Two series of SnO thin films, one doped with N and one doped with H, were deposited on c-plane sapphire by reactive ion beam sputter deposition starting from growth parameters optimized for stoichiometric SnO. The amounts of dopants incorporated into the SnO:H and SnO:N samples were quantified by secondary ion mass spectroscopy. The influence on the structural and electrical properties of SnO thin films was studied as a function of dopant concentration. In the case of N doping, all N incorporated, probably as NO, are active as the acceptor and exhibit long-term stability. We assign an acceptor activation energy of 100 to 150 meV to NO. However, we observe a change in the film morphology at a critical N concentration of about 7⋅1017cm−3, which deteriorates the structural properties of the films. In the case of SnO:H, the situation is different. We observe an outdiffusion of H after growth, i.e., the samples are not stable in the long term. Nevertheless, all H incorporated up to a H-content of 1019cm−3 seem to be electrically active and exhibit an activation energy between 150 and 250 meV, likely corresponding to Hi. Furthermore, at H contents above 1019cm−3, we observe molecular H2 inside the SnO:H thin films. We conclude that N doping of SnO is better suited for tuning the p-type conductivity of SnO. However, it will be essential to overcome the morphology change observed at the critical N concentration to fully explore the tunability of the p-type conductivity in device applications.

ZnO crystals grown by the vertical Bridgman technique were comprehensively characterized in view of the impurities and intrinsic defects in the material. It is shown that residual Al is the cause of the residual n-type conductivity and intrinsic defects play only a minor role in the samples. Annealing the samples at 1100 degrees C for 1 h in oxygen atmosphere improves the surface properties of the samples without having negative effects on their optical and electrical properties. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

physica status solidi (a)Volume 208, Issue 1 p. 11-15 ContentsFree Access Contents: (Phys. Status Solidi A 1/2011) First published: 12 January 2011 https://doi.org/10.1002/pssa.201121802AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume208, Issue1January 2011Pages 11-15 RelatedInformation

As-doping of zinc oxide has been approached by ion implantation and chemical vapor deposition. The effect of thermal annealing on the implanted samples has been investigated by using secondary ion mass spectrometry and Rutherford backscattering∕channeling geometry. The crystal damage, the distribution of the arsenic, the diffusion of impurities, and the formation of secondary phases is discussed. For the thin films grown by vapor deposition, the composition has been determined with regard to the growth parameters. The bonding state of arsenic was investigated for both series of samples using x-ray photoelectron spectroscopy.

In order to promote growth of ZnO films on ZnO substrates, defects introduced by the surface polishing procedure have to be removed. We investigate the influence of high temperature annealing in O-2-atmosphere on the structural properties of the ZnO substrates by atomic force microscopy. Only at temperatures above 1100 degrees C atomic steps (terraces) are seen, the remaining defects can be assigned to dislocations in a density between 10(4) to 10(5) cm(-2). Interestingly the electrical properties also change from high resistive to n-type conduction, which make the substrates - apart for the homoepitaxial growth on a perfect template suitable for top-to-bottom contacts. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report on the hetero- and homoepitaxial growth of ZnO thin films by the chemical vapor deposition technique. We compare the results obtained on sapphire substrates, on GaN-templates on sapphire substrates and on silicon (111) substrates. Even under optimized growth conditions with the insertion of buffer layers the films tend to grow 3-dimensionally. However, also ZnO substrates, expected to be the best choice, need to be prepared before being used in the epitaxial growth. After mechanical polishing of the ZnO substrates we employed a high temperature annealing step which produced atomically flat surfaces and removed all of the surface and subsurface damage. Thereafter, the two dimensional epitaxial growth was achieved without an additional buffer layer. The substrate had a rocking curve full width at half maximum of 27" which can be compared with that of the film of 22". The films had superior band edge luminescence as compared to the substrate for which the green luminescence band was dominating.

The authors investigate the influence of a high temperature annealing in O2 atmosphere on the structural properties of ZnO substrates. Only at temperatures above 1100°C are atomic step heights and terraces seen by atomic force microscopy. The structural properties of the substrates were determined from the full width at half maximum (FWHM) of the rocking curve of the (0002) reflection. The FWHM is between 28 and 33arcsec for different substrates cut from one ingot but does not change with the annealing. The electrical properties, however, change from highly resistive to n-type conductive, which makes the substrates suitable for top-to-bottom contacting.

We report on the homoepitaxial growth of ZnO thin films by chemical vapor deposition techniques. The preparation of the ZnO substrates after mechanical polishing employed a high temperature annealing step which produced atomically flat surfaces and removed all of the surface and subsurface damage. Two dimensional epitaxial growth was achieved without an additional buffer layer. The substrate had a rocking curve with a full width at half maximum of 27″ which can be compared with that of the film of 17″. The films had superior band edge luminescence as compared with the substrate for which the green luminescence band is dominating. The impurity content in the substrates especially Li is reduced by the high temperature annealing step and drops further close to the detection limit in the films. The low substrate temperatures around 660 °C allow for the incorporation of nitrogen on oxygen site as a shallow acceptor. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The shallow donor impurities in ZnO with binding energies between 46 and 56 meV have been studied in great detail in the recent years. They give rise to neutral donor bound exciton recombinations with the A- and B-valence bands, show rotator states and two-electron-satellite transitions. These properties allowed to establish the excited state splittings of the donors as well as confirming Hayne's rule in ZnO. So far they all seem to be of extrinsic origin, hydrogen, aluminum, gallium and indium in order of increasing binding energy. For many years it was common sense that intrinsic defects would dominate the n-type conductivity of ZnO. Interstitial zinc as well as oxygen vacancies should be double donors, and in order to contribute to the n-type-conduction they should have shallow levels, and low formation energies to be abundant. In PL-measurements at T∼100 K on various ZnO samples, single crystals as well as thin films, a luminescence around 3.31 eV was detected. Due to its line shape and temperature behaviour it is identified as bound-to-free recombination. If we assume that the 3.31 eV band with its level at EC ∼ 130 meV is the ++/+ level of the zinc interstitial we calculate for the binding energy of the +/0 level ∼ 130 meV, i.e. around 33 meV. Undoped Zn-rich epitaxial films grown by CVD show a dominant I 3 recombination at 3.367 eV which according to Haynes rule is consistent with a shallow donor level at 33 meV. Moreover, they have free n-type carrier densities of 2×10 19 cm −3 and as revealed by SIMS the common donor impurities (Al, Ga, In) cannot account for the high carrier densities.

For the homoepitaxial growth of ZnO it is inevitable to obtain a regular crystalline single crystal surface prior to growth. Commercially available, hydrothermally grown ZnO single crystals show amorphous surfaces due to mechanical cutting and polishing. Here we present the results of a thermal treatment on these ZnO single crystals. After annealing, a regular crystalline oxygen terminated surface can be obtained. Changes in surface roughness, residual defect concentration and electrical properties can be shown. The bulk crystallinity though was not affected.