Suppression of quantum well intermixing in GaAs/AlGaAs laser structures using phosphorus-doped SiO2 encapsulant layer

A phosphorus-doped silica (SiO${}_{\mathrm{2}}:$ P) cap containing 5 wt% P has been demonstrated to inhibit the bandgap shifts of p-i-n and n-i-p GaAs/AlGaAs quantum well laser structures after rapid thermal processing. The intermixing suppression has been attributed to the fact that SiO${}_{\mathrm{2}}:$ P is more dense and void free compared with standard SiO${}_{\mathrm{2}}$ together with a strain relaxation effect of the cap layer during annealing. Band gap shift differences as large as 100 meV have been observed from samples capped with SiO${}_{\mathrm{2}}$ and with SiO${}_{\mathrm{2}}:$ P. The n-i-p structure showed a higher degree of intermixing compared to p-i-n structure. This behaviour has been attributed to the rise of Fermi level in the n doped structure, through which the formation energy of Ga vacancies is reduced compared to the p doped structure.