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- 1. Physica B 401, 250 (2007) , Elsevier , “Doubly charged state of EL2 defect in MOCVD-grown GaAs ”, Nazir A. Naz, Umar S. Qurashi, Abdul Majid and M. Zafar IqbalEL2 is the ubiquitous native defect in crystalline GaAs grown by a variety of different techniques. It has been proposed to be a doubly charged deep-level center with two states having distinct energy levels in the band gap. While the singly charged state has been the subject of many experimental studies and is, therefore, well established, the doubly charged state has only been occasionally alluded to in the literature. This paper provides evidence for a dominant inadvertent deep level in p-type GaAs most likely to be the doubly charged state of the EL2 center. Deep-level transient spectroscopy (DLTS) has been applied to characterize epitaxial layers of p-type GaAs grown on p+ GaAs substrates by low-pressure metal organic chemical vapor deposition (LP-MOCVD). A pronounced peak is observed in the majority carrier (hole) emission deep-level spectra. Thermal emission rate of holes from the corresponding deep level is found to exhibit a strong electric field dependence, showing an increase of more than two orders of magnitude with an increase of the electric field by a factor of~2. The thermal activation energy for this level is found to vary from 0.29 to 0.61 eV as the electric field is varied from 2.8×105 to 1.4×105 V/cm. Direct pulse-filling measurements point to a temperature-dependent behavior of the hole capture cross section of this level. We identify this inadvertent deep-level defect, commonly observed in p-type AsGa grown by a variety of different methods, with the doubly charged state of the well-known AsGa antisite related defect, EL2. (Read more)
- 2. Advances in Science and Technology 46, 73 (2006) , Trans Tech Publications, Switzerland , “Electric-Field-Enhanced Thermal Emission from Osmium-Related”, M. Zafar Iqbal, A. Majid, A. Dadgar and D. BimbergDeep-level defects related with 5d transition metal, osmium (Os) have been studied in ntype GaAs. Os has been incorporated in epitaxial n-GaAs layers in situ, during growth by lowpressure metal-organic chemical vapour phase epitaxy (MOVPE) technique. Mesa p+nn+ junction diodes are fabricated for investigations by deep level transient spectroscopy (DLTS). Two deeplevel peaks, observed in majority carrier (electron) emission spectra, Os1 and Os2, show a significant shift in peak positions to lower temperatures with the applied junction reverse bias, demonstrating enhancement of the thermal emission rate by the junction electric field. Doublecorrelation DLTS (DDLTS) measurements have been employed for accurate quantitative investigations of the observed field dependence. However, in view of the relatively small concentration of the deep level Os1, this technique is found to yield reliable data only for the deep level corresponding to the dominant peak, Os2. Detailed data have been obtained on the field effect for Os2, extending over junction electric field values 3 x 106 V/m - 1.2 x 107 V/m. The measured emission rate signatures show a reduction of the thermal activation energy from 0.48 eV to 0.21 eV for Os2 over this electric field range. Analysis of the data in terms of the recent theoretical work on field dependence indicates that Os2 is associated with a substitutional Os donor. (Read more)
- 3. J. Appl. Phys. 100, 034503 (2006) , “Deep level defects in proton radiated GaAs grown on metamorphic SiGe/Si substrates”, M. González, C. L. Andre, R. J. Walters, S. R. Messenger, J. H. Warner, J. R. Lorentzen, A. J. Pitera, E. A. Fitzgerald, and S. A. RingelThe effect of 2 MeV proton radiation on the introduction of deep levels in GaAs grown on compositionally graded SiGe/Si substrates was investigated using deep level transient spectroscopy (DLTS). Systematic comparisons were made with identical layers grown on both GaAs and Ge substrates to directly... (Read more)
- 4. AIP Conf. Proc. 772, 147 (2005) , American Institute of Physics , “Deep levels in osmium doped p-type GaAs grown by metal organic chemical vapor deposition”, M. Zafar Iqbal, A. Majid, A. Dadgar, and D. BimbergResults of a preliminary study on deep level transient spectroscopy (DLTS) investigations of osmium (Os) impurity in p-type GaAs, introduced in situ during MOCVD crystal growth, are reported for the first time. Os is clearly shown to introduce two prominent deep levels in the lower half-bandgap of GaAs at energy positions Ev + 0.42 eV (OsA) and Ev + 0.72 eV (OsB). A minority-carrier emitting defect feature observed in the upper half-bandgap is shown to consist of a band of Os-related deep levels with a concentration significantly higher than that of the majority carrier emitting deep levels. Detailed data on the emission rate signatures and related parameters of the Os-related deep levels are reported. ©2005 American Institute of Physics (Read more)
- 5. AIP Conf. Proc. 772, 143 (2005) , American Institute of Physics , “Deep levels in Ruthenium doped p-type MOCVD GaAs”, A. Majid, M. Zafar Iqbal, A. Dadgar, and D. BimbergRuthenium is introduced into GaAs during epitaxial growth by MOCVD. Preliminary results of DLTS investigation of the defect states associated with this 4d transition-metal impurity are reported for the first time. At least three deep levels are identified with Ru in the lower half-bandgap of GaAs at energy positions Ev + 0.38 eV, Ev + 0.52 eV and Ev + 0.65 eV, the last with a relatively higher concentration than the first two. At least one Ru-related deep level is observed in the upper half-bandgap at Ec – 0.66 eV with a significantly high concentration. Emission rate signatures and associated characteristics of all these defect levels are reported. The Ev + 0.65 eV level is found to exhibit an electric field dependent thermal emission characteristic. ©2005 American Institute of Physics (Read more)
- 6. J. Appl. Phys. 98, 083709 (2005) , American Institute of Physics , “Osmium impurity-related deep levels in n-type GaAs”, A. Majid, M. Zafar Iqbal, A. Dadgar and D. BimbergThe 5d transition-metal impurity, osmium, has been incorporated during the growth of n-type GaAs epitaxial layers using low-pressure metal-organic chemical-vapor deposition to characterize defect states associated with this heavy and, therefore, thermally stable dopant impurity.... (Read more)
- 7. J. Appl. Phys. 94, 3115 (2003) , American Institute of Physics , “Characteristics of deep levels associated with rhodium impurity in n-type GaAs”, M. Zafar Iqbal, A. Majid, Shah Haidar Khan, Akbar Ali, Nasim Zafar, A. Dadgar and D. Bimberg.,Deep levels have been characterized in n-type GaAs crystalline films grown by metalorganic chemical vapor deposition, doped in situ with 4d transition metal, rhodium, using the deep level transient spectroscopy (DLTS) technique. Two prominent broad bands of deep levels are found... (Read more)
- 8. Physica B 340, 362 (2003) , Elsevier , “Deep levels in rhodium-doped p-type MOCVD GaAs ”, A. Majid, M. Zafar Iqbal, A. Dadgar, D. Bimbergp-type GaAs epilayers grown by metal-organic chemical vapour deposition (MOCVD) technique, doped in situ with rhodium (Rh) impurity, have been studied by deep level transient spectroscopy (DLTS). A composite peak consisting of emission signals from at least two deep levels in the lower-half band gap is identified with Rh. This peak is resolved using double-correlation DLTS (DDLTS) measurements, providing the clear energy positions of the Rh-related deep levels as Ev+0.35 eV and Ev+0.51 eV. Emission rate signatures and other parameters are reported for these deep levels. They are observed to show electric-field dependent emission signatures. No significant minority carrier (electron) deep level could be clearly identified with Rh due to the presence of significant inadvertent features in the injection DLTS spectrum. Results are compared with our earlier study of Rh-doped, n-type, MOCVD GaAs. (Read more)
- 9. Physica B 340, 358 (2003) , “Osmium related deep levels in n-type GaAs ”, M. Zafar Iqbal, A. Majid, A. Dadgar, D. BimbergDeep levels due to 5d transition metal, osmium (Os), in n-type GaAs epitaxial layers grown by metal-organic vapour-phase epitaxy are investigated using deep level transient spectroscopy (DLTS). Two clear and prominent peaks are observed in majority carrier (electron) emission spectra in GaAs:Os samples in addition to a weaker, broad feature at higher temperatures, which are absent in the Os-free, reference samples. The well-resolved, prominent peaks are attributed to deep levels associated with Os impurity having activation energies Ec−0.28 eV and Ec−0.41 eV at a junction electric field of not, vert, similar1.4×105 V/cm. Both of these peaks are found to be field dependent. Detailed data on emission rate signatures, apparent electron capture cross-sections and defect concentrations are reported for these levels. No Os-related deep level peaks could be clearly delineated in minority-carrier injection DLTS, at this stage, although some evidence is found for a low-energy deep level band. (Read more)
- 10. Physica B 308, 816 (2001) , Elsevier Science , “Rhodium-related deep levels in n-type MOCVD GaAs ”, M. Zafar Iqbal, A. Majid, S. Haidar Khan, Akbar Ali, Nasim Zafar, A. Dadgar and D. BimbergPreliminary results on the study of deep levels associated with 4d-transition metal, rhodium, in crystalline GaAs grown by metal-organic chemical vapour deposition (MOCVD) technique are reported for the first time. Deep level transient spectroscopy on n-type GaAs doped in situ with Rh during MOCVD growth reveals a broad majority carrier emission peak. The peak corresponds to a band of deep levels extending over the energy range 0.57–0.65 eV below the conduction band edge with lower-energy states having lower electron capture cross-sections. The deep levels show a pronounced dependence of electron emission rate on the junction electric field. Minority carrier (hole) emission spectra at zero bias show a pronounced Rh-related deep-level peak with a low-temperature shoulder. The dominant level in the lower half-gap is found to have a position Ev+0.44 eV, with a field-dependent emission rate signature. (Read more)
- 11. Jpn. J. Appl. Phys. 37, 1939-1944 (1999) , “Role of the EL2 Center on the Formation of Metastable Hydrogen-related Defects (M3/M4) in n-GaAs”, T. Shinagawa, T. OkumuraHydrogen-related metastable defects (M3/M4) in n-GaAs were studied in relation to the EL2 center. We found that the M3/M4 defects were observed only in the crystals containing the EL2 center in the as-grown state after exposure to a hydrogen plasma. The EL3 level, which was tentatively assigned as... (Read more)
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