Direct evidence for Sb as a Zn site impurity in ZnO

Abstract

The lattice location of ion implanted antimony in zinc oxide has been determined by means of β − emission channeling from the radioactive 124 Sb isotope. Following 30 keV implantation of 124 Sb into a single-crystalline ZnO sample to a fluence of 1×10 14 cm −2 , the angular-dependent emission rate of β − particles around several crystallographic directions was measured with a position-sensitive Si detector. The majority of Sb was found to occupy Zn sites, with the possible fraction on O sites being at maximum 5-6%. To date, the group V element antimony is one of the elements which have been used as p-type dopants in the II-VI semiconductor zinc oxide, the others being N, P and As (cf. Ref.[1] and Refs. therein). In the case of Sb, following the report of Sb-doped p-type ZnO by Aoki et al in 2002 [2] and further work by other authors [3][4][5][6], recently the realization of a wide range of optoelectronic devices incorporating pZnO:Sb layers have been reported, including homo-and heterojunction photodiodes [7][8], ultraviolet (UV) light emitting diodes (LEDs) [9][10][11][12], and UV lasers [13].While technological applications of p-type ZnO seem thus to have come within reach, the nature of the acceptors in P, As or Sb-doped ZnO continues to be disputed in the literature. From a simple viewpoint of chemical bonding, the substitution of O 2− cations in ZnO by P 3− , As 3− or Sb 3− should create fully ionized acceptors. However, due to the large mismatch of the ionic radii of P 3− (2.12 Å), As 3− (2.22 Å) and Sb 3− (2.45 Å) with the ionic radius of O 2− (1.38 Å) it was argued that those impurities should have a low solubility substituting for O [14]. Moreover, theory suggests that the energy levels of P, As and Sb replacing O are located deep in the band gap of ZnO [15][16]. In order to explain the p-type character of ZnO following As and Sb doping it was suggested that the acceptor action is actually due to As Zn -2V Zn or Sb Zn -2V Zn complexes, where an As or Sb atom occupies a Zn "anti-site" and is decorated with two Zn vacancies [16][17][18][19]. However, a complex acceptor model for P, As or Sb in ZnO is strongly disputed by some authors [20][21][22][23][24].Obviously knowledge on the lattice location of the group V elements in ZnO is crucial in order to assess the related mechanism of p-type doping. We have previously determined the lattice sites of ion implanted As by means of conversion electron emission channeling from radioactive 73 As [25][26][27] and found that As does not occupy substitutional O sites but mostly substitutional Zn sites. In this work we report on the lattice location of ion implanted radioactive 124 Sb (t 1/2 = 60.3 d) using β − emission channeling and we present direct experimental evidence that Sb preferentially occupies Zn sites. Emission channeling [28] is based on the fact that charged particles from nuclear decay (α, β − , β + , conversion electrons) experience channeling or blocking effects along major crystallographic axes and planes. The resulting anisotropic emission yield p...

Stable interstitial dopant–vacancy complexes in ZnO

“…Their presence is supported by a low calculated formation energy and agreement of their calculated transition levels with levels identified in experiments 2-10 , which range from 0.09 to 0.34 eV above the valence band maximum (VBM). In addition, D Zn -2V Zn complexes are consistent with experimental evidence that implanted As and Sb incorporate on Zn sites 11,12 . Furthermore, p-type conductivity emerging from these complexes is consistent with the need for O-rich growth or annealing conditions to create p-type samples, as these defects are stabilized by high oxygen partial pressures.…”

Precise lattice location of substitutional and interstitial Mg in AlN

“…Manybeam calculations were performed for a number of discrete electron energies which were then averaged according to the continuous β − spectrum of 27 Mg (average β energy 703 keV, endpoint energy 1767 keV) as described in Ref. 30. Some of the sites which were considered as possible impurity positions in GaN have been previously described 31 and the whole set is shown in a figure included in the supplemental material to this article.…”

Materials science and biophysics applications at the ISOLDE radioactive ion beam facility

“…During the last five years the EC experiments focused on the lattice location of dopants and impurities in Si [28][29], ZnO [30][31][32][33], GaN [34][35], AlN [36] and, most recently, also in Ge. In Ge, besides the preferred substitutional sites, up to now the following impurities were found to occupy the so-called bond-center (BC) site: Er [37], In [38], the transition metals Fe, Cu and Ag [39], and Sn [40].…”