ZnO Schottky barriers and Ohmic contacts

Brillson, Leonard J.; Lu, Yicheng

doi:doi:10.1063/1.3581173

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Bright up-conversion green photoluminescence in Ho³⁺-Yb³⁺ co-doped Bi₄Ti₃O₁₂ ferroelectric thin films

Ho3+-Yb3+ co-doped bismuth titanate ferroelectric thin films were prepared by a chemical solution deposition method on fused silica substrates and their up-conversion luminescence characteristics excited by a 980 nm diode laser were investigated. The two emission bands centered at 546 and 656 nm in the emission spectra can be assigned to 5F4 + 5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+ ions, respectively. A bright green emission was observed even when the laser pumping power was relatively low...

ZnO has emerged as a promising candidate for optoelectronic and microelectronic applications, whose development requires greater understanding and control of their electronic contacts. The rapid pace of ZnO research over the past decade has yielded considerable new information on the nature of ZnO interfaces with metals. Work on ZnO contacts over the past decade has now been carried out on high quality material, nearly free from complicating factors such as impurities, morphological and native point defects. Based on the high quality bulk and thin film crystals now available, ZnO exhibits a range of systematic interface electronic structure that can be understood at the atomic scale. Here we provide a comprehensive review of Schottky barrier and ohmic contacts including work extending over the past half century. For Schottky barriers, these results span the nature of ZnO surface charge transfer, the roles of surface cleaning, crystal quality, chemical interactions, and defect formation. For ohmic contacts, these studies encompass the nature of metal-specific interactions, the role of annealing, multilayered contacts, alloyed contacts, metallization schemes for state-of-the-art contacts, and their application to n-type versus p-type ZnO. Both ZnO Schottky barriers and ohmic contacts show a wide range of phenomena and electronic behavior, which can all be directly tied to chemical and structural changes on an atomic scale.

Article Outline

INTRODUCTION
TECHNICAL BACKGROUND
1. Schottky barriers
2. Ohmic contacts
EMERGING ZnO ELECTRONICS NEEDS
1. Schottky barrier contacts
2. Ohmic contacts
ZnO SURFACE EFFECTS
METAL-ZNO SCHOTTKY BARRIERS
1. Early contact studies
2. Surface cleaning effects
  1. Effects in vacuum
  2. Effects of impurities and defects
  3. Effects on Schottky barriers
    1. Crystal quality
    2. Surface treatment
    3. Measurement technique
3. Crystal quality and surface effects
  1. Crystal defect variations
  2. Electronic effects of crystal defects and impurities
  3. Morphology effects
  4. Polarity effects
4. Chemical effects on ZnO Schottky barriers
  1. Metal dependence of interface chemistry
  2. Interface chemistry and defect formation
  3. Defect formation and Schottky barriers
5. Complementary Schottky barrier mechanisms
OHMIC CONTACTS TO ZnO
1. Background of ohmic contacts to ZnO
2. Nonalloyed ohmic contacts to n -type ZnO
  1. Metallization schemes for nonalloyed ohmic contacts
    1. In-ZnO:
    2. Ti-ZnO:
    3. Al-ZnO:
    4. Al-Ti-ZnO:
    5. Pt-Ga-ZnO:
  2. Nonalloyed ohmic contacts to ZnO nanostructures
3. Alloyed ohmic contacts to n -type ZnO
  1. Single layer metallization schemes
  2. Double layer metallization schemes
  3. Multi-layer metallization schemes
4. Alloyed ohmic contacts to p -ZnO
  1. Single layer metallization schemes
  2. Double layer metallization schemes
  3. Multilayer metallization schemes
  4. Ohmic contacts to ZnO alloys
CONCLUSIONS

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KEYWORDS and PACS

Keywords

annealing, II-VI semiconductors, metallisation, ohmic contacts, Schottky barriers, semiconductor-metal boundaries, surface cleaning, surface conductivity, wide band gap semiconductors, zinc compounds

PACS

73.40.Ns

Metal-nonmetal contacts
73.30.+y

Surface double layers, Schottky barriers, and work functions
81.65.Cf

Surface cleaning, etching, patterning
61.72.Cc

Kinetics of defect formation and annealing
85.40.Ls

Metallization, contacts, interconnects; device isolation
73.25.+i

Surface conductivity and carrier phenomena

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3581173

PUBLICATION DATA

ISSN

0021-8979 (print)

1089-7550 (online)

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$abstract.society.value is a Member of CrossRef

American Institute of Physics

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