COPYROLYSIS OF ASH3 AND PH3 IN THE EPITAXIAL-GROWTH OF TERNARY AND QUATERNARY III-V ALLOYS

In the epitaxial growth of InGaAsP or GaAsP by metalorganic molecular beam epitaxy (MOMBE), the group V hydrides may be cracked separately o r combined in a single stream before entering the cracker. Combining A sH3 and PH3 yields the mixed gaseous species AsP, As2P2, As3P and AsP3 which are stable arriving in the ultra-high vacuum (UHV) chamber in a ddition to the species As, As2, As4, AsH, AsH3, H, H-2 and their P ana logs that would emanate from separate crackers. From statistical therm odynamics, we have evaluated all the thermodynamic functions (free-ene rgy function, entropy, etc.) of these mixed species. Subsequently, emp loying a robust free-energy minimization technique, the equilibrium pr oduct distribution for the 18 gaseous molecules at various input flowr ates of AsH3 + PH3 were determined. In MOMBE growth the concentration of AsP between P2 and AS2 is intermediate between P2 and As2. The calc ulations have also been extended to metalorganic vapor phase epitaxy ( MOVPE) conditions where the dominant species are P4 and AsP3. Here the findings are more significant for hot-walled than for cold-walled rea ctors. The results of the thermodynamic analysis are in good accord wi th mass spectrometric measurements.