Abstract
Resent progress in metal organic vapor phase epitaxy (MOVPE) of group-II oxides is reviewed. Firstly, the MOVPE fabrication process is explained, specifically motivating for the choice of the metal organic (MO) and oxidizer precursors. Particular attention is attracted to controlling the metal-versus-oxygen molar ratio supply to the reaction zone. In addition to an obvious possibility to dilute the precursor flows by different amounts of the carrier gas, the effect of the growth temperature (Tg) was investigated in details.
Indeed, the fact that the MO precursor starts to decompose only at a certain temperature (TMO), implies no epitaxy to occur at Tg < TMO. Further, assuming oxygen is available, the onset of the growth occurs in oxygen-rich conditions, gradually shifting to a stoichiometric situation with the increase of Tg. On the other hand, the upper limit for the reaction may be settled if the oxidizing activity decreases as a function of temperature – as it occurs for example for tertiary butanol (TB) – resulting in the oxygen-poor growth for temperatures above the TB corruption (TTB). Thus, within the TMO ≤ Tg ≤ TTB window the growth conditions are anticipated to evolve from the oxygen-rich to the metal-rich.
Properties of binary and ternary group-II oxides were systematically investigated as a function of the metal-versus-oxygen supply revealing prominent correlations and allowing to control the desirable properties, in particular: (i) type of dominating intrinsic defects, (ii) phase stability and strain accumulation, (iii) ability to incorporate dopants into metal/oxygen sites, (iv) variations in optoelectronic properties. Specific examples in (i-iv) are picked from recent publications as well as not yet published data.
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