Impurity States In Semiconductors Research Articles

Theoretical and Experimental Investigations on Effects of Native Point Defects and Nitrogen Doping on the Optical Band Structure of Spinel ZnGa2O4

Impurity states in semiconductors are so important for optical related properties that understanding the role of native and imported defects is essential to design highly active semiconductors. Here, the structural and electronic properties of ZnGa2O4 with native atomic substitution, oxygen vacancies, and imported N doping are first investigated by first-principles calculations. It is demonstrated that native atomic substitution is energetically unfavorable and the most stable existence forms for N doping and O vacancies are N1– and O2+ states in most cases under various chemical environments. The band structures and density of states reveal that the photochemical property is significantly enhanced only by 2Ns doping with a great increase of valence band maximum relative to the Fermi level, whereas single-N atom doping or import of O vacancies or simultaneous import of N doping and O vacancies just generates impurity states in the band gaps. Moreover, experimental characterizations including X-ray photoel...

Probing of local electron states in Pb1 − x Sn x Te(In) narrow-gap semiconductors by laser terahertz radiation

Local electron states in indium-doped lead telluride-based solid solutions exhibit a number of features which separate them from the diversity of impurity states in semiconductors. These features are most pronounced in terahertz photoconductivity. The results of the corresponding experiments performed during the last years and supported by the Russian Foundation for Basic Research are reviewed.

Tight-binding description of impurity states in semiconductors

Introductory textbooks in solid state physics usually present the hydrogenic impurity model to calculate the energy of carriers bound to donors or acceptors in semiconductors. This model treats the pure semiconductor as a homogeneous medium and the impurity is represented as a fixed point charge. This approach is only valid for shallow impurities and it also departs from the conventional view in solid state physics, where carriers move in a crystal lattice. As an alternative description of impurities in semiconductors, we present a minimal one-dimensional lattice model within the tight-binding approximation. The lattice model is valid for deep and shallow impurities. In the latter case, the results are in agreement with the predictions of the hydrogenic impurity model. The underlying ideas are simple and knowledge of advanced quantum mechanics is not required. Thus, this alternative model could be suitable for introductory courses in solid state physics and materials science.

Resonant Raman Scattering Studies of Localized Impurity States inSemiconductors

We review resonant Raman scattering studies of GaAs1−xNx, where nitrogen impurities are spatially localized in the host GaAs. The conventional intensity resonance could provide symmetry information regarding nitrogen-induced states, such as E+, which turned out to have significant components of an L and an X character, in addition to a Γ character. We also observed the rather unusual and distinctive phonon linewidth resonance due to spatially localized intermediate states that originated from a splitting of the L-point conduction band. We show that the resonant Raman scattering response, including asymmetric linewidth broadening resonances, can provide a powerful means to study semiconductor systems with strongly localized impurity states.

Low-threshold ZnSe microdisk laser based on fluorine impurity bound-exciton transitions

Impurity states in semiconductors, in which two long-lived ground states can be optically coupled to a single excited state, provide a powerful mechanism for applications including lasing without inversion, electromagnetically induced transparency, and optically addressable quantum memory for quantum information processing. We report low-threshold lasing from fluorine-doped ZnMgSe/ZnSe quantum wells in microdisk cavities. The lasing mechanism was studied by power-dependent photoluminescence spectroscopy. Lasing thresholds lower than 50 W cm −2 were observed and the fraction of spontaneous emission contributed to the lasing modes was about β=0.03–0.1.

Impurity absorption spectroscopy of the deep double donor sulfur in isotopically enriched silicon

The chalcogen deep double donor sulfur (S) has been studied extensively with optical methods in natural silicon ( Si nat ) . Recently, it was shown that the spectroscopic linewidths of absorption transitions from shallow impurities like boron and phosphorus is limited by inhomogeneous broadening due to a Si isotope effect which is removed with the use of highly enriched 28Si. In this work we extend these results to deep centers and show that the true homogeneous linewidths of many transitions can only be revealed in isotopically enriched Si. The S + 1 s ( T 2 ) Γ 7 transition exhibits a full width at half maximum (FWHM) of only 0.008 cm - 1 in 28Si—more than one order of magnitude sharper than in Si nat , and substantially narrower than the sharpest transitions of B and P in 28Si. Hence, it is the narrowest absorption line ever seen for impurity states in semiconductors. We also report dramatically narrower absorption transitions for the neutral S 0 center, together with higher excited states than previously observed. The isotope shifts of S absorption transitions between Si nat , 28Si and 30Si are also reported.

Electronic control and readout of qubits based on single impurity states in semiconductors

The authors demonstrate that a semiconductor n+∕i∕n+ junction is the most suitable candidate for electronic control and readout of semiconductor qubits based on shallow impurities. Tuning of the doping levels in n+ regions and self-induced interface barriers ensure that an impurity atom placed in i region is populated with one electron in equilibrium. They analyze Li donors in Si and show that a large signal qubit readout can be realized via polarization selective photoexcitation of resonant cotunneling current through an excited impurity state.

Evolution of electronic states inGaAs1−xNxprobed by resonant Raman spectroscopy

Two distinct maxima ${E}_{W}$ and ${E}_{W}^{\ensuremath{'}}$ are observed in the resonant Raman-scattering profile for the LO phonon asymmetric linewidth broadening in ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ and are attributed to states arising from a splitting of the quadruply degenerate conduction band near the L point. The data provide further insight into the physics underlying the giant band-gap bowing observed in ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x},$ as well as reveal asymmetric linewidth broadening to be a powerful signature for studying strongly localized impurity states in semiconductors.

Impurity states in semiconductors calculated via tight binding: A parameter sensitivity study

Acceptor binding energies in zinc-blende semiconductors are determined within the tight-binding formalism. The sensitivity of the calculated energies to the parameters that determine bulk masses and those that describe the coupling of the impurity to the host is investigated. Binding energies for Ge acceptors in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ alloys are calculated using two parametrizations recently proposed in the literature, and the results reveal the importance of fitting the valence-band masses in the (100) as well as (111) directions. New parametrizations are presented for GaAs, AlAs, and InAs that specifically fit the valence-band anisotropy, and the acceptor problem in these materials is investigated. A comparison is made between first-neighbor and second-neighbor hopping models. For shallow levels, both approaches give the same results. For deeper levels, however, important differences arise. Experimental evidence suggests that first-neighbor models are better suited for describing intermediate to deep levels.

Tight-binding scheme for impurity states in semiconductors

Tight-binding scheme for impurity states in semiconductors

Impurity states in doped fullerenes: C 59B and C 59N

Using the Car—Parrinello method we have investigated theoretically the properties of the recently synthesized C 59B and of the yet hypothetical C 59N molecules. We show that doping induces important changes in both ionic and electronic properties of C 60. The highest occupied molecular orbital is strongly localized and can act either as an electron acceptor state (C 59B) or as a donor state (C 59N). A parallel is drawn between this and the case of deep impurity states in semiconductors. Based on these results we speculate on potentially interesting properties of materials derived from these molecules.

The theory of impurity states in semiconductors

The basic theoretical methods for treating defects and, in particular, impurities in semiconductors are first reviewed. They split into two groups: the techniques appropriate to deep states (local density, empirical tight binding) or to shallow states (effective mass approximation). A discussion is given of how to handle the most difficult intermediate cases (corresponding to the shallow-deep instability) and of the possible coexistence of these two types of states.The second part describes applications of these general arguments to specific cases. This begins with the well documented case of transition metal impurities followed by recent results obtained for rare earth impurities. A fairly detailed analysis is performed in the case of EL2 showing that this center must be a complex involving the antisite. The case of the DX donor in Ga1-xAlxAs compounds is also reviewed, with the arguments in favor of the two competing models.

Shallow impurity states in semiconductors—the early years

This paper presents the author's recollections of the early years (roughly the early and middle 1950's) of the science of shallow impurity states, with emphasis on the theoretical aspects. It concludes with some reflections from the vantage point of today.

Interrelation between quasi-band and resonant scattering methods of calculating 3d impurity states in semiconductors

Analytical resonance scattering and numerical quasi-band approaches in the theory of semiconductors doped by transition metal ions are compared and the qualitative equivalence of the main results of both theories is demonstrated. A simplified illustrative model is considered in which both resonance scattering from the atomic d-levels and single-site Koster-Slater potential scattering are included on an equal footing. The analytical solution of this model containing the dangling bond hybrids and crystal field resonances in the valence and forbidden energy bands is presented. The multiplet corrections to the mean-field one-electron levels and the applicability of the scaling parameters lambda in calculating the Racah coefficients are discussed. The connection between different possible theoretical schemes and real experimental situations as occurring in elemental Si and Ge on the one hand and III-V and II-VI compounds on the other hand is established.

Shallow states of donor impurity at the surface of isotropic semiconductors

The perturbative variational method is applied to the surface impurity states in semiconductors. It is found that this method can be used to calculate any state, no matter how high it may be, and the surface impurity levels are obtained from those of the hydrogen atom simply by a redefinition of the charge. As a concrete example of the application numerical results are obtained for surface impurity states in GaAs using this method.

Limitations of variational methods for hydrogenic systems

Theoretical methods that give good approximations of the behaviours of hydrogen-like impurity states in semiconductors in uniform external magnetic fields are by now well established. With variational methods in mind the sizes of the determinants that give sufficiently accurate energies greatly depend on the quality of the wave functions chosen as these affect the rapidity of the series convergence. The recently developed hybrid functions enable hydrogenic energies to be calculated up ton=7 using fairly small determinants. However, it has emerged that there is a restricted region of variational parameters which maintains the numerical symmetry of the hamiltonian matrix elements for each group of states. Although each such parameter regime appears to narrow as the magnetic quantum number increases, the accuracies of the calculated eigenvalues remain satisfactory.

Embedding calculations for deep impurity states in semiconductors

Abstract A method of calculating deep impurity states in semiconductors is presented within the context of a multiple-scattering formulation. An embedding matrix for the host crystal is set up using matching Green function techniques at the impurity cluster surface in the host crystal. The method allows for a cluster of variable geometry to be embedded. Results for the non-self-consistent case are obtained for a number of impurities, including gold, manganese, oxygen and nitrogen, at unrelaxed positions in a silicon host crystal.

A new method for impurity states in semiconductors : M. A. Mekhtiev, G. B. Ibragimov and M. H. Hatamov. Solid St. Commun.52 (4), 385 (1984)

A new method for impurity states in semiconductors : M. A. Mekhtiev, G. B. Ibragimov and M. H. Hatamov. Solid St. Commun.52 (4), 385 (1984)

A new method for impurity states in semiconductors

The causes of inapplicability of the Luttinger method for the theoretical investigations of impurity states in small gap semiconductors are discussed. For this purpose a new method has been developed and applied to GaAs and InSp. It is shown that the impurity states spectrum in these semiconductors must be either of hydrogen-like or Dirac spectrum type.

Nonradiative Transitions in Deep Impurities in Semiconductors–Study in a Semiclassical Model

Nonradiative transitions in the deep impurity states in semiconductors are studied by a semiclassical model, in which the lattice distortion around the impurity is approximated as a classical harmonic oscillator modulating the potential depth for the electron. An integral equation is derived and solved numerically describing the nonadiabatic transition from the bound state to the scattering states which corresponds to the thermal ionization. Peculiar features in the transition dynamics are clarified in contrast with the transitions between discrete levels. In the adiabatic limit, which covers the situation at high temperatures in real semiconductors, the transition rate obeys the Arrhenius law with the pre-exponential factor given by the phonon frequency as pointed out by Sumi.