Shallow Donors In Si Research Articles

Electrical properties of heavily Si-doped GaAsN after annealing

In this study, electron traps in dilute GaAsN are investigated using the temperature dependence of electron concentration (n) and mobility (μe) for annealed heavily Si-doped GaAsN. The temperature dependence of n and μe depends on the annealing temperature, indicating that electrons are excited to the conduction band only from deep electron traps for heavily Si-doped GaAsN annealed at 580 °C. However, they are excited to the conduction band from both the deep electron traps and the shallow Si donor level for heavily Si-doped GaAsN annealed at 550 °C. The depth of the deep electron traps from the bottom of the conduction band for heavily Si-doped GaAsN annealed at 550 °C is almost equal to heavily Si-doped GaAsN annealed at 580 °C. The results demonstrate that these deep electron traps are inherent in dilute GaAsN because similar deep electron traps are also observed for the as-grown Si-doped GaAsN.

Effect of the Beryllium Acceptor Impurity upon the Optical Properties of Single-Crystal AlN

The influence of the high-temperature (T = 1880°C) diffusion of beryllium ions on the properties of single-crystal aluminum nitride is studied. It is shown that the postgrowth doping of AlN with Be brings about the compensation of shallow Si donor centers uncontrollably incorporated into the AlN lattice during growth. It is established that the introduction of Be into the AlN lattice results in a reduction in the optical absorption of AlN in the visible and ultraviolet regions. The set of results is attributed to a shift of the Fermi level to the top of the valence band of AlN upon the introduction of the Be acceptor impurity.

Magnetic field dependent polarizability and electric field dependent diamagnetic susceptibility of a donor in Si

The polarizability and diamagnetic susceptibility values of a shallow donor in Si are computed. These values are obtained for the cases \(\bar{E}\parallel \bar{B}\) and \(\bar{E}\, \bot \,\bar{B}\). The anisotropy introduced by these perturbations are properly taken care of in the expressions derived for polarizability and magnetic susceptibility. Our results show that the numerical value of the contribution from electric field to diamagnetic susceptibility is several orders smaller than that of the magnetic field effect. Polarizability values are obtained in a magnetic field by two different methods. The polarizability values decrease as the intensity of magnetic field increases. Using the Clausius–Mossotti relation, the anisotropic values of the refractive indices for different magnetic fields are estimated.

Silicon in AlN: shallow donor and DX behaviors

AbstractIn unintentionally Si‐doped AlN bulk samples, an electron paramagnetic resonance (EPR) spectrum with characteristics of a shallow donor, previously assigned to the shallow Si donor, was observed at room temperature in darkness. Temperature dependent studies of the EPR signal showed that Si is a DX center in AlN. However, with the negatively charged DX– state determined to be only ∼78 meV below the neutral shallow donor state, Si should behave as a shallow dopant in AlN at normal device operating temperatures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Negative capacitance in GaN∕AlGaN heterojunction dual-band detectors

A study of trap states in n+-GaN∕AlGaN heterostructures using electrical, thermal, and optical analyses is reported. Capacitance-voltage-frequency measurements showed negative capacitance and dispersion, indicating interface trap states. Infrared spectra identified three impurity related absorption centers attributed to shallow Si-donor (pinned to the AlGaN barrier), N-vacancy/C-donor, and deep Si-donor (pinned to the GaN emitter) impurities with corresponding activation energies of 30.8±0.2, 125±1, and 140±2meV, respectively. The shallow Si-donor impurity had a relaxation time of 155±9μs, while the C-donor/N-vacancy and deep Si-donor impurities appear to behave as a single trap state with a relaxation time of 1.77±0.05μs. Multiple analysis techniques allowed the determination of the activation energies of these impurity related centers and the study of the effects of trap states on the electrical behavior of the detector.

Metal–Insulator Transition and superconductivity in doped semiconductors

Using the effective mass theory and the variational method, the critical concentrations of shallow donors in Si at which the Mott Transition occurs are obtained. Our theory uses the experimentally available donor ionization energies in the low-concentration regime and a mass variation with interimpurity distance to account for the impurity bands. Since the experimentally available donor ionization energies are used, the central-cell effects and valley–orbit interactions are taken into account. Excellent agreement with the available experimental results is obtained for P, As, Sb and Bi donors in Si. Since the critical concentration at which superconductivity occurs in B doped Si is established recently, we predict the concentrations at which superconductivity should occur for these donors also.

Optical studies of MOCVD‐grown GaN‐based ferromagnetic semiconductor epilayers and devices

AbstractGa1–xMnxN epilayers and p‐i‐n device structures have been grown by metalorganic chemical vapor deposition. Optical studies were found to investigate the role of Mn concentration and the role of different co‐dopants to elucidate the origin of the room temperature ferromagnetism in Ga1–xMnxN epilayers. Increasing Mn concentration was found to significantly affect long‐range lattice ordering. This observation was supported by the existence of a disorder‐induced Raman mode at 300 cm–1 and local vibrational modes (LVMs) at 669 cm–1 that has been attributed to the formation of self‐compensating nitrogen. The E1(TO) phonon frequency was found to linearly increase with Mn composition, which is expressed by (558 + 2.7x) cm–1. The intensity and the linewidth of an absorption band near 1.5 eV was found to increase with Mn concentration, and is assigned to the e to t2 transition in the split 5T2 band of Mn3+. No absorption was detected in Si co‐doped Ga1–xMnxN. In this case, a significantly increased EPR signal of Mn2+ ions confirmed the trapping of electrons provided by the shallow Si donor and reduced the available states for ferromagnetic exchange. A change in the measured magnetization is observed under ultraviolet illumination, though the nature of this phenomenon is still not understood. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Shallow donor electron spins as qubits in Si and SiGe: a pulsed ESR study

X-band pulse electron spin resonance spectroscopy has been used to determine the characteristic phase memory time (TM) for phosphorous shallow donors in Si and Si1−xGex (x=0.052) which have been proposed as qubits in group IV based quantum computing devices. With fast intense microwave pulses, electron spin echoes, formally equivalent to single-qubit operations, can be detected providing the characteristic times as well as additional information on the coupling between the electron spin and its surroundings (other electron or nuclear spins). The electron spin echo envelope modulation due to the super-hyperfine interaction with 29Si and 73Ge, has been detected in the Si and Si1−xGex samples.

Central-cell corrections and shallow donor states in strong magnetic fields

Ionization energies and the central-cell corrections have been calculated for a few shallow donors in Si, GaP, and GaAs. We have assumed a short range potential with two parameters for the strength and the range for each donor, representing the central-cell effects. These parameters are fixed using the experimentally available ionization energies for each donor in a semiconductor. In the presence of a magnetic field the donor ionization energies are estimated using a variational procedure. Our results show that the ionization energies and the central-cell corrections increase with magnetic field. Our results are compared for GaAs with the recent work by Heron et al. [R. J. Heron, R. A. Lewis, P. E. Simmonds, R. P. Starret, A. V. Skougarevsky, R. G. Clark, and C. R. Stanley, J. Appl. Phys. 85, 893 (1999)].

Hydrogen-Defect Shallow Donors in Si

The influence of different original Si crystals and neutron fluence on the formation of hydrogen-defect shallow donors in neutron-irradiated floating-zone silicon grown in hydrogen atmosphere (FZ Si:H2) is studied. The annealing behavior of neutron-irradiated floating-zone silicon grown in argon atmosphere (FZ Si:Ar), neutron-irradiated FZ Si:H2 kept for three years at room temperature (RT) and only fast-neutron-irradiated FZ Si:H2 reveals that shallow donors are directly related to hydrogen and defects, especially to thermal-neutron-radiation point defects. The maximum concentration of the shallow donors approaches to a stable value with an increase in neutron fluence. Some characteristics of the shallow donors are discussed.

A comparison of the Hall-effect and secondary ion mass spectroscopy on the shallow oxygen donor in unintentionally doped GaN films

We report on temperature-dependent Hall-effect measurements and secondary ion mass spectroscopy on unintentionally doped, n-type conducting GaN epitaxial films. Over a wide range of free carrier concentrations we find a good correlation between the Hall measurements and the atomic oxygen concentration. We observe an increase of the oxygen concentration close to the interface between the film and the sapphire substrate, which is typical for the growth technique used (synthesis from galliumtrichloride and ammonia). It produces a degenerate n-type layer of ≈1.5 μm thickness and results in a temperature-independent mobility and Hall concentration at low temperatures (<50 K). The gradient in free carrier concentration can also be seen in spatially resolved Raman and cathodoluminescence experiments. Based on the temperature dependence of the Hall-effect, Fourier transform infrared absorption experiments, and photoluminescence we come to the conclusion that oxygen produces a shallow donor level with a binding energy comparable to the shallow Si donor.

Time-resolved study of yellow and blue luminescence in Si- and Mg-doped GaN

Time-resolved photoluminescence has been employed to study the donor-acceptor pair recombination kinetics of the yellow (∼2.3 eV) and blue (∼2.8 eV) luminescence bands in Si- and Mg-doped GaN layers, respectively. As the Si doping concentration in Si-doped GaN increases, the lifetime τ1/e of the yellow luminescence decreases, indicating that a shallow Si donor is the origin of the yellow luminescence. The blue luminescence is most likely due to a shallow Mg acceptor and a deep donor composed of a Mg acceptor-nitrogen vacancy complex, as seen by the independence of τ1/e on the Mg concentration measured by secondary ion mass spectroscopy in the range (2.5–6.0)×1019 cm−3. As the temperature is increased from 10 to 300 K, the lifetimes for the yellow and blue luminescence remain nearly constant, indicating that the distribution of electrons and holes bound to donors and acceptors does not change much with increasing temperature.

Far-Infrared Active Media Based on Shallow Impurity State Transitions in Silicon

Two mechanisms of the inverse population of shallow impurity states in silicon under optical pumping have been proposed and analyzed, using a procedure allowing to reduce the number of required matrix elements of transitions. The first mechanism is based on the resonance interaction of the 2p0 state in Si : Bi with optical phonons. The other one is based on the suppression of acous- tic-phonon-assisted relaxation from the 2p0 state in Si : P due to the momentum conservation law. Spontaneous emission was registered from shallow donors in Si : P under photoionization by a CO2 laser. The dependence of the spontaneous emission intensity on the intensity of pumping radiation confirms the possibility of amplification on impurity transitions. Introduction. The interest in far-infrared (FIR) active media based on shallow impu- rity states in silicon is caused by two reasons. The first one is the low level of lattice absorption of FIR radiation in silicon. The second is the cascade character of the main relaxation processes along the excited coulombic impurity states (1), allowing to expect high efficiency of pumping of impurity excited states population, which is important for reaching continuous lasing. Cascade relaxation means that transitions with a small re- duction of carrier energy are predominating, and the probability that a heated carrier takes part in the amplification is rather high when one of the first excited states or the group of excited states within the step of phonon relaxation are inversely populated. On the other hand, the fast acoustical-phonon-assisted relaxation causes the main complication in obtaining the inverse population of impurity states, since it tends to form the equilibrium distribution at lattice temperature. Thus, the inverse population of impurity states implies conditions in which the distribution is formed by processes with threshold character (interaction with optical phonons, optical pumping) and being faster than acoustical-phonon-assisted and Auger processes, or it implies conditions, where the latter are suppressed for particular states. The other complication originates from the fact that absorption for impurity transitions lies in the same frequency region as possi- ble amplification and thus can prevent it. Hence the possibility of amplification depends on the details of nonequilibrium distribution of charge carriers over excited impurity states.

Attempts to correlate hydrogen plasma-induced and Si 3N 4/GaAs interface-related surface states: a charge deep-level transient spectroscopy study

Heavily doped (100) GaAs:Si substrates were exposed for up to 32 min to H 2 + Ar discharges while keeping the substrates at 300°C. Both direct and remote mode plasma exposures were conducted with the aim of comparing the respective plasma-induced damages. After the remote hydrogen plasma treatment, not only the amount of charge released from plasma-induced deep levels in Al/GaAs diodes in the course of a DLTS scan had been reduced, moreover, the zero-bias crossover E FT of the Fermi level and the trap level could be shifted up to E C − E FT ≈ 0.01 eV. The latter shift was not connected with any changes of the Al/GaAs barrier height which was found to be essentially insensitive to the plasma treatment ( φ B ≈ 0.8 eV). Nevertheless, the distributed damage-related energy levels of all processed substrates could be characterized by a unique dependence of the capture cross-section σ on the activation enthalpy ΔE of the corresponding charge deep-level transient spectroscopy (DLTS) peaks as σ = σ 0 exp( ΔE E 0 ) , E 0 being a constant. Finally, we constructed an equivalent ln σ versus ΔE plot for charge DLTS data of Al/Si 3N 4/GaAs metal-insulator-semiconductor (MIS) structures with silicon nitride layers prepared in the same reactor at comparable temperatures, and included it in the Al/GaAs-related data. The combined data provided a single plot that exhibits two perfectly jointed branches differing in respective slopes. As expected, shallow Si-donor passivation could be detected too, the efficiency of the latter reaching 90% under the direct mode hydrogen plasma conditions.

Capture Process by Shallow Donors in Silicon at Low Temperatures

Thermal capture by shallow attractive impurities has been studied by the Monte Carlo method at low temperatures. In order to model this process, the perturbation produced by the highest excited impurity states associated to the ideal Coulombic potential and the multiphonon mechanism were combined in the same simulation procedure. These excited states are considered to produce an energy quasicontinuum or impurity band where the carrier can move assisted by lattice phonons. To characterize the ground-state capture, the transition rates of multiphonon transitions from the impurity band and from the conduction band have been included. Electron capture cross sections have been calculated as a function of the temperature and compared compared with experimental data from the P + , As + and Sb + shallow donors in Si, achieving a good fitting with the Huang-Rhys factor, S, as the only free parameter.

Two electron transitions of the exciton bound at the Si Donor confined in GaAs/AlxGa1-xAs quantum wells

The exciton bound to the shallow Si-donor confined in a 100A wide GaAs quantum well has been studied in selective photoluminescence (SPL) and photoluminescence excitation (PLE) spectroscopy. The transition from the ground state, ls(Γ6), to the first excited state, 2s(Γ6), of the confined Si donor has been observed via two-electron transitions (TETs) of the donor bound exciton observed in SPL for the first time to the best of our knowledge. The interpretation of the TET peaks is confirmed by PLE measurements. Further, from Zeeman measurements, the magnetic field dependence of the donor ls(Γ6)-2s(Γ6) transition energy has been determined.

Diamagnetic Susceptibility of Donors in Silicon

Diamagnetic susceptibility of shallow donors in Si is computed incorporating the multivalley conduction band structure and the spheroidal energy surfaces. Our result is compared with an earlier estimate of Kohn on the one-valley model [Solid State Phys. 5 (1955) 2573].

Excited 2s state of a donor confined in a GaAs/AlxGa1-xAs quantum well.

A spectroscopic study of the shallow Si donor and its bound exciton (BE) confined in narrow GaAs/Al x Ga 1-x As quantum wells (QW's) has been performed. The electronic structure has been investigated by means of selective photoluminescence and photoluminescence excitation spectroscopy. The energy separation between the ground state and the excited state of the confined Si donor has been monitored by means of two-electron transitions (TET's) of the confined-donor BE. It is concluded in this study that the TET satellite originates from the 1s-2s transition, in contrast to the bulk case, where the 1s-2pt and 1s-2po donor transitions are also strong

Shallow donor in separation by implantation of oxygen structures revealed by electric-field modulated electron spin resonance

Electric-field modulated K-band electron spin resonance measurements on Si/SiO2/Si structures, formed by implantation of oxygen (SIMOX), were carried out at 4.3–30 K. Large area metal-oxide-silicon capacitors were fabricated on these structures and optimized for cavity loading. Sweeping of the Si band gap through the Fermi level near the buried oxide interfaces resulted in the observation of a shallow donor in Si of fairly high local density (≊1018 cm−3), residing in this area; its electron spin resonance signal is turned on and off by positive and negative gate biasing, respectively. The same donor signal has previously been observed in γ-irradiated SIMOX, revealing that γ irradiation has the same effect as positive biasing.

Electron paramagnetic resonance of the shallow Sn donor in GaAs/Al0.68Ga0.32As:Sn heterostructures

A new, light-induced electron paramagnetic resonance (EPR) signal with apparent tetragonal symmetry has been observed in n-type Al0.68Ga0.32As:Sn layers grown on Sl-GaAs. A comparison with previous magnetic resonance data for the shallow Si donor indicates that the signal corresponds to the shallow, X-valley-associated effective-mass state of the Sn donor. The optical behaviour of the new signal shows that the shallow state is a metastable state of the Sn DX centre. The nearly vanishing EPR intensity for magnetic fields in the layer is attributed to the large spin-valley interaction expected for the shallow Sn donor in indirect AlGaAs.