Effect of Si doping on electrical and optical properties of ZnO thin films grown by sequential pulsed laser deposition

Abstract

The sequential pulsed laser deposition technique was used to grow highly transparent and c-axis oriented thin films of Si doped ZnO on sapphire substrates. On doping with Si, the resistivity of the virgin ZnO thin films was found to decrease from ∼3.0 × 10−2 to 6.2 × 10−4 Ω cm and its bandgap increased from about 3.28 to 3.44 eV at different doping concentrations. XPES measurements revealed that Si predominantly occupies the Zn lattice sites in the Si+3 state. The increase in the bandgap of the ZnO films with increasing Si concentration was found to be due to the collective effects of high carrier concentration induced Burstein–Moss blue shift and bandgap narrowing. Efficient photoluminescence (PL) was observed at room temperature from these Si doped ZnO films. The bandgaps obtained from the PL measurements were found to be Stokes shifted as compared with those obtained from the transmission spectra. Si doping of ZnO offers the possibility of developing superior transparent conducting electrodes for applications such as in display panels, solar cells and transparent resistive non-volatile memories.

Enhancement in UV emission and band gap by Fe doping in ZnO thin films

“…% doping). [9] In the light of the above discussion, it can be inferred that sp hybridization is responsible for the increase in the band gap of Fe doped ZnO with increase in dopant concen− tration in the present paper.…”

“…Intercept on the energy axis obtained by extrapolating the linear portion of the Tauc's plot, i.e., (ahv) 2 vs. hv plot, as shown in carrier concentration had been found to increase viz. Fe 3+ doped ZnO by Xu et al [20], Al doped ZnO by Shukla et al [1] and Das et al [9]. For Mg doped ZnO band gap enhance− ment is well known but reason is hardly reported.…”

“…Ca and Sr doped ZnO has also been reported as Love wave sensor [8]. Aluminium and Indium, valency three metals, have also been doped which respectively enhances [1,9] and decreases [10] the band gap of ZnO, as well as enhance its electrical conductivity by nearly two orders thus rendering ZnO a good candidate for transparent electronics. Rare−earths like Ce, Nd, etc.…”

Extraction of the sub-band gap density of states of Nb doped ZnO thin film transistors using C-V measurements

“…For a negative bias, an accumulation layer is induced at the oxide-Si interface and the ZnO:Nb is depleted; the opposite occurs for a positive bias. Large frequency dispersion is evident for the region of accumulation in the ZnO:Nb film (V N 0) and is attributed to capture-emission events occurring in the bulk of the disordered ZnO:Nb film, at the interface with the oxide together with a contribution from series resistance [6]. The bulk response is represented by effective localized (Q loc ) and free carrier (Q free ) states associated with the ZnO film which is considered to dominate the response.…”

“…The carrier concentration in ZnO is highly dependent on the deposition technique and conditions [3]. Another alternative approach is to add dopants such as Ga and In [4,5], Si [6] or as demonstrated in our previous work, Nb [7] and Mg [8]. The subband gap density of states (DOS), g(E), is a key parameter for characterizing ZnO films and a number of techniques have been reported for their extraction.…”