three-dimensional (3D) and two-dimensional (2D) photonic crystals based on III–V semiconductors are described. On the 3D photonic crystals, the development of complete photonic crystals at optical wavelengths and their applications to ultrasmall optical integrated circuits including 3D sharp bend waveguide are described. On the 2D photonic crystals, two-unique device and/or phenomena are demonstrated.     

Electronic structure of bond-centred hydrogen and muonium in III–V compound semiconductors: Ab initio cluster calculations

The molecular orbital model for bond-centred hydrogen or muonium in the III–V compound semiconductors is developed with the help of ab initio cluster calculations. The influence of the loss of symmetry in going from the elemental (group IV) to the compound (III–V) materials on the electronic structure is studied. The equilibrium configurations, potential energy surfaces and electronic structures of hydrogen or muonium near the bond-centred site in GaAs, GaP and InP are calculated at the ab initio HF level in the clusters Ga₄As₄H₁₈ and the corresponding one for GaP and InP using a split-valence basis set and ab initio pseudopotentials for the core orbitals. First results of the calculations using a large Ga₂₂As₂₂H₄₂ cluster are discussed. Preliminary results for InP indicate that ionization of the bond-centre defect may be considerably easier than in the other III–V compounds. which would explain why μSR-signals corresponding to the neutral Mu^* state have not been detected in this material.     

High-efficiency silicon light emitting diodes

Silicon has been regarded as a notoriously poor emitter of light fundamentally due to its indirect bandgap. However, as an elemental rather than a compound semiconductor, it has the advantage of fewer background defects as well as well-developed approaches to interface passivation. By minimising parasitic optical absorption and non-radiative bulk and surface recombination, and by enhancing the effective optical photon generation volume, respectable silicon light emission efficiencies are demonstrated. These are within the range of direct gap III–V semiconductors and higher than any at low powered densities. Possible applications are also discussed.     

Core-level shifts of the c(8 × 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) surfaces

We have studied In-stabilized c(8 × 2)-reconstructed InAs(1 0 0) and InSb(1 0 0) semiconductor surfaces, which play a key role in growing improved III–V interfaces for electronics devices, by core-level photoelectron spectroscopy and first-principles calculations. The calculated surface core-level shifts (SCLSs) for the ζ and ζa models, which have been previously established to describe the atomic structures of the III–V(1 0 0)c(8 × 2) surfaces, yield hitherto not reported interpretation for the As 3d, In 4d, and Sb 4d core-level spectra of the III–V(1 0 0)c(8 × 2) surfaces, concerning the number and origins of SCLSs. The fitting analysis of the measured spectra with the calculated ζ and ζa SCLS values shows that the InSb spectra are reproduced by the ζ SCLSs better than by the ζa SCLSs. Interestingly, the ζa fits agree better with the InAs spectra than the ζ fits do, indicating that the ζa model describes the InAs surface better than the InSb surface. These results are in agreement with previous X-ray diffraction data. Furthermore, an introduction of the complete-screening model, which includes both the initial and final state effects, does not improve the fitting of the InSb spectra, proposing the suitability of the initial-state model for the SCLSs of the III–V(1 0 0)c(8 × 2) surfaces. The found SCLSs are discussed with the ab initio on-site charges.