Structural and physical effects of Mg-doping on p-type CuCrO2 and CuAl0.5Cr0.5O2 thin films

Abstract

Magnesium doped thin films of CuCrO2 and CuAl0.5Cr0.5O2, both exhibiting delafossite structure, were synthesized via sol-gel processing. The influence of the dopant on the phase development during the subsequent 2-step annealing procedure was monitored by X-ray diffraction. Systematic variation of the dopant concentration between 2.5 and 15% revealed that the Mg inhibits crystallization and stabilizes spinel phases against thermal decomposition, whereby the amount of impurities in the delafossite films is increased. Nevertheless the p-type conductivity and surprisingly the transmittance of the CuCrO2 films were improved by Mg doping by two orders of magnitude and 16%, respectively. On the contrary the performance of the CuAl0.5Cr0.5O2 films hardly profits from Mg doping. The Seebeck-coefficients of this system even imply a decreasing charge carrier density with increasing dopant concentration, which can only be interpreted as an expulsion of the native defects acting as strong intrinsic doping. The band gap of both oxides remains constant, however

Raman spectra of p-type transparent semiconducting Cr2O3:Mg

“…While these studies are based on Cr 2 O 3 :Mg we believe that findings are more general and results can be applicable to other Mg doped oxide semiconductors in particular CuCrO 2 :Mg, where a similar formation of unwanted spinel phase has been reported [10]. The physical mechanisms of suppressing this localised dopant clustering during growth or post-growth by annealing in oxygen are likely very similar in Cr 2 O 3 and CuCrO 2 .…”

“…Despite its promising properties, the processing of this doped ternary oxide remains challenging and large variations in electrical properties depending on growth conditions have been reported [8]. Part of these problems is related to the dopant distribution and the other part is due to de-phasing of the ternary oxide itself [9][10][11]. Recently we have reported on a related doped binary oxide (Cr 2 O 3 :Mg and Cr 2 O 3 :Mg,N) with similar overall properties to CuCrO 2 :Mg [12][13][14].…”

Synthesis of nanocrystalline Cu deficient CuCrO2 – a high figure of merit p-type transparent semiconductor

“…[16][17][18] In contrast (excluding the report by Nagarajan et al) most papers using amorphous substrates report conductivities in the 1-10 Scm −1 range. 19,20 The transparency of these films is degraded by the doping; reduced to 40% for a 250 nm thick film. CuCrO 2 has also been grown by other methods such as chemical vapor deposition (CVD), spray pyrolysis (SP), and sol-gel synthesis, although the performance of these films is significantly reduced in comparison to physical vapor deposition (PVD) methods.…”

Transparent conductive CuCrO2thin films deposited by pulsed injection metal organic chemical vapor deposition: up-scalable process technology for an improved transparency/conductivity trade-off

“…Copper chromium oxides contrast with other delafossites, in terms of: (i) high density of state of 3d M cations (Cr 3+ ) near the valence band maximum, (ii) covalent mixing between chromium and oxygen ions and (iii) good dopability, [17][18][19][20][21][22] making CuCrO 2 a good p-type candidate for transparent electronic devices. Several methods were reported in the literature for the synthesis of CuCrO 2 : solid-state reaction (SS), 17,[20][21][22][23][24][25][26][27][28][29][30] sol-gel (SG), [31][32][33][34][35][36][37] pulsed laser deposition (PLD), [38][39][40][41][42] magnetron sputtering (MS) 16,[43][44][45][46] and chemical vapor deposition (CVD) including spray pyrolysis. [47][48][49][50] A summary of the electrical and optical properties versus the synthesis methods and the process temperature is given in are obtained with the films deposited by sol-gel, due to the low carrier concentration.…”