Hole Trap Levels Research Articles

Majority and minority carrier traps in monocrystalline CulnSe2

Electron and hole traps in Bridgman-grown monocrystalline CuInSe2 were investigated by carrying out deep level transient spectroscopy measurements on homojunctions, Al-CuInSe2 (p-type), and Au-CuInSe2 (n-type) Schottky junctions. Three hole trap levels and two electron trap levels were observed on these devices. Effects of oxygen and etching on the electron trap level at 182 ±15 meV from the conduction band edge were specifically studied. It was found that the election trap densities in the homojunctions prepared using the CuInSe2 samples treated in NH2NH2 solution, which absorbes oxygen atoms in the samples, were larger than the electron trap densities in the homojunctions prepared using untreated samples. Moreover, the electron trap densities in the homojunctions after prolonged heat treatment in O2 were less than that without prolonged heat treatment. The results thus suggested that oxygen atoms in CuInSe2 can reduce the electron trap density of p-type CuInSe2. The effects of chemical etching on these electron traps were also studied. The excess indium atoms in the CuInSe2 were considered to affect the electron traps.

Hole trap analysis in SiO2/Si structures by electron tunneling

AbstractHole trap parameters in Si/SiO2 structures are investigated by their charge relaxation after a foregoing hole trap population. A concept based on tunneling between extended Si states and localized SiO2 states is developed to explain the logarithmic time dependence, gate voltage dependence, and temperature dependence of hole trap depopulation. A positively charged hole trap level with a trap energy of E = (6.3 ± 0.2) eV above the SiO2 valence band edge is found. The corresponding value of the wave vector is |K(E)| = 6.1 nm−1 according to the two‐band approximation for the K(E) relation in the SiO2 gap. The hole trap concentration is N = 2 to 5 × 1019 cm−3 inside a small (5 nm) near‐interface region. These results are in agreement with EPR experiments and confirm that the E'‐centre (oxygen vacancy) constitutes a dominating paramagnetic defect and a hole trap.

Deep levels induced by high-energy boron ion implantation into p-silicon

Defects induced by B+ implantation at 0.7 MeV into n+p diodes were investigated using leakage current and deep level transient spectroscopy (DLTS). Leakage current increases drastically by implantation to a dose of more than 3×1013 cm−2. DLTS spectra reveal two hole trap levels in the shallower region than the projected range of B+. One level at 265 K (Ev+0.65 eV) is associated with point defects around dislocation kinks formed by B+ implantation to doses of more than 3×1013 cm−2. Another level at 290 K (Ev+0.67 eV) is mainly responsible for the excess leakage current. This level was, for the first time, found in p-Si after high-energy ion implantation followed by annealing.

Hole trap level generation in silicon during rapid thermal annealing: Influence of substrate type and process conditions

Hole trap level generation in boron-doped silicon by rapid thermal annealing between 900 and 1100 °C has been studied using deep level transient spectroscopy, with emphasis on the effects of substrate type and process parameters. A dominant hole trap level at Ev+0.30 eV and two accompanying hole trap levels at Ev+0.22 eV and Ev+0.40 eV in lower concentrations have been systematically detected in Czochralski, float zone, and epitaxial substrates, in a less than 5-μm-thick surface layer. The defect state concentrations were observed to increase monotonically with both the annealing temperature and the cooling rate. Higher concentrations of hole trap levels were measured in the Czochralski and epitaxial substrates than in the float zone substrate. Finally, both a silicidation and an oxidation reaction during the high-temperature plateau totally inhibited the formation of defect states. We suggest that the defect centers responsible for the observed hole trap levels could be formed during the high-temperature plateau with the participation of dissolved as-grown impurities and metal contaminants diffused from the wafer surface.

Direct current conductivity and thermally stimulated current of β-nickel phthalocyanine films using gold and aluminium electrodes

Current density-voltage characteristics and thermally stimulated currents have been obtained from thin films of β-nickel phthalocyanine particles dispersed in a polymer binder, when sandwiched between ohmic gold and blocking aluminium electrodes. At low voltages, the current in the forward direction varies exponentially with voltage. At higher voltages, two separate regions of space-charge limited current conduction under forward bias were observed. Under reverse bias, the conduction process at low voltages is determined by Schottky emission over a potential barrier of approximate height, 0·89 eV and thickness 65 nm. At higher voltages, the Poole-Frenkel effect was observed. The activation energy of the hole trapping level determined from the thermally stimulated current measurements has an electric field dependence. The results are interpreted in terms of the Poole-Frenkel effect.

Metastable Defects of Iron-Boron Pair in Silicon

ABSTRACTWe have found configuratlonally metastable Fe-B pairs in Si by using dark or photo capacitance-transient technique combined with minority-carrier injection. The metastable pairs are observed as four electron-trapping levels at Ec-0.43 eV, 0.46 eV, 0.52 eV, and 0.54 eV and as two hole-trapping levels at Ev+0.53 eV and 0.48 eV after the injection at 150 K. The production of each level is investigated under various injection conditions, and the annihilation process is studied by isochronal anneals.

Investigation of the electrical properties of Cd-doped indium selenide

Resistivity, Hall-effect, and deep-level transient spectroscopy measurements have been performed on Cd-doped InSe single crystals grown by the Bridgman–Stockbarger method. The temperature dependence of the hole mobility can be explained by combining the optical phonon and the ionized impurity scatterings. Two hole-trapping levels have been detected at 0.42 and 0.48 eV above the valence band with a capture cross section of about 10−17 cm2. Finally, we have found the latter trap to be a deep acceptor level, which is very probably associated with defects or defect complexes formed by the dopant atoms.

The thermally stimulated current of β-form oxotitanium phthalocyanine dispersed in polyester

A thermally stimulated current (TSC) has been applied to estimate the trap properties on a thin film of β-form oxotitanium phthalocyanine (β-TiOPc) dispersed in polyester. The hole trapping levels derived from the activation energies (Eas) were obtained by an initial rising method and heating rate dependence on TSC peaks. The Eas for an electric field of 2.5×103 V/cm were distributed from 0.033 eV for shallow traps to 0.42 eV for deep traps.

Plasma Damage Induced on Silicon Surface in a Barrel Asher

The damage generated in diffusion layers on silicon wafer surfaces during exposure to an oxygen plasma in a barrel asher has been studied. After exposure to the plasma, an increase in sheet resistance was commonly observed on boron‐, gallium‐, and aluminum‐implanted surfaces. An increase in the yield of channeled spectra by Rutherford backscattering also occurred on the surfaces, indicating the formation of lattice defects that can act as hole trap levels. An experiment using different doses suggests that the hole trap concentration is independent of the initial carrier concentration.

Hole trap level in Pt-Ti/p-InGaAs/n-InP heterostructures due to rapid thermal processing

Low-resistance ohmic contacts of Pt/Ti to p-InGaAs/n-InP heterostructures were formed by rapid thermal processing (RTP). Deep level transient spectroscopy and current-voltage temperature (I-V-T) measurements were used to characterize this system in order to evaluate the stability of the Pt/Ti ohmic contact and the effects of different RTP temperatures on the device performance. A new hole trap level with activation energy of 0.89 eV was found in samples treated at temperatures above 500 °C but not in those treated at lower temperatures. This trap, featured by a higher density when closer to the junction, was thought to be caused by Ti interdiffusion at high RTP temperature, in agreement with the analysis from Auger depth profiling. Four electron trap levels with activation energies of 0.61, 0.45, 0.35, and 0.30 eV were observed for all samples and believed to be native defects in InP. I-V-T measurements revealed current mechanisms independent of the RTP temperatures indicating that the new hole trap does not influence current conduction mechanisms.

Deep level spectroscopy in p-GaSe single crystals

Deep levels have been examined in nonintentionally doped p-type gallium selenide single crystals using photoinduced current transient spectroscopy measurements. Two hole trapping levels at 0.20 and 0.80 eV above the valence band have been observed and the corresponding thermal capture cross section evaluated. The possible origin and nature of these centers are also discussed.

Energy Band Model of Undoped a-Ge:H Prepared by Plasma CVD

The infrared absorption, electronic properties including dark- and photoconductivities and optical properties of hydrogenated amorphous Ge thin films prepared by rf plasma CVD method at a substrate temperature of 130°C have been studied. It is found that hydrogens bond to Ge in a monohydride manner. An energy band model is proposed through the experimental results; the energy band gap is 1.0 eV, the Fermi level lies 0.35 eV below the conduction band, the electron trap level corresponding to the band tail edge is located 0.15 eV below the conduction band, and the hole trap level to the tail edge on the valence band side is situated 0.20 eV above the valence band.

Optical-MCTS of proton-irradiated n-type gallium arsenide

Minority-carrier trap spectroscopy (MCTS) employing band-to-band optical production of the minority carriers has been applied to study the hole-trapping defect levels produced in n-GaAs Schottky diodes by irradiation with energetic protons. Our experiments demonstrate that a high-intensity LED can be used instead of a laser as a very effective optical excitation source. For 1.0 MeV proton irradiation at 298 K, the results give the emission characteristics of five irradiation-induced hole-trapping levels, at 0.25, 0.28, 0.42, 0.54 and 0.78 eV above the valence band, and of these we report the level at 0.28 eV as a new irradiation-induced hole trap in n-GaAs. The work shows also that the defect giving rise to the level at 0.42 eV is less thermally stable in n-GaAs than in p-GaAs.

Photoinduced structural defect levels in amorphous selenium films

Thermally stimulated discharge (TSD) behavior of native (dark rested) and irradiated amorphous selenium films (∼100 μm) has been studied. The TSD spectrum of nonirradiated films shows electron trapping levels at ∼0.99 eV and no detectable hole trapping levels. On the other hand, the irradiated films show both electron as well as hole trapping levels at 0.99 and 1.05 eV, respectively. These results have been explained in terms of trapping of charge carriers at intrinsic defect states and the photoinduced defect levels created during irradiation.

Traps in ZnS/Anodic Sulfide Film on Mercury Cadmium Telluride

ABSTRACTWe studied the influence of visible light on the ZnS/anodic sulfide/HgCdTe interface.We measured flatband voltage of metal-insulator-semiconductor diodes with semitransparent electrodes at 77 K. In the dark (i.e., without visible light). The flatband voltage of an metal-insulator-semiconductor diode is 0 V. We scanned visible light from 400 to 800 nm and measured the flatband voltage using the photocapacitance measurement. After an initial positive shift, the flatband voltage moved negative by as the wavelength shortened. We studied the relationship between the flatband voltage shift and photon energy using Fowler plots. Results suggest one electron trap level 1.5 eV above the valence band and two hole trap levels 1.7 and 2.3 eV below the conduction band.ZnS/anodic sulfide films on mercury cadmium telluride, studied using photoluminescence spectroscopy, showed broad photoluminescence peaks at 1.5, 1.7, and 2.3 eV, and the edge emission of the anodic sulfide.These results suggest that photoionization of the electron trap and two hole traps in the ZnS/anodic sulfide film causes the flatband shift.

Studies of majority-carrier traps in Zn-doped p-InP by thermally stimulated capacitance techniques

High-barrier Yb/p-InP Schottky diodes were used to study majority-carrier traps in the Zn-doped p-InP single-crystal substrates by thermally stimulated capacitance (TSCAP) techniques. The TSCAP studies involved a forward bias VF=0.6 V, cooling to 90 K, bias switching to reverse bias VR=4.0 V, and then heating at a constant heating rate to 450 K. The junction capacitance was recorded as a function of temperature for various heating rates between 0.05 and 0.5 K/s, and corrected for temperature dependence of the diffusion voltage and the dielectric constant. The trapping parameters of the strong hole trap level were determined from the plots of dΔC/dT vs T at different heating rates, and values of Eh1=EV+0.59 eV and σp1 =3×10−21 cm2 were obtained for the activation energy and capture cross section, respectively, of the hole trap. From the TSCAP data at a constant heating rate and using the Eremin, Strokan, and Turebekov [Sov. Phys. Semicond. 15, 1010 (1981)] method, a hole trap with Eh1=EV+0.62 eV and σp1 =2×10−21 cm2 was also detected. From the amplitude of the steady-state positive capacitance step, a value of NTP =2.7×1014 cm−3 for the concentration of the hole trap level was estimated.

Static magnetic and EPR studies of iron in the β-rhombohedral boron structure

Abstract The magnetic properties of iron atoms and their distribution in β-rhombohedral boron were studied using EPR and static magnetic susceptibility measurements in the temperature range 3.6–300 K. It has been shown that, for low concentrations, the iron atoms occupy the A holes of the β-rhombohedral structure and, after the concentration is increased, the D holes. Iron atoms in the A and D holes interact and form antiferromagnetic clusters (pairs). Iron atoms in the A hole are responsible for compensation of the hole trapping levels near the valence band edge. The charge state of iron in the A hole is Fe3+ and, as a result of the strong crystalline field of the ligands, a low spin value, S = 1 2 , was found. Iron in the D hole is in the Fe2+ state and experiences an intermediate crystal field strength with μeff = 4.20.

Dark current transients in SbI3-doped HgI2 crystals

The transient characteristics of the dark current have been measured in SbI3-doped HgI2 single crystals as a function of voltage and temperature for different dopant concentrations. The doping by Sb3+ was found to introduce a hole trapping level 0.5-eV deep, with a density which was of the same order of magnitude as the SbI3 content. The room-temperature effective hole mobility was 5×10−8 cm2/V s for 1.5 wt.% dopant content, as compared to about 2×10−6 cm2/V s for 0.1 wt.% dopant content. Previous results obtained with undoped crystals showed an effective mobility of 5×10−7 cm2/V s, but the trap depth was different, 0.7 eV, and the concentration was much lower, only of the order of 1015 cm−3.

Transition Metals in Electrically active Sites after Incoherent Light Annealing of Boron-Doped Czochralski-Grown Silicon

ABSTRACTTwo hole trap levels H(0.45) and H(0.29) with properties close to those of metal-related defect states were found in virgin or implanted CZ silicon substrates submitted to a short duration Rapid Thermal Annealing (RTA) around 1000 °C. These hole trap levels were assigned to the presence of Fe or Cr in interstitial solution after RTA. Control experiments using chromium-diffused samples allowed to verify the quenching mechanism of chromium atoms in electrically active site during the annealing treatment, with a cooling rate-dependent concentration. After a subsequent low temperature annealing, the supersaturated interstitial solution of chromium evolves toward more stable defect configurations.

Defect-state generation in Czochralski-grown (100) silicon rapidly annealed with incoherent light

Defect-state generation in Czochralski-grown (100) silicon after rapid thermal annealing has been studied. Deep-level transient spectroscopy experiments have been carried out using Schottky barriers made on n- or p-type as-grown wafers after irradiation with a commercially available incoherent light annealing device. Neither electrical degradation nor electron-trap generation appeared in the case of n-type silicon wafers annealed for 5 s. On the other hand, the junction degradation together with the generation of three hole-trap levels H1(0.45 eV), H2(0.29 eV), and H3(0.3 eV) have been observed in boron-doped silicon using a short duration (5 s) plateau temperature between 850 and 1050 °C. Peak concentrations ranging from 1013 to 1014 cm−3 were measured after annealing at 1000 °C for the three hole traps. By increasing the plateau duration up to 20 s hole traps were no longer detected in boron-doped Czochralski-grown silicon. Moreover H2(0.29 eV) is stable at room temperature whereas both H1(0.45 eV) and H3(0.3 eV) decayed in unbiased samples after several weeks. A comparison of the trap properties with those of already known defect states suggested that residual 3D metal traces (Fe, V, Cr) might be responsible for all the observed defect states. In addition the intrinsic defects generated during the temperature plateau are likely to play a significant role in the final defect-state concentration after rapid thermal annealing.