Isothermal Capacitance Transient Spectroscopy Measurements Research Articles

Admittance Spectroscopy Study of Defects in β-Ga2O3

We present a comprehensive investigation of electrically active defects and transport properties in commercial (2¯01) edge-defined film-fed growth β-Ga2O3 using admittance spectroscopy measurements from 14 K up to 450 K. Isothermal capacitance-frequency measurements were conducted from 410 to 450 K to resolve a defect ∼0.8 eV below the conduction band edge and compared with deep-level transient spectroscopy and isothermal capacitance transient spectroscopy measurements. We report significant non-Arrhenius behavior of a defect ∼100 meV below the conduction band and apply the Arrhenius transformation matching method to extract its temperature-dependent activation energy and capture cross-section in the temperature range of 75 to 195 K. At low temperatures (<50 K), we use bias-dependent admittance spectroscopy to extract the electron mobility in β-Ga2O3 from the modified dielectric relaxation frequency. Finally, we discuss the potential of admittance spectroscopy for defect characterization in wide bandgap semiconductors in terms of the defect detection range, instrument requirements, and the frequency-temperature experiment space.

Electron traps formed by gamma-ray irradiation in homoepitaxial n-type GaN and their annealing behavior

Gamma-ray irradiations of up to 500 kGy on homoepitaxial n-type GaN layers were carried out, and the formation of electron traps was investigated by deep-level transient spectroscopy (DLTS) using Ni Schottky barrier diodes (SBDs). Before performing DLTS, current–voltage (I–V) and capacitance–voltage (C–V) measurements of the SBDs were performed and it was found that there was no change in the net donor concentration, ideality factor, and Schottky barrier height after irradiation. In the DLTS measurements, two new peaks, labeled G1 and G2, were observed after irradiation. The filling pulse width dependence of G1 revealed that the peak consists of two electron trap levels, labeled G1a (EC − 0.13 eV) and G1b (EC − 0.14 eV). Isothermal capacitance transient spectroscopy measurements of samples with different Schottky barrier heights showed that the G2 peak is a complex peak consisting of at least three electron traps, labeled G2a (EC − 0.80 eV), G2b (EC − 0.98 eV), and G2c (EC − 1.08 eV). The production rates (formation rates of traps by gamma-ray irradiation) for each trap were obtained. Finally, we investigated the annealing behavior of each trap and found that G1b and G2b decreased by the same amount with increasing annealing temperature, suggesting that the behavior originates from a recombination of vacancy–interstitial (Frenkel) pairs.

Chemical vapor deposition and deep level analyses of 4H-SiC(112̄0)

Specular 4H-SiC layers have been homoepitaxially grown on 4H-SiC(112̄0), parallel to the c axis (〈0001〉), by chemical vapor deposition at 1500 °C. An x-ray diffraction analysis has revealed that a lattice-mismatch strain between n− epilayers and n+ substrates could be minimized by introducing n-type buffer layers. The donor concentration of unintentionally doped epilayers could be reduced down to 1×1014 cm−3 under a C-rich growth condition. Through isothermal capacitance transient spectroscopy measurements, three acceptor-like traps with activation energies of 0.27, 0.32, and 0.66 eV have been detected with a total trap concentration as low as 3.8×1012 cm−3. The capture cross section of the deepest trap, the Z1 center, at high temperatures has been determined.

Characterization of InGaAs Phosphidized by a Plasma Process

Phosphidization of InGaAs is attempted using a remote phosphine plasma. Au Schottky junctions are formed on the phosphidized and Ar-plasma-treated InGaAs layers and their electrical properties are characterized. Traps are investigated by isothermal capacitance transient spectroscopy measurements. Two electron traps are detected and designated as E1 and E2. The energy levels of the E1 and E2 traps are 0.35 eV and 0.48 eV below the conduction band edge, respectively. In the case where InGaAs is treated with PH3-added Ar plasma, a significant reduction in the densities of both E1 and E2 traps occurs in comparison with those of Ar-plasma-treated InGaAs. It is found that phosphorus atoms are effective in suppressing the generation of electron traps in InGaAs.

Characterization of GaAs surfaces treated with phosphine gas photodecomposed by an ArF excimer laser

Phosphidization of GaAs surfaces is attempted with phosphine gas photodecomposed by an ArF excimer laser. Electron traps at and near the phosphidized GaAs surfaces are characterized by isothermal capacitance transient spectroscopy measurements. Phosphidization leads to a reduction in the trap (Ec−0.81 eV) known as an EL2 center and generation of two traps (Ec−0.24 eV and Ec−0.49 eV), which are designated as NL1 and NL2, respectively. A significant metal work-function dependence of the barrier height is demonstrated for Schottky junctions formed on the GaAs surfaces phosphidized under optimum condition, suggesting that phosphidization is effective in reducing surface states of GaAs.

Behavior of Electron Traps Induced by Phosphidization and Nitridation of GaAs Surfaces

AbstractGaAs is treated with remote PH3 and N2 plasmas. Electron traps induced by plasma treatments are investigated by isothermal capacitance transient spectroscopy measurements. The EL2 trap is detected in the as-grown GaAs. The TP1 trap(Ec-0.26eV) is generated in GaAs phosphidized for 10min, while the TN1 trap(Ec-0.66eV) is induced in GaAs nitrided for 30min. It is found that the TP1 trap is changed to the another trap with an energy level as shallow as 0.16eV below the conduction band edge and a capture cross section as small as 1.8×10−21cm2 by treating with N2 plasma subsequently after PH3 plasma treatment.

Defects in MOVPE grown ZnSe on GaAs studied by deep level transient spectroscopy

Abstract The defect related properties of MOVPE grown ZnSe layers on GaAs were investigated by electrical measurements. Ditertiarybutylselenide and dimethylzinc-triethylamine were used as precursors for the ZnSe growth. In order to carry out nitrogen doping trimethylsilylacide triallylamine and bisditrimethylsilylamido-zinc were used as N precursors. The N doping was also performed by N 2 dc-plasma. Current-voltage ( I - V ) and capacitance-voltage ( C - V ) measurements reveal n-type behavior in all cases. The N D − N A net doping concentration amounts to 10 16 –10 17 cm −3 . An electron trap center with a thermal activation energy in a range of 0.30 to 0.33 eV and a capture cross section of about 10 −15 cm 2 was determined by means of deep level transient spectroscopy and isothermal capacitance transient spectroscopy measurements. This trap was detectable in all N-doped samples except in the case of a TMSiN doped sample. Since an electron trap center with comparable features has been also found in n-type single crystalline ZnSe and, as reported by other groups, also in n-type MBE ZnSe, it is assumed, that the existence of this state is related to a native defect in the as grown layer.

Characterization of electron traps in plasma-treated AlInAs

Electron traps have been investigated for molecular beam epitaxially grown n-AlInAs by isothermal capacitance transient spectroscopy measurement. Two traps, EOl(Ec−0.44 eV) and EO2(Ec−0.52 eV), appear for oxygen-plasma treated samples in addition to El(Ec−0.47 eV) and E2(Ec−0.69 eV) traps detected for control (as-chemically etched) sample. On the other hand, the EO1 trap is not detected for Ar plasma-treated sample. This suggests that the EO1 is generated by reaction of atomic oxygen with AllnAs and that the EO2 trap is induced by plasma damage. It is found that a reduction in the densities of the four traps occurs due to annealing subsequently after oxygen plasma treatment.

Si-SiO2 interface states enhanced by oxidation-induced stacking faults

It has been observed for the first time that interface states of Si metal-oxide-semiconductor diode are enhanced by the influence of oxidation-induced stacking faults (OSF). The observation has been carried out by isothermal capacitance transient spectroscopy measurement, using two kinds of samples. The samples are cut from the same CZ-Si wafer with ‘‘ring OSF.’’ One is prepared from the region with ‘‘ring OSF’’ and the other is prepared from the defect-free region.

Creation and passivation of electron traps in n-InP treated with hydrogen plasma

Studies on deep electron traps in n-InP treated with hydrogen plasma have been performed using isothermal capacitance transient spectroscopy measurements. Five electron trap levels, E1–E5, with activation energies of 0.21, 0.51, 0.32, 0.54, and 0.63 eV, respectively, below the conduction band are detected. Only E1 traps are observed in as-etched InP. Hydrogen-plasma treatment leads to enhancement of the density of E1 traps and creation of E2 and E5 traps. E1 and E5 traps are annealed out at 300 °C, while E2 traps are annealed out at a temperature as low as 150 °C. On the other hand, densities of E3 and E4 traps are significantly enhanced by annealing at 350 °C. This experimental result suggests that the E3 and E4 traps are generated during hydrogen-plasma exposure and are passivated by hydrogen atoms.

Analysis of recombination centers in (AlxGa1−x)0.5In0.5P quaternary alloys

We studied nonradiative recombination centers in undoped (AlxGa1−x)0.5In0.5Pgrown by metalorganic vapor phase epitaxy using transient capacitance spectroscopy. We found three deep energy levels, including a mid-gap level. We drew an equation to get a capture cross section for minority carriers, and obtained it using isothermal capacitance transient spectroscopy measurement. The mid-gap level had an electron capture cross section of 2 × 10−10 cm2 and a hole capture cross section of 1 × 10−15 cm2. The time constant of nonradiative recombination through the mid-gap level was found to be comparable to that of radiative recombination. We concluded that the mid-gap level is an effective nonradiative recombination center that reduces photoluminescence intensity.

Characterization of interface states in (Sr, Ca)TiO3−x based ceramics by ICTS analysis

Isothermal capacitance transient spectroscopy measurements were performed to study the reoxidizing induced change in interface states in (Sr, Ca)TiO3−x based ceramics. A discrete acceptor type trap level was detected with reoxidation below the oxidation temperature of grain surfaces, but two deep levels were detected with reoxidation above this temperature. These ICTS results are in good agreement with the previous report with the DLTS measurements. These interface states are considered to originate from chemisorbed oxygen (O2−, O−) on grain surfaces. The O− and O2− chemisorption levels contribute to the non-ohmic conduction with reoxidizing anneals below and above the oxidation temperature, respectively.

Reversible photoinduced modification of electron-capture cross section at localized states in a-Si:H

A reversible photoinduced modification of the electron-capture cross section at localized states in P-doped a-Si:H has been directly observed, being associated with the Staebler–Wronski effect. Isothermal capacitance transient spectroscopy measurement shows that the electron-capture cross section at the gap states located at around 0.5 eV below the conduction-band mobility edge (Ec) increases after the band-gap illumination and is nearly restored to its original value by thermal annealing below 200 °C. It has been suggested that a metastable state related with the dangling bond is created through the multiphonon emission when excess carriers recombine.