Surface traps in vapor-phase-grown bulk ZnO studied by deep level transient spectroscopy

Fang, Z-Q.; Claflin, B.; Dong, Yufeng; Mosbacker, H. L.; Brillson, L. J.

doi:10.1063/1.2978374

Cited by 25 publications

(31 citation statements)

References 29 publications

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“…19 DLTS of both Zn-and O-face diodes reveal two dominant traps, including the well-known bulk traps E 3 ͑0.27 eV͒ and E 4 ͑0.49͒. 20,21 However, a surface-related trap, E s ͑Ͻ ϳ 95 nm deep, 0.49 eV͒ for the Pd-/Zn-face SBDs, made on 1 h ROP-treated ZnO, was not observed on the SBDs in this study. Interestingly, preliminary DLTS results reveal that densities of the E 4 trap, consistent with the 2.5 eV emission, in the Au SBDs can be significantly influenced by the surface polarity, i.e., higher on the O face and lower on the Zn face.…”

Section: Figcontrasting

confidence: 57%

Zn- and O-face polarity effects at ZnO surfaces and metal interfaces

Dong

Fang

Look

et al. 2008

Applied Physics Letters

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Depth-resolved cathodoluminescence spectroscopy, current-voltage, capacitance-voltage, and deep level transient spectroscopy of ZnO (0001) Zn- and (0001¯) O-polar surfaces and metal interfaces show systematically higher Zn-face near band edge emission and lower near-surface defect emission. Even with remote plasma decreases of the 2.5 eV near-surface defect emission, (0001)-Zn face emission quality still exceeds that of (0001¯)-O face. Ultrahigh vacuum-deposited Au and Pd diodes on as-received and O2/He plasma-cleaned surfaces display a strong polarity dependence that correlates with defect emissions, traps, and interface chemistry. A comprehensive model accounts for the polarity-dependent transport properties and their correlations with carrier concentration profiles.

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Section: Figcontrasting

confidence: 57%

Zn- and O-face polarity effects at ZnO surfaces and metal interfaces

Dong

Fang

Look

et al. 2008

Applied Physics Letters

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“…For PdSCs on the Zn face, we see a similar behavior. For a 1 h ROP, a surface trap Es is observed, 4 while for a 2 h ROP, Es disappears, leaving a larger E3 peak and a very weak E4 trap ͑not shown͒. As reported previously, 4 Es ͑0.49 eV͒ is located at depths less than about 95 nm below the Pd/ ZnO interface and shows an electron capture behavior indicative of extended defects.…”

Section: Observation Of Surface Traps On Zn Facesupporting

confidence: 54%

“…For a 1 h ROP, a surface trap Es is observed, 4 while for a 2 h ROP, Es disappears, leaving a larger E3 peak and a very weak E4 trap ͑not shown͒. As reported previously, 4 Es ͑0.49 eV͒ is located at depths less than about 95 nm below the Pd/ ZnO interface and shows an electron capture behavior indicative of extended defects. Thus, from the comparisons presented above, we can conclude that a long ROP treatment is effective at removing extended-defect-related surface traps on the Zn face of ZnO.…”

Section: Observation Of Surface Traps On Zn Facesupporting

confidence: 54%

“…3,4 Electric-field-enhanced degradation was also observed on Pd-SCs on both O and Zn faces, with 2 h ROP treatment ͑not shown here͒. Degradation of the I-V characteristics, produced by exposure to high temperatures, for both Au-and Pd-SCs, was often found after DLTS measurements up to 400 K, as shown in Figs.…”

Section: A Rectification and Degradation Of The I-v Characteristicsmentioning

confidence: 76%

“…2,3 In addition to these optical studies, deep level transient spectroscopy ͑DLTS͒ has been used to observe a surface trap, Es ͑0.49 eV͒, in bulk vapor-phase ͑VP͒ grown ZnO, in addition to the well-known bulk traps E3 and E4. 4 In this work, we perform temperature-dependent I-V, C-V, DLTS, and photoluminescence ͑PL͒ measurements on thin metal/ZnO SCs and ZnO surfaces. We compare Au and Pd SCs, on both the Zn and O faces, as a function of the duration of ROP treatment.…”

Section: Introductionmentioning

confidence: 99%

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Metal contacts on bulk ZnO crystal treated with remote oxygen plasma

Fang

Claflin

Dong

et al. 2009

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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To study the quality of thin metal/ZnO Schottky contacts ͑SCs͒, temperature-dependent current-voltage ͑I-V͒, capacitance-voltage, deep level transient spectroscopy, and photoluminescence measurements were performed using bulk, vapor-phase ZnO, treated by remote oxygen plasma ͑ROP͒. Au/ ZnO and Pd/ ZnO contacts on both O and Zn faces are compared as a function of the ROP processing sequence and duration. We find that ͑i͒ as the duration of ROP treatment increases from 2 to 4 h, Au/ ZnO contacts on the Zn face, deposited before ROP treatment, become rectifying, while those on the O face remain Ohmic; ͑ii͒ with long-term ROP treatments prior to metallization, both Au/ ZnO and Pd/ ZnO show high-quality SCs; however, their I-V characteristics can be significantly degraded by electric field and high temperatures; ͑iii͒ ROP treatment can cause more H removal on the Zn face than on the O face, resulting in a decrease in the near-surface carrier concentration for the Zn face only; ͑iv͒ in addition to the dominant bulk-trap E3, surface traps, E6/E7 and E8, and Es, can be observed in Au/ ZnO and Pd/ ZnO SCs, respectively, on the Zn face, with shorter ROP treatment; and ͑v͒ with long-term ROP treatment, E3 ͑or L2͒ significantly increases and shifts in Au/ ZnO SCs on the Zn face.

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ZnO Surface Properties and Schottky Contacts

Brillson

2011

Zinc Oxide Materials for Electronic and Optoelectronic Device Applications

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With the development of exciting new optoelectronic and microelectronic device applications for ZnO, there is now renewed interest in the understanding and control of its electrical contact properties. Transparent thin film transistors, blue/UV light-emitting diodes (LEDs) and lasers, high electron mobility transistors, electronic nanostructures, and spintronics all require metal contacts and an understanding of metal-ZnO interfaces and processing techniques. Historically, there has been considerable research devoted to the surface physics and chemistry of ZnO, in large part due to the strong effect that surface and polarity have on ZnO interface charge transfer. This chapter will examine the results of surface and interface research produced over the past fifty years in the context of Schottky barriers.The challenge of ZnO surfaces and interfaces is evident from the wide and variable range of Schottky barriers measured for the same metal on the ZnO surface. In the case of Au/ZnO diodes, Schottky barrier heights F SB can range from 0 to 1.2 eV, depending on the experimental conditions. Similarly wide n-type F n SB energy ranges are observed for Pt/ ZnO and Ta/ZnO diodes. Furthermore, high work function metals exhibit lower than expected F n SB . Since the ZnO electron affinity x ZnO ¼ $4.2 eV, F n SB should be F M Àx ZnO ¼ 5.65À4.2 ¼ 1.45 eV for Pt, whereas measured F SB are limited to 0.96 eV for air-exposed surfaces and 0.75 eV for high vacuum-cleaved surfaces. Wide barrier variations are evident for Zinc Oxide Materials for Electronic and Optoelectronic Device Applications, First Edition. Edited by Cole W. Litton, Donald C. Reynolds and Thomas C. Collins.

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Surface traps in vapor-phase-grown bulk ZnO studied by deep level transient spectroscopy

Cited by 25 publications

References 29 publications

Zn- and O-face polarity effects at ZnO surfaces and metal interfaces

Zn- and O-face polarity effects at ZnO surfaces and metal interfaces

Metal contacts on bulk ZnO crystal treated with remote oxygen plasma

ZnO Surface Properties and Schottky Contacts

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