Activation Energies For Electron Emission Research Articles

Vacancy-related complexes in neutron-irradiated silicon

Electrically active defects induced by neutron irradiation in n-type Czochralski-grown (Cz)Si crystals have been studied by means of capacitance transient techniques. Theseneutron-induced defects are compared with those created by electron irradiation andself-ion implantation. Four electron traps with the activation energies for electronemission of 0.12, 0.16, 0.24 and 0.42 eV were observed after neutron irradiation inphosphorous-doped Cz Si crystals. It is inferred that the E(0.12) and E(0.16) traps arerelated to the single-acceptor states of the silicon self-interstitial–oxygen dimer complex(IO2i) and the vacancy–oxygen pair (VO), respectively. The E(0.24) trap is associatedwith the electron emission from the double-acceptor state of the divacancy(V2). However, an asymmetric peak with its maximum at around 220 K and an activationenergy for electron emission of 0.42 eV dominated the spectra. We used high resolutionLaplace DLTS to investigate the structure of E(0.42) and found that this signal iscomplex, consisting of contributions from several defects. From the annealingbehaviour, it was revealed that as some of these defects anneal out they aresources of vacancies evidenced by an increase in the concentration of VO andV2. It is suggested that some of the defects contributing to the E(0.42) peak are related tosmall vacancy clusters.

Defect reactions associated with divacancy elimination in silicon

Defect reactions associated with the elimination of divacancies(V2) have been studied in n-type Czochralski (Cz) grown and float-zone (FZ) grown Si crystals bymeans of conventional deep-level transient spectroscopy and high-resolution Laplace deep-leveltransient spectroscopy (LDLTS). Divacancies were introduced into the crystals by irradiationwith 4 MeV electrons. Temperature ranges of the divacancy disappearance were found to be225–275 °C in Cz Sicrystals and 300–350 °C in FZ Si crystals upon 30 min isochronal annealing. Simultaneously with theV2 disappearance in Cz Si crystals a correlated appearance of twoelectron traps with activation energies for electron emission 0.23 eV{E(0.23)} and0.47 eV {E(0.47)} was observed. It is argued that the main mechanism of theV2 disappearance in Cz Si crystals is related to the interaction of mobile divacancieswith interstitial oxygen atoms. This interaction results in the formation ofV2O centres, which areresponsible for the E(0.23) and E(0.47) traps. Electronicproperties of the V2O complex were found to be very similar to those ofV2 but energy levels of the two defects could easily be separated using LDLTS.In FZ Si crystals, a few electron traps appeared simultaneously with theV2 annihilation. The small concentration of these traps compared with theV2 concentration before annealing prevented their reliable identification.

Gold–hydrogen complexes in silicon

Electron emission from gold and gold–hydrogen complexes in n-type silicon have been studied using high resolution (Laplace) DLTS. This technique permits a clear separation of defects which have very similar carrier emission characteristics. At low hydrogen concentrations our results confirm those inferred previously from conventional DLTS. However by using ‘Laplace’ DLTS it has been possible to study the gold acceptor and G4 defect independently. G4 has an activation energy of 542±8 meV. By directly measuring the electron capture cross-section of G4 we conclude that it is acceptor like. At high hydrogen concentrations additional complexes are formed, notably a defect with emission characteristics similar to G4 (referred to as G4′) with an activation energy of 578±10 meV, and a state with an activation energy for electron emission of 276 5 meV. We put forward the hypothesis that these may be charge states of AuH 2 or AuH 3 complexes.

Laplace-transform deep-level transient spectroscopy studies of the G4 gold–hydrogen complex in silicon

We have studied n-type silicon containing gold and gold–hydrogen complexes using high-resolution “Laplace” deep-level transient spectroscopy. This technique has enabled two quite distinct electron emission rates to be observed at temperatures between 240 and 300 K. These are associated with the gold acceptor and the level referred to as G4, which is observed when hydrogen and gold are present in silicon. The gold acceptor has a measured activation energy for electron emission of 558±8 meV, and the G4 state of 542±8 meV. The directly measured electron capture cross section for G4 is determined to be 0.6±0.1 σn(gold acceptor) at 275 K from which it is inferred that the state is acceptor-like.

A donorlike deep level defect in Al0.12Ga0.88N characterized by capacitance transient spectroscopies

Si-doped, n-type heteroepitaxial layers of Al0.12Ga0.88N grown by metalorganic chemical vapor deposition on SiC substrates were characterized by capacitance transient spectroscopies. Conventional deep level transient spectroscopy (DLTS) reveals the presence of a dominant deep level with an activation energy for electron emission to the conduction band of (0.61±0.02) eV. The activation energy of this deep level displays a pronounced field dependence as determined from double-correlation DLTS (DDLTS), which is indicative of a deep donor level in n-type semiconductors. A deep level is observed by optical-DLTS (O-DLTS) with a threshold energy for electron photoemission to the conduction band of 0.77 eV, which appears to be of identical origin as the dominant deep level detected by DLTS. Two additional deep levels are detected with O-DLTS in the upper half of the band gap of our Al0.12Ga0.88N sample with threshold energies of 0.83 and 1.01 eV.

Deep-level defects responsible for persistent photoconductivity in Ga-doped Cd1-xMnxTe.

Bulk n-type ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te crystals heavily doped with Ga are known to exhibit strong persistent photoconductivity (PPC) at low temperatures (below \ensuremath{\sim}100 K). In order to identify the origin of the PPC effect, we investigated the electronic properties of deep-level defects present in this material by deep-level transient spectroscopy (DLTS) and by thermally stimulated capacitance (TSCAP) measurements. We used a ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te crystal with x=0.03 and a Ga doping level of 1\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$. The DLTS measurements revealed the presence of two deep levels, with thermal activation energies for electron emission of 0.25 and 0.43 eV. The electron capture process to the 0.25-eV level was found to be thermally activated, with a thermal energy barrier of 0.11 eV. DLTS measurements performed after sub-band-gap illumination at low temperatures established that, in addition to the PPC effect, the illumination causes also a strong increase in the concentration of the 0.25-eV states, which persist to temperatures as high as T=200 K. This finding indicates that---in addition to the metastability of conduction electrons with respect to the 0.25-eV states, which results in the PPC below 100 K---the 0.25-eV states are also metastable with respect to other (ground) states from which they are created by photoexcitation. Our TSCAP measurements detected also two transitions to two different deep levels, in agreement with these results. The first of these levels is donorlike, with an activation energy of 0.21 eV. The second level is acceptorlike, and the electron transition to this level requires a thermal energy of several hundreds of meV. Because the concentrations of both the 0.25- and the 0.43-eV states found by DLTS appear to be very close to each other, we propose a single defect model with two charge states, attributing the 0.43-eV level to an acceptorlike two-electron ground state of the defect, and the 0.25-eV level to the excited, donorlike one-electron state. According to this model, the defect possesses a positive Hubbard correlation energy (positive-U system). We discuss a configuration coordinate diagram of the defect in the paper.

Reduction of deep defect concentration in chlorine-doped ZnSe by after-growth thermal treatment

Deep-level transient spectroscopy was applied for investigating the effect of after-growth annealing on the concentration of deep defects in Cl-doped ZnSe epilayers. The samples were grown by molecular beam epitaxy on (100)-GaAs substrates, employing ZnCl2 as the dopant source. The ZnSe:Cl epilayers were annealed in Zn-rich atmosphere at temperatures 400–650 °C for 18–60 h, respectively. As a consequence of the thermal treatment, the total concentration of deep defects in the material was significantly reduced. In particular, annealing almost completely eliminated the dominant defects in the as-grown material (located 0.51 eV below the edge of the conduction band), which strongly supports the identification of the origin of these defects as zinc-vacancy complexes. We also note that the annealing process introduces a small concentration of new defects. The activation energies for electron emission and capture of these traps are 0.24 and 0.17 eV, respectively, indicating that this level lies at 0.07 eV below the conduction band.

Deep Level Defects in GaN Characterized by Capacitance Transient Spectroscopies

AbstractElectronic defects in MOCVD-grown n-type GaN were characterized by conventional deep level transient spectroscopy (DLTS) and by photoemission capacitance transient spectroscopy (O-DLTS) performed on Schottky diodes. With DLTS two deep levels were detected with thermal activation energies for electron emission to the conduction band of 0.16 eV and 0.44 eV. With O-DLTS we demonstrate four new deep levels with optical threshold energies for electron photoemission of ∼ 0.87 eV, 0.97 eV, 1.25 eV and 1.45 eV. The O-DLTS apparatus and the measurement are discussed in detail. We also report characterization of the Au-GaN barrier height of the Schottky diode by internal photoemission.

Deep level defects in n-type GaN

In n-type GaN grown by metalorganic chemical vapor deposition two new electronic defects were detected and characterized by deep level transient spectroscopy (DLTS). Schottky-barrier diodes with Ohmic back contacts and low series resistance were fabricated in GaN layers grown on sapphire. The diodes display well behaved current-voltage and capacitance-voltage characteristics and permit unambiguous DLTS evaluation. The new deep levels display thermal activation energies for electron emission of 0.49 and 0.18 eV.

Electron paramagnetic resonance study of thermal donors in Fe-doped InP

The effect of thermal annealing of semi-insulating InP wafers in the 660–820 °C temperature range under SiNx capping condition is studied by electron paramagnetic resonance (EPR) spectroscopy. The annealing leads to the formation of electrically active, deep thermal donors with total defect concentrations up to 1016 cm−3. The thermal donors are of intrinsic origin. By transient EPR spectroscopy the activation energies for electron emission of the dominant thermal donors were determined to be 0.40 and 0.14 eV, respectively.

Defects in single-crystal silicon induced by hydrogenation

It is demonstrated that hydrogenation induces microdefects and electronic deep levels in single-crystal silicon, which are unrelated to either plasma or radiation damage. After hydrogenation of either n-type or p-type silicon, transmission electron microscopy reveals defects that can be described as hydrogen-stabilized platelets or microcracks which appear within 0.1 \ensuremath{\mu}m of the exposed surface and are predominantly oriented along {111} crystallographic planes. These defects correlate with high concentrations of hydrogen or deuterium as measured by secondary-ion mass spectrometry and with the appearance of Si---H bonds as revealed by Raman spectroscopy. The concomitant introduction of electrically active gap states is demonstrated with both photoluminescence spectroscopy (PL) and deep-level transient spectroscopy (DLTS). In PL several H-induced radiative transitions are observed, with the dominant peak at 0.98 eV, which had previously been ascribed to plasma damage. In n-type Schottky diodes, DLTS detects two H-induced levels with thermal activation energies for electron emission of approximately 0.06 and 0.51 eV. These defects are detected at depths greater than the surface layer, are in low concentrations (${<10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$), are acceptorlike, and anneal with an activation energy of \ensuremath{\sim}0.3 eV.

Influence of alloy composition, substrate temperature, and doping concentration on electrical properties of Si-doped n-Alx Ga1−x As grown by molecular beam epitaxy

Capacitance and Hall effect measurements in the temperature range 10-300 K were performed to evaluate the deep and shallow level characteristics of Si-doped n-AlxGa-xAs layers with 0 × 0.4 grown by molecular beam epitaxy. For alloy compositions × 0.3 the overall trap concentration was found to be less than 10−2 of the carrier concentration. In this composition range the transport properties of the ternary alloy are comparable to those of n-GaAs:Si except for lower electron mobibities due to alloy scattering. With higher Al content one dominant electron trap determines the overall electrical properties of the material, and in n-Al0.35Ga0.65As:Si the deep trap concentration is already of the order of the free-carrier concentration or even higher. For the composition × = 0.35 ± 0.02 the influence of growth temperature and of Si dopant flux intensity on the deep trap concentration, on shallow and deep level activation energy, and on carrier freeze-out behaviour was studied and analyzed in detail. Our admittance measurements clearly revealed that the previously assumed deepening of the shallow level in n-Alx Ga1-x As of alloy composition close to the direct-indirect cross-over point does actuallynot exist. In this composition range an increase of the Si dopant flux leads to a reduction of the thermal activation energy for electron emission from shallow levels due to a lowering of the emission barrier by the electric field of the impurities. The increasing doping flux also enhances the concentration of the dominant electron trap strongly, thus indicating a participation of the dopant atoms in the formation of deep donor-type (D,X) centers. These results are in excellent agreement with the model first proposed by Lang et al. for interpretation of deep electron traps in n-Alx Ga1-x grown by liquid phase epitaxy.

Electronic Defects in Metalorganic GaAIAs

ABSTRACTElectronic defect levels have been measured in n-type epitaxial films of Gal - XAIXAs (0≤X≤0.33) which were grown by metalorganic chemical vapor deposition. Electron traps were characterized by transient capacitance spectroscopy on Schottky-barrier diodes. The thermal activation energy for electron emission from the near-midgap defect level is found to be larger in Ga1 - XAIXAs than the value of 0.83 eV generally observed in GaAs.

Analysis of the Uhlig Defect Model of Oxidation Kinetics

A self‐consistent development is given of a model of oxidation kinetics in which growth rate is determined by thermionic emission of electrons over a potential barrier due to the metal‐oxide work‐function and modified by space charge due to trapped electrons in the oxide and compensating surface charge at the metal‐oxide interface. The following expression is derived for the growth rate where is the oxide film thickness at time , and is the characteristic thickness at which a uniform concentration of trapped electrons of charge attenuates the growth rate significantly at temperature , ε is the relative dielectric constant of the oxide, and is the Boltzmann constant. The parameter can be considered to determine the time scale, where is the flux of electrons (or charge) in the parent metal which impinges on the potential barrier of height φ represented by the oxide, and β is the volume of oxide formed per electron (or per unit of charge) which traverses the oxide film. This growth‐rate expression clearly does not lead to a direct‐logarithmic growth law. Moreover, the characteristic film thickness at which rate is significantly attenuated is of the order of the Debye length, in contrast with the conclusion reached by Nwoko and Uhlig that space‐charge effects should be much larger. A development of the activation barrier for electron emission illustrates that the electron affinity of adsorbed oxygen is not a factor in the activation energy for electron emission when the emission process is rate‐limiting. This results in a modification of the time scale for the kinetics by many orders of magnitude relative to that of Uhlig and Nwoko. Finally, the nonzero ionic current will perturb the rate‐limiting electron current; the “coupled currents” method previously developed by the present author, in which the currents are balanced by the surface charge field, is suggested to be appropriate for studying this effect.