The transformations of the EL6 deep level defect in n-GaAs: is EL6 a DX-like center?

Symposium Theme: Defect and impurity engineered semiconductors IIBased on the charge redistribution effect, as observed by the present authors, and the earlier reported large lattice relaxation and persistent photoconductivity phenomena associated with the EL6 defect seen in doped, undoped, semiinsulating(SI) and low temperature grown GaAs (LT-GaAs), it is suggested that this defect be classified as a DX-center. A tentative unified atomic model is proposed for all the native defects EL2, EL3, EL5, and EL6 observed in GaAs.published_or_final_versio

A deep level transient spectroscopy study of electron irradiation induced deep levels in p-type 6H–SiC

1.7 MeV electron irradiation-induced deep levels in p-type 6H–SiC have been studied using deep level transient spectroscopy. Two deep hole traps are observed, which are located at EV+0.55 eV and EV+0.78 eV. They have been identified as two different defects because they have different thermal behaviors. These defects at EV+0.55 eV and EV+0.78 eV are annealed out at 500–200 °C, respectively, and are different from the main defects E1/E2, Z1/Z2 observed in electron irradiated n-type 6H–SiC. This indicates that new defects have been formed in p-type 6H–SiC during electron irradiation. ©1999 American Institute of Physics.published_or_final_versio

Electron-irradiation-induced deep levels in n-type 6H–SiC

The fluence-dependent properties and the annealing behavior of electron-irradiation-induced deep levels in n-type 6H–SiC have been studied using deep-level transient spectroscopy (DLTS). Sample annealing reveals that the dominant DLTS signal at EC – 0.36 eV (labeled as E1 by others) consists of two overlapping deep levels (labeled as ED3L and ED3H). The breakup temperature of the defect ED3L is about 700 °C. The ED3H center together with another deep level located at EC – 0.44 eV (so-called E2) can withstand high-temperature annealing up to 1600 °C. It is argued that the involvement of the defect ED3L is the reason that various concentration ratios of E1/E2 were observed in the previous work. The revised value of the capture cross section of the deep-level ED3H has been measured after removing ED3L by annealing. A deep level found at EC – 0.50 eV is identified as a vacancy–impurity complex since it was found to have a lower saturated concentration and weak thermal stability. Two other deep levels, EC – 0.27 eV and EC – 0.32 eV, which were not observed by others because of the carrier freeze-out effect, are also reported. ©1999 American Institute of Physics.published_or_final_versio

Deep level transient spectroscopy study of particle irradiation induced defects in n-6H-SiC (Abstract)

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Spatial distribution of carrier concentration in un-doped GaN film grown on sapphire (Abstract)

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Electric-field distribution in Au–semi-insulating GaAs contact investigated by positron-lifetime technique

Positron-lifetime spectroscopy has been used to investigate the electric-field distribution occurring at the Au–semi-insulating GaAs interface. Positrons implanted from a 22Na source and drifted back to the interface are detected through their characteristic lifetime at interface traps. The relative intensity of this fraction of interface-trapped positrons reveals that the field strength in the depletion region saturates at applied biases above 50 V, an observation that cannot be reconciled with a simple depletion approximation model. The data, are, however, shown to be fully consistent with recent direct electric-field measurements and the theoretical model proposed by McGregor et al. [J. Appl. Phys. 75, 7910 (1994)] of an enhanced EL2+ electron-capture cross section above a critical electric field that causes a dramatic reduction of the depletion region’s net charge density. Two theoretically derived electric field profiles, together with an experimentally based profile, are used to estimate a positron mobility of ∼95±35 cm2 V-1 s-1 under the saturation field. This value is higher than previous experiments would suggest, and reasons for this effect are discussed.published_or_final_versio

Aluminum-implantation-induced deep levels in n-type 6H–SiC

Deep-level defect centers on the n-side of p+n junction diodes formed by low and elevated temperature aluminum-ion implantation into n-type 6H–SiC have been studied using deep-level transient spectroscopy. Two shallow Al-acceptor levels have been observed in the n region just beyond the implantation depth through their minority-carrier emission signatures. The dominant level is situated at 0.26 eV above the valence band and is accompanied by a shallower level of small intensity. Comparison with photoluminescence results suggests the dominant level (labeled Ak) and the shallower level (labeled Ah), are associated with the cubic and hexagonal lattice sites, respectively. Unlike previously reported results, which show many different implantation-induced donors within the implantation region, only one deep donor level at EC – 0.44 eV is found to occur in the postimplantation region, indicating that the various crystal damage sites occur with different spatial distributions. ©1998 American Institute of Physics.published_or_final_versio

Aluminum and electron-irradiation induced deep-levels in n-type and p-type 6H-SiC

Two deep levels, located at Ev+0.26eV and Ec-0.44eV, in Al-implanted n-type samples and one at Ev+0.48eV in p-type samples have been observed by the deep level transient spectroscopy. The level of Ev+0.26eV is identified as the shallower aluminum-acceptor. The 1.7 MeV electron-irradiation, used as a probe to distinguish the implantation induced deep-levels, induces at least six electron traps in the n-SiC and one hole-trap in the p-type material. The peak positions of these deep-levels in DLTS spectra are quite different from those induced by Al-implantation. This result suggests that various damages are formed after heavy ion (Al) and light particle (e') irradiation.published_or_final_versio

Study of microvoids in high-rate a-Si:H using positron annihilation

Theme: Amorphous and microcrystalline silicon technologyIn this paper, we have carried out the positron annihilation measurement on high-rate and low-rate a-Si;H thin films deposited by PECVD. By means of the slow positron beam Doppler-broadening technique, the depth profiles of microvoids in a-Si:H have been determined. We have also studied the vacancy-type defect in the surface region in high-rate grown a-Si:H, making comparison between high-rate and low-rate a-Si:H. By plotting S and W parameters in the (S, W) plane, we have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature.published_or_final_versio

Interface characterisation and internal electric field evaluation of a-Si:H pin solar cell by variable energy positron annhilation spectroscopy

Symposium Theme: Amorphous and microcrystalline silicon technologyBy means of the slow positron beam Doppler-broadening technique, the depth profile of microvoids across a p-i-n double junction solar cell has been resolved. VEPFIT fitting results indicate an approximately uniform density of the defects throughout the solar cell, but with an enhanced concentration at all of the interfaces possibly due to network mismatch. In order to evaluate the internal electric field, Variable Energy Positron Annihilation Spectroscopy (VEPAS) measurements have been performed on a single junction pin solar cell at different biases. The internal electric field effect on positrons has also been examined in terms of the bias dependence of positron drift in a-Si:H single junction pin solar cell.published_or_final_versio