Hole Binding Energy Research Articles

Franck - Condon shift and temperature dependence of the zero-phonon binding energy of the deep selenium centre in silicon

Using the steady-state photocurrent technique spectral distributions of the photoionization cross section for holes of the deep selenium centre in silicon have been measured at 11 temperatures within the temperature range . A novel analytical model is proposed which properly accounts for the competing ionization processes into the light- and heavy-hole valence bands. Curve fittings based on detailed numerical calculations of convolution integrals result in a Franck - Condon shift of about meV together with an effective phonon energy of about meV. The partial shrinkage coefficient quantifying the shrinkage of the zero-phonon binding energy for holes, , with respect to that of the bandgap was found to be about , indicating an approximate pinning of the deep single substitutional selenium level to the conduction band edge. A hole binding energy of meV at T = 0 was obtained from an extrapolation of the fitted curve.

Double acceptor doped Ge: A new medium for inter-valence-band lasers

We report on intervalence-band laser emission from Be- and Zn-doped germanium crystals. The duty cycle of 10−3 at a repetition rate of 1 kHz is one order of magnitude larger than the highest duty cycle reported for p-Ge lasers doped by group II acceptors. This improvement is due to the much larger hole binding energy of double acceptors Be and Zn which results in a strong reduction of the internal absorption of the generated far-infrared radiation. Laser action has been achieved with crystal volumes as small as 0.04 cm−3, and a laser pulse length of 25 μs has been reached. Germanium crystals doped with these acceptors may offer an opportunity for achieving the ultimate goal of continuous wave operation.

Photoluminescence due to positively charged excitons in undoped GaAs/AlxGa1-xAs quantum wells.

We study the photoluminescence (PL) spectra of nominally undoped GaAs/${\mathrm{Al}}_{0.33}$${\mathrm{Ga}}_{0.67}$As quantum wells, as a function of well width, temperature, excitation energy, and intensity, and an applied magnetic field. A doublet is observed for temperatures below 10 K, whose components we demonstrate derive from the neutral (X) and positively charged (${\mathit{X}}^{+}$) excitons. The latter appears due to the binding of excitons to holes in the quantum well originating from the background concentration of acceptors in the ${\mathrm{Al}}_{0.33}$${\mathrm{Ga}}_{0.67}$As barriers. Our assignment of ${\mathit{X}}^{+}$ is motivated by the striking similarity of the PL spectra to those recorded on quantum wells with acceptors deliberately incorporated in the barriers. Consistent with our assignment, we see a strengthening of the ${\mathit{X}}^{+}$ transition when more holes are introduced into the well by photoexcitation. The dependence of the doublet splitting on well width is in close agreement with a Monte Carlo calculation of the second hole binding energy in ${\mathit{X}}^{+}$. The PL peak due to ${\mathit{X}}^{+}$ may have been falsely ascribed in previous work to a biexciton. \textcopyright{} 1996 The American Physical Society.

Hole-polaron formation in the two-dimensional Holstein t-J model: A variational Lanczos study.

Polaronic features of dopant-induced charge carriers are manifest in recent experiments on ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4+\mathit{y}}$ and ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$${\mathrm{CuO}}_{4+\mathit{y}}$. To study the formation of hole (bi)polarons in such systems exhibiting strong Coulomb interactions, the Holstein t-J model is examined by means of a variational diagonalization technqiue for a wide range of phonon frequencies and electron-phonon (EP) couplings on finite square lattices, up to 18 effective sites in size. Including static displacement field, polaron, and squeezing effects, our approach allows for the description of nearly free polarons in the weak-coupling limit as well as for adiabatic Holstein polarons and nonadiabatic Lang-Firsov polarons in the case of strong EP interactions. At low doping levels and low phonon frequencies we demonstrate that antiferromagnetic spin correlations and EP interactions reinforce each other to the effect of lowering the threshold for polaronic self-localization in a strongly distorted lattice. This is contrasted with the nonadiabatic regime, where we observe the formation of Lang-Firsov polarons with moderate polaronic mass enhancement in a nearly undistorted lattice. In the case of two doped holes, the hole binding energy is analyzed in detail and we find that hole binding is enhanced as a dynamical (static) effect of a rather weak (extremely strong) EP interaction for delocalized (self-trapped) polarons. At quarter-filling we notice, in the adiabatic regime, a sequence of transitions as the EP coupling increases from nearly free mobile polarons to a polaronic superlattice and finally to a charge-separated state. The ordering of polarons disappears at higher phonon frequencies.

Electronic states created in p-Si subjected to plasma etching: The role of inherent impurities, point defects, and hydrogen

Reactive ion etching and magnetically enhanced reactive ion etching with CHF3/O2 are employed to remove SiO2 from boron-doped Si substrates. Etch-induced gap states in the substrate are monitored using deep-level transient spectroscopy. The dominant state is found to be a donor with a hole binding energy of 0.36 eV. The state has been identified as that of the carbon-interstitial oxygen-interstitial pair. The depth profile of the pair is determined by two competing mechanisms: the pair generation and its electrical deactivation by atomic hydrogen. The latter process is especially prevalent in the presence of a magnetic field.

Recent Developments in Doping Techniques for Compound Semiconductors

AbstractWe report new methods to dope compound semiconductors. First, we demonstrate the concept of doping engineering whereby it becomes possible to tailor the activation energy of the dopant in a host semiconductor for the first time. In this application, the band offset of a thin, sacrificial semiconductor is used to lower the activation energy of the dopant below its value in the host semiconductor. This allows the freedom to control dopant activity in ways not accessible to a uniformly placed dopant. We chose δ-Be-AlGaAs/GaAs as a model example and show the hole binding energy is reduced by a factor of five. Secondly, we demonstrate overcoming the p-type solubility limit in GaAs by use of monolayer δ-Be in a GaAs base of an HBT. Here, an effective hole concentration of > 1021cm−3 is measured in real devices. We present a qualatative view of doping solubility limitations that are controlled by surface processes.

Acceptorlike bound excitons in semiconductors.

An effective-mass equation for the hole binding energy of an acceptorlike bound exciton in semiconductors is developed. The motion of the electron is represented by an effective charge which modifies the Coulomb interaction. An expression for the oscillator strength of the bound exciton is given in terms of the wave function of the bound-exciton state. The theory is applied to the GaP:N system, which gives hole binding energies for excitons bound to nitrogen pairs in good agreement with experiment, and predicts that the electron binding energy for an isolated-nitrogen-bound exciton is about 6 meV.

Superconductivity in ladders and coupled planes.

We discuss an electronic model consisting of two chains or planes, each described by a t-J model, coupled by t'-J' interactions between them. For J'\ensuremath{\sim}J or larger we show the presence of a spin-gap and hole-pair formation upon doping. The model exhibits superconducting pairing correlations away from half filling. We support our claims by numerical studies of the spin gap, the binding energy of holes, and the pairing correlations on finite clusters. The hole-pairing operator is a spin singlet with one member of the pair in each chain or plane. Our model belongs to the universality class of the U0 Hubbard model with \ensuremath{\Vert}U\ensuremath{\Vert}\ensuremath{\gg}t. We argue that this model may be physically realized by doping the orthorhombic compound (VO${)}_{2}$${\mathrm{P}}_{2}$${\mathrm{O}}_{7}$.

Hole dynamics in a strongly correlated two-dimensional spin background.

In this paper we present results of finite-lattice studies of the t-J and the t-t'-J model for 18 (20) sites with up to 4 (2) holes. A modified Lanczos algorithm allowed for the classification of the ground state according to total spin S. In the one-hole sector we find evidence for the existence of hole pockets. We calculate the effective quasiparticle band and show qualitative differences between the t-J and t-t'-J model for J\ensuremath{\gtrsim}0.2. As U increases we notice a substantial band narrowing, which is maximal at the Nagaoka transition, accompanied by S-level crossings rendering a quasiparticle description difficult. In the high-doping regime we present hole binding energies for up to six holes for the t-J model. Evidence for phase separation is only found for J>t. We also studied the magnetic structure of the ground state on the 18-site lattice in the limit J=0. We present a complete ground-state classification for all numbers of holes ${\mathit{N}}_{\mathit{h}}$ and find S=${\mathit{S}}_{\mathrm{max}}$ at quarter filling in addition to the Nagaoka case.

On the possibility of phase separation in the extended Hubbard model

Abstract The one-band extended Hubbard model on the square lattice in the strong interaction limit is investigated using an exact diagonalization technique. The main emphasis was on the possibility of a phase separation. It is shown that the instability of the system against separation into a no-hole antiferromagnetic phase and an hole-rich phase that takes place at low hole concentrations is effectively destroyed through the inclusion of a moderate interatomic Coulomb interaction. In the two-phase region, i.e. at small interaction energies, a negative hole-binding energy indicates that the hole-rich phase is build up by hole-pairs. We comment on the relevance of our results for the description of the copper-oxide superconductors.

Growth and characteristics of HgGaInS4 single crystals

AbstractSingle crystals of the HgGaInS4 layered compound were grown by the iodine transport technique. Results of their optical, photoelectric, and radiative properties' study are presented. The band gap and the binding energy of holes on the sensitizing centres were determined to be Eg = 2.41 eV and Ea = 0.2 eV, respectively. A presence of quasi‐continuously distributed states was stated which are responsible for the exponential segment of the absorption edge and which take part in the radiative recombination.

Photoluminescence studies of bound excitons in copper-doped GaAs

The photoluminescence (pl) of copper-related bound excitons (BE’s) in GaAs is investigated by means of resonantly excited and time-resolved photoluminescence, as well as photoluminescence-excitation (ple) spectroscopy. Observation of the 2s and 3s two-hole transitions leads to a precise value of 193 meV for the hole binding energy of the acceptor associated with the F complex. No evidence for such two-hole transitions was ever detected for the C complex. The lifetimes of the C0 and the F0 BE’s are reported in addition to that of a line found at 1501.5 meV. C0 BE exhibit an excited state 3.7 meV above the ground state, while no excited states were detected for F0.

Electron paramagnetic resonance and thermally stimulated luminescence studies of uranyl doped calcium sulphate

Electron paramagnetic resonance (EPR) and thermally stimulated luminescence (TSL) studies were conducted onγ-irradiated CaSO4:UO22+ to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain the trap parameters (trap depth and frequency factor). Intense TSL glow peaks around 140, 375, 400 and 438±2K are observed and their spectral characteristics have shown that UO22+ and UO66− act as luminescent centres. EPR studies have shown the peaks at 140 and 400/438K to be associated with the thermal destruction of O− and SO4− radical ion in two stages respectively. The maximum rate of thermal destruction of SO4− ions (as seen by EPR) in various alkaline earth sulphate matrices investigated in our laboratory is also summarized. The activation energy which characterizes the electron transfer reaction between SO4− and the dopant ion lies in the range of (0.95±0.15 eV). This value is independent of the dopant and therefore seems to be characteristic of the binding energy of hole in the SO4− radical ion.

Binding of holes in the Hubbard model with next-nearest-neighbor hopping.

We study the two-dimensional Hubbard model with next-nearest-neighbor hoppings and its related strong-coupling effective Hamiltonian by exact diagonalization. We found that the binding energy of holes tends to be smaller than with nearest neighbors only. However, the tendency towards phase separation is reduced by increasing the next-nearest-neighbor hopping. By studying pairing correlations, we found that the mode is strongly enhanced when the second-neighbor interactions are turned on.

Excitons Bound to Te Impurities in CdS, ZnS, and Their Mixed Compounds with Wurtzite Structure

AbstractA calculation is made of the binding energy of holes to isolated, pairs and clusters of three Te impurities in ZnS, CdS, and their mixed compound ZnxCd1−xS. The calculation takes into account the multiband nature of the bound state as well as the relaxation induced by the incorporation of the impurity, the growing importance of which is shown when going from CdS to ZnS. The only imput parameters are the electronegativity difference between the exchanged atoms modeled by the energy difference of the free corresponding atomic s and p levels and the relaxation of the nearest neighbour distance as previously determined by Martins and Zunger. A very good agreement is obtained between the calculated values and the experimental data.

Electron, hole and exciton binding energies on interface defects of single quantum well structures

We report on variational calculations of binding energies of electrons, holes and excitons on quantum well interface defects. The defects are modelled by cylindrical protrusions of the well-acting material into the barrier-acting one. We have also examined the effect of adding an attractive coulombic potential to either an attractive or a repulsive interface defect.

Photoluminescence Study of the Gallium Defect Spectrum at ≈ 0.928 ev (ga3) in Irradiated Silicon

AbstractA detailed investigation is made of the Ga3 luminescence spectrum observed in gallium doped silicon after electron irradiation and annealing at ≈ 250 °C. The spectrum exhibits exciton singlet—triplet pair no‐phonon transitions at 0.9291 or 0.9272 eV, respectively, and quasi‐localized modes of vibration energy 10.3, 24.4, and 56.9 meV along with combination modes and lattice phonon bands. An additional higher energy no‐phonon transition is due to an excited exciton state at excess energy of 3.8 meV thermalizing with the singlet—triplet states. The isotropic Zeeman splitting of the triplet (g = 2.00 ± 0.05) shows that the orbital momentum of the excitonic hole is entirely quenched. This and the low thermal dissociation energy of the exciton (16 meV) are used to deduce a strong hole binding energy (≈ 226 meV) whereas the 16 meV energy is attributed to the electron localization. The low electron binding energy is consistent with uniaxial stress measurements which are quantitatively explainable in terms of effective‐mass valley—orbit electron states. This defect represents the first example of a luminescent center in silicon which under uniaxial stress exhibits the whole multiplicity of valley—orbit‐states. The valley—orbit nature of the electron and the quenching of the hole orbital momentum render a symmetry classification of the defect impossible.

Shallow Positive Acceptor in Germanium Doped with Deep Zinc Impurity

An A + center, a positively charged acceptor, is observed below 2.8 K in far-infrared photoconductivity measurement on Zn doped Ge under exposure to the room temperature black body radiation. The hole binding energy of the A + center is estimated as 1.9 meV from the low energy threshold of photoconductivity. Low temperature photoconductivity for the sample with low impurity concentration ( N A =1.2×10 14 cm -3 ) is due to isolated A + centers. The photoconductivity peak shifts to higher energy with increase of impurity concentration. The shifted peak corresponds to the transition from an A + related complex to the valence band. Magneto-oscillations of photoconductivity due to isolated A + centers are first observed. The peak photon energies converge to 1.9 meV in the zero field limit.

Intensity enhancement of self-activated blue luminescence of ZnS phosphors by Mg 2+ions

Addition of < 1 mol.% Mg 2+ ions enhances the intensity of blue photo- and cathodo-luminescence in ZnS phosphor with λ max at 468 nm. All characteristics of this emission indicate that the luminescence involves (V Zn-Br S)' centres whose hole binding energy modified by the presence of Mg 2+ in the vicinity. The oscillator strength of the transition for ZnS: 0.5 Mg is larger than that of self-activated ZnS. The capture cross section for electrons (6×10 −19cm 2) and holes (2×10 −15cm 2) are also increased by the presence of Mg 2+. The recombination energy of the electron-hole pair transferred to (V Zn-Br S)' via Mg 2+, causing enhancement in emission intensity.

Long distance electron transfer in polymers and proteins

Initial work in our labs and many others has shown that some aspects of long distance electron transfer is simple glasses are reasonably described by current theories. 2–4,12–14 For example, electron transfer rates do decrease exponentially with increasing donor acceptor separation. Also, when diffusion is precluded, the full dependence of rate on exothermicity emerges, which is otherwise obscured. Some aspects of theory based on nuclear tunneling may require serious reexamination: for example, it appears that the dependence of long distance rate on electron (hole) binding energy is weaker than suggested by many popular theories. Work with proteins shows that while nature is a subtle designer, the general reactivity trends observed in proteins are quite similar to those found in polar glasses. Such studies of protein electron transfer have provided some surprises and challenges for experimentalists and theorists alike. As a clearer understanding of the governing principles of long distance biological electron transfer emerge, we hope it will become easier to design meaningful “biomimetic” strategies for solar energy conversion.