Defects in zinc-implanted ZnO thin films

Abstract

Defects in zinc-implanted and thermally annealed ZnO thin films were investigated by means of capacitance-voltage spectroscopy (C-V), thermal admittance spectroscopy (TAS), deep level transient spectroscopy (DLTS), and photoluminescence (PL) spectroscopy. The authors report on the formation of two donor states approximately 35 and 190meV below the conduction band edge, observed by TAS and DLTS, respectively. In the PL spectra of a reference sample a peak at 3.366eV was present, which diminished after the implantation, while a new peak at 3.364eV was observed only in the spectrum of the implanted sample. Since only intrinsic ions were implanted, the authors consider the defects formed by the zinc implantation and annealing to be intrinsic.

On the T2 trap in zinc oxide thin films

“…This required samples with different T2 concentrations. The implantation of zinc ions generates T2 as we previously demonstrated [11]. In this report we showed a relation between the implantation profile of 250 keV zinc ions and the T2 profile.…”

“…In Table 1 E a and s 1 n of these levels are collected. Although E a ranges from 140 to 280 meV and s 1 n varies over more than three orders of magnitude, we are convinced that these levels are identical to a deep-level T2 which we previously found in zinc-implanted ZnO thin films [11]. A relation among these levels is supported by the fact that the published data pairs (E a , s The concentration of T2 in ZnO samples is often up to 10 16 cm À3 and does therefore significantly influence the electron concentration.…”

“…Also the implantation of zinc or copper ions, respectively, increased N T2 . In the case of the implantation of zinc ions we previously demonstrated [11] that the T2 concentration roughly follows the implantation profile of the zinc ions. The introduction of T2 by doping ZnO with copper was previously observed by Kanai [10] who attributed this level to copper on zinc lattice site, Cu Zn .…”

“…The knowledge on acceptor states in the vicinity of the valence band edge is scarce, see for example [13][14][15][16]. Junction capacitance techniques like deep-level transient spectroscopy (DLTS) [7,11,[15][16][17][18][19][20][21][22], deep-level optical spectroscopy (DLOS) [15], optical DLTS (ODLTS) [23] and photo-capacitance [16,22] have been used to study the properties of deep-levels in the zinc oxide band-gap. In doing so, knowledge on deep-levels was gained especially in the upper third of the zinc oxide band-gap.…”

“…A set of shallow donor levels with binding energies ranging from 10 to 100 meV has been detected by Hall effect measurements [1][2][3][4][5][6][7][8], admittance spectroscopy [7][8][9][10][11] and photo-luminescence spectroscopy [5,8,12]. ZnO is naturally n-type conducting and p-doping is still a challenge.…”