Optical properties of annealed, single GaAs quantum wells: Cap doping and mask width dependence

Abstract

Band edge absorption measurements are used to characterize the degree of Al-Ga intermixing (blue-shifting) and the linear optical loss of waveguides formed in five annealed and encapsulated single GaAs quantum well laser heterostructure wafers which differed only by the amount of Zn doping in the GaAs cap layer. In addition to the transmission measurements, secondary ion mass spectroscopy data was used to verify the diffusion of Zn before and after annealing. High zinc doping in the cap is observed to cause quantum well disordering below the encapsulant (Si₃N₄) and is attributed to impurity induced layer disordering. Moderate doping in the cap results in selective area intermixing via controlled gallium vacancy production. A stripe width dependence is also observed, which suggests a role of lateral diffusion of species which affect the intermixing. For an undoped (n⁻) cap, the degree of intermixing is heavily dependent on the arsenic overpressure used during the anneal and is independent of the nitride stripe width suggestive of a volumetric Fermi level dependent production of vacancies within the cap.