Impurity-free intermixing of GaAs/AlGaAs quantum wells using SiOx capping:Effect of nitrous oxide flow rate

In this work, impurity-free interdiffusion of GaAs/AlGaAs quantum wells was investigated as a function of the quality of SiOx capping layers grown by plasma-enhanced chemical vapor deposition. The quality of dielectric layers was varied by changing the nitrous oxide flow rate N (30 sccm less than or equal to N less than or equal to 710 sccm), while maintaining a fixed sila ne flow rate. The pressure, substrate temperature, and rf power were also k ept constant during depositions. Deposited films were characterized by Ruth erford backscattering spectroscopy, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. Following rapid thermal annealing, we hav e observed an increase in the energy shift of quantum wells with increasing N with a maximum in the range 100 sccm < N < 200 sccm. Any further increas e in N resulted in a lowering in blueshift, and reached an almost constant value for N > 350 sccm. The variation of energy shift with N cannot be expl ained by considering only the oxygen content of the SiOx layer. It is shown that the deposition rate of the capping layer plays an important role in d etermining the extent of quantum well intermixing. Effects related to the s tress imposed by the capping layer on the GaAs/AlGaAs heterostructure and t he presence of hydrogen in the capping layer are also discussed. (C) 2001 A merican Vacuum Society.