Photoinduced Current Transient Spectroscopy Spectra Research Articles

Electrical properties of α-Ga2O3 films grown by halide vapor phase epitaxy on sapphire with α-Cr2O3 buffers

We report on growth and electrical properties of α-Ga2O3 films prepared by halide vapor phase epitaxy (HVPE) at 500 °C on α-Cr2O3 buffers predeposited on sapphire by magnetron sputtering. The α-Cr2O3 buffers showed a wide microcathodoluminescence (MCL) peak near 350 nm corresponding to the α-Cr2O3 bandgap and a sharp MCL line near 700 nm due to the Cr+ intracenter transition. Ohmic contacts to Cr2O3 were made with both Ti/Au or Ni, producing linear current–voltage (I–V) characteristics over a wide temperature range with an activation energy of conductivity of ∼75 meV. The sign of thermoelectric power indicated p-type conductivity of the buffers. Sn-doped, 2-μm-thick α-Ga2O3 films prepared on this buffer by HVPE showed donor ionization energies of 0.2–0.25 eV, while undoped films were resistive with the Fermi level pinned at EC of 0.3 eV. The I–V and capacitance–voltage (C–V) characteristics of Ni Schottky diodes on Sn-doped samples using a Cr2O3 buffer indicated the presence of two face-to-face junctions, one between n-Ga2O3 and p-Cr2O3, the other due to the Ni Schottky diode with n-Ga2O3. The spectral dependence of the photocurrent measured on the structure showed the presence of three major deep traps with optical ionization thresholds near 1.3, 2, and 2.8 eV. Photoinduced current transient spectroscopy spectra of the structures were dominated by deep traps with an ionization energy of 0.95 eV. These experiments suggest another pathway to obtain p–n heterojunctions in the α-Ga2O3 system.

Deep Levels in 4H Silicon Carbide Epilayers Induced by Neutron-Irradiation up to 1016 n/cm2

AbstractWe investigated the electronic levels of defects introduced in 4H-SiC α-particle detectors by irradiation with 1 MeV neutrons up to a fluence equal to 8x1015 n/cm2. As well, we investigated their effect on the detector radiation hardness. This study was carried out by deep level transient spectroscopy (DLTS) and photo-induced current transient spectroscopy (PICTS). As the irradiation level approaches fluences in the order of 1015 n/cm2, the material behaves as highly resistive due to a very great compensation effect but the diodes are still able to detect with a acceptably good charge collection efficiency (CCE) equal to 80%. By further increasing fluence, CCE decreases reaching the value of ≈ 20% at fluence of 8x1015 n/cm2.The dominant peaks in the PICTS spectra occur in the temperature range [400, 700] K. Enthalpy, capture cross-section and order of magnitude of the density of such deep levels were calculated. In the above said temperature range the deep levels associated to the radiation induced defects play the key role in the degradation of the CCE. Two deep levels at Et = 1.18 eV and Et = 1.50 eV are likely to be responsible of such dramatic decrease of the charge collection efficiency. These levels were reasonably associated to an elementary defect involving a carbon vacancy and to a defect complex involving a carbon and a silicon vacancy, respectively.

Traps in undoped semi-insulating InP obtained by high temperature annealing

The presence and evolution of traps in undoped semi-insulating (SI) InP obtained by high temperature annealing (900 °C for 90 h) in poor or rich phosphorus atmosphere has been studied by means of photoinduced current transient spectroscopy. Six traps named A1 to A6 having activation energies ranging from 0.2 to 0.6 eV have been detected in three samples submitted to the same annealing process. The samples differ in the Fe concentration of the starting material and the applied phosphorus pressure in the annealing process. A comparison of the corresponding photoinduced current transient spectroscopy spectra shows that among the observed traps, the 0.2 eV one can be related to a phosphorus deficiency, and the 0.3 eV and 0.4 eV traps could be due to an excess of phosphorus during annealing. Moreover, the trap corresponding to iron (0.6 eV) has been observed in all the studied samples.

Closed tube vapour growth of CdTe:V and CdTe:Ti and its characterization

The vapour growth of CdTe:V and CdTe:Ti by the sublimation travelling heater method (STHM) is reported for the first time. Characterization of the crystals has been performed by time dependent charge measurement (TDCM) and photoinduced current transient spectroscopy (PICTS). Axial cuts of CdTe:V crystals showed a very homogeneous and high resistivity distribution in the range of 1010 ω · cm. The PICTS spectra depict three levels which can be attributed to transition metal doping. The expected deep donor level can be identified clearly to be at Ev + 0.95 and 0.94 eV in CdTe:V and CdTe:Ti, respectively.

Interpretation of deep levels in Si-GaAs crystals observed by photo-induced current transient spectroscopy

Abstract Deep levels measured by Photo-Induced Current Transient Spectroscopy (PICTS) are interpreted taking into account different bulk and surface properties of semi-insulating crystals, results of directly measured isothermal transients and types of observed deep levels determined from the measurements with different voltage polarity. The principal interest is focused on the temperature interval 250–450 K where peaks related to the deep levels causing semiinsulating properties are observed in the PICTS spectra. Majority of deep levels observed in various samples may be ascribed to the EL2, EL3, EL4, HL1 and HL9 levels. Maxima exhibiting inverse polarity in PICTS spectra are not related to EL2 or HL1.

Comparison of PICTS measurements on Si-GaAs interpreted within generalized physical models

Abstract Experimental data measured by the Photo-Induced Current Transient Spectroscopy (PICTS), i.e. the temperature positions of maxima in PICTS spectra versus the time positions of boxcar gates, have been fitted within physical models with different stage of generalization. This procedure has been applied to several important deep levels observed in semiinsulating undoped and chromium doped GaAs crystals and the obtained results have been compared with each other.