OPTICAL MONITORING OF THE GROWTH-RATE REDUCTION BY CCL4 DURING METALORGANIC VAPOR-PHASE EPITAXY DEPOSITION OF CARBON-DOPED GAAS

Metalorganic vapor-phase epitaxy (MOVPE) growth of heavily doped GaAs has been studied by reflectometry with a 632.8 nm laser beam. The meas urement of reflection intensity gives the growth rate and the morpholo gy of the layer. Small changes in the refractive index due to high car bon doping (10(20) cm(-3) and above) gives rise to oscillations in the reflectometric signal. A reduction in the growth rate of C-doped GaAs , was attributed to the etching by GaClx (x = 1-3) species associated with the use of CCl4. There is no significant change in the growth rat e if the growth temperature is ;smaller than a critical value dependin g on [Ga(CH3)(3)]/[CCl4] ratio. However, above this critical temperatu re, a steep decrease in the growth rate and a poor morphology of the s urface layer are observed and lead to the reduction in reflection inte nsities. These results are analyzed using microscopic observations and a thermodynamic calculation. (C) 1998 Elsevier Science B.V. All right s reserved.