Spectroscopy Of Gap States Research Articles

Fermi level scan spectroscopy of gap states in Ge and Si–Ge alloys based on the kinetics of neutron transmutation doping

A study of the kinetics of neutron transmutation doping of Ge served as a basis for a number of methods that yielded the exact values of some nuclear parameters of Ge isotopes, precisely characterized the neutron-transmutation-doped Ge, and made it possible to create the so-called “Fermi level scan spectroscopy” for analysis of deep-level electronic states in the energy gap. The development of this technique is reported and illustrated by application to the long-standing problem of double Se donor states in Ge. Possible applications of the method to the states in the energy gap of “dirty” Ge and Si–Ge alloys are considered as well.

Surface photovoltage phenomena: theory, experiment, and applications

The theoretical concepts, experimental tools, and applications of surface photovoltage (SPV) techniques are reviewed in detail. The theoretical discussion is divided into two sections. The first reviews the electrical properties of semiconductor surfaces and the second discusses SPV phenomena. Next, the most common tools for SPV measurements and their relative advantages and disadvantages are reviewed. These include the Kelvin probe and the use of MIS structures, as well as other less used techniques. Recent novel high-spatial-resolution SPV measurement techniques are also presented. Applications include surface photovoltage spectroscopy (SPS) which is a very effective tool for gap state spectroscopy. An in-depth review of quantitative analyses, which permit the extraction of various important surface and bulk parameters, follows. These analyses include: carrier diffusion length; surface band bending, charge, and dipole; surface and bulk recombination rates; surface state distribution and properties; distinction between surface and bulk states; spectroscopy of thin films, heterostructures and quantum structures; and construction of band diagrams. Finally, concluding remarks are given.

Surface photovoltage spectroscopy of gap states at GaAs and InP metal interfaces

Surface photovoltage spectroscopy has been used in order to investigate surface states at Al/n-GaAs (110), Au/n-GaAs (110) and Al/p-InP (110), Au/p-InP (110),(100) interfaces. Our results show formation of metal-induced surface states, which can be correlated with Fermi level pinning positions. The observed energy positions are found to be in good agreement with electrically measured Schottky barrier heights. The results obtained for these metals and the different surface types are discussed and compared to published data.

Gap states in undoped amorphous silicon studied by below-gap modulated photocurrent spectroscopy

Abstract The energetic distribution and nature of dangling-bond states in undoped a-Si: H have been investigated by a newly developed gap-state spectroscopy which is based on the frequency-resolved spectrum of modulated photocurrent with below-gap photoexcitation. The energy scale is directly specified by the energy of the below-gap light populating the particular gap states. The result has led to the conclusion that the peak of the gap-state distribution associated with doubly occupied dangling bonds (D-) is located about 0•5 eV below the conduction band edge. The analysis for the pre-exponential factor of the thermal emission rate of electron from the D- centre suggests that the emission occurs in two stages through excited states.

Energy level and photoionization cross section of gap states in a-Si:H

We propose a novel gap-state spectroscopy, namely, the photo-isothermal capacitance transient spectroscopy (ICTS) using below-gap excitation. Using this method, the energy level spectrum as well as the photoionization cross sections of gap states in P-doped a-Si:H have been determined: two features exist at 0.5–0.6 eV and 1.0–1.2 eV below the conduction band edge Ec in the gap-state profile and the photoionization cross section of the gap states has been found to be almost independent of their energy level location and to have value of order of 10 −16 cm 2.

Gap state spectroscopy in amorphous As 2Se 3 films

The distribution of gap states in a-As 2Se 3 thin films evaporated onto substrates held at the glass transition temperature (T=T samples) and near room temperature (T=310K samples) has been investigated by time-of-flight, modulated photocurrent and steady state photocurrent measurements. It is found that the shallow states decrease exponentially with energy away from the valence-band edge with a characteristic temperature of 500 and 560K for T s=T g and T s=310K samples respectively, whereas the deep states decrease with a characteristic temperature of 350K for both samples. The characteristic temperature of the shallow states for the T s=310K samples.changes into 500K by annealing at the T g for 1 hour.

Electrophotographic spectroscopy of gap states in hydrogenated amorphous silicon

The localized density of states g(E) near midgap for undoped and doped amorphous silicons have been estimated by the electrophotographic method. The deduced energy positions of neutral dangling bonds D 0 and doubly occupied D − are 0.85 ∼ 0.88 eV from the valence band and 0.65 ∼ 0.67 eV from the conduction band, respectively. These energies are different from those obtained from the deep-level transient spectroscopy (DLTS) and photothermal deflection spectroscopy (PDS).

Photoinduced Absorption Spectroscopy of Gap States in Polyacetylene

Abstract We measured steady-state photoinduced absorption in trans and in cis-rich (CH)X from 0.1 to 2.5 eV. By assigning the s° optical transitions to the 1.A5 eV band we can fully account for both the bleaching and absorption parts of the spectrum. The e-e correlation energy involved in the soliton defects is found to be ∼ 0.5 eV.

Isothermal Photocurrent Transient Spectroscopy of Gap States in Amorphous Chalcogenide Semiconductors

Gap state spectroscopy for determining the density and distribution of gap states in amorphous chalcogenide semiconductors is described. The method is based on the analysis of the transient current after a light pulse. The applicability of the method for determining the gap states in a-Se:Te films has been experimentally demonstrated. The experiments reveal that the gap states are relatively discrete states at energies of 0.42 eV and 0.34 eV above the valence band edge for 12 at.% Te:Se films and 18 at.% Te:Se films respectively.

Surface photovoltage measurements and Fermi level pinning: comments on “development and confirmation of the unified model for Schottky barrier formation and MOS interface states on III-V compounds”

The theoretical concepts, experimental tools, and applications of surface photovoltage (SPV) techniques are reviewed in detail. The theoretical discussion is divided into two sections. The first reviews the electrical properties of semiconductor surfaces and the second discusses SPV phenomena. Next, the most common tools for SPV measurements and their relative advantages and disadvantages are reviewed. These include the Kelvin probe and the use of MIS structures, as well as other less used techniques. Recent novel high-spatial-resolution SPV measurement techniques are also presented. Applications include surface photovoltage spectroscopy (SPS) which is a very effective tool for gap state spectroscopy. An in-depth review of quantitative analyses, which permit the extraction of various important surface and bulk parameters, follows. These analyses include: carrier diffusion length; surface band bending, charge, and dipole; surface and bulk recombination rates; surface state distribution and properties; distinction between surface and bulk states; spectroscopy of thin films, heterostructures and quantum structures; and construction of band diagrams. Finally, concluding remarks are given.

Xerographic spectroscopy of gap states in amorphous semiconductors

Analysis of the temperature-dependent decay of surface voltage on an amorphous film after charging but prior to exposure (xerographic dark decay) and of residual decay after exposure can, in combination, be used to map the density of states and position the Fermi level. The procedure is illustrated for $a$-Se where both electron and hole residuals can be measured. $a$-Se is found to be characterized by a relatively discrete gap-state structure. These measurements readily discern thermostructural and photostructural effects on gap-state populations. Thus, during structural relaxation of glassy films in the As:Se alloy system, systematic variation in a number of localized states distributed throughout the mobility gap is observed. This observation is consistent with the view that native defects play a key role in photoelectronic behavior of amorphous chalcogenides.

Gap state spectroscopy using two beam photoconductivity in A-SI:H

Infrared quenching and enhancement of photoconductivity of amorphous silicon have been observed at room temperature using two beam photo-conductivity techniques. The photocurrent is established with hν > 1.5eV photons and modulated with photons with 0.6eV <hν < 1.4eV. The modulation signal spectrum is sensitive to sample preparation conditions and doping. Results are discussed in terms of simple two recombination center models.