Acceptors In Silicon Research Articles

GaAs Surface Stabilization by Vacuum Anneal with SiO

ABSTRACTWe find a significant alteration of the surface properties of SI- GaAs as a result of a thermal treatment with SiO under vacuum. Low temperature photoluminescence measurements reveal a tenfold increase in emissions attributed to free or donor bound excitons and the exciton bound to a silicon acceptor. A paramagnetic center is also generated as a result of this treatment. The EPR signal has a g-value of 2.0017 and a linewidth of 0.1 mT. The enhanced photoluminescence and the EPR signal are both quenched by a short exposure to hydrogen plasma at room temperature. Chemical and spectroscopic evidence indicates that the resonance is due to a silicon related center near the GaAs surface. The surface stabilization is attributed to a reaction or incorporation of SiO with the arsenic depleted GaAs surface.

Ionization energy of the Si acceptor on AlxGa1-xAs

Using Hall effect and photoluminescence investigations the impurity incorporation was characterized on n-type MBE-grown AlxGa1-xAs:Si. Although the compensation ratio was small, silicon was also observed as both a donor and an acceptor in low doped material. Starting from the value in GaAs (EaSi(GaAs)=34.8 meV) the activation depth of the isolated silicon acceptor with respect to the valence band increases in the range 0<or=x<or=0.4 corresponding to the relation EaSi(x)=34.8+47.3x+4.65*102x3.5 (EaSi in meV). The activation depths of the five-site acceptors carbon, silicon and germanium are correlated as a function of the chemical composition and compared with the theoretical predictions of Baldereschi and co-workers (1980). The excellent material quality is evidenced by the small FWHM=1, 4 and 5 meV of the donor bound excitons for the x-values 0.09, 0.25 and 0.38 respectively. Especially for x=0.09 the radiative decay of donor and acceptor bound as well as free excitons were observed.

Direct evidence for localized motion of hydrogen in Cd-H complexes in silicon.

The locally restricted motion of hydrogen and deuterium trapped at Cd acceptors in silicon has been studied by perturbed-angular-correlation spectroscopy. Close Cd-H and Cd-D pairs were identified by their characteristic electric-field gradients. The kinetics of these complexes was extracted directly from the time spectra. Between 270 and 430 K clear evidence has been found for thermally activated motion of hydrogen or deuterium about the Cd with an activation energy of 0.21 eV for both hydrogen as well as deuterium. The isotopic-mass-dependent attempt frequencies are on the order of 10 9 s -1

Two-step debonding of hydrogen from boron acceptors in silicon

Previous work has demonstrated that B⋅H pairs in silicon thermally dissociate obeying simple first-order kinetics if they are located in a region depleted of majority carriers. B⋅H debonding in equilibrium, however, is a slower, more complex process. We have investigated the dissociation of B⋅H pairs under a variety of equilibrium and nonequilibrium conditions and have demonstrated that the dissociation process is strongly influenced by the local concentration of majority and minority carriers. In particular, we show that injection of minority carriers can markedly accelerate the dissociation process. A model is proposed which suggests that hydrogen released from an acceptor, while initially positive, must always be neutralized before escape is possible. This picture correctly describes the time dependence of debonding in both equilibrium and forward-biased diodes.

Defect-free growth of AlxGa1−xAs by liquid-phase epitaxy on V-grooved (001) GaAs substrates

The crystalline quality of AlxGa1−xAs grown on a V-grooved (001) GaAs substrate is characterized by low-temperature cathodoluminescence and transmission electron microscopy. High-crystalline perfection visualized by narrow neutral donor bound exciton luminescence is attained above the groove. Growth of (Al, Ga) As in the groove takes place without significant change of the aluminium distribution. An order of magnitude increase of silicon acceptor concentration induced by As-vacancy creation is detected at the interface n-GaAs substrate/V groove. Transmission electron microscopy pictures taken from sample cross sections do not show any kind of defects in the groove.

Theory of hydrogen-impurity complexes in semiconductors

In this review of theory, the focus will be on a collection of hydrogen-containing complexes of current interest and controversy, with more general implications summarized where appropriate. In particular, I will include hydrogen complexes with single donors and acceptors in silicon and compound semiconductors, and with double donors and acceptors in silicon. Also, included is a brief discussion of the hydrogen-vacancy and hydrogen-molecule systems in silicon. The phenomena of interest include the equilibrium geometries, and the motion of the impurities as they vibrate, reorient, and dissociate within the solid. These characteristics are described as calculated using quantum mechanical methods; hence, electronic-structure methods are summarized as well.

The Electron Structure and Spectra of Shallow Non-Hydrogenlike Impurities in Semiconductors. II. Acceptors in Silicon

The Electron Structure and Spectra of Shallow Non-Hydrogenlike Impurities in Semiconductors. II. Acceptors in Silicon

Ground-state configuration of double acceptors in silicon and germanium.

The ground-state manifold of double-acceptor impurities in Si and Ge shows small splittings. An explanation of this fine structure is presented. It is based on a calculation containing tight-binding p functions at the top of the valence band. The approach takes spin-orbit coupling and hole-hole interaction fully into account. The results indicate that the various experimentally observed orderings of levels may be explained by a short-range hole-hole nearest-neighbor intersite interaction that, because of dynamical effects, may in some cases be attractive.

Long Range Coulomb Effects on Hydrogen Debonding from Boron Acceptors in Silicon

ABSTRACTPrevious work has demonstrated that B-H pairs in silicon thermally dissociate obeying simple first order kinetics if theyare located in a region depleted of majority carriers. B.H debonding in equilibrium, however, is a slower, more complex process. We have investigated the dissociation of B.H pairs under a variety of equilibrium and non-equilibrium conditionsand have demonstrated that the dissociation process is strongly influenced by the local concentration of majority and minority carriers. In particular, we show that injection of minority carriers can markedly accelerate the dissociation process. A model is proposed which suggests that hydrogen released from an acceptor, while initially positive, must always beneutralized before escape is possible. This picture correctly describes the time dependence of debonding in equilibrium, and it predicts the enhanced debonding in forward biassed diodes provided the characteristic time for H charge conversionislong.

Perturbed angular correlation spectroscopy of hydrogen-passivated indium acceptors in silicon

Hydrogen-passivated 111In atoms in boron-doped silicon samples are investigated with respect to their thermal properties by the perturbed angular correlation method. The temperature dependence of one of the electric field gradients induced by the formation of close 111InH pairs reflects the electron capture decay of 111In into 111Cd. A model based on the thermally activated population of a 111CdH acceptor fits quantitatively to the temperature data, yielding an acceptor level close to 0.1 eV above the valence band.

Hydrogen passivation and thermal reactivation of zinc double acceptors in silicon

Zinc-diffused silicon samples are investigated by deep level transient spectroscopy (DLTS). The isolated zinc double acceptor ( Zn 0 − , Zn − 2− ) as well as two zinc-related centres (Zn(X1), Zn(X2)) are observed in the DLTS spectra. The electrically active concentrations of these centres can be reduced below the detection limit by a hydrogenation process. The zinc double acceptor and centre Zn(X1) recover again after a heat treatment. A reactivation of centre Zn(X2) cannot be observed because it is not stable at temperatures above 400°C. Using first-order kinetics, the reactivation energy of the zinc double acceptor is determined as 2.2 ± 0.3 eV.

Fano profiles of absorption lines from the localised vibrational modes of Be acceptors in GaAs and B acceptors in silicon

Infrared absorption measurements have been made of the LVMS of 9Be acceptors in MBE GaAs and 10B and 11B acceptors in ion-implanted Si. The former line is asymmetric, while the latter lines occur as anti-resonances in the electronic continuum. Following 2 MeV electron irradiation to effect electrical compensation, symmetrical lines were observed. The new data for GaAs:Be explain an apparent anomaly relating to LVM line strengths in hydrogen-passivated material.

Piezoreflectance characterization of resonant tunneling and modulation-doped heterostructures

We used piezoreflectance, a stress modulation technique, to optically characterize both double-barrier resonant tunneling structures and modulation-doped heterostructures. This technique easily probed the single quantum wells buried below the ∼0.5-μm-thick n+ GaAs surface layers required for ohmic contacts. In fact, the positions of salient piezoreflectance spectral features denoted subtle variations of well width and barrier height and width; lineshapes indicated interface roughness. Since piezoreflectance spectra of our modulation-doped samples had sharp features associated with quantum confinement, and the corresponding photoreflectence spectra had Franz-Keldysh oscillations that depended on the built-in electric field, we could calculate energy levels that reflected not only growth parameters but experimentally determined potential profiles as well. Moreover, the sensitivity of piezoreflectance to carbon and silicon acceptor states permitted us to assess the material quality.

Hydrogen Passivation of Shallow Acceptors in Silicon

The common observation that point defects in semiconductors can be passivated by hydrogen is illustrated for the case of shallow acceptors in silicon. Earlier results of experimental and theoretical studies are briefly reviewed and recent progress in the understanding of the microscopic structure of acceptor-hydrogen complexes in crystalline Si is presented, with special emphasis on substitutional boron passivation as studied by nuclear techniques and Raman scattering.

Infrared Absorption Study of Zinc-Doped Silicon.

AbstractWe report high resolution infrared absorption spectra associated with the deep zinc acceptor in silicon. The optical transitions between ground and bound excited “p-like” states of the neutral helium-like double acceptor Zn0 center have been observed for the first time. The absorption cross section for the hole transition is found to be very small, of the order of 10-17 cm2. Energy spacings of the P3/2 Rydberg series are very similar to the spacings of the group-III acceptors, suggesting that, in spite of the large ground state binding energy, effective mass approximation still applies to the bound excited states. This represents one more case where the strong central cell potential does not significantly disturb the neutral helium-like bound excited states. Similar observations have been made for the less deep neutral double acceptor Be, and for the chalcogens donors S, Se and Te.The optical ionization energy of Zn0/- has been determined to be 2575 cm-1 (319 meV).Two additional sets of absorption lines related to zinc have been observed at 2130 cm-1 and 2758 cm-1. Their origin will be discussed.

Phonon interactions at the deep platinum acceptor in silicon.

Phonon interactions at the deep platinum acceptor in silicon.

Lattice location of deuterium interacting with the boron acceptor in silicon.

The lattice location of deuterium diffused into boron-doped silicon has been studied by means of channeling. After removal of a 0.2-\ensuremath{\mu}m-thick surface layer, it is found that 87% of the deuterium atoms occupy near-bond-center sites, whereas the remaining 13% are located close to tetrahedral sites. It is argued that the near-bond-center sites are related to boron-deuterium pairs, and the structure of these is discussed.

Deep-level defects in silicon and the band-edge hydrostatic deformation potentials.

Evidence for an energy reference level based on substitutional transition-metal defect levels in semiconductors is presented and used to obtain the values for the band-edge hydrostatic deformation potentials in silicon. From the pressure derivatives of Pt and Pd acceptors in silicon we derive values of ${\ensuremath{\Xi}}_{d}=\ensuremath{-}0.5$ eV and ${a}_{v}=+0.9$ eV. These values are consistent with recent theoretical calculations and with the analysis of acoustic-phonon-limited electron and hole mobility.

IR-spectroscopy of impurity complexes in germanium

A large number of impurity complexes which create shallow levels, have been discovered in pure and doped germanium single crystals. The structure and the composition of several of these complexes have been determined using far-infrared spectroscopy and information about crystal growth related residual impurities. In general, the complexes consist of a heavy substitutional impurity binding one or more light. interstitial impurities such as hydrogen or lithium. The coupling between the tunneling motion of the interstitial component and the electronic structure of the complexes can create complicated ground state manifolds which contain stress insensitive components. Spectroscopy further shows that multivariate centers, such as double or triple acceptors, become hydrogenic complexes upon binding one or two hydrogen atoms, respectively. Neutralization of shallow acceptors in silicon, which has recently attracted attention, appears to be the same phenomenon as the valency reduction of multiple acceptors in germanium.

Pressure dependence of impurity levels in semiconductors: The deep gold acceptor level and shallow donor and acceptor levels in silicon.

The effects of hydrostatic pressure on the properties of the deep gold (Au) acceptor level and on the binding energies of shallow donors and acceptors in silicon are presented and discussed. The pressure dependences of the Gibbs free energy, enthalpy, and entropy associated with electron emission from the Au acceptor were determined from measurements of the electron emission rate and electron-capture cross section (${\ensuremath{\sigma}}_{n}$) as functions of pressure and temperature. The results allow determination of the breathing-mode lattice relaxation accompanying electron emission from this center. The relaxation is found to be relatively large and inward (i.e., contraction). This appears to be the first quantitative determination of this relaxation for any electronic level in any semiconductor. Other highlights of the results on the Au acceptor are the findings that (i) the energy of this level is pinned to neither the conduction- nor valence-band edges, contrary to earlier belief and (ii) ${\ensuremath{\sigma}}_{n}$, which is known to be temperature independent, is also pressure independent. This latter result is discussed in terms of possible mechanisms for nonradiative electron capture. For the shallow donors and acceptors, the pressure derivatives of the binding energies are over an order of magnitude smaller than those of the energy gap and the Au acceptor, i.e., these levels remain essentially pinned to their corresponding band edges, as expected. These results can be understood in terms of effective-mass theory.