Shallow carrier traps in hydrothermal ZnO crystals

Abstract

Native and hydrogen-plasma induced shallow traps in hydrothermally grown ZnO crystals have been investigated by charge-based deep level transient spectroscopy, photoluminescence and cathodoluminescence microanalysis. The as-grown ZnO exhibits a trap state at 23 meV, while H-doped ZnO produced by plasma doping shows two levels at 22 meV and 11 meV below the conduction band. As-grown ZnO displays the expected thermal decay of bound excitons with increasing temperature from 7 K, while we observed an anomalous behaviour of the excitonic emission in H-doped ZnO, in which its intensity increases with increasing temperature in the range 140-300 K. Based on a multitude of optical results, a qualitative model is developed which explains the Y line structural defects, which act as an electron trap with an activation energy of 11 meV, being responsible for the anomalous temperature-dependent cathodoluminescence of H-doped ZnO. 2 1 2 1 . For electrons, the gate timed charge difference is [22, 23]: 2 New J. Phys. 16 (2014) 083040 C Ton-That et al

Enhanced wetting of Cu on ZnO by migration of subsurface oxygen vacancies

“…Although a number of different surface reconstructions on the ZnO(0001) surface were revealed by low-energy electron diffraction (see ref. 16 and references therein), the structure was never, to the best of our knowledge, resolved atomically by STM, possibly because of the relatively poor conductivity of ZnO (refs 39 , 40 ). The most commonly observed morphology of ZnO(0001) consists of a large number of variable-size triangular terraces (presumably (1 × 1) terminated 11 ) and a significantly smaller number of triangular pits with O-terminated step edges as first reported by Dulub et al .…”

Deep levels and acceptors in Zn(Mg)O: effect of N-doping

“…The origin for this defect can be consistent with the level observed by Q-DLTS by Ton-That et al [137], which was related with the presence of H. Indeed, as it was indicated during chapter 1, shallow donors have been observed by different techniques, some of them related to H, which despite not being present during growth, can easily diffuse into the material later after exposure to the ambient.…”

“…This technique was specifically designed to measure shallow defects. H-doped crystals show a splitting of the level in two at 22 meV and 11 meV [137].…”

“…For example, Auret et al [7] report levels at 31 and 64 meV, the latter assigned to the Al Zn impurity. The most extended report is that from Ton-That et al [137] that shows a very shallow donor at only 23 meV from the CBM in as-grown ZnO, measured using charge-DLTS (Q-DLTS). This technique was specifically designed to measure shallow defects.…”

Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods

“…Theoretically, the anionic surface can give greater barrier heights on polar surfaces, and first-principles calculations by D’Amico et al predict the O-polar interfaces to have a larger 0.7 eV barrier height with Au than the 0.3 eV at the Zn-polar interface. , The metal contacts formed here on as-grown polar facets were treated only with oxygen plasma and as such can be expected to have a surface structure close to that of free and reconstructed polar ZnO with a mix of terminating O or Zn atoms and not epitaxial with the Au. Furthermore, numerous techniques have identified a range of deep and shallow traps in ZnO that are inherent from the growth process or they can be introduced by plasma exposure, although not all of these are electrically active at 300 K . Predominantly, carrier traps are assigned to various defects such as V O , V Zn , Zn interstitials, and divacancies of ZnO, with V O being the most common that can act as a trap for both electrons and holes. , Electrically active defects located in the depletion region may appear in the transport measurements identified as the splitting of the I – V trace seen in some of the contacts (Figure d) particularly in reverse bias.…”