A comparative study of the electrical properties of Pd/ZnO Schottky contacts fabricated using electron beam deposition and resistive/thermal evaporation techniques

Abstract

A systematic investigation to check the quality of Pd Schottky contacts deposited on ZnO has been performed on electron beam (e-beam) deposited and resistively/thermally evaporated samples using current-voltage, IV, and conventional deep level transient spectroscopy (DLTS) measurements. Room temperature IV measurements reveal the dominance of pure thermionic emission on the resistively evaporated contacts, while the e-beam deposited contacts show the dominance of generation recombination at low voltages, <0.30 V, and the dominance of pure thermionic emission at high voltages, greater than 0.30 V. The resistively evaporated contacts have very low reverse currents of the order of 10 À10 A at a reverse voltage of 1.0 V whereas the e-beam deposited contacts have reverse currents of the order of 10 À6 A at 1.0 V. Average ideality factors have been determined as (1.43 6 0.01) and (1.66 6 0.02) for the resistively evaporated contacts and e-beam deposited contacts, respectively. The IV barrier heights have been calculated as (0.721 6 0.002) eV and (0.624 6 0.005) eV for the resistively evaporated and e-beam deposited contacts, respectively. Conventional DLTS measurements reveal the presence of three prominent defects in both the resistive and e-beam contacts. Two extra peaks with energy levels of 0.60 and 0.81 eV below the conduction band minimum have been observed in the e-beam deposited contacts. These have been explained as contributing to the generation recombination current that dominates at low voltages and high leakage currents. Based on the reverse current at 1.0 V, the degree of rectification, the dominant current transport mechanism and the observed defects, we conclude that the resistive evaporation technique yields better quality Schottky contacts for use in solar cells and ultraviolet detectors compared to the e-beam deposition technique. The 0.60 eV has been identified as possibly related to the unoccupied level for the doubly charged oxygen vacancy, V o 2þ .

Effects of high temperature annealing on single crystal ZnO and ZnO devices

“…Pd Schottky contacts with a diameter of 0.6 mm were then fabricated on the Zn-polar face using the resistive evaporation technique to ensure that no process-induced defects were introduced into the material, as has been reported. 15 In the second part of the experiment, the remaining samples from each set were each annealed at the same temperature at which they were annealed before, but this time in oxygen ambient. The cleaning of the samples was the same as the one outlined in the first part of the experiment.…”

A study of the T2 defect and the emission properties of the E3 deep level in annealed melt grown ZnO single crystals

“…The E4 and E5 deep levels are being observed for the first time in the as-received samples from Cermet. Since we have not observed the E4 and E5 in as-received samples before, 13,18,19,23 we attribute these defects to sample growth conditions. A defect with an activation enthalpy similar to the one we have measured has been observed by Frank et al…”

“…techniques. [14][15][16][17][18][24][25][26][27] However, the microscopic origins of this defect are not clear as yet. Annealing ZnO samples in different ambient increases the intensity of the DLTS peak for the E3 defect (Figure 3(a)), with the highest intensity being observed for the Ar þ O 2 annealed samples.…”

“…Research performed on ZnO, however, has the vast majority of reports assigning it to an oxygen vacancy related defect, [14][15][16] while other reports suggest it to be a transition metal ion related defect. 17,18 Debate about the identity of E3 is still raging. With the difficulty in growing reproducible p-type ZnO, knowing the identity of E3 and its behaviour, i.e., in terms of its annealing behaviour can be essential as this might assist in controlling material doping.…”

Microstructural evolution of sputtered ZnO thin films with rapid thermal annealing

“…Basically, the synthesis of high quality ZnO thin film is mostly required for the enhancement in the performance of electronic devices. In current days, varieties of growth techniques are being implemented for deposition of thin films comprising of physical and chemical routes, such as pulsed laser deposition, thermal evaporation, chemical vapor deposition and magnetron sputtering [7][8][9]. Among these techniques, RF magnetron sputtering has several advantages such as its simplicity, low thermal budget, low-cost, nontoxic, and its ability to produce films of better quality with desired properties [10].…”