Electrical Properties and Microstructure of Transparent ZnO Contacts to GaN

Abstract

Transparent conducting ZnO contacts to GaN, of light transmittance >70% in the visible spectrum have been prepared by thermal oxidation of vacuum deposited zinc. For low-doped p-GaN the contact exhibits ohmic behaviour (1 Â 10 -2 W cm 2 ); on low-doped n-GaN a Schottky barrier (0.56 eV) is observed. We find the properties of ZnO contact promising for optoelectronic device applications.Introduction There is a consensus in the nitride community, that the lack of reliable p-type doping and p-type contacting procedures is hampering the development of GaNbased optoelectronics. Usually, bilayer Ni/Au [1] or Pt-based metallizations [2,3] are used to fabricate ohmic contacts for LEDs and laser diodes. To achieve optical transparency, metallization of a thickness reduced to 5-10 nm is applied, but at the expense of increased contact resistivity and reduced long-term stability. The growing interest is observed in the use of transparent conducting metal oxides (TCOs) for III-V semiconductors contacting purposes [4]. TCOs electro-optical properties are unique in nature in providing high optical transmittance in the visible range of wavelength as well as excellent electrical conductivity. TCO-based hole-injecting anodes are implemented in the majority of organic LEDs [5]. Work on TCO contacts to GaAs, InP and GaN focused on sputter deposited indium tin oxide (ITO) films. ITO as a contact to both p-type and n-type GaN exhibits non-linear behaviour [6]. However, ITO-contacted GaN-based LEDs showed uniform luminescence, indicating effective current-spreading and hole injection [7].In this paper we report on properties of an alternative TCO contact to GaN, namely zinc oxide. Similarly to GaN, ZnO is a wide direct gap semiconductor of wurtzite structure, with a very small mismatch to GaN lattice. This study is aimed at understanding the relation between the consecutive processing steps and the final optical, electrical and structural contact characteristics. Consequently, special attention is paid to the preparation of damage-and contamination-free GaN surface, prior to ZnO deposition. ZnO was formed by oxidation of vacuum deposited zinc.

Applications of ZnO:Al deposited by RF sputtering to InN low‐cost technology

“…For this purpose, the thickness of the layer was set to 180 nm, showing a resistivity of 2.0 × 10 −3 Ω cm. This value is in the range of those showed by other authors for contact to GaN 19.…”

ZnO/AlN Clad Waveguides for AlGaN-Based Quantum Cascade Lasers

“…The analysis above does not account for additional resistance due to effects of electron transport across the ZnO/AlGaN interface, where the conduction band offset varies between 0.7 eV (ZnO/GaN) 38) and 3 eV (ZnO/ AlN). 39) Measurements of the resistivity of n-type ZnO/ GaN 40) and ZnO/Al 0:15 Ga 0:85 N interfaces 41) suggest that a resistivity as low as 1 Â 10 À4 Ácm 2 can be achieved, which would translate into an additional resistance of only a few ohms. The insertion of highly doped thin layers at the interface may enable an even lower resistivity, although at the expense of a somewhat higher FCA loss.…”

50 Years of Compounds Semiconductors at the Institute of Electron Technology, Warsaw

“…• Copernicus '95, the subject of which were tunable GaInAsSb/AlGaAsSb DH laser diodes for environmental pollutions control [45] (iii) fabrication of metal/oxide multilayer structures for interferometric studies and SnO 2 and ZnO diffractive elements for nanostructured gas sensors [65][66][67][68]; (iv) novel approaches to the fabrication of ohmic contacts to GaN [69][70][71][72][73][74][75][76][77][78][79][80], e.g., n-type doping by creating nitrogen vacancies in the contact region of Ti-based metallizations [69], enhanced activation of the Mg acceptor to increase p-type doping of subcontact region of the ZrN/ZrB 2 ohmic contacts [70], nand p-type doping via solid phase regrowth (SPR) for the ohmic contacts to n-and p-GaN [71,72], engineering ZnO/GaN interface for the transparent ohmic contact to p-GaN [73,74], engineering electronic structure of p-GaN surface via appropriate surface preparation procedure [75], advanced refractory metal-based metallizations with enhanced antidiffusion capabilities [76][77][78][79][80]; (v) passivation of GaN-based heterostructures by a thin film of ZnO [81].…”